contrib/debugcmdserver.py

subrepo: print the status line before creating the peer for better diagnostics

I ran into a problem where I tried updating to a different branch, and the
process appeared to hang.  It turned out that the subrepo revision wasn't
available locally, and I must have originally cloned it from an `hg serve -S` on
a machine that currently wasn't serving anything.  It took 2+ minutes to
timeout, and didn't mention what it was connecting to even then.

There are a couple of other issues in this scenario too.

  - The repo is dirty after the failed checkout because the top level repo is
    updated first.  We should probably make 2 passes- top down to pull
    everything needed, and then do an update once everything is in place.

  - Something must be reading .hgsubstate from wdir because if the same merge
    command is run after the timeout, a prompt is issued that the local and
    remote subrepo diverged, instead of hanging.  But it lists the local version
    and remote version as having the same hash.

#!/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()