From: Kevan Carstensen Date: Tue, 2 Aug 2011 01:41:19 +0000 (-0700) Subject: interfaces: change interfaces to work with MDMF X-Git-Tag: trac-5200~31 X-Git-Url: https://git.rkrishnan.org/pf/content/simplejson/frontends/architecture.txt?a=commitdiff_plain;h=126d1ad010d6469f5c95953e4581b0098f0d535e;p=tahoe-lafs%2Ftahoe-lafs.git interfaces: change interfaces to work with MDMF A lot of this work concerns #993, in that it unifies (to an extent) the interfaces of mutable and immutable files. --- diff --git a/src/allmydata/interfaces.py b/src/allmydata/interfaces.py index e9b7af1b..a25bb91e 100644 --- a/src/allmydata/interfaces.py +++ b/src/allmydata/interfaces.py @@ -4,6 +4,10 @@ from foolscap.api import StringConstraint, ListOf, TupleOf, SetOf, DictOf, \ ChoiceOf, IntegerConstraint, Any, RemoteInterface, Referenceable HASH_SIZE=32 +SALT_SIZE=16 + +SDMF_VERSION=0 +MDMF_VERSION=1 Hash = StringConstraint(maxLength=HASH_SIZE, minLength=HASH_SIZE)# binary format 32-byte SHA256 hash @@ -417,6 +421,72 @@ class IStorageBroker(Interface): """ +class IMutableSlotWriter(Interface): + """ + The interface for a writer around a mutable slot on a remote server. + """ + def set_checkstring(checkstring, *args): + """ + Set the checkstring that I will pass to the remote server when + writing. + + @param checkstring A packed checkstring to use. + + Note that implementations can differ in which semantics they + wish to support for set_checkstring -- they can, for example, + build the checkstring themselves from its constituents, or + some other thing. + """ + + def get_checkstring(): + """ + Get the checkstring that I think currently exists on the remote + server. + """ + + def put_block(data, segnum, salt): + """ + Add a block and salt to the share. + """ + + def put_encprivey(encprivkey): + """ + Add the encrypted private key to the share. + """ + + def put_blockhashes(blockhashes=list): + """ + Add the block hash tree to the share. + """ + + def put_sharehashes(sharehashes=dict): + """ + Add the share hash chain to the share. + """ + + def get_signable(): + """ + Return the part of the share that needs to be signed. + """ + + def put_signature(signature): + """ + Add the signature to the share. + """ + + def put_verification_key(verification_key): + """ + Add the verification key to the share. + """ + + def finish_publishing(): + """ + Do anything necessary to finish writing the share to a remote + server. I require that no further publishing needs to take place + after this method has been called. + """ + + class IURI(Interface): def init_from_string(uri): """Accept a string (as created by my to_string() method) and populate @@ -473,6 +543,11 @@ class IImmutableFileURI(IFileURI): class IMutableFileURI(Interface): """I am a URI which represents a mutable filenode.""" + def get_extension_params(): + """Return the extension parameters in the URI""" + + def set_extension_params(): + """Set the extension parameters that should be in the URI""" class IDirectoryURI(Interface): pass @@ -496,6 +571,175 @@ class MustBeReadonlyError(CapConstraintError): class MustNotBeUnknownRWError(CapConstraintError): """Cannot add an unknown child cap specified in a rw_uri field.""" + +class IReadable(Interface): + """I represent a readable object -- either an immutable file, or a + specific version of a mutable file. + """ + + def is_readonly(): + """Return True if this reference provides mutable access to the given + file or directory (i.e. if you can modify it), or False if not. Note + that even if this reference is read-only, someone else may hold a + read-write reference to it. + + For an IReadable returned by get_best_readable_version(), this will + always return True, but for instances of subinterfaces such as + IMutableFileVersion, it may return False.""" + + def is_mutable(): + """Return True if this file or directory is mutable (by *somebody*, + not necessarily you), False if it is is immutable. Note that a file + might be mutable overall, but your reference to it might be + read-only. On the other hand, all references to an immutable file + will be read-only; there are no read-write references to an immutable + file.""" + + def get_storage_index(): + """Return the storage index of the file.""" + + def get_size(): + """Return the length (in bytes) of this readable object.""" + + def download_to_data(): + """Download all of the file contents. I return a Deferred that fires + with the contents as a byte string.""" + + def read(consumer, offset=0, size=None): + """Download a portion (possibly all) of the file's contents, making + them available to the given IConsumer. Return a Deferred that fires + (with the consumer) when the consumer is unregistered (either because + the last byte has been given to it, or because the consumer threw an + exception during write(), possibly because it no longer wants to + receive data). The portion downloaded will start at 'offset' and + contain 'size' bytes (or the remainder of the file if size==None). + + The consumer will be used in non-streaming mode: an IPullProducer + will be attached to it. + + The consumer will not receive data right away: several network trips + must occur first. The order of events will be:: + + consumer.registerProducer(p, streaming) + (if streaming == False):: + consumer does p.resumeProducing() + consumer.write(data) + consumer does p.resumeProducing() + consumer.write(data).. (repeat until all data is written) + consumer.unregisterProducer() + deferred.callback(consumer) + + If a download error occurs, or an exception is raised by + consumer.registerProducer() or consumer.write(), I will call + consumer.unregisterProducer() and then deliver the exception via + deferred.errback(). To cancel the download, the consumer should call + p.stopProducing(), which will