[PATCH 1/2] CL/git: add format version 1

[David Bremner <david@tethera.net>]

The original nmbug format (now called version 0) creates 1
subdirectory of 'tags/' per message. This causes problems for more
than (roughly) 100k messages.

Version 1 introduces 2 layers of hashed directories. This scheme was
chose to balance the number of subdirectories with the number of extra
directories (and git objects) created via hashing.

This should be upward compatible in the sense that old repositories
will continue to work with the updated notmuch-git.
---
 doc/man1/notmuch-git.rst | 40 +++++++++++++++++++++++++++----
 notmuch-git.py           | 52 ++++++++++++++++++++++++++++++++++------
 test/T850-git.sh         | 48 ++++++++++++++++++-------------------
 test/test-lib.sh         |  4 ++++
 4 files changed, 109 insertions(+), 35 deletions(-)

diff --git a/doc/man1/notmuch-git.rst b/doc/man1/notmuch-git.rst
index fa7a748e..389371bf 100644
--- a/doc/man1/notmuch-git.rst
+++ b/doc/man1/notmuch-git.rst
@@ -235,15 +235,47 @@ REPOSITORY CONTENTS
 ===================
 
 The tags are stored in the git repo (and exported) as a set of empty
-files. For a message with Message-Id *id*, for each tag *tag*, there
+files. These empty files are contained within a directory named after
+the message-id.
+
+In what follows `encode()` represents a POSIX filesystem safe
+encoding. The encoding preserves alphanumerics, and the characters
+`+-_@=.,:`.  All other octets are replaced with `%` followed by a two
+digit hex number.
+
+Currently :any:`notmuch-git` can read any format version, but can only
+create (via :any:`init`) :ref:`version 1 <format_version_1>` repositories.
+
+.. _format_version_0:
+
+Version 0
+---------
+
+This is the legacy format created by the `nmbug` tool prior to release
+0.37.  For a message with Message-Id *id*, for each tag *tag*, there
 is an empty file with path
 
        tags/ `encode` (*id*) / `encode` (*tag*)
 
-The encoding preserves alphanumerics, and the characters `+-_@=.,:`.
-All other octets are replaced with `%` followed by a two digit hex
-number.
+.. _format_version_1:
+
+Version 1
+---------
+
+In format version 1 and later, the format version is contained in a
+top level file called FORMAT.
+
+For a message with Message-Id *id*, for each tag *tag*, there
+is an empty file with path
+
+       tags/ `hash1` (*id*) / `hash2` (*id*) `encode` (*id*) / `encode` (*tag*)
+
+The hash functions each represent one byte of the `blake2b` hex
+digest.
 
+Compared to :ref:`version 0 <format_version_0>`, this reduces the
+number of subdirectories within each directory.
+       
 .. _repo_location:
 
 REPOSITORY LOCATION
diff --git a/notmuch-git.py b/notmuch-git.py
index f188660c..8781e3d1 100644
--- a/notmuch-git.py
+++ b/notmuch-git.py
@@ -46,10 +46,12 @@ _LOG.addHandler(_logging.StreamHandler())
 
 NOTMUCH_GIT_DIR = None
 TAG_PREFIX = None
+FORMAT_VERSION = 0
 
 _HEX_ESCAPE_REGEX = _re.compile('%[0-9A-F]{2}')
 _TAG_DIRECTORY = 'tags/'
-_TAG_FILE_REGEX = _re.compile(_TAG_DIRECTORY + '(?P<id>[^/]*)/(?P<tag>[^/]*)')
+_TAG_FILE_REGEX = ( _re.compile(_TAG_DIRECTORY + '(?P<id>[^/]*)/(?P<tag>[^/]*)'),
+                    _re.compile(_TAG_DIRECTORY + '([0-9a-f]{2}/){2}(?P<id>[^/]*)/(?P<tag>[^/]*)'))
 
