From: Zooko O'Whielacronx <zooko@zooko.com>
Date: Wed, 13 Feb 2008 03:48:37 +0000 (-0700)
Subject: use base62 encoding for storage indexes, on disk and in verifier caps, and in logging... 
X-Git-Tag: allmydata-tahoe-0.8.0~87
X-Git-Url: https://git.rkrishnan.org/pf/content/de.html?a=commitdiff_plain;h=3f8df27063cfea5414142e906c1ccd2f39150405;p=tahoe-lafs%2Ftahoe-lafs.git

use base62 encoding for storage indexes, on disk and in verifier caps, and in logging and diagnostic tools
base62 encoding fits more information into alphanumeric chars while avoiding the troublesome non-alphanumeric chars of base64 encoding.  In particular, this allows us to work around the ext3 "32,000 entries in a directory" limit while retaining the convenient property that the intermediate directory names are leading prefixes of the storage index file names.
---

diff --git a/src/allmydata/checker.py b/src/allmydata/checker.py
index 0f47cad5..d03f6799 100644
--- a/src/allmydata/checker.py
+++ b/src/allmydata/checker.py
@@ -11,8 +11,8 @@ from twisted.internet import defer
 from twisted.application import service
 from twisted.python import log
 from allmydata.interfaces import IVerifierURI
-from allmydata import uri, download
-from allmydata.util import hashutil, idlib
+from allmydata import uri, download, storage
+from allmydata.util import hashutil
 
 class SimpleCHKFileChecker:
     """Return a list of (needed, total, found, sharemap), where sharemap maps
@@ -136,7 +136,7 @@ class SimpleCHKFileVerifier(download.FileDownloader):
                                 }
 
     def init_logging(self):
-        self._log_prefix = prefix = idlib.b2a(self._storage_index)[:6]
+        self._log_prefix = prefix = storage.si_b2a(self._storage_index)[:5]
         num = self._client.log("SimpleCHKFileVerifier(%s): starting" % prefix)
         self._log_number = num
 
@@ -149,7 +149,7 @@ class SimpleCHKFileVerifier(download.FileDownloader):
 
 
     def start(self):
-        log.msg("starting download [%s]" % idlib.b2a(self._storage_index)[:6])
+        log.msg("starting download [%s]" % storage.si_b2a(self._storage_index)[:5])
 
         # first step: who should we download from?
         d = defer.maybeDeferred(self._get_all_shareholders)
diff --git a/src/allmydata/download.py b/src/allmydata/download.py
index 4d382771..5229e6a6 100644
--- a/src/allmydata/download.py
+++ b/src/allmydata/download.py
@@ -365,9 +365,9 @@ class FileDownloader:
                                 }
 
     def init_logging(self):
-        self._log_prefix = prefix = idlib.b2a(self._storage_index)[:6]
+        self._log_prefix = prefix = storage.si_b2a(self._storage_index)[:5]
         num = self._client.log(format="FileDownloader(%(si)s): starting",
-                               si=idlib.b2a(self._storage_index))
+                               si=storage.si_b2a(self._storage_index))
         self._log_number = num
 
     def log(self, *args, **kwargs):
diff --git a/src/allmydata/encode.py b/src/allmydata/encode.py
index 993b12f1..c06b1054 100644
--- a/src/allmydata/encode.py
+++ b/src/allmydata/encode.py
@@ -4,7 +4,7 @@ import time
 from zope.interface import implements
 from twisted.internet import defer
 from foolscap import eventual
-from allmydata import uri
+from allmydata import storage, uri
 from allmydata.hashtree import HashTree
 from allmydata.util import mathutil, hashutil, idlib, log
 from allmydata.util.assertutil import _assert, precondition
@@ -89,7 +89,7 @@ class Encoder(object):
 
     def __repr__(self):
         if hasattr(self, "_storage_index"):
-            return "<Encoder for %s>" % idlib.b2a(self._storage_index)[:6]
+            return "<Encoder for %s>" % storage.si_b2a(self._storage_index)[:5]
         return "<Encoder for unknown storage index>"
 
     def log(self, *args, **kwargs):
diff --git a/src/allmydata/mutable.py b/src/allmydata/mutable.py
index 6a588ab9..fc1b4c33 100644
--- a/src/allmydata/mutable.py
+++ b/src/allmydata/mutable.py
@@ -8,7 +8,7 @@ from foolscap.eventual import eventually
 from allmydata.interfaces import IMutableFileNode, IMutableFileURI
 from allmydata.util import hashutil, mathutil, idlib, log
 from allmydata.uri import WriteableSSKFileURI
-from allmydata import hashtree, codec
+from allmydata import hashtree, codec, storage
 from allmydata.encode import NotEnoughPeersError
 from pycryptopp.publickey import rsa
 from pycryptopp.cipher.aes import AES
@@ -207,7 +207,7 @@ class Retrieve:
         self._readkey = filenode.get_readkey()
         self._last_failure = None
         self._log_number = None
-        self._log_prefix = prefix = idlib.b2a(self._storage_index)[:6]
+        self._log_prefix = prefix = storage.si_b2a(self._storage_index)[:5]
         num = self._node._client.log("Retrieve(%s): starting" % prefix)
         self._log_number = num
 
