contrib/debugcmdserver.py

sslutil: emit warning when no CA certificates loaded

If no CA certificates are loaded, that is almost certainly a/the
reason certificate verification fails when connecting to a server.

The modern ssl module in Python 2.7.9+ provides an API to access
the list of loaded CA certificates. This patch emits a warning
on modern Python when certificate verification fails and there are
no loaded CA certificates.

There is no way to detect the number of loaded CA certificates
unless the modern ssl module is present. Hence the differences
in test output depending on whether modern ssl is available.

It's worth noting that a test which specifies a CA file still
renders this warning. That is because the certificate it is loading
is a x509 client certificate and not a CA certificate. This
test could be updated if anyone is so inclined.

#!/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()