[PATCH 6 of 6 zstd-wireproto V3] protocol: send application/mercurial-0.2 responses to capable clients

Gregory Szorc gregory.szorc at gmail.com
Sat Dec 24 17:33:10 EST 2016


# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1482618572 25200
#      Sat Dec 24 15:29:32 2016 -0700
# Node ID fee9a440173e103e96b46ad278e497636c4b6b53
# Parent  e78404d994d9da719af16647f6decaa8aeaa56b7
protocol: send application/mercurial-0.2 responses to capable clients

With this commit, the HTTP transport now parses the X-HgProto-<N>
header to determine what media type and compression engine to use for
responses. So far, we only compress responses that are already being
compressed with zlib today (stream response types to specific
commands). We can expand things to cover additional response types
later.

The practical side-effect of this commit is that non-zlib compression
engines will be used if both ends support them. This means if both
ends have zstd support, zstd - not zlib - will be used to compress
data!

When cloning the mozilla-unified repository between a local HTTP
server and client, the benefits of non-zlib compression are quite
noticeable:

  engine     server CPU (s)   client CPU (s)    bundle size
zlib (l=6)      174.1            283.2         1,148,547,026
zstd (l=1)       99.2            267.3         1,127,513,841
zstd (l=3)      103.1            266.9         1,018,861,363
zstd (l=7)      128.3            269.7           919,190,278
zstd (l=10)     162.0               -            894,547,179
none             95.3            277.2         4,097,566,064

The default zstd compression level is 3. So if you deploy zstd
capable Mercurial to your clients and servers and CPU time on
your server is dominated by "getbundle" requests (clients cloning
and pulling) - and my experience at Mozilla tells me this is often
the case - this commit could drastically reduce your server-side
CPU usage *and* save on bandwidth costs!

Another benefit of this change is that server operators can install
*any* compression engine. While it isn't enabled by default, the
"none" compression engine can now be used to disable wire protocol
compression completely. Previously, commands like "getbundle" always
zlib compressed output, adding considerable overhead to generating
responses. If you are on a high speed network and your server is under
high load, it might be advantageous to trade bandwidth for CPU.
Although, zstd at level 1 doesn't use that much CPU, so I'm not
convinced that disabling compression wholesale is worthwhile. And, my
data seems to indicate a slow down on the client without compression.
I suspect this is due to a lack of buffering resulting in an increase
in socket read() calls and/or the fact we're transferring an extra 3 GB
of data (parsing HTTP chunked transfer and processing extra TCP packets
can add up). This is definitely worth investigating and optimizing. But
since the "none" compressor isn't enabled by default, I'm inclined to
punt on this issue.

This commit introduces tons of tests. Some of these should arguably
have been implemented on previous commits. But it was difficult to
test without the server functionality in place.

diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -1606,8 +1606,20 @@ Controls generic server settings.
     but sends more bytes to clients.
 
     This option only impacts the HTTP server.
 
+``zstdlevel``
+    Integer between ``1`` and ``22`` that controls the zstd compression level
+    for wire protocol commands. ``1`` is the minimal amount of compression and
+    ``22`` is the highest amount of compression.
+
+    The default (``3``) should be significantly faster than zlib while likely
+    delivering better compression ratios.
+
+    This option only impacts the HTTP server.
+
+    See also ``server.zliblevel``.
+
 ``smtp``
 --------
 
 Configuration for extensions that need to send email messages.
diff --git a/mercurial/hgweb/protocol.py b/mercurial/hgweb/protocol.py
--- a/mercurial/hgweb/protocol.py
+++ b/mercurial/hgweb/protocol.py
@@ -7,8 +7,9 @@
 
 from __future__ import absolute_import
 
 import cgi
+import struct
 
 from .common import (
     HTTP_OK,
 )
@@ -22,8 +23,9 @@ stringio = util.stringio
 urlerr = util.urlerr
 urlreq = util.urlreq
 
