2 = The Tahoe REST-ful Web API =
4 1. Enabling the web-API port
5 2. Basic Concepts: GET, PUT, DELETE, POST
6 3. URLs, Machine-Oriented Interfaces
7 4. Browser Operations: Human-Oriented Interfaces
8 5. Welcome / Debug / Status pages
9 6. Static Files in /public_html
10 7. Safety and security issues -- names vs. URIs
14 == Enabling the web-API port ==
16 Every Tahoe node is capable of running a built-in HTTP server. To enable
17 this, just write a port number into the "[node]web.port" line of your node's
18 tahoe.cfg file. For example, writing "web.port = 3456" into the "[node]"
19 section of $NODEDIR/tahoe.cfg will cause the node to run a webserver on port
22 This string is actually a Twisted "strports" specification, meaning you can
23 get more control over the interface to which the server binds by supplying
24 additional arguments. For more details, see the documentation on
25 twisted.application.strports:
26 http://twistedmatrix.com/documents/current/api/twisted.application.strports.html
28 Writing "tcp:3456:interface=127.0.0.1" into the web.port line does the same
29 but binds to the loopback interface, ensuring that only the programs on the
30 local host can connect. Using
31 "ssl:3456:privateKey=mykey.pem:certKey=cert.pem" runs an SSL server.
33 This webport can be set when the node is created by passing a --webport
34 option to the 'tahoe create-node' command. By default, the node listens on
35 port 3456, on the loopback (127.0.0.1) interface.
39 As described in architecture.txt, each file and directory in a Tahoe virtual
40 filesystem is referenced by an identifier that combines the designation of
41 the object with the authority to do something with it (such as read or modify
42 the contents). This identifier is called a "read-cap" or "write-cap",
43 depending upon whether it enables read-only or read-write access. These
44 "caps" are also referred to as URIs.
46 The Tahoe web-based API is "REST-ful", meaning it implements the concepts of
47 "REpresentational State Transfer": the original scheme by which the World
48 Wide Web was intended to work. Each object (file or directory) is referenced
49 by a URL that includes the read- or write- cap. HTTP methods (GET, PUT, and
50 DELETE) are used to manipulate these objects. You can think of the URL as a
51 noun, and the method as a verb.
53 In REST, the GET method is used to retrieve information about an object, or
54 to retrieve some representation of the object itself. When the object is a
55 file, the basic GET method will simply return the contents of that file.
56 Other variations (generally implemented by adding query parameters to the
57 URL) will return information about the object, such as metadata. GET
58 operations are required to have no side-effects.
60 PUT is used to upload new objects into the filesystem, or to replace an
61 existing object. DELETE it used to delete objects from the filesystem. Both
62 PUT and DELETE are required to be idempotent: performing the same operation
63 multiple times must have the same side-effects as only performing it once.
65 POST is used for more complicated actions that cannot be expressed as a GET,
66 PUT, or DELETE. POST operations can be thought of as a method call: sending
67 some message to the object referenced by the URL. In Tahoe, POST is also used
68 for operations that must be triggered by an HTML form (including upload and
69 delete), because otherwise a regular web browser has no way to accomplish
70 these tasks. In general, everything that can be done with a PUT or DELETE can
71 also be done with a POST.
73 Tahoe's web API is designed for two different kinds of consumer. The first is
74 a program that needs to manipulate the virtual file system. Such programs are
75 expected to use the RESTful interface described above. The second is a human
76 using a standard web browser to work with the filesystem. This user is given
77 a series of HTML pages with links to download files, and forms that use POST
78 actions to upload, rename, and delete files.
80 When an error occurs, the HTTP response code will be set to an appropriate
81 400-series code (like 404 Not Found for an unknown childname, or 400 Bad Request
82 when the parameters to a webapi operation are invalid), and the HTTP response
83 body will usually contain a few lines of explanation as to the cause of the
84 error and possible responses. Unusual exceptions may result in a
85 500 Internal Server Error as a catch-all, with a default response body containing
86 a Nevow-generated HTML-ized representation of the Python exception stack trace
87 that caused the problem. CLI programs which want to copy the response body to
88 stderr should provide an "Accept: text/plain" header to their requests to get
89 a plain text stack trace instead. If the Accept header contains */*, or
90 text/*, or text/html (or if there is no Accept header), HTML tracebacks will
95 Tahoe uses a variety of read- and write- caps to identify files and
96 directories. The most common of these is the "immutable file read-cap", which
97 is used for most uploaded files. These read-caps look like the following:
99 URI:CHK:ime6pvkaxuetdfah2p2f35pe54:4btz54xk3tew6nd4y2ojpxj4m6wxjqqlwnztgre6gnjgtucd5r4a:3:10:202
101 The next most common is a "directory write-cap", which provides both read and
102 write access to a directory, and look like this:
104 URI:DIR2:djrdkfawoqihigoett4g6auz6a:jx5mplfpwexnoqff7y5e4zjus4lidm76dcuarpct7cckorh2dpgq
106 There are also "directory read-caps", which start with "URI:DIR2-RO:", and
107 give read-only access to a directory. Finally there are also mutable file
108 read- and write- caps, which start with "URI:SSK", and give access to mutable
111 (Later versions of Tahoe will make these strings shorter, and will remove the
112 unfortunate colons, which must be escaped when these caps are embedded in
115 To refer to any Tahoe object through the web API, you simply need to combine
116 a prefix (which indicates the HTTP server to use) with the cap (which
117 indicates which object inside that server to access). Since the default Tahoe
118 webport is 3456, the most common prefix is one that will use a local node
119 listening on this port:
121 http://127.0.0.1:3456/uri/ + $CAP
123 So, to access the directory named above (which happens to be the
124 publically-writeable sample directory on the Tahoe test grid, described at
125 http://allmydata.org/trac/tahoe/wiki/TestGrid), the URL would be:
127 http://127.0.0.1:3456/uri/URI%3ADIR2%3Adjrdkfawoqihigoett4g6auz6a%3Ajx5mplfpwexnoqff7y5e4zjus4lidm76dcuarpct7cckorh2dpgq/
129 (note that the colons in the directory-cap are url-encoded into "%3A"
132 Likewise, to access the file named above, use:
134 http://127.0.0.1:3456/uri/URI%3ACHK%3Aime6pvkaxuetdfah2p2f35pe54%3A4btz54xk3tew6nd4y2ojpxj4m6wxjqqlwnztgre6gnjgtucd5r4a%3A3%3A10%3A202
136 In the rest of this document, we'll use "$DIRCAP" as shorthand for a read-cap
137 or write-cap that refers to a directory, and "$FILECAP" to abbreviate a cap
138 that refers to a file (whether mutable or immutable). So those URLs above can
141 http://127.0.0.1:3456/uri/$DIRCAP/
142 http://127.0.0.1:3456/uri/$FILECAP
144 The operation summaries below will abbreviate these further, by eliding the
145 server prefix. They will be displayed like this:
153 Tahoe directories contain named child entries, just like directories in a regular
154 local filesystem. These child entries, called "dirnodes", consist of a name,
155 metadata, a write slot, and a read slot. The write and read slots normally contain
156 a write-cap and read-cap referring to the same object, which can be either a file
157 or a subdirectory. The write slot may be empty (actually, both may be empty,
158 but that is unusual).
160 If you have a Tahoe URL that refers to a directory, and want to reference a
161 named child inside it, just append the child name to the URL. For example, if
162 our sample directory contains a file named "welcome.txt", we can refer to
165 http://127.0.0.1:3456/uri/$DIRCAP/welcome.txt
167 (or http://127.0.0.1:3456/uri/URI%3ADIR2%3Adjrdkfawoqihigoett4g6auz6a%3Ajx5mplfpwexnoqff7y5e4zjus4lidm76dcuarpct7cckorh2dpgq/welcome.txt)
169 Multiple levels of subdirectories can be handled this way:
171 http://127.0.0.1:3456/uri/$DIRCAP/tahoe-source/docs/webapi.txt
173 In this document, when we need to refer to a URL that references a file using
174 this child-of-some-directory format, we'll use the following string:
176 /uri/$DIRCAP/[SUBDIRS../]FILENAME
178 The "[SUBDIRS../]" part means that there are zero or more (optional)
179 subdirectory names in the middle of the URL. The "FILENAME" at the end means
180 that this whole URL refers to a file of some sort, rather than to a
183 When we need to refer specifically to a directory in this way, we'll write:
185 /uri/$DIRCAP/[SUBDIRS../]SUBDIR
188 Note that all components of pathnames in URLs are required to be UTF-8
189 encoded, so "resume.doc" (with an acute accent on both E's) would be accessed
192 http://127.0.0.1:3456/uri/$DIRCAP/r%C3%A9sum%C3%A9.doc
194 Also note that the filenames inside upload POST forms are interpreted using
195 whatever character set was provided in the conventional '_charset' field, and
196 defaults to UTF-8 if not otherwise specified. The JSON representation of each
197 directory contains native unicode strings. Tahoe directories are specified to
198 contain unicode filenames, and cannot contain binary strings that are not
199 representable as such.
201 All Tahoe operations that refer to existing files or directories must include
202 a suitable read- or write- cap in the URL: the webapi server won't add one
203 for you. If you don't know the cap, you can't access the file. This allows
204 the security properties of Tahoe caps to be extended across the webapi
207 == Slow Operations, Progress, and Cancelling ==
209 Certain operations can be expected to take a long time. The "t=deep-check",
210 described below, will recursively visit every file and directory reachable
211 from a given starting point, which can take minutes or even hours for
212 extremely large directory structures. A single long-running HTTP request is a
213 fragile thing: proxies, NAT boxes, browsers, and users may all grow impatient
214 with waiting and give up on the connection.