@@ -695,7 +695,7 @@ class Publish:
     def __init__(self, filenode):
         self._node = filenode
         self._storage_index = self._node.get_storage_index()
-        self._log_prefix = prefix = idlib.b2a(self._storage_index)[:6]
+        self._log_prefix = prefix = storage.si_b2a(self._storage_index)[:5]
         num = self._node._client.log("Publish(%s): starting" % prefix)
         self._log_number = num
 
@@ -974,7 +974,7 @@ class Publish:
         # one-per-peer in the normal permuted order.
         while shares_needing_homes:
             if not reachable_peers:
-                prefix = idlib.b2a(self._node.get_storage_index())[:6]
+                prefix = storage.si_b2a(self._node.get_storage_index())[:5]
                 raise NotEnoughPeersError("ran out of peers during upload of (%s); shares_needing_homes: %s, reachable_peers: %s" % (prefix, shares_needing_homes, reachable_peers,))
             shnum = shares_needing_homes.pop(0)
             possible_homes = reachable_peers.keys()
diff --git a/src/allmydata/offloaded.py b/src/allmydata/offloaded.py
index acc24138..49d84ece 100644
--- a/src/allmydata/offloaded.py
+++ b/src/allmydata/offloaded.py
@@ -136,7 +136,7 @@ class CHKUploadHelper(Referenceable, upload.CHKUploader):
         self._helper = helper
         self._incoming_file = incoming_file
         self._encoding_file = encoding_file
-        upload_id = idlib.b2a(storage_index)[:6]
+        upload_id = storage.si_b2a(storage_index)[:5]
         self._log_number = log_number
         self._results = results
         self._upload_status = upload.UploadStatus()
@@ -481,7 +481,7 @@ class Helper(Referenceable, service.MultiService):
     def remote_upload_chk(self, storage_index):
         r = upload.UploadResults()
         started = time.time()
-        si_s = idlib.b2a(storage_index)
+        si_s = storage.si_b2a(storage_index)
         lp = self.log(format="helper: upload_chk query for SI %(si)s", si=si_s)
         incoming_file = os.path.join(self._chk_incoming, si_s)
         encoding_file = os.path.join(self._chk_encoding, si_s)
diff --git a/src/allmydata/scripts/debug.py b/src/allmydata/scripts/debug.py
index 6ec68f11..36bef836 100644
--- a/src/allmydata/scripts/debug.py
+++ b/src/allmydata/scripts/debug.py
@@ -243,7 +243,7 @@ def _dump_secrets(storage_index, secret, nodeid, out):
             print >>out, " lease cancel secret:", b2a(cancel)
 
 def dump_uri_instance(u, nodeid, secret, out, err, show_header=True):
-    from allmydata import uri
+    from allmydata import storage, uri
     from allmydata.util.idlib import b2a
     from allmydata.util import hashutil
 
@@ -254,7 +254,7 @@ def dump_uri_instance(u, nodeid, secret, out, err, show_header=True):
         print >>out, " UEB hash:", b2a(u.uri_extension_hash)
         print >>out, " size:", u.size
         print >>out, " k/N: %d/%d" % (u.needed_shares, u.total_shares)
-        print >>out, " storage index:", b2a(u.storage_index)
+        print >>out, " storage index:", storage.si_b2a(u.storage_index)
         _dump_secrets(u.storage_index, secret, nodeid, out)
     elif isinstance(u, uri.CHKFileVerifierURI):
         if show_header:
@@ -262,7 +262,7 @@ def dump_uri_instance(u, nodeid, secret, out, err, show_header=True):
         print >>out, " UEB hash:", b2a(u.uri_extension_hash)
         print >>out, " size:", u.size
         print >>out, " k/N: %d/%d" % (u.needed_shares, u.total_shares)
-        print >>out, " storage index:", b2a(u.storage_index)
+        print >>out, " storage index:", storage.si_b2a(u.storage_index)
 
