contrib/debugcmdserver.py

chgserver: backport py3 buffered I/O workarounds from procutil

I've recently switched to new machine and I found chg's stdout is fully
buffered.

Even though chg server is a daemon process, it inherits the environment
where the chg client originally forked the server. This means the server's
stdout might have been wrapped by LineBufferedWrapper. That's why we need
to do wrap/unwrap in both ways.

The "if" condition in _restoreio() looks weird, but I'm not willing to
clean things up because stdio behavior is fundamentally different between
py2 and py3, and py2 support will be dropped anyway.

#!/usr/bin/env python3
#
# 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()