216 For this reason, long-running operations have an "operation handle", which
217 can be used to poll for status/progress messages while the operation
218 proceeds. This handle can also be used to cancel the operation. These handles
219 are created by the client, and passed in as a an "ophandle=" query argument
220 to the POST or PUT request which starts the operation. The following
221 operations can then be used to retrieve status:
223 GET /operations/$HANDLE?output=HTML (with or without t=status)
224 GET /operations/$HANDLE?output=JSON (same)
226 These two retrieve the current status of the given operation. Each operation
227 presents a different sort of information, but in general the page retrieved
230 * whether the operation is complete, or if it is still running
231 * how much of the operation is complete, and how much is left, if possible
233 Note that the final status output can be quite large: a deep-manifest of a
234 directory structure with 300k directories and 200k unique files is about
235 275MB of JSON, and might take two minutes to generate. For this reason, the
236 full status is not provided until the operation has completed.
238 The HTML form will include a meta-refresh tag, which will cause a regular
239 web browser to reload the status page about 60 seconds later. This tag will
240 be removed once the operation has completed.
242 There may be more status information available under
243 /operations/$HANDLE/$ETC : i.e., the handle forms the root of a URL space.
245 POST /operations/$HANDLE?t=cancel
247 This terminates the operation, and returns an HTML page explaining what was
248 cancelled. If the operation handle has already expired (see below), this
249 POST will return a 404, which indicates that the operation is no longer
250 running (either it was completed or terminated). The response body will be
251 the same as a GET /operations/$HANDLE on this operation handle, and the
252 handle will be expired immediately afterwards.
254 The operation handle will eventually expire, to avoid consuming an unbounded
255 amount of memory. The handle's time-to-live can be reset at any time, by
256 passing a retain-for= argument (with a count of seconds) to either the
257 initial POST that starts the operation, or the subsequent GET request which
258 asks about the operation. For example, if a 'GET
259 /operations/$HANDLE?output=JSON&retain-for=600' query is performed, the
260 handle will remain active for 600 seconds (10 minutes) after the GET was
263 In addition, if the GET includes a release-after-complete=True argument, and
264 the operation has completed, the operation handle will be released
267 If a retain-for= argument is not used, the default handle lifetimes are:
269 * handles will remain valid at least until their operation finishes
270 * uncollected handles for finished operations (i.e. handles for operations
271 which have finished but for which the GET page has not been accessed since
272 completion) will remain valid for one hour, or for the total time consumed
273 by the operation, whichever is greater.
274 * collected handles (i.e. the GET page has been retrieved at least once
275 since the operation completed) will remain valid for ten minutes.
277 Many "slow" operations can begin to use unacceptable amounts of memory when
278 operating on large directory structures. The memory usage increases when the
279 ophandle is polled, as the results must be copied into a JSON string, sent
280 over the wire, then parsed by a client. So, as an alternative, many "slow"
281 operations have streaming equivalents. These equivalents do not use operation
282 handles. Instead, they emit line-oriented status results immediately. Client
283 code can cancel the operation by simply closing the HTTP connection.
285 == Programmatic Operations ==
287 Now that we know how to build URLs that refer to files and directories in a
288 Tahoe virtual filesystem, what sorts of operations can we do with those URLs?
289 This section contains a catalog of GET, PUT, DELETE, and POST operations that
290 can be performed on these URLs. This set of operations are aimed at programs
291 that use HTTP to communicate with a Tahoe node. A later section describes
292 operations that are intended for web browsers.
294 === Reading A File ===
297 GET /uri/$DIRCAP/[SUBDIRS../]FILENAME
299 This will retrieve the contents of the given file. The HTTP response body
300 will contain the sequence of bytes that make up the file.
302 To view files in a web browser, you may want more control over the
303 Content-Type and Content-Disposition headers. Please see the next section
304 "Browser Operations", for details on how to modify these URLs for that
307 === Writing/Uploading A File ===
310 PUT /uri/$DIRCAP/[SUBDIRS../]FILENAME
312 Upload a file, using the data from the HTTP request body, and add whatever
313 child links and subdirectories are necessary to make the file available at
314 the given location. Once this operation succeeds, a GET on the same URL will
315 retrieve the same contents that were just uploaded. This will create any
316 necessary intermediate subdirectories.
318 To use the /uri/$FILECAP form, $FILECAP must be a write-cap for a mutable file.
320 In the /uri/$DIRCAP/[SUBDIRS../]FILENAME form, if the target file is a
321 writeable mutable file, that file's contents will be overwritten in-place. If
322 it is a read-cap for a mutable file, an error will occur. If it is an
323 immutable file, the old file will be discarded, and a new one will be put in
326 When creating a new file, if "mutable=true" is in the query arguments, the
327 operation will create a mutable file instead of an immutable one.
329 This returns the file-cap of the resulting file. If a new file was created
330 by this method, the HTTP response code (as dictated by rfc2616) will be set
331 to 201 CREATED. If an existing file was replaced or modified, the response
334 Note that the 'curl -T localfile http://127.0.0.1:3456/uri/$DIRCAP/foo.txt'
335 command can be used to invoke this operation.
339 This uploads a file, and produces a file-cap for the contents, but does not
340 attach the file into the filesystem. No directories will be modified by
341 this operation. The file-cap is returned as the body of the HTTP response.
343 If "mutable=true" is in the query arguments, the operation will create a
344 mutable file, and return its write-cap in the HTTP respose. The default is
345 to create an immutable file, returning the read-cap as a response.
347 === Creating A New Directory ===
352 Create a new empty directory and return its write-cap as the HTTP response
353 body. This does not make the newly created directory visible from the
354 filesystem. The "PUT" operation is provided for backwards compatibility:
355 new code should use POST.
357 POST /uri?t=mkdir-with-children
359 Create a new directory, populated with a set of child nodes, and return its
360 write-cap as the HTTP response body. The new directory is not attached to
361 any other directory: the returned write-cap is the only reference to it.
363 Initial children are provided as the body of the POST form (this is more
364 efficient than doing separate mkdir and set_children operations). If the
365 body is empty, the new directory will be empty. If not empty, the body will
366 be interpreted as a UTF-8 JSON-encoded dictionary of children with which the
367 new directory should be populated, using the same format as would be
368 returned in the 'children' value of the t=json GET request, described below.
369 Each dictionary key should be a child name, and each value should be a list
370 of [TYPE, PROPDICT], where PROPDICT contains "rw_uri", "ro_uri", and
371 "metadata" keys (all others are ignored). For example, the PUT request body
375 "Fran\u00e7ais": [ "filenode", {
376 "ro_uri": "URI:CHK:...",
379 "ctime": 1202777696.7564139,
380 "mtime": 1202777696.7564139,
382 "linkcrtime": 1202777696.7564139,
383 "linkmotime": 1202777696.7564139
385 "subdir": [ "dirnode", {
386 "rw_uri": "URI:DIR2:...",
387 "ro_uri": "URI:DIR2-RO:...",
389 "ctime": 1202778102.7589991,
390 "mtime": 1202778111.2160511,
392 "linkcrtime": 1202777696.7564139,
393 "linkmotime": 1202777696.7564139
397 For forward-compatibility, a mutable directory can also contain caps in
398 a format that is unknown to the webapi server. When such caps are retrieved
399 from a mutable directory in a "ro_uri" field, they will be prefixed with
400 the string "ro.", indicating that they must not be decoded without
401 checking that they are read-only. The "ro." prefix must not be stripped
402 off without performing this check. (Future versions of the webapi server
403 will perform it where necessary.)
405 If both the "rw_uri" and "ro_uri" fields are present in a given PROPDICT,
406 and the webapi server recognizes the rw_uri as a write cap, then it will
407 reset the ro_uri to the corresponding read cap and discard the original
408 contents of ro_uri (in order to ensure that the two caps correspond to the
409 same object and that the ro_uri is in fact read-only). However this may not
410 happen for caps in a format unknown to the webapi server. Therefore, when
411 writing a directory the webapi client should ensure that the contents
412 of "rw_uri" and "ro_uri" for a given PROPDICT are a consistent
413 (write cap, read cap) pair if possible. If the webapi client only has
414 one cap and does not know whether it is a write cap or read cap, then
415 it is acceptable to set "rw_uri" to that cap and omit "ro_uri". The
416 client must not put a write cap into a "ro_uri" field.
418 Note that the webapi-using client application must not provide the
419 "Content-Type: multipart/form-data" header that usually accompanies HTML
420 form submissions, since the body is not formatted this way. Doing so will
421 cause a server error as the lower-level code misparses the request body.
423 Child file names should each be expressed as a unicode string, then used as
424 keys of the dictionary. The dictionary should then be converted into JSON,
425 and the resulting string encoded into UTF-8. This UTF-8 bytestring should
426 then be used as the POST body.
428 POST /uri?t=mkdir-immutable
430 Like t=mkdir-with-children above, but the new directory will be
431 deep-immutable. This means that the directory itself is immutable, and that
432 it can only contain objects that are treated as being deep-immutable, like
433 immutable files, literal files, and deep-immutable directories.
435 For forward-compatibility, a deep-immutable directory can also contain caps
436 in a format that is unknown to the webapi server. When such caps are retrieved
437 from a deep-immutable directory in a "ro_uri" field, they will be prefixed
438 with the string "imm.", indicating that they must not be decoded without
439 checking that they are immutable. The "imm." prefix must not be stripped
440 off without performing this check. (Future versions of the webapi server
441 will perform it where necessary.)
443 The cap for each child may be given either in the "rw_uri" or "ro_uri"
444 field of the PROPDICT (not both). If a cap is given in the "rw_uri" field,
445 then the webapi server will check that it is an immutable read-cap of a
446 *known* format, and give an error if it is not. If a cap is given in the
447 "ro_uri" field, then the webapi server will still check whether known
448 caps are immutable, but for unknown caps it will simply assume that the
449 cap can be stored, as described above. Note that an attacker would be
450 able to store any cap in an immutable directory, so this check when
451 creating the directory is only to help non-malicious clients to avoid
452 accidentally giving away more authority than intended.
454 A non-empty request body is mandatory, since after the directory is created,
455 it will not be possible to add more children to it.
457 POST /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir
458 PUT /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir
460 Create new directories as necessary to make sure that the named target
461 ($DIRCAP/SUBDIRS../SUBDIR) is a directory. This will create additional
462 intermediate mutable directories as necessary. If the named target directory
463 already exists, this will make no changes to it.