     elif isinstance(u, uri.LiteralFileURI):
         if show_header:
@@ -274,7 +274,7 @@ def dump_uri_instance(u, nodeid, secret, out, err, show_header=True):
             print >>out, "SSK Writeable URI:"
         print >>out, " writekey:", b2a(u.writekey)
         print >>out, " readkey:", b2a(u.readkey)
-        print >>out, " storage index:", b2a(u.storage_index)
+        print >>out, " storage index:", storage.si_b2a(u.storage_index)
         print >>out, " fingerprint:", b2a(u.fingerprint)
         print >>out
         if nodeid:
@@ -287,12 +287,12 @@ def dump_uri_instance(u, nodeid, secret, out, err, show_header=True):
         if show_header:
             print >>out, "SSK Read-only URI:"
         print >>out, " readkey:", b2a(u.readkey)
-        print >>out, " storage index:", b2a(u.storage_index)
+        print >>out, " storage index:", storage.si_b2a(u.storage_index)
         print >>out, " fingerprint:", b2a(u.fingerprint)
     elif isinstance(u, uri.SSKVerifierURI):
         if show_header:
             print >>out, "SSK Verifier URI:"
-        print >>out, " storage index:", b2a(u.storage_index)
+        print >>out, " storage index:", storage.si_b2a(u.storage_index)
         print >>out, " fingerprint:", b2a(u.fingerprint)
 
     elif isinstance(u, uri.NewDirectoryURI):
@@ -330,7 +330,7 @@ def find_shares(config, out=sys.stdout, err=sys.stderr):
     from allmydata import storage
     from allmydata.util import idlib
 
-    sharedir = storage.storage_index_to_dir(idlib.a2b(config.si_s))
+    sharedir = storage.storage_index_to_dir(storage.si_a2b(config.si_s))
     for d in config.nodedirs:
         d = os.path.join(os.path.expanduser(d), "storage/shares", sharedir)
         if os.path.exists(d):
diff --git a/src/allmydata/storage.py b/src/allmydata/storage.py
index d720ef9b..06db965e 100644
--- a/src/allmydata/storage.py
+++ b/src/allmydata/storage.py
@@ -9,7 +9,7 @@ from zope.interface import implements
 from allmydata.interfaces import RIStorageServer, RIBucketWriter, \
      RIBucketReader, IStorageBucketWriter, IStorageBucketReader, HASH_SIZE, \
      BadWriteEnablerError, IStatsProducer
-from allmydata.util import fileutil, idlib, mathutil, log
+from allmydata.util import base62, fileutil, idlib, mathutil, log
 from allmydata.util.assertutil import precondition, _assert
 import allmydata # for __version__
 
@@ -47,8 +47,15 @@ NUM_RE=re.compile("^[0-9]+$")
 #   B+0x44: expiration time, 4 bytes big-endian seconds-since-epoch
 #   B+0x48: next lease, or end of record
 
+def si_b2a(storageindex):
+    return base62.b2a(storageindex)
+
+def si_a2b(ascii_storageindex):
+    return base62.a2b(ascii_storageindex)
+
 def storage_index_to_dir(storageindex):
-    return os.path.join(idlib.b2a_l(storageindex[:2], 14), idlib.b2a(storageindex))
+    sia = si_b2a(storageindex)
+    return os.path.join(sia[:2], sia)
 
 class ShareFile:
     LEASE_SIZE = struct.calcsize(">L32s32sL")
@@ -919,7 +926,7 @@ class StorageServer(service.MultiService, Referenceable):
                                                secrets,
                                                test_and_write_vectors,
                                                read_vector):
-        si_s = idlib.b2a(storage_index)
+        si_s = si_b2a(storage_index)
         si_dir = storage_index_to_dir(storage_index)
         (write_enabler, renew_secret, cancel_secret) = secrets
         # shares exist if there is a file for them
@@ -997,7 +1004,7 @@ class StorageServer(service.MultiService, Referenceable):
         return share
 
