tests/test-wireproto.py

posix: always seek to EOF when opening a file in append mode

Python 3 already does this, so skip it there.

Consider the program:

   #include <stdio.h>

   int main() {
     FILE *f = fopen("narf", "w");
     fprintf(f, "narf\n");
     fclose(f);

     f = fopen("narf", "a");
     printf("%ld\n", ftell(f));
     fprintf(f, "troz\n");
     printf("%ld\n", ftell(f));

     return 0;
   }

on macOS, FreeBSD, and Linux with glibc, this program prints

   5
   10

but on musl libc (Alpine Linux and probably others) this prints

   0
   10

By my reading of
https://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html
this is technically correct, specifically:

> Opening a file with append mode (a as the first character in the
> mode argument) shall cause all subsequent writes to the file to be
> forced to the then current end-of-file, regardless of intervening
> calls to fseek().

in other words, the file position doesn't really matter in append-mode
files, and we can't depend on it being at all meaningful unless we
perform a seek() before tell() after open(..., 'a'). Experimentally
after a .write() we can do a .tell() and it'll always be reasonable,
but I'm unclear from reading the specification if that's a smart thing
to rely on. This matches what we do on Windows and what Python 3 does
for free, so let's just be consistent. Thanks to Yuya for the idea.

from __future__ import absolute_import, print_function

import sys

from mercurial import (
    error,
    pycompat,
    ui as uimod,
    util,
    wireprototypes,
    wireprotov1peer,
    wireprotov1server,
)
from mercurial.utils import (
    stringutil,
)
stringio = util.stringio

class proto(object):
    def __init__(self, args):
        self.args = args
        self.name = 'dummyproto'

    def getargs(self, spec):
        args = self.args
        args.setdefault(b'*', {})
        names = spec.split()
        return [args[n] for n in names]

    def checkperm(self, perm):
        pass

wireprototypes.TRANSPORTS['dummyproto'] = {
    'transport': 'dummy',
    'version': 1,
}

class clientpeer(wireprotov1peer.wirepeer):
    def __init__(self, serverrepo, ui):
        self.serverrepo = serverrepo
        self.ui = ui

    def url(self):
        return b'test'

    def local(self):
        return None

    def peer(self):
        return self

    def canpush(self):
        return True

    def close(self):
        pass

    def capabilities(self):
        return [b'batch']

    def _call(self, cmd, **args):
        args = pycompat.byteskwargs(args)
        res = wireprotov1server.dispatch(self.serverrepo, proto(args), cmd)
        if isinstance(res, wireprototypes.bytesresponse):
            return res.data
        elif isinstance(res, bytes):
            return res
        else:
            raise error.Abort('dummy client does not support response type')

    def _callstream(self, cmd, **args):
        return stringio(self._call(cmd, **args))

    @wireprotov1peer.batchable
    def greet(self, name):
        f = wireprotov1peer.future()
        yield {b'name': mangle(name)}, f
        yield unmangle(f.value)

class serverrepo(object):
    def __init__(self, ui):
        self.ui = ui

    def greet(self, name):
        return b"Hello, " + name

    def filtered(self, name):
        return self

def mangle(s):
    return b''.join(pycompat.bytechr(ord(c) + 1) for c in pycompat.bytestr(s))
def unmangle(s):
    return b''.join(pycompat.bytechr(ord(c) - 1) for c in pycompat.bytestr(s))

def greet(repo, proto, name):
    return mangle(repo.greet(unmangle(name)))

wireprotov1server.commands[b'greet'] = (greet, b'name')

srv = serverrepo(uimod.ui())
clt = clientpeer(srv, uimod.ui())

def printb(data, end=b'\n'):
    out = getattr(sys.stdout, 'buffer', sys.stdout)
    out.write(data + end)
    out.flush()

printb(clt.greet(b"Foobar"))

with clt.commandexecutor() as e:
    fgreet1 = e.callcommand(b'greet', {b'name': b'Fo, =;:<o'})
    fgreet2 = e.callcommand(b'greet', {b'name': b'Bar'})

printb(stringutil.pprint([f.result() for f in (fgreet1, fgreet2)],
                         bprefix=True))