comparison tests/test-http-protocol.t @ 30764:e75463e3179f

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.

30763:a520aefb96f1

  $ cat hg.pid > $DAEMON_PIDS
  $ get-with-headers.py 127.0.0.1:$HGPORT '?cmd=capabilities' | tr ' ' '\n' | grep compression
  compression=none,zlib

  $ killdaemons.py

30764:e75463e3179f

  $ cat hg.pid > $DAEMON_PIDS
  $ 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|