result in an exception being delivered + via deferred.errback(). + + See src/allmydata/util/consumer.py for an example of a simple + download-to-memory consumer. + """ + + +class IWritable(Interface): + """ + I define methods that callers can use to update SDMF and MDMF + mutable files on a Tahoe-LAFS grid. + """ + # XXX: For the moment, we have only this. It is possible that we + # want to move overwrite() and modify() in here too. + def update(data, offset): + """ + I write the data from my data argument to the MDMF file, + starting at offset. I continue writing data until my data + argument is exhausted, appending data to the file as necessary. + """ + # assert IMutableUploadable.providedBy(data) + # to append data: offset=node.get_size_of_best_version() + # do we want to support compacting MDMF? + # for an MDMF file, this can be done with O(data.get_size()) + # memory. For an SDMF file, any modification takes + # O(node.get_size_of_best_version()). + + +class IMutableFileVersion(IReadable): + """I provide access to a particular version of a mutable file. The + access is read/write if I was obtained from a filenode derived from + a write cap, or read-only if the filenode was derived from a read cap. + """ + + def get_sequence_number(): + """Return the sequence number of this version.""" + + def get_servermap(): + """Return the IMutableFileServerMap instance that was used to create + this object. + """ + + def get_writekey(): + """Return this filenode's writekey, or None if the node does not have + write-capability. This may be used to assist with data structures + that need to make certain data available only to writers, such as the + read-write child caps in dirnodes. The recommended process is to have + reader-visible data be submitted to the filenode in the clear (where + it will be encrypted by the filenode using the readkey), but encrypt + writer-visible data using this writekey. + """ + + # TODO: Can this be overwrite instead of replace? + def replace(new_contents): + """Replace the contents of the mutable file, provided that no other + node has published (or is attempting to publish, concurrently) a + newer version of the file than this one. + + I will avoid modifying any share that is different than the version + given by get_sequence_number(). However, if another node is writing + to the file at the same time as me, I may manage to update some shares + while they update others. If I see any evidence of this, I will signal + UncoordinatedWriteError, and the file will be left in an inconsistent + state (possibly the version you provided, possibly the old version, + possibly somebody else's version, and possibly a mix of shares from + all of these). + + The recommended response to UncoordinatedWriteError is to either + return it to the caller (since they failed to coordinate their + writes), or to attempt some sort of recovery. It may be sufficient to + wait a random interval (with exponential backoff) and repeat your + operation. If I do not signal UncoordinatedWriteError, then I was + able to write the new version without incident. + + I return a Deferred that fires (with a PublishStatus object) when the + update has completed. + """ + + def modify(modifier_cb): + """Modify the contents of the file, by downloading this version, + applying the modifier function (or bound method), then uploading + the new version. This will succeed as long as no other node + publishes a version between the download and the upload. + I return a Deferred that fires (with a PublishStatus object) when + the update is complete. + + The modifier callable will be given three arguments: a string (with + the old contents), a 'first_time' boolean, and a servermap. As with + download_to_data(), the old contents will be from this version, + but the modifier can use the servermap to make other decisions + (such as refusing to apply the delta if there are multiple parallel + versions, or if there is evidence of a newer unrecoverable version). + 'first_time' will be True the first time the modifier is called, + and False on any subsequent calls. + + The callable should return a string with the new contents. The + callable must be prepared to be called multiple times, and must + examine the input string to see if the change that it wants to make + is already present in the old version. If it does not need to make + any changes, it can either return None, or return its input string. + + If the modifier raises an exception, it will be returned in the + errback. + """ + + # The hierarchy looks like this: # IFilesystemNode # IFileNode @@ -586,6 +830,7 @@ class IFilesystemNode(Interface): def raise_error(): """Raise any error associated with this node.""" + # XXX: These may not be appropriate outside the context of an IReadable. def get_size(): """Return the length (in bytes) of the data this node represents. For directory nodes, I return the size of the backing store. I return @@ -602,43 +847,45 @@ class IFilesystemNode(Interface): class IFileNode(IFilesystemNode): """I am a node which represents a file: a sequence of bytes. I am not a container, like IDirectoryNode.""" + def get_best_readable_version(): + """Return a Deferred that fires with an IReadable for the 'best' + available version of the file. The IReadable provides only read + access, even if this filenode was derived from a write cap. -class IImmutableFileNode(IFileNode): - def read(consumer, offset=0, size=None): - """Download a portion (possibly all) of the file's contents, making - them available to the given IConsumer. Return a Deferred that fires - (with the consumer) when the consumer is unregistered (either because - the last byte has been given to it, or because the consumer threw an - exception during write(), possibly because it no longer wants to - receive data). The portion downloaded will start at 'offset' and - contain 'size' bytes (or the remainder of the file if size==None). - - The consumer will be used in non-streaming mode: an IPullProducer - will be attached to it. + For an immutable file, there is only one version. For a mutable + file, the 'best' version is the recoverable version with the + highest sequence number. If no uncoordinated writes have occurred, + and if enough shares are available, then this will be the most + recent version that has been uploaded. If no version is recoverable, + the Deferred will errback with an UnrecoverableFileError. + """ - The consumer will not receive data right away: several network trips - must occur first. The order of events will be:: + def download_best_version(): + """Download the contents of the version that would be returned + by get_best_readable_version(). This is equivalent to calling + download_to_data() on the IReadable given by that method. - consumer.registerProducer(p, streaming) - (if streaming == False):: - consumer does p.resumeProducing() - consumer.write(data) - consumer does p.resumeProducing() - consumer.write(data).. (repeat until all data is written) - consumer.unregisterProducer() - deferred.callback(consumer) + I return a Deferred that fires with a byte string when the file + has been fully downloaded. To support streaming download, use + the 'read' method of IReadable. If no version is recoverable, + the Deferred will errback with an UnrecoverableFileError. + """ - If a download error occurs, or an exception is raised by - consumer.registerProducer() or consumer.write(), I will call - consumer.unregisterProducer() and then deliver the exception via - deferred.errback(). To cancel the download, the consumer should call - p.stopProducing(), which will result in an exception being delivered - via deferred.errback(). + def get_size_of_best_version(): + """Find the size of the version that would be returned by + get_best_readable_version(). - See src/allmydata/util/consumer.py for an example of a simple - download-to-memory consumer. + I return a Deferred that fires with an integer. If no version + is recoverable, the Deferred will errback with an + UnrecoverableFileError. """ + +class IImmutableFileNode(IFileNode, IReadable): + """I am a node representing an immutable file. Immutable files have + only one version""" + + class IMutableFileNode(IFileNode): """I provide access to a 'mutable file', which retains its identity regardless of what contents are put in it. @@ -698,26 +945,16 @@ class IMutableFileNode(IFileNode): only be retrieved and updated all-at-once, as a single big string. Future versions of our mutable files will remove this restriction. """ - - def download_best_version(): - """Download the 'best' available version of the file, meaning one of - the recoverable versions with the highest sequence number. If no + def get_best_mutable_version(): + """Return a Deferred that fires with an IMutableFileVersion for + the 'best' available version of the file. The best version is + the recoverable version with the highest sequence number. If no uncoordinated writes have occurred, and if enough shares are - available, then this will be the most recent version that has been - uploaded. - - I update an internal servermap with MODE_READ, determine which - version of the file is indicated by - servermap.best_recoverable_version(), and return a Deferred that - fires with its contents. If no version is recoverable, the Deferred - will errback with UnrecoverableFileError. - """ - - def get_size_of_best_version(): - """Find the size of the version that would be downloaded with - download_best_version(), without actually downloading the whole file. + available, then this will be the most recent version that has + been uploaded. - I return a Deferred that fires with an integer. + If no version is recoverable, the Deferred will errback with an + UnrecoverableFileError. """ def overwrite(new_contents): @@ -756,7 +993,6 @@ class IMutableFileNode(IFileNode): errback. """ - def get_servermap(mode): """Return a Deferred that fires with an IMutableFileServerMap instance, updated using the given mode. @@ -810,6 +1046,9 @@ class IMutableFileNode(IFileNode): writer-visible data using this writekey. """ + def get_version(): + """Returns the mutable file protocol version.""" + class NotEnoughSharesError(Exception): """Download was unable to get enough shares""" @@ -1646,6 +1885,37 @@ class IUploadable(Interface): """The upload is finished, and whatever filehandle was in use may be closed.""" + +class IMutableUploadable(Interface): + """ + I represent content that is due to be uploaded to a mutable filecap. + """ + # This is somewhat simpler than the IUploadable interface above + # because mutable files do not need to be concerned with possibly + # generating a CHK, nor with per-file keys. It is a subset of the + # methods in IUploadable, though, so we could just as well implement + # the mutable uploadables as IUploadables that don't happen to use + # those methods (with the understanding that the unused methods will + # never be called on such objects) + def get_size(): + """ + Returns a Deferred that fires with the size of the content held + by the uploadable. + """ + + def read(length): + """ + Returns a list of strings which, when concatenated, are the next + length bytes of the file, or fewer if there are fewer bytes + between the current location and the end of the file. + """ + + def close(): + """ + The process that used the Uploadable is finished using it, so + the uploadable may be closed. + """ + class IUploadResults(Interface): """I am returned by upload() methods. I contain a number of public attributes which can be read to determine the results of the upload. Some