 # magic hash for Git (git hash-object -t blob /dev/null)
 _EMPTYBLOB = 'e69de29bb2d1d6434b8b29ae775ad8c2e48c5391'
@@ -265,7 +267,7 @@ def archive(treeish='HEAD', args=()):
     Each tag $tag for message with Message-Id $id is written to
     an empty file
 
-      tags/encode($id)/encode($tag)
+      tags/hash1(id)/hash2(id)/encode($id)/encode($tag)
 
     The encoding preserves alphanumerics, and the characters
     "+-_@=.:," (not the quotes).  All other octets are replaced with
@@ -469,9 +471,17 @@ def init(remote=None):
     _git(args=['config', 'core.logallrefupdates', 'true'], wait=True)
     # create an empty blob (e69de29bb2d1d6434b8b29ae775ad8c2e48c5391)
     _git(args=['hash-object', '-w', '--stdin'], input='', wait=True)
+    # create a blob for the FORMAT file
+    (status, stdout, _) = _git(args=['hash-object', '-w', '--stdin'], stdout=_subprocess.PIPE,
+                               input='1\n', wait=True)
+    verhash=stdout.rstrip()
+    _LOG.debug('hash of FORMAT blob = {:s}'.format(verhash))
+    # Add FORMAT to the index
+    _git(args=['update-index', '--add', '--cacheinfo', '100644,{:s},FORMAT'.format(verhash)], wait=True)
+               
     _git(
         args=[
-            'commit', '--allow-empty', '-m', 'Start a new nmbug repository'
+            'commit', '-m', 'Start a new notmuch-git repository'
         ],
         additional_env={'GIT_WORK_TREE': NOTMUCH_GIT_DIR},
         wait=True)
@@ -821,7 +831,7 @@ def _clear_tags_for_message(index, id):
     Neither 'id' nor the tags in 'tags' should be encoded/escaped.
     """
 
-    dir = 'tags/{id}'.format(id=_hex_quote(string=id))
+    dir = _id_path(id)
 
     with _git(
             args=['ls-files', dir],
@@ -838,6 +848,21 @@ def _read_database_lastmod():
         (count,uuid,lastmod_str) = notmuch.stdout.readline().split()
         return (count,uuid,int(lastmod_str))
 
+def _id_path(id):
+    hid=_hex_quote(string=id)
+    from hashlib import blake2b
+
+    if FORMAT_VERSION==0:
+        return 'tags/{hid}'.format(hid=hid)
+    elif FORMAT_VERSION==1:
+        idhash = blake2b(hid.encode('utf8'), digest_size=2).hexdigest()
+        return 'tags/{dir1}/{dir2}/{hid}'.format(
+            hid=hid,
+            dir1=idhash[0:2],dir2=idhash[2:])
+    else:
+        _LOG.error("Unknown format version",FORMAT_VERSION)
+        _sys.exit(1)
+
 def _index_tags_for_message(id, status, tags):
     """
     Update the Git index to either create or delete an empty file.
@@ -852,8 +877,7 @@ def _index_tags_for_message(id, status, tags):
         hash = '0000000000000000000000000000000000000000'
 
     for tag in tags:
-        path = 'tags/{id}/{tag}'.format(
-            id=_hex_quote(string=id), tag=_hex_quote(string=tag))
+        path = '{ipath}/{tag}'.format(ipath=_id_path(id),tag=_hex_quote(string=tag))
         yield '{mode} {hash}\t{path}\n'.format(mode=mode, hash=hash, path=path)
 
 
@@ -869,7 +893,7 @@ def _diff_refs(filter, a='HEAD', b='@{upstream}'):
 def _unpack_diff_lines(stream):
     "Iterate through (id, tag) tuples in a diff stream."
     for line in stream:
-        match = _TAG_FILE_REGEX.match(line.strip())
+        match = _TAG_FILE_REGEX[FORMAT_VERSION].match(line.strip())
         if not match:
             message = 'non-tag line in diff: {!r}'.format(line.strip())
             if line.startswith(_TAG_DIRECTORY):
@@ -907,6 +931,17 @@ def _notmuch_config_get(key):
         _sys.exit(1)
     return stdout.rstrip()
 