 HGTYPE = 'application/mercurial-0.1'
+HGTYPE2 = 'application/mercurial-0.2'
 HGERRTYPE = 'application/hg-error'
 
 def decodevaluefromheaders(req, headerprefix):
     """Decode a long value from multiple HTTP request headers."""
@@ -82,26 +84,82 @@ class webproto(wireproto.abstractserverp
         val = self.ui.fout.getvalue()
         self.ui.ferr, self.ui.fout = self.oldio
         return val
 
-    def compresschunks(self, chunks):
-        # Don't allow untrusted settings because disabling compression or
-        # setting a very high compression level could lead to flooding
-        # the server's network or CPU.
-        opts = {'level': self.ui.configint('server', 'zliblevel', -1)}
-        return util.compengines['zlib'].compressstream(chunks, opts)
-
     def _client(self):
         return 'remote:%s:%s:%s' % (
             self.req.env.get('wsgi.url_scheme') or 'http',
             urlreq.quote(self.req.env.get('REMOTE_HOST', '')),
             urlreq.quote(self.req.env.get('REMOTE_USER', '')))
 
+    def responsetype(self, v1compressible=False):
+        """Determine the appropriate response type and compression settings.
+
+        The ``v1compressible`` argument states whether the response with
+        application/mercurial-0.1 media types should be zlib compressed.
+
+        Returns a tuple of (mediatype, compengine, engineopts).
+        """
+        # For now, if it isn't compressible in the old world, it's never
+        # compressible. We can change this to send uncompressed 0.2 payloads
+        # later.
+        if not v1compressible:
+            return HGTYPE, None, None
+
+        # Determine the response media type and compression engine based
+        # on the request parameters.
+        protocaps = decodevaluefromheaders(self.req, 'X-HgProto').split(' ')
+
+        if '0.2' in protocaps:
+            # Default as defined by wire protocol spec.
+            compformats = ['zlib', 'none']
+            for cap in protocaps:
+                if cap.startswith('comp='):
+                    compformats = cap[5:].split(',')
+                    break
+
+            # Now find an agreed upon compression format.
+            for engine in wireproto.supportedcompengines(self.ui, self,
+                                                         util.SERVERROLE):
+                if engine.wireprotosupport().name in compformats:
+                    opts = {}
+                    level = self.ui.configint('server',
+                                              '%slevel' % engine.name())
+                    if level is not None:
+                        opts['level'] = level
+
+                    return HGTYPE2, engine, opts
+
+            # No mutually supported compression format. Fall back to the
+            # legacy protocol.
+
+        # Don't allow untrusted settings because disabling compression or
+        # setting a very high compression level could lead to flooding
+        # the server's network or CPU.
+        opts = {'level': self.ui.configint('server', 'zliblevel', -1)}
+        return HGTYPE, util.compengines['zlib'], opts
+
 def iscmd(cmd):
     return cmd in wireproto.commands
 
 def call(repo, req, cmd):
     p = webproto(req, repo.ui)
+
+    def genversion2(gen, compress, engine, engineopts):
+        # application/mercurial-0.2 always sends a payload header
+        # identifying the compression engine.
+        name = engine.wireprotosupport().name
+        assert 0 < len(name) < 256
+        yield struct.pack('B', len(name))
+        yield name
+
+        if compress:
+            for chunk in engine.compressstream(gen, opts=engineopts):
+                yield chunk
+        else:
+            for chunk in gen:
+                yield chunk
+
     rsp = wireproto.dispatch(repo, p, cmd)
     if isinstance(rsp, str):
         req.respond(HTTP_OK, HGTYPE, body=rsp)
         return []
@@ -110,12 +168,18 @@ def call(repo, req, cmd):
             gen = iter(lambda: rsp.reader.read(32768), '')
         else:
             gen = rsp.gen
 
-        if rsp.v1compressible:
-            gen = p.compresschunks(gen)
+        # This code for compression should not be streamres specific. It
+        # is here because we only compress streamres at the moment.
+        mediatype, engine, engineopts = p.responsetype(rsp.v1compressible)
 