465 If the final directory is created, it will be empty.
467 This operation will return an error if a blocking file is present at any of
468 the parent names, preventing the server from creating the necessary parent
469 directory; or if it would require changing an immutable directory.
471 The write-cap of the new directory will be returned as the HTTP response
474 POST /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir-with-children
476 Like /uri?t=mkdir-with-children, but the final directory is created as a
477 child of an existing mutable directory. This will create additional
478 intermediate mutable directories as necessary. If the final directory is
479 created, it will be populated with initial children from the POST request
480 body, as described above.
482 This operation will return an error if a blocking file is present at any of
483 the parent names, preventing the server from creating the necessary parent
484 directory; or if it would require changing an immutable directory; or if
485 the immediate parent directory already has a a child named SUBDIR.
487 POST /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir-immutable
489 Like /uri?t=mkdir-immutable, but the final directory is created as a child
490 of an existing mutable directory. The final directory will be deep-immutable,
491 and will be populated with the children specified as a JSON dictionary in
492 the POST request body.
494 In Tahoe 1.6 this operation creates intermediate mutable directories if
495 necessary, but that behaviour should not be relied on; see ticket #920.
497 This operation will return an error if the parent directory is immutable,
498 or already has a child named SUBDIR.
500 POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=NAME
502 Create a new empty mutable directory and attach it to the given existing
503 directory. This will create additional intermediate directories as necessary.
505 This operation will return an error if a blocking file is present at any of
506 the parent names, preventing the server from creating the necessary parent
507 directory, or if it would require changing any immutable directory.
509 The URL of this operation points to the parent of the bottommost new directory,
510 whereas the /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir operation above has a URL
511 that points directly to the bottommost new directory.
513 POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir-with-children&name=NAME
515 Like /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=NAME, but the new directory will
516 be populated with initial children via the POST request body. This command
517 will create additional intermediate mutable directories as necessary.
519 This operation will return an error if a blocking file is present at any of
520 the parent names, preventing the server from creating the necessary parent
521 directory; or if it would require changing an immutable directory; or if
522 the immediate parent directory already has a a child named NAME.
524 Note that the name= argument must be passed as a queryarg, because the POST
525 request body is used for the initial children JSON.
527 POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir-immutable&name=NAME
529 Like /uri/$DIRCAP/[SUBDIRS../]?t=mkdir-with-children&name=NAME, but the
530 final directory will be deep-immutable. The children are specified as a
531 JSON dictionary in the POST request body. Again, the name= argument must be
532 passed as a queryarg.
534 In Tahoe 1.6 this operation creates intermediate mutable directories if
535 necessary, but that behaviour should not be relied on; see ticket #920.
537 This operation will return an error if the parent directory is immutable,
538 or already has a child named NAME.
540 === Get Information About A File Or Directory (as JSON) ===
542 GET /uri/$FILECAP?t=json
543 GET /uri/$DIRCAP?t=json
544 GET /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=json
545 GET /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=json
547 This returns a machine-parseable JSON-encoded description of the given
548 object. The JSON always contains a list, and the first element of the list is
549 always a flag that indicates whether the referenced object is a file or a
550 directory. If it is a capability to a file, then the information includes
551 file size and URI, like this:
553 GET /uri/$FILECAP?t=json :
557 "verify_uri": verify_uri,
562 If it is a capability to a directory followed by a path from that directory
563 to a file, then the information also includes metadata from the link to the
564 file in the parent directory, like this:
566 GET /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=json :
570 "verify_uri": verify_uri,
574 "ctime": 1202777696.7564139,
575 "mtime": 1202777696.7564139,
577 "linkcrtime": 1202777696.7564139,
578 "linkmotime": 1202777696.7564139
581 If it is a directory, then it includes information about the children of
582 this directory, as a mapping from child name to a set of data about the
583 child (the same data that would appear in a corresponding GET?t=json of the
584 child itself). The child entries also include metadata about each child,
585 including link-creation- and link-change- timestamps. The output looks like
588 GET /uri/$DIRCAP?t=json :
589 GET /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=json :
592 "rw_uri": read_write_uri,
593 "ro_uri": read_only_uri,
594 "verify_uri": verify_uri,
597 "foo.txt": [ "filenode", {
601 "ctime": 1202777696.7564139,
602 "mtime": 1202777696.7564139,
604 "linkcrtime": 1202777696.7564139,
605 "linkmotime": 1202777696.7564139
607 "subdir": [ "dirnode", {
611 "ctime": 1202778102.7589991,
612 "mtime": 1202778111.2160511,
614 "linkcrtime": 1202777696.7564139,
615 "linkmotime": 1202777696.7564139
619 In the above example, note how 'children' is a dictionary in which the keys
620 are child names and the values depend upon whether the child is a file or a
621 directory. The value is mostly the same as the JSON representation of the
622 child object (except that directories do not recurse -- the "children"
623 entry of the child is omitted, and the directory view includes the metadata
624 that is stored on the directory edge).
626 The rw_uri field will be present in the information about a directory
627 if and only if you have read-write access to that directory. The verify_uri
628 field will be present if and only if the object has a verify-cap
629 (non-distributed LIT files do not have verify-caps).
631 If the cap is of an unknown format, then the file size and verify_uri will
634 GET /uri/$UNKNOWNCAP?t=json :
637 "ro_uri": unknown_read_uri
640 GET /uri/$DIRCAP/[SUBDIRS../]UNKNOWNCHILDNAME?t=json :
643 "rw_uri": unknown_write_uri,
644 "ro_uri": unknown_read_uri,
647 "ctime": 1202777696.7564139,
648 "mtime": 1202777696.7564139,
650 "linkcrtime": 1202777696.7564139,
651 "linkmotime": 1202777696.7564139
654 As in the case of file nodes, the metadata will only be present when the
655 capability is to a directory followed by a path. The "mutable" field is also
656 not always present; when it is absent, the mutability of the object is not
659 ==== About the metadata ====
661 The value of the 'mtime' key and of the 'tahoe':'linkmotime' is updated
662 whenever a link to a child is set. The value of the 'ctime' key and of the
663 'tahoe':'linkcrtime' key is updated whenever a link to a child is created --
664 i.e. when there was not previously a link under that name.
666 In Tahoe earlier than v1.4.0, only the 'mtime'/'ctime' keys were populated.
667 Starting in Tahoe v1.4.0, the 'linkmotime'/'linkcrtime' keys in the 'tahoe'
668 sub-dict are also populated.
670 The reason we added the new values in Tahoe v1.4.0 is that there is a
671 "set_children" API (described below) which you can use to overwrite the
672 values of the 'mtime'/'ctime' pair, and this API is used by the "tahoe
673 backup" command (both in Tahoe v1.3.0 and in Tahoe v1.4.0) to set the
674 'mtime' and 'ctime' values when backing up files from a local filesystem
675 into the Tahoe filesystem. As of Tahoe v1.4.0, the set_children API cannot
676 be used to set anything under the 'tahoe' key of the metadata dict -- if
677 you include 'tahoe' keys in your 'metadata' arguments then it will silently
680 Therefore, if the 'tahoe' sub-dict is present, you can rely on the
681 'linkcrtime' and 'linkmotime' values therein to have the semantics described
682 above. (This is assuming that only official Tahoe clients have been used to
683 write those links, and that their system clocks were set to what you expected
684 -- there is nothing preventing someone from editing their Tahoe client or
685 writing their own Tahoe client which would overwrite those values however
686 they like, and there is nothing to constrain their system clock from taking
689 The meaning of the 'ctime'/'mtime' fields are slightly more complex.
691 The meaning of the 'mtime' field is: whenever the edge is updated (by an HTTP
692 PUT or POST, as is done by the "tahoe cp" command), then the mtime is set to
693 the current time on the clock of the updating client. Whenever the edge is
694 updated by "tahoe backup" then the mtime is instead set to the value which
695 the updating client read from its local filesystem for the "mtime" of the
696 local file in question, which means the last time the contents of that file
697 were changed. Note however, that if the edge in the Tahoe filesystem points
698 to a mutable file and the contents of that mutable file is changed then the
699 "mtime" value on that edge will *not* be updated, since the edge itself
700 wasn't updated -- only the mutable file was.
702 The meaning of the 'ctime' field is even more complex. Whenever a new edge is
703 created (by an HTTP PUT or POST, as is done by "tahoe cp") then the ctime is
704 set to the current time on the clock of the updating client. Whenever the
705 edge is created *or updated* by "tahoe backup" then the ctime is instead set
706 to the value which the updating client read from its local filesystem. On
707 Windows, it reads the timestamp of when the local file was created and puts
708 that into the "ctime", and on other platforms it reads the timestamp of the
709 most recent time that either the contents or the metadata of the local file
710 was changed and puts that into the ctime. Again, if the edge points to a
711 mutable file and the content of that mutable file is changed then the ctime
712 will not be updated in any case.
714 Therefore there are several ways that the 'ctime' field could be confusing:
716 1. You might be confused about whether it reflects the time of the creation
717 of a link in the Tahoe filesystem or a timestamp copied in from a local
720 2. You might be confused about whether it is a copy of the file creation time
721 (if "tahoe backup" was run on a Windows system) or of the last
722 contents-or-metadata change (if "tahoe backup" was run on a different
725 3. You might be confused by the fact that changing the contents of a mutable
726 file in Tahoe don't have any effect on any links pointing at that file in any
727 directories, although "tahoe backup" sets the link 'ctime'/'mtime' to reflect
728 timestamps about the local file corresponding to the Tahoe file to which the
731 4. Also, quite apart from Tahoe, you might be confused about the meaning of
732 the 'ctime' in UNIX local filesystems, which people sometimes think means
733 file creation time, but which actually means, in UNIX local filesystems, the
734 most recent time that the file contents or the file metadata (such as owner,
735 permission bits, extended attributes, etc.) has changed. Note that although
736 'ctime' does not mean file creation time in UNIX, it does mean link creation
737 time in Tahoe, unless the "tahoe backup" command has been used on that link,
738 in which case it means something about the local filesystem file which
739 corresponds to the Tahoe file which is pointed at by the link. It means
740 either file creation time of the local file (if "tahoe backup" was run on
741 Windows) or file-contents-or-metadata-update-time of the local file (if
742 "tahoe backup" was run on a different operating system).