     def remote_slot_readv(self, storage_index, shares, readv):
-        si_s = idlib.b2a(storage_index)
+        si_s = si_b2a(storage_index)
         lp = log.msg("storage: slot_readv %s %s" % (si_s, shares),
                      facility="tahoe.storage", level=log.OPERATIONAL)
         si_dir = storage_index_to_dir(storage_index)
diff --git a/src/allmydata/test/test_base62.py b/src/allmydata/test/test_base62.py
new file mode 100644
index 00000000..833d96a8
--- /dev/null
+++ b/src/allmydata/test/test_base62.py
@@ -0,0 +1,77 @@
+#!/usr/bin/env python
+#
+# Copyright (c) 2002-2008 Bryce "Zooko" Wilcox-O'Hearn
+# mailto:zooko@zooko.com
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this work to deal in this work without restriction (including the rights
+# to use, modify, distribute, sublicense, and/or sell copies).
+
+import random, unittest
+
+from allmydata.util import base62, mathutil
+
+def insecurerandstr(n):
+    return ''.join(map(chr, map(random.randrange, [0]*n, [256]*n)))
+
+class T(unittest.TestCase):
+    def _test_num_octets_that_encode_to_this_many_chars(self, chars, octets):
+        assert base62.num_octets_that_encode_to_this_many_chars(chars) == octets, "%s != %s <- %s" % (octets, base62.num_octets_that_encode_to_this_many_chars(chars), chars)
+
+    def _test_ende(self, bs):
+        as=base62.b2a(bs)
+        bs2=base62.a2b(as)
+        assert bs2 == bs, "bs2: %s:%s, bs: %s:%s, as: %s:%s" % (len(bs2), `bs2`, len(bs), `bs`, len(as), `as`)
+
+    def test_num_octets_that_encode_to_this_many_chars(self):
+        return self._test_num_octets_that_encode_to_this_many_chars(2, 1)
+        return self._test_num_octets_that_encode_to_this_many_chars(3, 2)
+        return self._test_num_octets_that_encode_to_this_many_chars(5, 3)
+        return self._test_num_octets_that_encode_to_this_many_chars(6, 4)
+
+    def test_ende_0x00(self):
+        return self._test_ende('\x00')
+
+    def test_ende_0x01(self):
+        return self._test_ende('\x01')
+
+    def test_ende_0x0100(self):
+        return self._test_ende('\x01\x00')
+
+    def test_ende_0x010000(self):
+        return self._test_ende('\x01\x00\x00')
+
+    def test_ende_0x000000(self):
+        return self._test_ende('\x00\x00\x00')
+
+    def test_ende_0x010000(self):
+        return self._test_ende('\x01\x00\x00')
+
+    def test_ende_randstr(self):
+        return self._test_ende(insecurerandstr(2**4))
+
+    def test_ende_longrandstr(self):
+        return self._test_ende(insecurerandstr(random.randrange(0, 2**10)))
+
+    def test_odd_sizes(self):
+        for j in range(2**6):
+            lib = random.randrange(1, 2**8)
+            numos = mathutil.div_ceil(lib, 8)
+            bs = insecurerandstr(numos)
+            # zero-out unused least-sig bits
+            if lib%8:
+                b=ord(bs[-1])
+                b = b >> (8 - (lib%8))
+                b = b << (8 - (lib%8))
+                bs = bs[:-1] + chr(b)
+            asl = base62.b2a_l(bs, lib)
+            assert len(asl) == base62.num_chars_that_this_many_octets_encode_to(numos) # the size of the base-62 encoding must be just right
+            bs2l = base62.a2b_l(asl, lib)
+            assert len(bs2l) == numos # the size of the result must be just right
+            assert bs == bs2l
+
+def suite():
+    suite = unittest.makeSuite(base62TestCase, 'test')
+    return suite
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/src/allmydata/test/test_cli.py b/src/allmydata/test/test_cli.py
index 37f581ea..30611731 100644
--- a/src/allmydata/test/test_cli.py
+++ b/src/allmydata/test/test_cli.py
@@ -93,7 +93,7 @@ class CLI(unittest.TestCase):
         self.failUnless("UEB hash: hd7rwri6djiapo6itg5hcxa7ze5im7z9qwcdu8oka6qinahsbiuo" in output)
         self.failUnless("size: 1234" in output)
         self.failUnless("k/N: 25/100" in output)
-        self.failUnless("storage index: kckbjgwsckzrj5srjdniw9h3ke" in output)
+        self.failUnless("storage index: 2WlXTYP4ahK2VBkx1pckfC" in output, output)
 
         output = self._dump_cap("--client-secret", "p3w849k9whqhw6b9fkf4xjs5xc",
                                 u.to_string())
@@ -104,7 +104,7 @@ class CLI(unittest.TestCase):
         self.failUnless("UEB hash: hd7rwri6djiapo6itg5hcxa7ze5im7z9qwcdu8oka6qinahsbiuo" in output)
         self.failUnless("size: 1234" in output)
         self.failUnless("k/N: 25/100" in output)
-        self.failUnless("storage index: kckbjgwsckzrj5srjdniw9h3ke" in output)
+        self.failUnless("storage index: 2WlXTYP4ahK2VBkx1pckfC" in output, output)
 
