misc/make-canary-files.py: tool to create 'canary files', explained in the docstring

diff --git a/misc/make-canary-files.py b/misc/make-canary-files.py
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+#! /usr/bin/python
+
+"""
+Given a list of nodeids and a 'convergence' file, create a bunch of files
+that will (when encoded at k=1,N=1) be uploaded to specific nodeids.
+
+Run this as follows:
+
+ make-canary-files.py -c PATH/TO/convergence -n PATH/TO/nodeids -k 1 -N 1
+
+It will create a directory named 'canaries', with one file per nodeid named
+'$NODEID-$NICKNAME.txt', that contains some random text.
+
+The 'nodeids' file should contain one base32 nodeid per line, followed by the
+optional nickname, like:
+
+---
+5yyqu2hbvbh3rgtsgxrmmg4g77b6p3yo  server12
+vb7vm2mneyid5jbyvcbk2wb5icdhwtun  server13
+...
+---
+
+The resulting 'canaries/5yyqu2hbvbh3rgtsgxrmmg4g77b6p3yo-server12.txt' file
+will, when uploaded with the given (convergence,k,N) pair, have its first
+share placed on the 5yyq/server12 storage server. If N>1, the other shares
+will be placed elsewhere, of course.
+
+This tool can be useful to construct a set of 'canary' files, which can then
+be uploaded to storage servers, and later downloaded to test a grid's health.
+If you are able to download the canary for server12 via some tahoe node X,
+then the following properties are known to be true:
+
+ node X is running, and has established a connection to server12
+ server12 is running, and returning data for at least the given file
+
+Using k=1/N=1 creates a separate test for each server. The test process is
+then to download the whole directory of files (perhaps with a t=deep-check
+operation).
+
+Alternatively, you could upload with the usual k=3/N=10 and then move/delete
+shares to put all N shares on a single server.
+
+Note that any changes to the nodeid list will affect the placement of shares.
+Shares should be uploaded with the same nodeid list as this tool used when
+constructing the files.
+
+Also note that this tool uses the Tahoe codebase, so it should be run on a
+system where Tahoe is installed, or in a source tree with setup.py like this:
+
+ setup.py run_with_pythonpath -p -c 'misc/make-canary-files.py ARGS..'
+"""
+
+import os, sha
+from twisted.python import usage
+from allmydata.immutable import upload
+from allmydata.util import base32
+
+class Options(usage.Options):
+    optParameters = [
+        ("convergence", "c", None, "path to NODEDIR/private/convergence"),
+        ("nodeids", "n", None, "path to file with one base32 nodeid per line"),
+        ("k", "k", 1, "number of necessary shares, defaults to 1", int),
+        ("N", "N", 1, "number of total shares, defaults to 1", int),
+        ]
+    optFlags = [
+        ("verbose", "v", "Be noisy"),
+        ]
+
+opts = Options()
+opts.parseOptions()
+
+verbose = bool(opts["verbose"])
+
+nodes = {}
+for line in open(opts["nodeids"], "r").readlines():
+    line = line.strip()
+    if not line or line.startswith("#"):
+        continue
+    pieces = line.split(None, 1)
+    if len(pieces) == 2:
+        nodeid_s, nickname = pieces
+    else:
+        nodeid_s = pieces[0]
+        nickname = None
+    nodeid = base32.a2b(nodeid_s)
+    nodes[nodeid] = nickname
+
+if opts["k"] != 3 or opts["N"] != 10:
+    print "note: using non-default k/N requires patching the Tahoe code"
+    print "src/allmydata/client.py line 55, DEFAULT_ENCODING_PARAMETERS"
+
+convergence_file = os.path.expanduser(opts["convergence"])
+convergence_s = open(convergence_file, "rb").read().strip()
+convergence = base32.a2b(convergence_s)
+
+def get_permuted_peers(key):
+    results = []
+    for nodeid in nodes:
+        permuted = sha.new(key + nodeid).digest()
+        results.append((permuted, nodeid))
+    results.sort(lambda a,b: cmp(a[0], b[0]))
+    return [ r[1] for r in results ]
+
+def find_share_for_target(target):
+    target_s = base32.b2a(target)
+    prefix = "The first share of this file will be placed on " + target_s + "\n"
+    prefix += "This data is random: "
+    attempts = 0
+    while True:
+        attempts += 1
+        suffix = base32.b2a(os.urandom(10))
+        if verbose: print " trying", suffix,
+        data = prefix + suffix + "\n"
+        assert len(data) > 55  # no LIT files
+        # now, what storage index will this get?
+        u = upload.Data(data, convergence)
+        eu = upload.EncryptAnUploadable(u)
+        d = eu.get_storage_index() # this happens to run synchronously
+        def _got_si(si):
+            if verbose: print "SI", base32.b2a(si),
+            peerlist = get_permuted_peers(si)
+            if peerlist[0] == target:
+                # great!
+                if verbose: print "  yay!"
+                fn = base32.b2a(target)
+                if nodes[target]:
+                    nickname = nodes[target].replace("/", "_")
+                    fn += "-" + nickname
+                fn += ".txt"
+                fn = os.path.join("canaries", fn)
+                open(fn, "w").write(data)
+                return True
+            # nope, must try again
+            if verbose: print "  boo"
+            return False
+        d.addCallback(_got_si)
+        # get sneaky and look inside the Deferred for the synchronous result
+        if d.result:
+            return attempts
+
+os.mkdir("canaries")
+attempts = []
+for target in nodes:
+    target_s = base32.b2a(target)
+    print "working on", target_s
+    attempts.append(find_share_for_target(target))
+print "done"
+print "%d attempts total, avg %d per target, max %d" % \
+      (sum(attempts), 1.0* sum(attempts) / len(nodes), max(attempts))
+
+