744 === Attaching an existing File or Directory by its read- or write- cap ===
746 PUT /uri/$DIRCAP/[SUBDIRS../]CHILDNAME?t=uri
748 This attaches a child object (either a file or directory) to a specified
749 location in the virtual filesystem. The child object is referenced by its
750 read- or write- cap, as provided in the HTTP request body. This will create
751 intermediate directories as necessary.
753 This is similar to a UNIX hardlink: by referencing a previously-uploaded file
754 (or previously-created directory) instead of uploading/creating a new one,
755 you can create two references to the same object.
757 The read- or write- cap of the child is provided in the body of the HTTP
758 request, and this same cap is returned in the response body.
760 The default behavior is to overwrite any existing object at the same
761 location. To prevent this (and make the operation return an error instead
762 of overwriting), add a "replace=false" argument, as "?t=uri&replace=false".
763 With replace=false, this operation will return an HTTP 409 "Conflict" error
764 if there is already an object at the given location, rather than
765 overwriting the existing object. To allow the operation to overwrite a
766 file, but return an error when trying to overwrite a directory, use
767 "replace=only-files" (this behavior is closer to the traditional UNIX "mv"
768 command). Note that "true", "t", and "1" are all synonyms for "True", and
769 "false", "f", and "0" are synonyms for "False", and the parameter is
772 Note that this operation does not take its child cap in the form of
773 separate "rw_uri" and "ro_uri" fields. Therefore, it cannot accept a
774 child cap in a format unknown to the webapi server, unless its URI
775 starts with "ro." or "imm.". This restriction is necessary because the
776 server is not able to attenuate an unknown write cap to a read cap.
777 Unknown URIs starting with "ro." or "imm.", on the other hand, are
778 assumed to represent read caps. The client should not prefix a write
779 cap with "ro." or "imm." and pass it to this operation, since that
780 would result in granting the cap's write authority to holders of the
783 === Adding multiple files or directories to a parent directory at once ===
785 POST /uri/$DIRCAP/[SUBDIRS..]?t=set_children
786 POST /uri/$DIRCAP/[SUBDIRS..]?t=set-children (Tahoe >= v1.6)
788 This command adds multiple children to a directory in a single operation.
789 It reads the request body and interprets it as a JSON-encoded description
790 of the child names and read/write-caps that should be added.
792 The body should be a JSON-encoded dictionary, in the same format as the
793 "children" value returned by the "GET /uri/$DIRCAP?t=json" operation
794 described above. In this format, each key is a child names, and the
795 corresponding value is a tuple of (type, childinfo). "type" is ignored, and
796 "childinfo" is a dictionary that contains "rw_uri", "ro_uri", and
797 "metadata" keys. You can take the output of "GET /uri/$DIRCAP1?t=json" and
798 use it as the input to "POST /uri/$DIRCAP2?t=set_children" to make DIR2
799 look very much like DIR1 (except for any existing children of DIR2 that
800 were not overwritten, and any existing "tahoe" metadata keys as described
803 When the set_children request contains a child name that already exists in
804 the target directory, this command defaults to overwriting that child with
805 the new value (both child cap and metadata, but if the JSON data does not
806 contain a "metadata" key, the old child's metadata is preserved). The
807 command takes a boolean "overwrite=" query argument to control this
808 behavior. If you use "?t=set_children&overwrite=false", then an attempt to
809 replace an existing child will instead cause an error.
811 Any "tahoe" key in the new child's "metadata" value is ignored. Any
812 existing "tahoe" metadata is preserved. The metadata["tahoe"] value is
813 reserved for metadata generated by the tahoe node itself. The only two keys
814 currently placed here are "linkcrtime" and "linkmotime". For details, see
815 the section above entitled "Get Information About A File Or Directory (as
816 JSON)", in the "About the metadata" subsection.
818 Note that this command was introduced with the name "set_children", which
819 uses an underscore rather than a hyphen as other multi-word command names
820 do. The variant with a hyphen is now accepted, but clients that desire
821 backward compatibility should continue to use "set_children".
824 === Deleting a File or Directory ===
826 DELETE /uri/$DIRCAP/[SUBDIRS../]CHILDNAME
828 This removes the given name from its parent directory. CHILDNAME is the
829 name to be removed, and $DIRCAP/SUBDIRS.. indicates the directory that will
832 Note that this does not actually delete the file or directory that the name
833 points to from the tahoe grid -- it only removes the named reference from
834 this directory. If there are other names in this directory or in other
835 directories that point to the resource, then it will remain accessible
836 through those paths. Even if all names pointing to this object are removed
837 from their parent directories, then someone with possession of its read-cap
838 can continue to access the object through that cap.
840 The object will only become completely unreachable once 1: there are no
841 reachable directories that reference it, and 2: nobody is holding a read-
842 or write- cap to the object. (This behavior is very similar to the way
843 hardlinks and anonymous files work in traditional UNIX filesystems).
845 This operation will not modify more than a single directory. Intermediate
846 directories which were implicitly created by PUT or POST methods will *not*
847 be automatically removed by DELETE.
849 This method returns the file- or directory- cap of the object that was just
852 == Browser Operations ==
854 This section describes the HTTP operations that provide support for humans
855 running a web browser. Most of these operations use HTML forms that use POST
856 to drive the Tahoe node. This section is intended for HTML authors who want
857 to write web pages that contain forms and buttons which manipulate the Tahoe
860 Note that for all POST operations, the arguments listed can be provided
861 either as URL query arguments or as form body fields. URL query arguments are
862 separated from the main URL by "?", and from each other by "&". For example,
863 "POST /uri/$DIRCAP?t=upload&mutable=true". Form body fields are usually
864 specified by using <input type="hidden"> elements. For clarity, the
865 descriptions below display the most significant arguments as URL query args.
867 === Viewing A Directory (as HTML) ===
869 GET /uri/$DIRCAP/[SUBDIRS../]
871 This returns an HTML page, intended to be displayed to a human by a web
872 browser, which contains HREF links to all files and directories reachable
873 from this directory. These HREF links do not have a t= argument, meaning
874 that a human who follows them will get pages also meant for a human. It also
875 contains forms to upload new files, and to delete files and directories.
876 Those forms use POST methods to do their job.
878 === Viewing/Downloading a File ===
881 GET /uri/$DIRCAP/[SUBDIRS../]FILENAME
883 This will retrieve the contents of the given file. The HTTP response body
884 will contain the sequence of bytes that make up the file.
886 If you want the HTTP response to include a useful Content-Type header,
887 either use the second form (which starts with a $DIRCAP), or add a
888 "filename=foo" query argument, like "GET /uri/$FILECAP?filename=foo.jpg".
889 The bare "GET /uri/$FILECAP" does not give the Tahoe node enough information
890 to determine a Content-Type (since Tahoe immutable files are merely
891 sequences of bytes, not typed+named file objects).
893 If the URL has both filename= and "save=true" in the query arguments, then
894 the server to add a "Content-Disposition: attachment" header, along with a
895 filename= parameter. When a user clicks on such a link, most browsers will
896 offer to let the user save the file instead of displaying it inline (indeed,
897 most browsers will refuse to display it inline). "true", "t", "1", and other
898 case-insensitive equivalents are all treated the same.
900 Character-set handling in URLs and HTTP headers is a dubious art[1]. For
901 maximum compatibility, Tahoe simply copies the bytes from the filename=
902 argument into the Content-Disposition header's filename= parameter, without
903 trying to interpret them in any particular way.
906 GET /named/$FILECAP/FILENAME
908 This is an alternate download form which makes it easier to get the correct
909 filename. The Tahoe server will provide the contents of the given file, with
910 a Content-Type header derived from the given filename. This form is used to
911 get browsers to use the "Save Link As" feature correctly, and also helps
912 command-line tools like "wget" and "curl" use the right filename. Note that
913 this form can *only* be used with file caps; it is an error to use a
914 directory cap after the /named/ prefix.
916 === Get Information About A File Or Directory (as HTML) ===
918 GET /uri/$FILECAP?t=info
919 GET /uri/$DIRCAP/?t=info
920 GET /uri/$DIRCAP/[SUBDIRS../]SUBDIR/?t=info
921 GET /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=info
923 This returns a human-oriented HTML page with more detail about the selected
924 file or directory object. This page contains the following items:
929 raw contents (text/plain)
930 access caps (URIs): verify-cap, read-cap, write-cap (for mutable objects)
931 check/verify/repair form
932 deep-check/deep-size/deep-stats/manifest (for directories)
933 replace-conents form (for mutable files)
935 === Creating a Directory ===
939 This creates a new empty directory, but does not attach it to the virtual
942 If a "redirect_to_result=true" argument is provided, then the HTTP response
943 will cause the web browser to be redirected to a /uri/$DIRCAP page that
944 gives access to the newly-created directory. If you bookmark this page,
945 you'll be able to get back to the directory again in the future. This is the
946 recommended way to start working with a Tahoe server: create a new unlinked
947 directory (using redirect_to_result=true), then bookmark the resulting
948 /uri/$DIRCAP page. There is a "create directory" button on the Welcome page
949 to invoke this action.
951 If "redirect_to_result=true" is not provided (or is given a value of
952 "false"), then the HTTP response body will simply be the write-cap of the
955 POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=CHILDNAME
957 This creates a new empty directory as a child of the designated SUBDIR. This
958 will create additional intermediate directories as necessary.
960 If a "when_done=URL" argument is provided, the HTTP response will cause the
961 web browser to redirect to the given URL. This provides a convenient way to
962 return the browser to the directory that was just modified. Without a
963 when_done= argument, the HTTP response will simply contain the write-cap of
964 the directory that was just created.