         prefixed_u = "http://127.0.0.1/uri/%s" % urllib.quote(u.to_string())
         output = self._dump_cap(prefixed_u)
@@ -113,7 +113,7 @@ class CLI(unittest.TestCase):
         self.failUnless("UEB hash: hd7rwri6djiapo6itg5hcxa7ze5im7z9qwcdu8oka6qinahsbiuo" in output)
         self.failUnless("size: 1234" in output)
         self.failUnless("k/N: 25/100" in output)
-        self.failUnless("storage index: kckbjgwsckzrj5srjdniw9h3ke" in output)
+        self.failUnless("storage index: 2WlXTYP4ahK2VBkx1pckfC" in output, output)
 
     def test_dump_cap_lit(self):
         u = uri.LiteralFileURI("this is some data")
@@ -130,7 +130,7 @@ class CLI(unittest.TestCase):
         self.failUnless("SSK Writeable URI:" in output)
         self.failUnless("writekey: yryonyebyryonyebyryonyebyr" in output)
         self.failUnless("readkey: zhgqsyrkuywo3rha41b1d7xrar" in output)
-        self.failUnless("storage index: toz9zpxrzjzwoxtuq6xr3ygdze" in output)
+        self.failUnless("storage index: 4GWqxTUinIqKqWj770lRIA" in output, output)
         self.failUnless("fingerprint: 959x79z6959x79z6959x79z6959x79z6959x79z6959x79z6959y" in output)
 
         output = self._dump_cap("--client-secret", "p3w849k9whqhw6b9fkf4xjs5xc",
@@ -165,13 +165,13 @@ class CLI(unittest.TestCase):
         output = self._dump_cap(u.to_string())
         self.failUnless("SSK Read-only URI:" in output)
         self.failUnless("readkey: zhgqsyrkuywo3rha41b1d7xrar" in output)
-        self.failUnless("storage index: toz9zpxrzjzwoxtuq6xr3ygdze" in output)
+        self.failUnless("storage index: 4GWqxTUinIqKqWj770lRIA" in output, output)
         self.failUnless("fingerprint: 959x79z6959x79z6959x79z6959x79z6959x79z6959x79z6959y" in output)
 
         u = u.get_verifier()
         output = self._dump_cap(u.to_string())
         self.failUnless("SSK Verifier URI:" in output)
-        self.failUnless("storage index: toz9zpxrzjzwoxtuq6xr3ygdze" in output)
+        self.failUnless("storage index: 4GWqxTUinIqKqWj770lRIA" in output, output)
         self.failUnless("fingerprint: 959x79z6959x79z6959x79z6959x79z6959x79z6959x79z6959y" in output)
 
     def test_dump_cap_directory(self):
@@ -184,7 +184,7 @@ class CLI(unittest.TestCase):
         self.failUnless("Directory Writeable URI:" in output)
         self.failUnless("writekey: yryonyebyryonyebyryonyebyr" in output)
         self.failUnless("readkey: zhgqsyrkuywo3rha41b1d7xrar" in output)
-        self.failUnless("storage index: toz9zpxrzjzwoxtuq6xr3ygdze" in output)
+        self.failUnless("storage index: 4GWqxTUinIqKqWj770lRIA" in output, output)
         self.failUnless("fingerprint: 959x79z6959x79z6959x79z6959x79z6959x79z6959x79z6959y" in output)
 
         output = self._dump_cap("--client-secret", "p3w849k9whqhw6b9fkf4xjs5xc",
@@ -207,12 +207,12 @@ class CLI(unittest.TestCase):
         output = self._dump_cap(u.to_string())
         self.failUnless("Directory Read-only URI:" in output)
         self.failUnless("readkey: zhgqsyrkuywo3rha41b1d7xrar" in output)
-        self.failUnless("storage index: toz9zpxrzjzwoxtuq6xr3ygdze" in output)
+        self.failUnless("storage index: 4GWqxTUinIqKqWj770lRIA" in output, output)
         self.failUnless("fingerprint: 959x79z6959x79z6959x79z6959x79z6959x79z6959x79z6959y" in output)
 
         u = u.get_verifier()
         output = self._dump_cap(u.to_string())
         self.failUnless("Directory Verifier URI:" in output)
-        self.failUnless("storage index: toz9zpxrzjzwoxtuq6xr3ygdze" in output)
+        self.failUnless("storage index: 4GWqxTUinIqKqWj770lRIA" in output, output)
         self.failUnless("fingerprint: 959x79z6959x79z6959x79z6959x79z6959x79z6959x79z6959y" in output)
 
diff --git a/src/allmydata/test/test_helper.py b/src/allmydata/test/test_helper.py
index 6e0c8322..31468fff 100644
--- a/src/allmydata/test/test_helper.py
+++ b/src/allmydata/test/test_helper.py
@@ -6,7 +6,7 @@ from twisted.application import service
 from foolscap import Tub, eventual
 from foolscap.logging import log
 
