streamclone: support for producing and consuming stream clone bundles

Up to this point, stream clones only existed as a dynamically generated
data format produced and consumed during streaming clones. In order to
support this efficient cloning format with the clone bundles feature, we
need a more formal, on disk representation of the streaming clone data.

This patch introduces a new "bundle" type for streaming clones. Unlike
existing bundles, it does not contain changegroup data. It does,
however, share the same concepts like the 4 byte header which identifies
the type of data that follows and the 2 byte abbreviation for
compression types (of which only "UN" is currently supported).

The new bundle format is essentially the existing stream clone version 1
data format with some headers at the beginning.

Content negotiation at stream clone request time checked for repository
format/requirements compatibility before initiating a stream clone. We
can't do active content negotiation when using clone bundles. So, we put
this set of requirements inside the payload so consumers have a built-in
mechanism for checking compatibility before reading and applying lots of
data. Of course, we will also advertise this requirements set in clone
bundles. But that's for another patch.

We currently don't have a mechanism to produce and consume this new
bundle format. This will be implemented in upcoming patches.

It's worth noting that if a legacy client attempts to `hg unbundle` a
stream clone bundle (with the "HGS1" header), it will abort with:
"unknown bundle version S1," which seems appropriate.

mercurial/streamclone.py

@@ -1,292 +1,392 b''
 # streamclone.py - producing and consuming streaming repository data
 #
 # Copyright 2015 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
+import struct
 import time
 
 from .i18n import _
 from . import (
     branchmap,
     error,
     store,
     util,
 )
 
 def canperformstreamclone(pullop, bailifbundle2supported=False):
     """Whether it is possible to perform a streaming clone as part of pull.
 
     ``bailifbundle2supported`` will cause the function to return False if
     bundle2 stream clones are supported. It should only be called by the
     legacy stream clone code path.
 
     Returns a tuple of (supported, requirements). ``supported`` is True if
     streaming clone is supported and False otherwise. ``requirements`` is
     a set of repo requirements from the remote, or ``None`` if stream clone
     isn't supported.
     """
     repo = pullop.repo
     remote = pullop.remote
 
     bundle2supported = False
     if pullop.canusebundle2:
         if 'v1' in pullop.remotebundle2caps.get('stream', []):
             bundle2supported = True
         # else
             # Server doesn't support bundle2 stream clone or doesn't support
             # the versions we support. Fall back and possibly allow legacy.
 
     # Ensures legacy code path uses available bundle2.
     if bailifbundle2supported and bundle2supported:
         return False, None
     # Ensures bundle2 doesn't try to do a stream clone if it isn't supported.
     #elif not bailifbundle2supported and not bundle2supported:
     #    return False, None
 
     # Streaming clone only works on empty repositories.
     if len(repo):
         return False, None
 
     # Streaming clone only works if all data is being requested.
     if pullop.heads:
         return False, None
 
     streamrequested = pullop.streamclonerequested
 
     # If we don't have a preference, let the server decide for us. This
     # likely only comes into play in LANs.
     if streamrequested is None:
         # The server can advertise whether to prefer streaming clone.
         streamrequested = remote.capable('stream-preferred')
 
     if not streamrequested:
         return False, None
 
     # In order for stream clone to work, the client has to support all the
     # requirements advertised by the server.
     #
     # The server advertises its requirements via the "stream" and "streamreqs"
     # capability. "stream" (a value-less capability) is advertised if and only
     # if the only requirement is "revlogv1." Else, the "streamreqs" capability
     # is advertised and contains a comma-delimited list of requirements.
     requirements = set()
     if remote.capable('stream'):
         requirements.add('revlogv1')
     else:
         streamreqs = remote.capable('streamreqs')
         # This is weird and shouldn't happen with modern servers.
         if not streamreqs:
             return False, None
 
         streamreqs = set(streamreqs.split(','))
         # Server requires something we don't support. Bail.
         if streamreqs - repo.supportedformats:
             return False, None
         requirements = streamreqs
 
     return True, requirements
 
 def maybeperformlegacystreamclone(pullop):
     """Possibly perform a legacy stream clone operation.
 
     Legacy stream clones are performed as part of pull but before all other
     operations.
 