+def read_format_version():
+    try:
+        (status, stdout, stderr) = _git(
+            args=['cat-file', 'blob', 'master:FORMAT'],      
+            stdout=_subprocess.PIPE, stderr=_subprocess.PIPE, wait=True)
+    except SubprocessError as e:
+        _LOG.debug("failed to read FORMAT file from git, assuming format version 0")
+        return 0
+    
+    return int(stdout)
+    
 # based on BaseDirectory.save_data_path from pyxdg (LGPL2+)
 def xdg_data_path(profile):
     resource = _os.path.join('notmuch',profile,'git')
@@ -1104,6 +1139,9 @@ if __name__ == '__main__':
     _LOG.debug('prefix = {:s}'.format(TAG_PREFIX))
     _LOG.debug('repository = {:s}'.format(NOTMUCH_GIT_DIR))
 
+    FORMAT_VERSION = read_format_version()
+    _LOG.debug('FORMAT_VERSION={:d}'.format(FORMAT_VERSION))
+               
     if args.func == help:
         arg_names = ['command']
     else:
diff --git a/test/T850-git.sh b/test/T850-git.sh
index 7ea50939..342cc31b 100755
--- a/test/T850-git.sh
+++ b/test/T850-git.sh
@@ -40,10 +40,10 @@ notmuch tag -new-prefix::foo id:20091117190054.GU3165@dottiness.seas.harvard.edu
 test_begin_subtest "committing new prefix works with force"
 notmuch tag +new-prefix::foo id:20091117190054.GU3165@dottiness.seas.harvard.edu
 notmuch git -l debug -p 'new-prefix::' -C force-prefix.git commit --force
-git -C force-prefix.git ls-tree -r --name-only HEAD | xargs dirname | sort -u | sed s,tags/,id:, > OUTPUT
+git -C force-prefix.git ls-tree -r --name-only HEAD |  notmuch_git_sanitize | xargs dirname | sort -u > OUTPUT
 notmuch tag -new-prefix::foo id:20091117190054.GU3165@dottiness.seas.harvard.edu
 cat <<EOF>EXPECTED
-id:20091117190054.GU3165@dottiness.seas.harvard.edu
+20091117190054.GU3165@dottiness.seas.harvard.edu
 EOF
 test_expect_equal_file_nonempty EXPECTED OUTPUT
 
@@ -62,8 +62,8 @@ test_expect_equal_file_nonempty EXPECTED OUTPUT
 
 test_begin_subtest "commit"
 notmuch git -C tags.git commit --force
-git -C tags.git ls-tree -r --name-only HEAD | xargs dirname | sort -u | sed s,tags/,id:, > OUTPUT
-notmuch search --output=messages '*' | sort > EXPECTED
+git -C tags.git ls-tree -r --name-only HEAD | notmuch_git_sanitize | xargs dirname | sort -u > OUTPUT
+notmuch search --output=messages '*' | sed s/^id:// | sort > EXPECTED
 test_expect_equal_file_nonempty EXPECTED OUTPUT
 