-from allmydata import upload, offloaded
+from allmydata import offloaded, storage, upload
 from allmydata.util import hashutil, fileutil, idlib, mathutil
 from pycryptopp.cipher.aes import AES
 
@@ -153,7 +153,7 @@ class AssistedUpload(unittest.TestCase):
         assert len(key) == 16
         encryptor = AES(key)
         SI = hashutil.storage_index_hash(key)
-        SI_s = idlib.b2a(SI)
+        SI_s = storage.si_b2a(SI)
         encfile = os.path.join(self.basedir, "CHK_encoding", SI_s)
         f = open(encfile, "wb")
         f.write(encryptor.process(DATA))
diff --git a/src/allmydata/test/test_system.py b/src/allmydata/test/test_system.py
index 51d0f608..e4aa9bd9 100644
--- a/src/allmydata/test/test_system.py
+++ b/src/allmydata/test/test_system.py
@@ -498,7 +498,7 @@ class SystemTest(testutil.SignalMixin, testutil.PollMixin, unittest.TestCase):
                 assert pieces[-5].startswith("client")
                 client_num = int(pieces[-5][-1])
                 storage_index_s = pieces[-1]
-                storage_index = idlib.a2b(storage_index_s)
+                storage_index = storage.si_a2b(storage_index_s)
                 for sharename in filenames:
                     shnum = int(sharename)
                     filename = os.path.join(dirpath, sharename)
diff --git a/src/allmydata/upload.py b/src/allmydata/upload.py
index af51cd11..7ff7b3ef 100644
--- a/src/allmydata/upload.py
+++ b/src/allmydata/upload.py
@@ -84,7 +84,7 @@ class PeerTracker:
     def __repr__(self):
         return ("<PeerTracker for peer %s and SI %s>"
                 % (idlib.shortnodeid_b2a(self.peerid),
-                   idlib.b2a(self.storage_index)[:6]))
+                   storage.si_b2a(self.storage_index)[:5]))
 
     def query(self, sharenums):
         d = self._storageserver.callRemote("allocate_buckets",
@@ -659,7 +659,7 @@ class CHKUploader:
         self._storage_index_elapsed = now - started
         storage_index = encoder.get_param("storage_index")
         self._storage_index = storage_index
-        upload_id = idlib.b2a(storage_index)[:6]
+        upload_id = storage.si_b2a(storage_index)[:5]
         self.log("using storage index %s" % upload_id)
         peer_selector = self.peer_selector_class(upload_id, self._log_number,
                                                  self._upload_status)
diff --git a/src/allmydata/uri.py b/src/allmydata/uri.py
index a630f188..acd31f43 100644
--- a/src/allmydata/uri.py
+++ b/src/allmydata/uri.py
@@ -2,7 +2,8 @@
 import re, urllib
 from zope.interface import implements
 from twisted.python.components import registerAdapter
-from allmydata.util import idlib, hashutil
+from allmydata import storage
+from allmydata.util import base62, idlib, hashutil
 from allmydata.interfaces import IURI, IDirnodeURI, IFileURI, IVerifierURI, \
      IMutableFileURI, INewDirectoryURI, IReadonlyNewDirectoryURI
 
@@ -12,6 +13,7 @@ from allmydata.interfaces import IURI, IDirnodeURI, IFileURI, IVerifierURI, \
 
 ZBASE32STR_128bits = '(%s{25}%s)' % (idlib.ZBASE32CHAR, idlib.ZBASE32CHAR_3bits)
 ZBASE32STR_256bits = '(%s{51}%s)' % (idlib.ZBASE32CHAR, idlib.ZBASE32CHAR_1bits)
+ZBASE62STR_128bits = '(%s{22})' % (base62.ZBASE62CHAR)
 
 SEP='(?::|%3A)'
 NUMBER='([0-9]+)'
@@ -101,10 +103,10 @@ class CHKFileURI(_BaseURI):
 class CHKFileVerifierURI(_BaseURI):
     implements(IVerifierURI)
 
-    STRING_RE=re.compile('^URI:CHK-Verifier:'+ZBASE32STR_128bits+':'+
+    STRING_RE=re.compile('^URI:CHK-Verifier:'+ZBASE62STR_128bits+':'+
                          ZBASE32STR_256bits+':'+NUMBER+':'+NUMBER+':'+NUMBER)
     HUMAN_RE=re.compile('^'+OPTIONALHTTPLEAD+'URI'+SEP+'CHK-Verifier'+SEP+
-                        ZBASE32STR_128bits+SEP+ZBASE32STR_256bits+SEP+NUMBER+
+                        ZBASE62STR_128bits+SEP+ZBASE32STR_256bits+SEP+NUMBER+
                         SEP+NUMBER+SEP+NUMBER)
 
