view contrib/debugcmdserver.py @ 39862:5a9ab91e0a45

revlog: new API to emit revision data

I recently refactored changegroup generation code to make it more
storage agnostic. I made significant progress. But there is still
a bit of work to be done. Specifically:

* Changegroup code is looking at low-level storage attributes to
  influence sorting. Sorting should be done at the storage layer.
* The linknode lookup and sorting code for ellipsis is very
  complicated.
* Linknodes are just generally wonky because e.g. file storage doesn't
  know how to translate a linkrev to a changelog node.
* We regressed performance when introducing the request-response
  objects.

Having thought about this problem a bit, I think I've come up with
a better interface for emitting revision deltas.

This commit defines and implements that interface. See the docstring
in repository.py for more info.

This API adds 3 notable features over the previous one.

First, it defers node ordering to the storage implementation in
the common case but allows overriding as necessary. We have a
facility for requesting an exact ordering (used in ellipsis
mode). We have another facility for storage order (used for changelog).

Second, we have an argument specifying assumptions about parents
revisions. This can be used to force a fulltext revision when we
don't know the receiver has a parent revision to delta against.

Third, we can control whether revision data is emitted. This makes
the API suitable as a generic "index data retrieval" API as well
as for producing revision deltas - possibly in the same operation!

The new API is much simpler: we no longer need a complicated "request"
object to encapsulate the delta generation request. I'm optimistic
this will restore performance loss associated with
emitrevisiondeltas().

Storage unit tests for the new API have been implemented.

Future commits will port existing consumers of emitrevisiondeltas()
to the new API then remove emitrevisiondeltas().

Differential Revision: https://phab.mercurial-scm.org/D4722

#!/usr/bin/env python
#
# Dumps output generated by Mercurial's command server in a formatted style to a
# given file or stderr if '-' is specified. Output is also written in its raw
# format to stdout.
#
# $ ./hg serve --cmds pipe | ./contrib/debugcmdserver.py -
# o, 52   -> 'capabilities: getencoding runcommand\nencoding: UTF-8'

from __future__ import absolute_import, print_function
import struct
import sys

if len(sys.argv) != 2:
    print('usage: debugcmdserver.py FILE')
    sys.exit(1)

outputfmt = '>cI'
outputfmtsize = struct.calcsize(outputfmt)

if sys.argv[1] == '-':
    log = sys.stderr
else:
    log = open(sys.argv[1], 'a')

def read(size):
    data = sys.stdin.read(size)
    if not data:
        raise EOFError
    sys.stdout.write(data)
    sys.stdout.flush()
    return data

try:
    while True:
        header = read(outputfmtsize)
        channel, length = struct.unpack(outputfmt, header)
        log.write('%s, %-4d' % (channel, length))
        if channel in 'IL':
            log.write(' -> waiting for input\n')
        else:
            data = read(length)
            log.write(' -> %r\n' % data)
        log.flush()
except EOFError:
    pass
finally:
    if log != sys.stderr:
        log.close()