tests/printenv.py

worker: avoid potential partial write of pickled data

Previously, the code wrote the pickled data using os.write(). However,
os.write() can write less bytes than passed to it. To trigger the problem, the
pickled data had to be larger than 2147479552 bytes on my system.

Instead, open a file object and pass it to pickle.dump(). This also has the
advantage that it doesn’t buffer the whole pickled data in memory.

Note that the opened file must be buffered because pickle doesn’t support
unbuffered streams because unbuffered streams’ write() method might write less
bytes than passed to it (like os.write()) but pickle.dump() relies on that all
bytes are written (see https://github.com/python/cpython/issues/93050).

The side effect of using a file object and a with statement is that wfd is
explicitly closed now while it seems like before it was implicitly closed by
process exit.

#!/usr/bin/env python3
#
# simple script to be used in hooks
#
# put something like this in the repo .hg/hgrc:
#
#     [hooks]
#     changegroup = python "$TESTDIR/printenv.py" <hookname> [exit] [output]
#
#   - <hookname> is a mandatory argument (e.g. "changegroup")
#   - [exit] is the exit code of the hook (default: 0)
#   - [output] is the name of the output file (default: use sys.stdout)
#              the file will be opened in append mode.
#
import argparse
import os
import sys

try:
    import msvcrt

    msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
    msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
    msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)
except ImportError:
    pass

parser = argparse.ArgumentParser()
parser.add_argument("name", help="the hook name, used for display")
parser.add_argument(
    "exitcode",
    nargs="?",
    default=0,
    type=int,
    help="the exit code for the hook",
)
parser.add_argument(
    "out", nargs="?", default=None, help="where to write the output"
)
parser.add_argument(
    "--line",
    action="store_true",
    help="print environment variables one per line instead of on a single line",
)
args = parser.parse_args()

if args.out is None:
    out = sys.stdout
    out = getattr(out, "buffer", out)
else:
    out = open(args.out, "ab")

# variables with empty values may not exist on all platforms, filter
# them now for portability sake.
env = [(k, v) for k, v in os.environ.items() if k.startswith("HG_") and v]
env.sort()

out.write(b"%s hook: " % args.name.encode('ascii'))
if os.name == 'nt':
    filter = lambda x: x.replace('\\', '/')
else:
    filter = lambda x: x

vars = [
    b"%s=%s" % (k.encode('ascii'), filter(v).encode('ascii')) for k, v in env
]

# Print variables on out
if not args.line:
    out.write(b" ".join(vars))
else:
    for var in vars:
        out.write(var)
        out.write(b"\n")

out.write(b"\n")
out.close()

sys.exit(args.exitcode)