     def __init__(self, storage_index, uri_extension_hash,
@@ -126,8 +128,8 @@ class CHKFileVerifierURI(_BaseURI):
     @classmethod
     def init_from_string(cls, uri):
         mo = cls.STRING_RE.search(uri)
-        assert mo, uri
-        return cls(idlib.a2b(mo.group(1)), idlib.a2b(mo.group(2)),
+        assert mo, (uri, cls, cls.STRING_RE)
+        return cls(storage.si_a2b(mo.group(1)), idlib.a2b(mo.group(2)),
                    int(mo.group(3)), int(mo.group(4)), int(mo.group(5)))
 
     def to_string(self):
@@ -136,7 +138,7 @@ class CHKFileVerifierURI(_BaseURI):
         assert isinstance(self.size, (int,long))
 
         return ('URI:CHK-Verifier:%s:%s:%d:%d:%d' %
-                (idlib.b2a(self.storage_index),
+                (storage.si_b2a(self.storage_index),
                  idlib.b2a(self.uri_extension_hash),
                  self.needed_shares,
                  self.total_shares,
@@ -281,8 +283,8 @@ class SSKVerifierURI(_BaseURI):
     implements(IVerifierURI)
 
     BASE_STRING='URI:SSK-Verifier:'
-    STRING_RE=re.compile('^'+BASE_STRING+ZBASE32STR_128bits+':'+ZBASE32STR_256bits+'$')
-    HUMAN_RE=re.compile('^'+OPTIONALHTTPLEAD+'URI'+SEP+'SSK-RO'+SEP+ZBASE32STR_128bits+SEP+ZBASE32STR_256bits+'$')
+    STRING_RE=re.compile('^'+BASE_STRING+ZBASE62STR_128bits+':'+ZBASE32STR_256bits+'$')
+    HUMAN_RE=re.compile('^'+OPTIONALHTTPLEAD+'URI'+SEP+'SSK-RO'+SEP+ZBASE62STR_128bits+SEP+ZBASE32STR_256bits+'$')
 
     def __init__(self, storage_index, fingerprint):
         assert len(storage_index) == 16
@@ -293,18 +295,18 @@ class SSKVerifierURI(_BaseURI):
     def init_from_human_encoding(cls, uri):
         mo = cls.HUMAN_RE.search(uri)
         assert mo, uri
-        return cls(idlib.a2b(mo.group(1)), idlib.a2b(mo.group(2)))
+        return cls(storage.si_a2b(mo.group(1)), idlib.a2b(mo.group(2)))
 
     @classmethod
     def init_from_string(cls, uri):
         mo = cls.STRING_RE.search(uri)
-        assert mo, uri
-        return cls(idlib.a2b(mo.group(1)), idlib.a2b(mo.group(2)))
+        assert mo, (uri, cls)
+        return cls(storage.si_a2b(mo.group(1)), idlib.a2b(mo.group(2)))
 
     def to_string(self):
         assert isinstance(self.storage_index, str)
         assert isinstance(self.fingerprint, str)
-        return 'URI:SSK-Verifier:%s:%s' % (idlib.b2a(self.storage_index),
+        return 'URI:SSK-Verifier:%s:%s' % (storage.si_b2a(self.storage_index),
                                            idlib.b2a(self.fingerprint))
 
