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.
$ . $TESTDIR/wireprotohelpers.sh
$ hg init server
$ enablehttpv2 server
$ cd server
$ hg debugdrawdag << EOF
> C D
> |/
> B
> |
> A
> EOF
$ hg phase --public -r C
$ hg book -r C @
$ hg log -T '{rev}:{node} {desc}\n'
3:be0ef73c17ade3fc89dc41701eb9fc3a91b58282 D
2:26805aba1e600a82e93661149f2313866a221a7b C
1:112478962961147124edd43549aedd1a335e44bf B
0:426bada5c67598ca65036d57d9e4b64b0c1ce7a0 A
$ hg serve -p $HGPORT -d --pid-file hg.pid -E error.log
$ cat hg.pid > $DAEMON_PIDS
Request for namespaces works
$ sendhttpv2peer << EOF
> command listkeys
> namespace namespaces
> EOF
creating http peer for wire protocol version 2
sending listkeys command
response: {
b'bookmarks': b'',
b'namespaces': b'',
b'phases': b''
}
Request for phases works
$ sendhttpv2peer << EOF
> command listkeys
> namespace phases
> EOF
creating http peer for wire protocol version 2
sending listkeys command
response: {
b'be0ef73c17ade3fc89dc41701eb9fc3a91b58282': b'1',
b'publishing': b'True'
}
Request for bookmarks works
$ sendhttpv2peer << EOF
> command listkeys
> namespace bookmarks
> EOF
creating http peer for wire protocol version 2
sending listkeys command
response: {
b'@': b'26805aba1e600a82e93661149f2313866a221a7b'
}
$ cat error.log