     A legacy stream clone will not be performed if a bundle2 stream clone is
     supported.
     """
     supported, requirements = canperformstreamclone(pullop)
 
     if not supported:
         return
 
     repo = pullop.repo
     remote = pullop.remote
 
     # Save remote branchmap. We will use it later to speed up branchcache
     # creation.
     rbranchmap = None
     if remote.capable('branchmap'):
         rbranchmap = remote.branchmap()
 
     repo.ui.status(_('streaming all changes\n'))
 
     fp = remote.stream_out()
     l = fp.readline()
     try:
         resp = int(l)
     except ValueError:
         raise error.ResponseError(
             _('unexpected response from remote server:'), l)
     if resp == 1:
         raise error.Abort(_('operation forbidden by server'))
     elif resp == 2:
         raise error.Abort(_('locking the remote repository failed'))
     elif resp != 0:
         raise error.Abort(_('the server sent an unknown error code'))
 
     l = fp.readline()
     try:
         filecount, bytecount = map(int, l.split(' ', 1))
     except (ValueError, TypeError):
         raise error.ResponseError(
             _('unexpected response from remote server:'), l)
 
     lock = repo.lock()
     try:
         consumev1(repo, fp, filecount, bytecount)
 
         # new requirements = old non-format requirements +
         #                    new format-related remote requirements
         # requirements from the streamed-in repository
         repo.requirements = requirements | (
                 repo.requirements - repo.supportedformats)
         repo._applyopenerreqs()
         repo._writerequirements()
 
         if rbranchmap:
             branchmap.replacecache(repo, rbranchmap)
 
         repo.invalidate()
     finally:
         lock.release()
 
 def allowservergeneration(ui):
     """Whether streaming clones are allowed from the server."""
     return ui.configbool('server', 'uncompressed', True, untrusted=True)
 
 # This is it's own function so extensions can override it.
 def _walkstreamfiles(repo):
     return repo.store.walk()
 
 def generatev1(repo):
     """Emit content for version 1 of a streaming clone.
 
     This returns a 3-tuple of (file count, byte size, data iterator).
 
     The data iterator consists of N entries for each file being transferred.
     Each file entry starts as a line with the file name and integer size
     delimited by a null byte.
 
     The raw file data follows. Following the raw file data is the next file
     entry, or EOF.
 
     When used on the wire protocol, an additional line indicating protocol
     success will be prepended to the stream. This function is not responsible
     for adding it.
 
     This function will obtain a repository lock to ensure a consistent view of
     the store is captured. It therefore may raise LockError.
     """
     entries = []
     total_bytes = 0
     # Get consistent snapshot of repo, lock during scan.
     lock = repo.lock()
     try:
         repo.ui.debug('scanning\n')
         for name, ename, size in _walkstreamfiles(repo):
             if size:
                 entries.append((name, size))
                 total_bytes += size
     finally:
             lock.release()
 
     repo.ui.debug('%d files, %d bytes to transfer\n' %
                   (len(entries), total_bytes))
 
     svfs = repo.svfs
     oldaudit = svfs.mustaudit
     debugflag = repo.ui.debugflag
     svfs.mustaudit = False
 
     def emitrevlogdata():
         try:
             for name, size in entries:
                 if debugflag:
                     repo.ui.debug('sending %s (%d bytes)\n' % (name, size))
                 # partially encode name over the wire for backwards compat
                 yield '%s\0%d\n' % (store.encodedir(name), size)
                 if size <= 65536:
                     fp = svfs(name)
                     try:
                         data = fp.read(size)
                     finally:
                         fp.close()
                     yield data
                 else:
                     for chunk in util.filechunkiter(svfs(name), limit=size):
                         yield chunk
         finally:
             svfs.mustaudit = oldaudit
 
     return len(entries), total_bytes, emitrevlogdata()
 
 def generatev1wireproto(repo):
     """Emit content for version 1 of streaming clone suitable for the wire.
 
     This is the data output from ``generatev1()`` with a header line
     indicating file count and byte size.
     """
     filecount, bytecount, it = generatev1(repo)
     yield '%d %d\n' % (filecount, bytecount)
     for chunk in it:
         yield chunk
 