967 === Uploading a File ===
971 This uploads a file, and produces a file-cap for the contents, but does not
972 attach the file into the filesystem. No directories will be modified by
975 The file must be provided as the "file" field of an HTML encoded form body,
976 produced in response to an HTML form like this:
977 <form action="/uri" method="POST" enctype="multipart/form-data">
978 <input type="hidden" name="t" value="upload" />
979 <input type="file" name="file" />
980 <input type="submit" value="Upload Unlinked" />
983 If a "when_done=URL" argument is provided, the response body will cause the
984 browser to redirect to the given URL. If the when_done= URL has the string
985 "%(uri)s" in it, that string will be replaced by a URL-escaped form of the
986 newly created file-cap. (Note that without this substitution, there is no
987 way to access the file that was just uploaded).
989 The default (in the absence of when_done=) is to return an HTML page that
990 describes the results of the upload. This page will contain information
991 about which storage servers were used for the upload, how long each
994 If a "mutable=true" argument is provided, the operation will create a
995 mutable file, and the response body will contain the write-cap instead of
996 the upload results page. The default is to create an immutable file,
997 returning the upload results page as a response.
1000 POST /uri/$DIRCAP/[SUBDIRS../]?t=upload
1002 This uploads a file, and attaches it as a new child of the given directory,
1003 which must be mutable. The file must be provided as the "file" field of an
1004 HTML-encoded form body, produced in response to an HTML form like this:
1005 <form action="." method="POST" enctype="multipart/form-data">
1006 <input type="hidden" name="t" value="upload" />
1007 <input type="file" name="file" />
1008 <input type="submit" value="Upload" />
1011 A "name=" argument can be provided to specify the new child's name,
1012 otherwise it will be taken from the "filename" field of the upload form
1013 (most web browsers will copy the last component of the original file's
1014 pathname into this field). To avoid confusion, name= is not allowed to
1017 If there is already a child with that name, and it is a mutable file, then
1018 its contents are replaced with the data being uploaded. If it is not a
1019 mutable file, the default behavior is to remove the existing child before
1020 creating a new one. To prevent this (and make the operation return an error
1021 instead of overwriting the old child), add a "replace=false" argument, as
1022 "?t=upload&replace=false". With replace=false, this operation will return an
1023 HTTP 409 "Conflict" error if there is already an object at the given
1024 location, rather than overwriting the existing object. Note that "true",
1025 "t", and "1" are all synonyms for "True", and "false", "f", and "0" are
1026 synonyms for "False". the parameter is case-insensitive.
1028 This will create additional intermediate directories as necessary, although
1029 since it is expected to be triggered by a form that was retrieved by "GET
1030 /uri/$DIRCAP/[SUBDIRS../]", it is likely that the parent directory will
1033 If a "mutable=true" argument is provided, any new file that is created will
1034 be a mutable file instead of an immutable one. <input type="checkbox"
1035 name="mutable" /> will give the user a way to set this option.
1037 If a "when_done=URL" argument is provided, the HTTP response will cause the
1038 web browser to redirect to the given URL. This provides a convenient way to
1039 return the browser to the directory that was just modified. Without a
1040 when_done= argument, the HTTP response will simply contain the file-cap of
1041 the file that was just uploaded (a write-cap for mutable files, or a
1042 read-cap for immutable files).
1044 POST /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=upload
1046 This also uploads a file and attaches it as a new child of the given
1047 directory, which must be mutable. It is a slight variant of the previous
1048 operation, as the URL refers to the target file rather than the parent
1049 directory. It is otherwise identical: this accepts mutable= and when_done=
1052 POST /uri/$FILECAP?t=upload
1054 This modifies the contents of an existing mutable file in-place. An error is
1055 signalled if $FILECAP does not refer to a mutable file. It behaves just like
1056 the "PUT /uri/$FILECAP" form, but uses a POST for the benefit of HTML forms
1059 === Attaching An Existing File Or Directory (by URI) ===
1061 POST /uri/$DIRCAP/[SUBDIRS../]?t=uri&name=CHILDNAME&uri=CHILDCAP
1063 This attaches a given read- or write- cap "CHILDCAP" to the designated
1064 directory, with a specified child name. This behaves much like the PUT t=uri
1065 operation, and is a lot like a UNIX hardlink. It is subject to the same
1066 restrictions as that operation on the use of cap formats unknown to the
1069 This will create additional intermediate directories as necessary, although
1070 since it is expected to be triggered by a form that was retrieved by "GET
1071 /uri/$DIRCAP/[SUBDIRS../]", it is likely that the parent directory will
1074 This accepts the same replace= argument as POST t=upload.
1076 === Deleting A Child ===
1078 POST /uri/$DIRCAP/[SUBDIRS../]?t=delete&name=CHILDNAME
1080 This instructs the node to remove a child object (file or subdirectory) from
1081 the given directory, which must be mutable. Note that the entire subtree is
1082 unlinked from the parent. Unlike deleting a subdirectory in a UNIX local
1083 filesystem, the subtree need not be empty; if it isn't, then other references
1084 into the subtree will see that the child subdirectories are not modified by
1085 this operation. Only the link from the given directory to its child is severed.
1087 === Renaming A Child ===
1089 POST /uri/$DIRCAP/[SUBDIRS../]?t=rename&from_name=OLD&to_name=NEW
1091 This instructs the node to rename a child of the given directory, which must
1092 be mutable. This has a similar effect to removing the child, then adding the
1093 same child-cap under the new name, except that it preserves metadata. This
1094 operation cannot move the child to a different directory.
1096 This operation will replace any existing child of the new name, making it
1097 behave like the UNIX "mv -f" command.
1099 === Other Utilities ===
1103 This causes a redirect to /uri/$CAP, and retains any additional query
1104 arguments (like filename= or save=). This is for the convenience of web
1105 forms which allow the user to paste in a read- or write- cap (obtained
1106 through some out-of-band channel, like IM or email).
1108 Note that this form merely redirects to the specific file or directory
1109 indicated by the $CAP: unlike the GET /uri/$DIRCAP form, you cannot
1110 traverse to children by appending additional path segments to the URL.
1112 GET /uri/$DIRCAP/[SUBDIRS../]?t=rename-form&name=$CHILDNAME
1114 This provides a useful facility to browser-based user interfaces. It
1115 returns a page containing a form targetting the "POST $DIRCAP t=rename"
1116 functionality described above, with the provided $CHILDNAME present in the
1117 'from_name' field of that form. I.e. this presents a form offering to
1118 rename $CHILDNAME, requesting the new name, and submitting POST rename.
1120 GET /uri/$DIRCAP/[SUBDIRS../]CHILDNAME?t=uri
1122 This returns the file- or directory- cap for the specified object.
1124 GET /uri/$DIRCAP/[SUBDIRS../]CHILDNAME?t=readonly-uri
1126 This returns a read-only file- or directory- cap for the specified object.
1127 If the object is an immutable file, this will return the same value as
1130 === Debugging and Testing Features ===
1132 These URLs are less-likely to be helpful to the casual Tahoe user, and are
1133 mainly intended for developers.
1137 This triggers the FileChecker to determine the current "health" of the
1138 given file or directory, by counting how many shares are available. The
1139 page that is returned will display the results. This can be used as a "show
1140 me detailed information about this file" page.
1142 If a verify=true argument is provided, the node will perform a more
1143 intensive check, downloading and verifying every single bit of every share.
1145 If an add-lease=true argument is provided, the node will also add (or
1146 renew) a lease to every share it encounters. Each lease will keep the share
1147 alive for a certain period of time (one month by default). Once the last
1148 lease expires or is explicitly cancelled, the storage server is allowed to
1151 If an output=JSON argument is provided, the response will be
1152 machine-readable JSON instead of human-oriented HTML. The data is a
1153 dictionary with the following keys:
1155 storage-index: a base32-encoded string with the objects's storage index,
1156 or an empty string for LIT files
1157 summary: a string, with a one-line summary of the stats of the file
1158 results: a dictionary that describes the state of the file. For LIT files,
1159 this dictionary has only the 'healthy' key, which will always be
1160 True. For distributed files, this dictionary has the following
1162 count-shares-good: the number of good shares that were found
1163 count-shares-needed: 'k', the number of shares required for recovery
1164 count-shares-expected: 'N', the number of total shares generated
1165 count-good-share-hosts: the number of distinct storage servers with
1166 good shares. If this number is less than
1167 count-shares-good, then some shares are doubled
1168 up, increasing the correlation of failures. This
1169 indicates that one or more shares should be
1170 moved to an otherwise unused server, if one is
1172 count-wrong-shares: for mutable files, the number of shares for
1173 versions other than the 'best' one (highest
1174 sequence number, highest roothash). These are
1176 count-recoverable-versions: for mutable files, the number of
1177 recoverable versions of the file. For
1178 a healthy file, this will equal 1.
1179 count-unrecoverable-versions: for mutable files, the number of
1180 unrecoverable versions of the file.
1181 For a healthy file, this will be 0.
1182 count-corrupt-shares: the number of shares with integrity failures
1183 list-corrupt-shares: a list of "share locators", one for each share
1184 that was found to be corrupt. Each share locator
1185 is a list of (serverid, storage_index, sharenum).
1186 needs-rebalancing: (bool) True if there are multiple shares on a single
1187 storage server, indicating a reduction in reliability
1188 that could be resolved by moving shares to new
1190 servers-responding: list of base32-encoded storage server identifiers,
1191 one for each server which responded to the share
1193 healthy: (bool) True if the file is completely healthy, False otherwise.
1194 Healthy files have at least N good shares. Overlapping shares
1195 (indicated by count-good-share-hosts < count-shares-good) do not
1196 currently cause a file to be marked unhealthy. If there are at
1197 least N good shares, then corrupt shares do not cause the file to
1198 be marked unhealthy, although the corrupt shares will be listed
1199 in the results (list-corrupt-shares) and should be manually
1200 removed to wasting time in subsequent downloads (as the
1201 downloader rediscovers the corruption and uses alternate shares).