 test_begin_subtest "commit --force succeeds"
@@ -88,22 +88,22 @@ test_expect_equal_file_nonempty BEFORE AFTER
 test_begin_subtest "commit (incremental)"
 notmuch tag +test id:20091117190054.GU3165@dottiness.seas.harvard.edu
 notmuch git -C tags.git commit
-git -C tags.git ls-tree -r --name-only HEAD |
+git -C tags.git ls-tree -r --name-only HEAD | notmuch_git_sanitize | \
     grep 20091117190054 | sort > OUTPUT
 echo "--------------------------------------------------" >> OUTPUT
 notmuch tag -test id:20091117190054.GU3165@dottiness.seas.harvard.edu
 notmuch git -C tags.git commit
-git -C tags.git ls-tree -r --name-only HEAD |
+git -C tags.git ls-tree -r --name-only HEAD | notmuch_git_sanitize | \
     grep 20091117190054 | sort >> OUTPUT
 cat <<EOF > EXPECTED
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/signed
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/test
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/unread
+20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
+20091117190054.GU3165@dottiness.seas.harvard.edu/signed
+20091117190054.GU3165@dottiness.seas.harvard.edu/test
+20091117190054.GU3165@dottiness.seas.harvard.edu/unread
 --------------------------------------------------
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/signed
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/unread
+20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
+20091117190054.GU3165@dottiness.seas.harvard.edu/signed
+20091117190054.GU3165@dottiness.seas.harvard.edu/unread
 EOF
 test_expect_equal_file_nonempty EXPECTED OUTPUT
 
@@ -111,18 +111,18 @@ test_begin_subtest "commit (change prefix)"
 notmuch tag +test::one id:20091117190054.GU3165@dottiness.seas.harvard.edu
 notmuch git -C tags.git -p 'test::' commit --force
 git -C tags.git ls-tree -r --name-only HEAD |
-    grep 20091117190054 | sort > OUTPUT
+    grep 20091117190054 | notmuch_git_sanitize | sort > OUTPUT
 echo "--------------------------------------------------" >> OUTPUT
 notmuch tag -test::one id:20091117190054.GU3165@dottiness.seas.harvard.edu
 notmuch git -C tags.git commit --force
-git -C tags.git ls-tree -r --name-only HEAD |
+git -C tags.git ls-tree -r --name-only HEAD | notmuch_git_sanitize | \
     grep 20091117190054 | sort >> OUTPUT
 cat <<EOF > EXPECTED
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/one
+20091117190054.GU3165@dottiness.seas.harvard.edu/one
 --------------------------------------------------
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/signed
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/unread
+20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
+20091117190054.GU3165@dottiness.seas.harvard.edu/signed
+20091117190054.GU3165@dottiness.seas.harvard.edu/unread
 EOF
 test_expect_equal_file_nonempty EXPECTED OUTPUT
 
@@ -151,12 +151,12 @@ test_expect_equal_file_nonempty BEFORE AFTER
 
 test_begin_subtest "archive"
 notmuch git -C tags.git archive | tar tf - | \
-    grep 20091117190054.GU3165@dottiness.seas.harvard.edu | sort > OUTPUT
+    grep 20091117190054.GU3165@dottiness.seas.harvard.edu | notmuch_git_sanitize | sort > OUTPUT
 cat <<EOF > EXPECTED
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/signed
-tags/20091117190054.GU3165@dottiness.seas.harvard.edu/unread
+20091117190054.GU3165@dottiness.seas.harvard.edu/
+20091117190054.GU3165@dottiness.seas.harvard.edu/inbox
+20091117190054.GU3165@dottiness.seas.harvard.edu/signed
+20091117190054.GU3165@dottiness.seas.harvard.edu/unread
 EOF
 notmuch git -C tags.git checkout
 test_expect_equal_file EXPECTED OUTPUT
diff --git a/test/test-lib.sh b/test/test-lib.sh
index 59b6079d..dfbee365 100644
--- a/test/test-lib.sh
+++ b/test/test-lib.sh
@@ -545,6 +545,10 @@ notmuch_date_sanitize () {
 	-e 's/^Date: Fri, 05 Jan 2001 .*0000/Date: GENERATED_DATE/'
 }
 
+# remove redundant parts of notmuch-git internal paths
+notmuch_git_sanitize () {
+    sed  -e 's,tags/\([0-9a-f]\{2\}/\)\{2\},,' -e '/FORMAT/d'
+}
 notmuch_uuid_sanitize () {
     sed 's/[0-9a-f]\{8\}-[0-9a-f]\{4\}-[0-9a-f]\{4\}-[0-9a-f]\{4\}-[0-9a-f]\{12\}/UUID/g'
 }
-- 
2.35.2