-        req.respond(HTTP_OK, HGTYPE)
+        if mediatype == HGTYPE and rsp.v1compressible:
+            gen = engine.compressstream(gen, engineopts)
+        elif mediatype == HGTYPE2:
+            gen = genversion2(gen, rsp.v1compressible, engine, engineopts)
+
+        req.respond(HTTP_OK, mediatype)
         return gen
     elif isinstance(rsp, wireproto.pushres):
         val = p.restore()
         rsp = '%d\n%s' % (rsp.res, val)
diff --git a/tests/get-with-headers.py b/tests/get-with-headers.py
--- a/tests/get-with-headers.py
+++ b/tests/get-with-headers.py
@@ -34,15 +34,24 @@ formatjson = False
 if '--json' in sys.argv:
     sys.argv.remove('--json')
     formatjson = True
 
+hgproto = None
+if '--hgproto' in sys.argv:
+    idx = sys.argv.index('--hgproto')
+    hgproto = sys.argv[idx + 1]
+    sys.argv.pop(idx)
+    sys.argv.pop(idx)
+
 tag = None
 def request(host, path, show):
     assert not path.startswith('/'), path
     global tag
     headers = {}
     if tag:
         headers['If-None-Match'] = tag
+    if hgproto:
+        headers['X-HgProto-1'] = hgproto
 
     conn = httplib.HTTPConnection(host)
     conn.request("GET", '/' + path, None, headers)
     response = conn.getresponse()
diff --git a/tests/test-http-protocol.t b/tests/test-http-protocol.t
--- a/tests/test-http-protocol.t
+++ b/tests/test-http-protocol.t
@@ -41,4 +41,127 @@ Order of engines can also change
   $ get-with-headers.py 127.0.0.1:$HGPORT '?cmd=capabilities' | tr ' ' '\n' | grep compression
   compression=none,zlib
 