1202 sharemap: dict mapping share identifier to list of serverids
1203 (base32-encoded strings). This indicates which servers are
1204 holding which shares. For immutable files, the shareid is
1205 an integer (the share number, from 0 to N-1). For
1206 immutable files, it is a string of the form
1207 'seq%d-%s-sh%d', containing the sequence number, the
1208 roothash, and the share number.
1210 POST $URL?t=start-deep-check (must add &ophandle=XYZ)
1212 This initiates a recursive walk of all files and directories reachable from
1213 the target, performing a check on each one just like t=check. The result
1214 page will contain a summary of the results, including details on any
1215 file/directory that was not fully healthy.
1217 t=start-deep-check can only be invoked on a directory. An error (400
1218 BAD_REQUEST) will be signalled if it is invoked on a file. The recursive
1219 walker will deal with loops safely.
1221 This accepts the same verify= and add-lease= arguments as t=check.
1223 Since this operation can take a long time (perhaps a second per object),
1224 the ophandle= argument is required (see "Slow Operations, Progress, and
1225 Cancelling" above). The response to this POST will be a redirect to the
1226 corresponding /operations/$HANDLE page (with output=HTML or output=JSON to
1227 match the output= argument given to the POST). The deep-check operation
1228 will continue to run in the background, and the /operations page should be
1229 used to find out when the operation is done.
1231 Detailed check results for non-healthy files and directories will be
1232 available under /operations/$HANDLE/$STORAGEINDEX, and the HTML status will
1233 contain links to these detailed results.
1235 The HTML /operations/$HANDLE page for incomplete operations will contain a
1236 meta-refresh tag, set to 60 seconds, so that a browser which uses
1237 deep-check will automatically poll until the operation has completed.
1239 The JSON page (/options/$HANDLE?output=JSON) will contain a
1240 machine-readable JSON dictionary with the following keys:
1242 finished: a boolean, True if the operation is complete, else False. Some
1243 of the remaining keys may not be present until the operation
1245 root-storage-index: a base32-encoded string with the storage index of the
1246 starting point of the deep-check operation
1247 count-objects-checked: count of how many objects were checked. Note that
1248 non-distributed objects (i.e. small immutable LIT
1249 files) are not checked, since for these objects,
1250 the data is contained entirely in the URI.
1251 count-objects-healthy: how many of those objects were completely healthy
1252 count-objects-unhealthy: how many were damaged in some way
1253 count-corrupt-shares: how many shares were found to have corruption,
1254 summed over all objects examined
1255 list-corrupt-shares: a list of "share identifiers", one for each share
1256 that was found to be corrupt. Each share identifier
1257 is a list of (serverid, storage_index, sharenum).
1258 list-unhealthy-files: a list of (pathname, check-results) tuples, for
1259 each file that was not fully healthy. 'pathname' is
1260 a list of strings (which can be joined by "/"
1261 characters to turn it into a single string),
1262 relative to the directory on which deep-check was
1263 invoked. The 'check-results' field is the same as
1264 that returned by t=check&output=JSON, described
1266 stats: a dictionary with the same keys as the t=start-deep-stats command
1269 POST $URL?t=stream-deep-check
1271 This initiates a recursive walk of all files and directories reachable from
1272 the target, performing a check on each one just like t=check. For each
1273 unique object (duplicates are skipped), a single line of JSON is emitted to
1274 the HTTP response channel (or an error indication, see below). When the walk
1275 is complete, a final line of JSON is emitted which contains the accumulated
1276 file-size/count "deep-stats" data.
1278 This command takes the same arguments as t=start-deep-check.
1280 A CLI tool can split the response stream on newlines into "response units",
1281 and parse each response unit as JSON. Each such parsed unit will be a
1282 dictionary, and will contain at least the "type" key: a string, one of
1283 "file", "directory", or "stats".
1285 For all units that have a type of "file" or "directory", the dictionary will
1286 contain the following keys:
1288 "path": a list of strings, with the path that is traversed to reach the
1290 "cap": a write-cap URI for the file or directory, if available, else a
1292 "verifycap": a verify-cap URI for the file or directory
1293 "repaircap": an URI for the weakest cap that can still be used to repair
1295 "storage-index": a base32 storage index for the object
1296 "check-results": a copy of the dictionary which would be returned by
1297 t=check&output=json, with three top-level keys:
1298 "storage-index", "summary", and "results", and a variety
1299 of counts and sharemaps in the "results" value.
1301 Note that non-distributed files (i.e. LIT files) will have values of None
1302 for verifycap, repaircap, and storage-index, since these files can neither
1303 be verified nor repaired, and are not stored on the storage servers.
1304 Likewise the check-results dictionary will be limited: an empty string for
1305 storage-index, and a results dictionary with only the "healthy" key.
1307 The last unit in the stream will have a type of "stats", and will contain
1308 the keys described in the "start-deep-stats" operation, below.
1310 If any errors occur during the traversal (specifically if a directory is
1311 unrecoverable, such that further traversal is not possible), an error
1312 indication is written to the response body, instead of the usual line of
1313 JSON. This error indication line will begin with the string "ERROR:" (in all
1314 caps), and contain a summary of the error on the rest of the line. The
1315 remaining lines of the response body will be a python exception. The client
1316 application should look for the ERROR: and stop processing JSON as soon as
1317 it is seen. Note that neither a file being unrecoverable nor a directory
1318 merely being unhealthy will cause traversal to stop. The line just before
1319 the ERROR: will describe the directory that was untraversable, since the
1320 unit is emitted to the HTTP response body before the child is traversed.
1323 POST $URL?t=check&repair=true
1325 This performs a health check of the given file or directory, and if the
1326 checker determines that the object is not healthy (some shares are missing
1327 or corrupted), it will perform a "repair". During repair, any missing
1328 shares will be regenerated and uploaded to new servers.
1330 This accepts the same verify=true and add-lease= arguments as t=check. When
1331 an output=JSON argument is provided, the machine-readable JSON response
1332 will contain the following keys:
1334 storage-index: a base32-encoded string with the objects's storage index,
1335 or an empty string for LIT files
1336 repair-attempted: (bool) True if repair was attempted
1337 repair-successful: (bool) True if repair was attempted and the file was
1338 fully healthy afterwards. False if no repair was
1339 attempted, or if a repair attempt failed.
1340 pre-repair-results: a dictionary that describes the state of the file
1341 before any repair was performed. This contains exactly
1342 the same keys as the 'results' value of the t=check
1343 response, described above.
1344 post-repair-results: a dictionary that describes the state of the file
1345 after any repair was performed. If no repair was
1346 performed, post-repair-results and pre-repair-results
1347 will be the same. This contains exactly the same keys
1348 as the 'results' value of the t=check response,
1351 POST $URL?t=start-deep-check&repair=true (must add &ophandle=XYZ)
1353 This triggers a recursive walk of all files and directories, performing a
1354 t=check&repair=true on each one.
1356 Like t=start-deep-check without the repair= argument, this can only be
1357 invoked on a directory. An error (400 BAD_REQUEST) will be signalled if it
1358 is invoked on a file. The recursive walker will deal with loops safely.
1360 This accepts the same verify= and add-lease= arguments as
1361 t=start-deep-check. It uses the same ophandle= mechanism as
1362 start-deep-check. When an output=JSON argument is provided, the response
1363 will contain the following keys:
1365 finished: (bool) True if the operation has completed, else False
1366 root-storage-index: a base32-encoded string with the storage index of the
1367 starting point of the deep-check operation
1368 count-objects-checked: count of how many objects were checked
1370 count-objects-healthy-pre-repair: how many of those objects were completely
1371 healthy, before any repair
1372 count-objects-unhealthy-pre-repair: how many were damaged in some way
1373 count-objects-healthy-post-repair: how many of those objects were completely
1374 healthy, after any repair
1375 count-objects-unhealthy-post-repair: how many were damaged in some way
1377 count-repairs-attempted: repairs were attempted on this many objects.
1378 count-repairs-successful: how many repairs resulted in healthy objects
1379 count-repairs-unsuccessful: how many repairs resulted did not results in
1380 completely healthy objects
1381 count-corrupt-shares-pre-repair: how many shares were found to have
1382 corruption, summed over all objects
1383 examined, before any repair
1384 count-corrupt-shares-post-repair: how many shares were found to have
1385 corruption, summed over all objects
1386 examined, after any repair
1387 list-corrupt-shares: a list of "share identifiers", one for each share
1388 that was found to be corrupt (before any repair).
1389 Each share identifier is a list of (serverid,
1390 storage_index, sharenum).
1391 list-remaining-corrupt-shares: like list-corrupt-shares, but mutable shares
1392 that were successfully repaired are not
1393 included. These are shares that need
1394 manual processing. Since immutable shares
1395 cannot be modified by clients, all corruption
1396 in immutable shares will be listed here.
1397 list-unhealthy-files: a list of (pathname, check-results) tuples, for
1398 each file that was not fully healthy. 'pathname' is
1399 relative to the directory on which deep-check was
1400 invoked. The 'check-results' field is the same as
1401 that returned by t=check&repair=true&output=JSON,
1403 stats: a dictionary with the same keys as the t=start-deep-stats command
1406 POST $URL?t=stream-deep-check&repair=true
1408 This triggers a recursive walk of all files and directories, performing a
1409 t=check&repair=true on each one. For each unique object (duplicates are
1410 skipped), a single line of JSON is emitted to the HTTP response channel (or
1411 an error indication). When the walk is complete, a final line of JSON is
1412 emitted which contains the accumulated file-size/count "deep-stats" data.
1414 This emits the same data as t=stream-deep-check (without the repair=true),
1415 except that the "check-results" field is replaced with a
1416 "check-and-repair-results" field, which contains the keys returned by
1417 t=check&repair=true&output=json (i.e. repair-attempted, repair-successful,
1418 pre-repair-results, and post-repair-results). The output does not contain
1419 the summary dictionary that is provied by t=start-deep-check&repair=true
1420 (the one with count-objects-checked and list-unhealthy-files), since the
1421 receiving client is expected to calculate those values itself from the
1422 stream of per-object check-and-repair-results.