 class _NewDirectoryBaseURI(_BaseURI):
diff --git a/src/allmydata/util/base62.py b/src/allmydata/util/base62.py
new file mode 100644
index 00000000..638d045c
--- /dev/null
+++ b/src/allmydata/util/base62.py
@@ -0,0 +1,118 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2002-2008 Bryce "Zooko" Wilcox-O'Hearn
+# mailto:zooko@zooko.com
+# Permission is hereby granted to any person obtaining a copy of this work to
+# deal in this work without restriction (including the rights to use, modify,
+# distribute, sublicense, and/or sell copies).
+
+# from the Python Standard Library
+import string
+
+from allmydata.util.mathutil import div_ceil, log_ceil, log_floor
+
+chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+ZBASE62CHAR = '[' + chars + ']'
+
+vals = ''.join([chr(i) for i in range(62)])
+c2vtranstable = string.maketrans(chars, vals)
+v2ctranstable = string.maketrans(vals, chars)
+identitytranstable = string.maketrans(chars, chars)
+
+def b2a(os):
+    """
+    @param os the data to be encoded (a string)
+
+    @return the contents of os in base-62 encoded form
+    """
+    cs = b2a_l(os, len(os)*8)
+    assert num_octets_that_encode_to_this_many_chars(len(cs)) == len(os), "%s != %s, numchars: %s" % (num_octets_that_encode_to_this_many_chars(len(cs)), len(os), len(cs))
+    return cs
+
+def b2a_l(os, lengthinbits):
+    """
+    @param os the data to be encoded (a string)
+    @param lengthinbits the number of bits of data in os to be encoded
+
+    b2a_l() will generate a base-62 encoded string big enough to encode
+    lengthinbits bits.  So for example if os is 3 bytes long and lengthinbits is
+    17, then b2a_l() will generate a 3-character- long base-62 encoded string
+    (since 3 chars is sufficient to encode more than 2^17 values).  If os is 3
+    bytes long and lengthinbits is 18 (or None), then b2a_l() will generate a
+    4-character string (since 4 chars are required to hold 2^18 values).  Note
+    that if os is 3 bytes long and lengthinbits is 17, the least significant 7
+    bits of os are ignored.
+
+    Warning: if you generate a base-62 encoded string with b2a_l(), and then someone else tries to
+    decode it by calling a2b() instead of  a2b_l(), then they will (potentially) get a different
+    string than the one you encoded!  So use b2a_l() only when you are sure that the encoding and
+    decoding sides know exactly which lengthinbits to use.  If you do not have a way for the
+    encoder and the decoder to agree upon the lengthinbits, then it is best to use b2a() and
+    a2b().  The only drawback to using b2a() over b2a_l() is that when you have a number of
+    bits to encode that is not a multiple of 8, b2a() can sometimes generate a base-62 encoded
+    string that is one or two characters longer than necessary.
+
+    @return the contents of os in base-62 encoded form
+    """
+    os = [ord(o) for o in reversed(os)] # treat os as big-endian -- and we want to process the least-significant o first
+
+    value = 0
+    numvalues = 1 # the number of possible values that value could be
+    for o in os:
+        o *= numvalues
+        value += o
+        numvalues *= 256
+
+    chars = []
+    while numvalues > 0:
+        chars.append(value % 62)
+        value //= 62
+        numvalues //= 62
+
+    return string.translate(''.join([chr(c) for c in reversed(chars)]), v2ctranstable) # make it big-endian
+
+def num_octets_that_encode_to_this_many_chars(numcs):
+    return log_floor(62**numcs, 256)
+
+def num_chars_that_this_many_octets_encode_to(numos):
+    return log_ceil(256**numos, 62)
+
+def a2b(cs):
+    """
+    @param cs the base-62 encoded data (a string)
+    """
+    return a2b_l(cs, num_octets_that_encode_to_this_many_chars(len(cs))*8)
+
+def a2b_l(cs, lengthinbits):
+    """
+    @param lengthinbits the number of bits of data in encoded into cs
+
+    a2b_l() will return a result just big enough to hold lengthinbits bits.  So
+    for example if cs is 2 characters long (encoding between 5 and 12 bits worth
+    of data) and lengthinbits is 8, then a2b_l() will return a string of length
+    1 (since 1 byte is sufficient to store 8 bits), but if lengthinbits is 9,
+    then a2b_l() will return a string of length 2.
+
+    Please see the warning in the docstring of b2a_l() regarding the use of
+    b2a() versus b2a_l().
+
+    @return the data encoded in cs
+    """
+    cs = [ord(c) for c in reversed(string.translate(cs, c2vtranstable))] # treat cs as big-endian -- and we want to process the least-significant c first
+
+    value = 0
+    numvalues = 1 # the number of possible values that value could be
+    for c in cs:
+        c *= numvalues
+        value += c
+        numvalues *= 62
+
+    numvalues = 2**lengthinbits
+    bytes = []
+    while numvalues > 1:
+        bytes.append(value % 256)
+        value //= 256
+        numvalues //= 256
+
+    return ''.join([chr(b) for b in reversed(bytes)]) # make it big-endian
diff --git a/src/allmydata/util/mathutil.py b/src/allmydata/util/mathutil.py
index b95dbaa8..1d83e28c 100644
--- a/src/allmydata/util/mathutil.py
+++ b/src/allmydata/util/mathutil.py
@@ -49,3 +49,27 @@ def next_power_of_k(n, k):
 def ave(l):
     return sum(l) / len(l)
 
+def log_ceil(n, b):
+    """
+    The smallest integer k such that b^k >= n.
+
+    log_ceil(n, 2) is the number of bits needed to store any of n values, e.g.
+    the number of bits needed to store any of 128 possible values is 7.
+    """
+    p = 1
+    k = 0
+    while p < n:
+        p *= b
+        k += 1
+    return k
+
+def log_floor(n, b):
+    """
+    The largest integer k such that b^k <= n.
+    """
+    p = 1
+    k = 0
+    while p <= n:
+        p *= b
+        k += 1
+    return k - 1