   $ killdaemons.py
+
+Start a default server again
+
+  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+Server should send application/mercurial-0.1 to clients if no Accept is used
+
+  $ get-with-headers.py --headeronly 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' -
+  200 Script output follows
+  content-type: application/mercurial-0.1
+  date: * (glob)
+  server: * (glob)
+  transfer-encoding: chunked
+
+Server should send application/mercurial-0.1 when client says it wants it
+
+  $ get-with-headers.py --hgproto '0.1' --headeronly 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' -
+  200 Script output follows
+  content-type: application/mercurial-0.1
+  date: * (glob)
+  server: * (glob)
+  transfer-encoding: chunked
+
+Server should send application/mercurial-0.2 when client says it wants it
+
+  $ get-with-headers.py --hgproto '0.2' --headeronly 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' -
+  200 Script output follows
+  content-type: application/mercurial-0.2
+  date: * (glob)
+  server: * (glob)
+  transfer-encoding: chunked
+
+  $ get-with-headers.py --hgproto '0.1 0.2' --headeronly 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' -
+  200 Script output follows
+  content-type: application/mercurial-0.2
+  date: * (glob)
+  server: * (glob)
+  transfer-encoding: chunked
+
+Requesting a compression format that server doesn't support results will fall back to 0.1
+
+  $ get-with-headers.py --hgproto '0.2 comp=aa' --headeronly 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' -
+  200 Script output follows
+  content-type: application/mercurial-0.1
+  date: * (glob)
+  server: * (glob)
+  transfer-encoding: chunked
+
+#if zstd
+zstd is used if available
+
+  $ get-with-headers.py --hgproto '0.2 comp=zstd' 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' > resp
+  $ f --size --hexdump --bytes 36 --sha1 resp
+  resp: size=248, sha1=4d8d8f87fb82bd542ce52881fdc94f850748
+  0000: 32 30 30 20 53 63 72 69 70 74 20 6f 75 74 70 75 |200 Script outpu|
+  0010: 74 20 66 6f 6c 6c 6f 77 73 0a 0a 04 7a 73 74 64 |t follows...zstd|
+  0020: 28 b5 2f fd                                     |(./.|
+
+#endif
+
+application/mercurial-0.2 is not yet used on non-streaming responses
+
+  $ get-with-headers.py --hgproto '0.2' 127.0.0.1:$HGPORT '?cmd=heads' -
+  200 Script output follows
+  content-length: 41
+  content-type: application/mercurial-0.1
+  date: * (glob)
+  server: * (glob)
+  
+  e93700bd72895c5addab234c56d4024b487a362f
+
+Now test protocol preference usage
+
+  $ killdaemons.py
+  $ hg --config server.compressionengines=none,zlib -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+No Accept will send 0.1+zlib, even though "none" is preferred b/c "none" isn't supported on 0.1
+
+  $ get-with-headers.py --headeronly 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000' Content-Type
+  200 Script output follows
+  content-type: application/mercurial-0.1
+
+  $ get-with-headers.py 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000'  > resp
+  $ f --size --hexdump --bytes 28 --sha1 resp
+  resp: size=227, sha1=35a4c074da74f32f5440da3cbf04
+  0000: 32 30 30 20 53 63 72 69 70 74 20 6f 75 74 70 75 |200 Script outpu|
+  0010: 74 20 66 6f 6c 6c 6f 77 73 0a 0a 78             |t follows..x|
+
+Explicit 0.1 will send zlib because "none" isn't supported on 0.1
+
+  $ get-with-headers.py --hgproto '0.1' 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000'  > resp
+  $ f --size --hexdump --bytes 28 --sha1 resp
+  resp: size=227, sha1=35a4c074da74f32f5440da3cbf04
+  0000: 32 30 30 20 53 63 72 69 70 74 20 6f 75 74 70 75 |200 Script outpu|
+  0010: 74 20 66 6f 6c 6c 6f 77 73 0a 0a 78             |t follows..x|
+
+0.2 with no compression will get "none" because that is server's preference
+(spec says ZL and UN are implicitly supported)
+
+  $ get-with-headers.py --hgproto '0.2' 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000'  > resp
+  $ f --size --hexdump --bytes 32 --sha1 resp
+  resp: size=432, sha1=ac931b412ec185a02e0e5bcff98dac83
+  0000: 32 30 30 20 53 63 72 69 70 74 20 6f 75 74 70 75 |200 Script outpu|
+  0010: 74 20 66 6f 6c 6c 6f 77 73 0a 0a 04 6e 6f 6e 65 |t follows...none|
+
+Client receives server preference even if local order doesn't match
+
+  $ get-with-headers.py --hgproto '0.2 comp=zlib,none' 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000'  > resp
+  $ f --size --hexdump --bytes 32 --sha1 resp
+  resp: size=432, sha1=ac931b412ec185a02e0e5bcff98dac83
+  0000: 32 30 30 20 53 63 72 69 70 74 20 6f 75 74 70 75 |200 Script outpu|
+  0010: 74 20 66 6f 6c 6c 6f 77 73 0a 0a 04 6e 6f 6e 65 |t follows...none|
+
+Client receives only supported format even if not server preferred format
+
+  $ get-with-headers.py --hgproto '0.2 comp=zlib' 127.0.0.1:$HGPORT '?cmd=getbundle&heads=e93700bd72895c5addab234c56d4024b487a362f&common=0000000000000000000000000000000000000000'  > resp
+  $ f --size --hexdump --bytes 33 --sha1 resp
+  resp: size=232, sha1=a1c727f0c9693ca15742a75c30419bc36
+  0000: 32 30 30 20 53 63 72 69 70 74 20 6f 75 74 70 75 |200 Script outpu|
+  0010: 74 20 66 6f 6c 6c 6f 77 73 0a 0a 04 7a 6c 69 62 |t follows...zlib|
+  0020: 78                                              |x|


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