1424 Note that the "ERROR:" indication will only be emitted if traversal stops,
1425 which will only occur if an unrecoverable directory is encountered. If a
1426 file or directory repair fails, the traversal will continue, and the repair
1427 failure will be indicated in the JSON data (in the "repair-successful" key).
1429 POST $DIRURL?t=start-manifest (must add &ophandle=XYZ)
1431 This operation generates a "manfest" of the given directory tree, mostly
1432 for debugging. This is a table of (path, filecap/dircap), for every object
1433 reachable from the starting directory. The path will be slash-joined, and
1434 the filecap/dircap will contain a link to the object in question. This page
1435 gives immediate access to every object in the virtual filesystem subtree.
1437 This operation uses the same ophandle= mechanism as deep-check. The
1438 corresponding /operations/$HANDLE page has three different forms. The
1439 default is output=HTML.
1441 If output=text is added to the query args, the results will be a text/plain
1442 list. The first line is special: it is either "finished: yes" or "finished:
1443 no"; if the operation is not finished, you must periodically reload the
1444 page until it completes. The rest of the results are a plaintext list, with
1445 one file/dir per line, slash-separated, with the filecap/dircap separated
1448 If output=JSON is added to the queryargs, then the results will be a
1449 JSON-formatted dictionary with six keys. Note that because large directory
1450 structures can result in very large JSON results, the full results will not
1451 be available until the operation is complete (i.e. until output["finished"]
1454 finished (bool): if False then you must reload the page until True
1455 origin_si (base32 str): the storage index of the starting point
1456 manifest: list of (path, cap) tuples, where path is a list of strings.
1457 verifycaps: list of (printable) verify cap strings
1458 storage-index: list of (base32) storage index strings
1459 stats: a dictionary with the same keys as the t=start-deep-stats command
1462 POST $DIRURL?t=start-deep-size (must add &ophandle=XYZ)
1464 This operation generates a number (in bytes) containing the sum of the
1465 filesize of all directories and immutable files reachable from the given
1466 directory. This is a rough lower bound of the total space consumed by this
1467 subtree. It does not include space consumed by mutable files, nor does it
1468 take expansion or encoding overhead into account. Later versions of the
1469 code may improve this estimate upwards.
1471 The /operations/$HANDLE status output consists of two lines of text:
1476 POST $DIRURL?t=start-deep-stats (must add &ophandle=XYZ)
1478 This operation performs a recursive walk of all files and directories
1479 reachable from the given directory, and generates a collection of
1480 statistics about those objects.
1482 The result (obtained from the /operations/$OPHANDLE page) is a
1483 JSON-serialized dictionary with the following keys (note that some of these
1484 keys may be missing until 'finished' is True):
1486 finished: (bool) True if the operation has finished, else False
1487 count-immutable-files: count of how many CHK files are in the set
1488 count-mutable-files: same, for mutable files (does not include directories)
1489 count-literal-files: same, for LIT files (data contained inside the URI)
1490 count-files: sum of the above three
1491 count-directories: count of directories
1492 count-unknown: count of unrecognized objects (perhaps from the future)
1493 size-immutable-files: total bytes for all CHK files in the set, =deep-size
1494 size-mutable-files (TODO): same, for current version of all mutable files
1495 size-literal-files: same, for LIT files
1496 size-directories: size of directories (includes size-literal-files)
1497 size-files-histogram: list of (minsize, maxsize, count) buckets,
1498 with a histogram of filesizes, 5dB/bucket,
1499 for both literal and immutable files
1500 largest-directory: number of children in the largest directory
1501 largest-immutable-file: number of bytes in the largest CHK file
1503 size-mutable-files is not implemented, because it would require extra
1504 queries to each mutable file to get their size. This may be implemented in
1507 Assuming no sharing, the basic space consumed by a single root directory is
1508 the sum of size-immutable-files, size-mutable-files, and size-directories.
1509 The actual disk space used by the shares is larger, because of the
1510 following sources of overhead:
1513 expansion due to erasure coding
1514 share management data (leases)
1515 backend (ext3) minimum block size
1517 POST $URL?t=stream-manifest
1519 This operation performs a recursive walk of all files and directories
1520 reachable from the given starting point. For each such unique object
1521 (duplicates are skipped), a single line of JSON is emitted to the HTTP
1522 response channel (or an error indication, see below). When the walk is
1523 complete, a final line of JSON is emitted which contains the accumulated
1524 file-size/count "deep-stats" data.
1526 A CLI tool can split the response stream on newlines into "response units",
1527 and parse each response unit as JSON. Each such parsed unit will be a
1528 dictionary, and will contain at least the "type" key: a string, one of
1529 "file", "directory", or "stats".
1531 For all units that have a type of "file" or "directory", the dictionary will
1532 contain the following keys:
1534 "path": a list of strings, with the path that is traversed to reach the
1536 "cap": a write-cap URI for the file or directory, if available, else a
1538 "verifycap": a verify-cap URI for the file or directory
1539 "repaircap": an URI for the weakest cap that can still be used to repair
1541 "storage-index": a base32 storage index for the object
1543 Note that non-distributed files (i.e. LIT files) will have values of None
1544 for verifycap, repaircap, and storage-index, since these files can neither
1545 be verified nor repaired, and are not stored on the storage servers.
1547 The last unit in the stream will have a type of "stats", and will contain
1548 the keys described in the "start-deep-stats" operation, below.
1550 If any errors occur during the traversal (specifically if a directory is
1551 unrecoverable, such that further traversal is not possible), an error
1552 indication is written to the response body, instead of the usual line of
1553 JSON. This error indication line will begin with the string "ERROR:" (in all
1554 caps), and contain a summary of the error on the rest of the line. The
1555 remaining lines of the response body will be a python exception. The client
1556 application should look for the ERROR: and stop processing JSON as soon as
1557 it is seen. The line just before the ERROR: will describe the directory that
1558 was untraversable, since the manifest entry is emitted to the HTTP response
1559 body before the child is traversed.
1561 == Other Useful Pages ==
1563 The portion of the web namespace that begins with "/uri" (and "/named") is
1564 dedicated to giving users (both humans and programs) access to the Tahoe
1565 virtual filesystem. The rest of the namespace provides status information
1566 about the state of the Tahoe node.
1568 GET / (the root page)
1570 This is the "Welcome Page", and contains a few distinct sections:
1572 Node information: library versions, local nodeid, services being provided.
1574 Filesystem Access Forms: create a new directory, view a file/directory by
1575 URI, upload a file (unlinked), download a file by
1578 Grid Status: introducer information, helper information, connected storage
1583 This page lists all active uploads and downloads, and contains a short list
1584 of recent upload/download operations. Each operation has a link to a page
1585 that describes file sizes, servers that were involved, and the time consumed
1586 in each phase of the operation.
1588 A GET of /status/?t=json will contain a machine-readable subset of the same
1589 data. It returns a JSON-encoded dictionary. The only key defined at this
1590 time is "active", with a value that is a list of operation dictionaries, one
1591 for each active operation. Once an operation is completed, it will no longer
1592 appear in data["active"] .
1594 Each op-dict contains a "type" key, one of "upload", "download",
1595 "mapupdate", "publish", or "retrieve" (the first two are for immutable
1596 files, while the latter three are for mutable files and directories).
1598 The "upload" op-dict will contain the following keys:
1600 type (string): "upload"
1601 storage-index-string (string): a base32-encoded storage index
1602 total-size (int): total size of the file
1603 status (string): current status of the operation
1604 progress-hash (float): 1.0 when the file has been hashed
1605 progress-ciphertext (float): 1.0 when the file has been encrypted.
1606 progress-encode-push (float): 1.0 when the file has been encoded and
1607 pushed to the storage servers. For helper
1608 uploads, the ciphertext value climbs to 1.0
1609 first, then encoding starts. For unassisted
1610 uploads, ciphertext and encode-push progress
1611 will climb at the same pace.
1613 The "download" op-dict will contain the following keys:
1615 type (string): "download"
1616 storage-index-string (string): a base32-encoded storage index
1617 total-size (int): total size of the file
1618 status (string): current status of the operation
1619 progress (float): 1.0 when the file has been fully downloaded
1621 Front-ends which want to report progress information are advised to simply
1622 average together all the progress-* indicators. A slightly more accurate
1623 value can be found by ignoring the progress-hash value (since the current
1624 implementation hashes synchronously, so clients will probably never see
1625 progress-hash!=1.0).
1629 This page provides a basic tool to predict the likely storage and bandwidth
1630 requirements of a large Tahoe grid. It provides forms to input things like
1631 total number of users, number of files per user, average file size, number
1632 of servers, expansion ratio, hard drive failure rate, etc. It then provides
1633 numbers like how many disks per server will be needed, how many read
1634 operations per second should be expected, and the likely MTBF for files in
1635 the grid. This information is very preliminary, and the model upon which it
1636 is based still needs a lot of work.
1640 If the node is running a helper (i.e. if [helper]enabled is set to True in
1641 tahoe.cfg), then this page will provide a list of all the helper operations
1642 currently in progress. If "?t=json" is added to the URL, it will return a
1643 JSON-formatted list of helper statistics, which can then be used to produce
1644 graphs to indicate how busy the helper is.
1648 This page provides "node statistics", which are collected from a variety of
1651 load_monitor: every second, the node schedules a timer for one second in
1652 the future, then measures how late the subsequent callback
1653 is. The "load_average" is this tardiness, measured in
1654 seconds, averaged over the last minute. It is an indication
1655 of a busy node, one which is doing more work than can be
1656 completed in a timely fashion. The "max_load" value is the
1657 highest value that has been seen in the last 60 seconds.