+def generatebundlev1(repo, compression='UN'):
+    """Emit content for version 1 of a stream clone bundle.
+
+    The first 4 bytes of the output ("HGS1") denote this as stream clone
+    bundle version 1.
+
+    The next 2 bytes indicate the compression type. Only "UN" is currently
+    supported.
+
+    The next 16 bytes are two 64-bit big endian unsigned integers indicating
+    file count and byte count, respectively.
+
+    The next 2 bytes is a 16-bit big endian unsigned short declaring the length
+    of the requirements string, including a trailing \0. The following N bytes
+    are the requirements string, which is ASCII containing a comma-delimited
+    list of repo requirements that are needed to support the data.
+
+    The remaining content is the output of ``generatev1()`` (which may be
+    compressed in the future).
+
+    Returns a tuple of (requirements, data generator).
+    """
+    if compression != 'UN':
+        raise ValueError('we do not support the compression argument yet')
+
+    requirements = repo.requirements & repo.supportedformats
+    requires = ','.join(sorted(requirements))
+
+    def gen():
+        yield 'HGS1'
+        yield compression
+
+        filecount, bytecount, it = generatev1(repo)
+        repo.ui.status(_('writing %d bytes for %d files\n') %
+                         (bytecount, filecount))
+
+        yield struct.pack('>QQ', filecount, bytecount)
+        yield struct.pack('>H', len(requires) + 1)
+        yield requires + '\0'
+
+        # This is where we'll add compression in the future.
+        assert compression == 'UN'
+
+        seen = 0
+        repo.ui.progress(_('bundle'), 0, total=bytecount)
+
+        for chunk in it:
+            seen += len(chunk)
+            repo.ui.progress(_('bundle'), seen, total=bytecount)
+            yield chunk
+
+        repo.ui.progress(_('bundle'), None)
+
+    return requirements, gen()
+
 def consumev1(repo, fp, filecount, bytecount):
     """Apply the contents from version 1 of a streaming clone file handle.
 
     This takes the output from "streamout" and applies it to the specified
     repository.
 
     Like "streamout," the status line added by the wire protocol is not handled
     by this function.
     """
     lock = repo.lock()
     try:
         repo.ui.status(_('%d files to transfer, %s of data\n') %
                        (filecount, util.bytecount(bytecount)))
         handled_bytes = 0
         repo.ui.progress(_('clone'), 0, total=bytecount)
         start = time.time()
 
         tr = repo.transaction(_('clone'))
         try:
             for i in xrange(filecount):
                 # XXX doesn't support '\n' or '\r' in filenames
                 l = fp.readline()
                 try:
                     name, size = l.split('\0', 1)
                     size = int(size)
                 except (ValueError, TypeError):
                     raise error.ResponseError(
                         _('unexpected response from remote server:'), l)
                 if repo.ui.debugflag:
                     repo.ui.debug('adding %s (%s)\n' %
                                   (name, util.bytecount(size)))
                 # for backwards compat, name was partially encoded
                 ofp = repo.svfs(store.decodedir(name), 'w')
                 for chunk in util.filechunkiter(fp, limit=size):
                     handled_bytes += len(chunk)
                     repo.ui.progress(_('clone'), handled_bytes, total=bytecount)
                     ofp.write(chunk)
                 ofp.close()
             tr.close()
         finally:
             tr.release()
 
         # Writing straight to files circumvented the inmemory caches
         repo.invalidate()
 
         elapsed = time.time() - start
         if elapsed <= 0:
             elapsed = 0.001
         repo.ui.progress(_('clone'), None)
         repo.ui.status(_('transferred %s in %.1f seconds (%s/sec)\n') %
                        (util.bytecount(bytecount), elapsed,
                         util.bytecount(bytecount / elapsed)))
     finally:
         lock.release()
+
+def applybundlev1(repo, fp):
+    """Apply the content from a stream clone bundle version 1.
+
+    We assume the 4 byte header has been read and validated and the file handle
+    is at the 2 byte compression identifier.
+    """
+    if len(repo):
+        raise error.Abort(_('cannot apply stream clone bundle on non-empty '
+                            'repo'))
+
+    compression = fp.read(2)
+    if compression != 'UN':
+        raise error.Abort(_('only uncompressed stream clone bundles are '
+            'supported; got %s') % compression)
+
+    filecount, bytecount = struct.unpack('>QQ', fp.read(16))
+    requireslen = struct.unpack('>H', fp.read(2))[0]
+    requires = fp.read(requireslen)
+
+    if not requires.endswith('\0'):
+        raise error.Abort(_('malformed stream clone bundle: '
+                            'requirements not properly encoded'))
+
+    requirements = set(requires.rstrip('\0').split(','))
+    missingreqs = requirements - repo.supportedformats
+    if missingreqs:
+        raise error.Abort(_('unable to apply stream clone: '
+                            'unsupported format: %s') %
+                            ', '.join(sorted(missingreqs)))
+
+    consumev1(repo, fp, filecount, bytecount)
+
+class streamcloneapplier(object):
+    """Class to manage applying streaming clone bundles.
+
+    We need to wrap ``applybundlev1()`` in a dedicated type to enable bundle
+    readers to perform bundle type-specific functionality.
+    """
+    def __init__(self, fh):
+        self._fh = fh
+
+    def apply(self, repo):
+        return applybundlev1(repo, self._fh)