1659 cpu_monitor: every minute, the node uses time.clock() to measure how much
1660 CPU time it has used, and it uses this value to produce
1661 1min/5min/15min moving averages. These values range from 0%
1662 (0.0) to 100% (1.0), and indicate what fraction of the CPU
1663 has been used by the Tahoe node. Not all operating systems
1664 provide meaningful data to time.clock(): they may report 100%
1665 CPU usage at all times.
1667 uploader: this counts how many immutable files (and bytes) have been
1668 uploaded since the node was started
1670 downloader: this counts how many immutable files have been downloaded
1671 since the node was started
1673 publishes: this counts how many mutable files (including directories) have
1674 been modified since the node was started
1676 retrieves: this counts how many mutable files (including directories) have
1677 been read since the node was started
1679 There are other statistics that are tracked by the node. The "raw stats"
1680 section shows a formatted dump of all of them.
1682 By adding "?t=json" to the URL, the node will return a JSON-formatted
1683 dictionary of stats values, which can be used by other tools to produce
1684 graphs of node behavior. The misc/munin/ directory in the source
1685 distribution provides some tools to produce these graphs.
1687 GET / (introducer status)
1689 For Introducer nodes, the welcome page displays information about both
1690 clients and servers which are connected to the introducer. Servers make
1691 "service announcements", and these are listed in a table. Clients will
1692 subscribe to hear about service announcements, and these subscriptions are
1693 listed in a separate table. Both tables contain information about what
1694 version of Tahoe is being run by the remote node, their advertised and
1695 outbound IP addresses, their nodeid and nickname, and how long they have
1698 By adding "?t=json" to the URL, the node will return a JSON-formatted
1699 dictionary of stats values, which can be used to produce graphs of connected
1700 clients over time. This dictionary has the following keys:
1702 ["subscription_summary"] : a dictionary mapping service name (like
1703 "storage") to an integer with the number of
1704 clients that have subscribed to hear about that
1706 ["announcement_summary"] : a dictionary mapping service name to an integer
1707 with the number of servers which are announcing
1709 ["announcement_distinct_hosts"] : a dictionary mapping service name to an
1710 integer which represents the number of
1711 distinct hosts that are providing that
1712 service. If two servers have announced
1713 FURLs which use the same hostnames (but
1714 different ports and tubids), they are
1715 considered to be on the same host.
1718 == Static Files in /public_html ==
1720 The webapi server will take any request for a URL that starts with /static
1721 and serve it from a configurable directory which defaults to
1722 $BASEDIR/public_html . This is configured by setting the "[node]web.static"
1723 value in $BASEDIR/tahoe.cfg . If this is left at the default value of
1724 "public_html", then http://localhost:3456/static/subdir/foo.html will be
1725 served with the contents of the file $BASEDIR/public_html/subdir/foo.html .
1727 This can be useful to serve a javascript application which provides a
1728 prettier front-end to the rest of the Tahoe webapi.
1731 == Safety and security issues -- names vs. URIs ==
1733 Summary: use explicit file- and dir- caps whenever possible, to reduce the
1734 potential for surprises when the filesystem structure is changed.
1736 Tahoe provides a mutable filesystem, but the ways that the filesystem can
1737 change are limited. The only thing that can change is that the mapping from
1738 child names to child objects that each directory contains can be changed by
1739 adding a new child name pointing to an object, removing an existing child name,
1740 or changing an existing child name to point to a different object.
1742 Obviously if you query Tahoe for information about the filesystem and then act
1743 to change the filesystem (such as by getting a listing of the contents of a
1744 directory and then adding a file to the directory), then the filesystem might
1745 have been changed after you queried it and before you acted upon it. However,
1746 if you use the URI instead of the pathname of an object when you act upon the
1747 object, then the only change that can happen is if the object is a directory
1748 then the set of child names it has might be different. If, on the other hand,
1749 you act upon the object using its pathname, then a different object might be in
1750 that place, which can result in more kinds of surprises.
1752 For example, suppose you are writing code which recursively downloads the
1753 contents of a directory. The first thing your code does is fetch the listing
1754 of the contents of the directory. For each child that it fetched, if that
1755 child is a file then it downloads the file, and if that child is a directory
1756 then it recurses into that directory. Now, if the download and the recurse
1757 actions are performed using the child's name, then the results might be
1758 wrong, because for example a child name that pointed to a sub-directory when
1759 you listed the directory might have been changed to point to a file (in which
1760 case your attempt to recurse into it would result in an error and the file
1761 would be skipped), or a child name that pointed to a file when you listed the
1762 directory might now point to a sub-directory (in which case your attempt to
1763 download the child would result in a file containing HTML text describing the
1766 If your recursive algorithm uses the uri of the child instead of the name of
1767 the child, then those kinds of mistakes just can't happen. Note that both the
1768 child's name and the child's URI are included in the results of listing the
1769 parent directory, so it isn't any harder to use the URI for this purpose.
1771 The read and write caps in a given directory node are separate URIs, and
1772 can't be assumed to point to the same object even if they were retrieved in
1773 the same operation (although the webapi server attempts to ensure this
1774 in most cases). If you need to rely on that property, you should explicitly
1775 verify it. More generally, you should not make assumptions about the
1776 internal consistency of the contents of mutable directories. As a result
1777 of the signatures on mutable object versions, it is guaranteed that a given
1778 version was written in a single update, but -- as in the case of a file --
1779 the contents may have been chosen by a malicious writer in a way that is
1780 designed to confuse applications that rely on their consistency.
1782 In general, use names if you want "whatever object (whether file or
1783 directory) is found by following this name (or sequence of names) when my
1784 request reaches the server". Use URIs if you want "this particular object".
1786 == Concurrency Issues ==
1788 Tahoe uses both mutable and immutable files. Mutable files can be created
1789 explicitly by doing an upload with ?mutable=true added, or implicitly by
1790 creating a new directory (since a directory is just a special way to
1791 interpret a given mutable file).
1793 Mutable files suffer from the same consistency-vs-availability tradeoff that
1794 all distributed data storage systems face. It is not possible to
1795 simultaneously achieve perfect consistency and perfect availability in the
1796 face of network partitions (servers being unreachable or faulty).
1798 Tahoe tries to achieve a reasonable compromise, but there is a basic rule in
1799 place, known as the Prime Coordination Directive: "Don't Do That". What this
1800 means is that if write-access to a mutable file is available to several
1801 parties, then those parties are responsible for coordinating their activities
1802 to avoid multiple simultaneous updates. This could be achieved by having
1803 these parties talk to each other and using some sort of locking mechanism, or
1804 by serializing all changes through a single writer.
1806 The consequences of performing uncoordinated writes can vary. Some of the
1807 writers may lose their changes, as somebody else wins the race condition. In
1808 many cases the file will be left in an "unhealthy" state, meaning that there
1809 are not as many redundant shares as we would like (reducing the reliability
1810 of the file against server failures). In the worst case, the file can be left
1811 in such an unhealthy state that no version is recoverable, even the old ones.
1812 It is this small possibility of data loss that prompts us to issue the Prime
1813 Coordination Directive.
1815 Tahoe nodes implement internal serialization to make sure that a single Tahoe
1816 node cannot conflict with itself. For example, it is safe to issue two
1817 directory modification requests to a single tahoe node's webapi server at the
1818 same time, because the Tahoe node will internally delay one of them until
1819 after the other has finished being applied. (This feature was introduced in
1820 Tahoe-1.1; back with Tahoe-1.0 the web client was responsible for serializing
1821 web requests themselves).
1823 For more details, please see the "Consistency vs Availability" and "The Prime
1824 Coordination Directive" sections of mutable.txt, in the same directory as
1828 [1]: URLs and HTTP and UTF-8, Oh My
1830 HTTP does not provide a mechanism to specify the character set used to
1831 encode non-ascii names in URLs (rfc2396#2.1). We prefer the convention that
1832 the filename= argument shall be a URL-encoded UTF-8 encoded unicode object.
1833 For example, suppose we want to provoke the server into using a filename of
1834 "f i a n c e-acute e" (i.e. F I A N C U+00E9 E). The UTF-8 encoding of this
1835 is 0x66 0x69 0x61 0x6e 0x63 0xc3 0xa9 0x65 (or "fianc\xC3\xA9e", as python's
1836 repr() function would show). To encode this into a URL, the non-printable
1837 characters must be escaped with the urlencode '%XX' mechansim, giving us
1838 "fianc%C3%A9e". Thus, the first line of the HTTP request will be "GET
1839 /uri/CAP...?save=true&filename=fianc%C3%A9e HTTP/1.1". Not all browsers
1840 provide this: IE7 uses the Latin-1 encoding, which is fianc%E9e.
1842 The response header will need to indicate a non-ASCII filename. The actual
1843 mechanism to do this is not clear. For ASCII filenames, the response header
1846 Content-Disposition: attachment; filename="english.txt"
1848 If Tahoe were to enforce the utf-8 convention, it would need to decode the
1849 URL argument into a unicode string, and then encode it back into a sequence
1850 of bytes when creating the response header. One possibility would be to use
1851 unencoded utf-8. Developers suggest that IE7 might accept this:
1853 #1: Content-Disposition: attachment; filename="fianc\xC3\xA9e"
1854 (note, the last four bytes of that line, not including the newline, are
1855 0xC3 0xA9 0x65 0x22)
1857 RFC2231#4 (dated 1997): suggests that the following might work, and some
1858 developers (http://markmail.org/message/dsjyokgl7hv64ig3) have reported that
1859 it is supported by firefox (but not IE7):
1861 #2: Content-Disposition: attachment; filename*=utf-8''fianc%C3%A9e
1863 My reading of RFC2616#19.5.1 (which defines Content-Disposition) says that
1864 the filename= parameter is defined to be wrapped in quotes (presumeably to
1865 allow spaces without breaking the parsing of subsequent parameters), which
1868 #3: Content-Disposition: attachment; filename*=utf-8''"fianc%C3%A9e"
1870 However this is contrary to the examples in the email thread listed above.
1872 Developers report that IE7 (when it is configured for UTF-8 URL encoding,
1873 which is not the default in asian countries), will accept:
1875 #4: Content-Disposition: attachment; filename=fianc%C3%A9e
1877 However, for maximum compatibility, Tahoe simply copies bytes from the URL
1878 into the response header, rather than enforcing the utf-8 convention. This
1879 means it does not try to decode the filename from the URL argument, nor does
1880 it encode the filename into the response header.