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send-pack: use buffered I/O to talk to pack-objects 

We start a pack-objects process and then write all of the
positive and negative sha1s to it over a pipe. We do so by
formatting each item into a fixed-size buffer and then
writing each individually. This has two drawbacks:

  1. There's some manual computation of the buffer size,
     which is not immediately obvious is correct (though it
     is).

  2. We write() once per sha1, which means a lot more system
     calls than are necessary.

We can solve both by wrapping the pipe descriptor in a stdio
handle; this is the same technique used by upload-pack when
serving fetches.

Note that we can also simplify and improve the error
handling here. The original detected a single write error
and broke out of the loop (presumably to avoid writing the
error message over and over), but never actually acted on
seeing an error; we just fed truncated input and took
whatever pack-objects returned.

In practice, this probably didn't matter, as the likely
errors would be caused by pack-objects dying (and we'd
probably just die with SIGPIPE anyway). But we can easily
make this simpler and more robust; the stdio handle keeps an
error flag, which we can check at the end.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Jeff King 2016-06-08 15:42:16 -04:00 committed by Junio C Hamano
parent 0b65a8dbdb
commit f0bca72dc7
1 changed files with 16 additions and 17 deletions
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33
send-pack.c
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@ -36,18 +36,15 @@ int option_parse_push_signed(const struct option *opt,
die("bad %s argument: %s", opt->long_name, arg);
}

static int feed_object(const unsigned char *sha1, int fd, int negative)
static void feed_object(const unsigned char *sha1, FILE *fh, int negative)
{
char buf[42];

if (negative && !has_sha1_file(sha1))
return 1;
return;

memcpy(buf + negative, sha1_to_hex(sha1), 40);
if (negative)
buf[0] = '^';
buf[40 + negative] = '\n';
return write_or_whine(fd, buf, 41 + negative, "send-pack: send refs");
putc('^', fh);
fputs(sha1_to_hex(sha1), fh);
putc('\n', fh);
}

/*
@ -73,6 +70,7 @@ static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, stru
NULL,
};
struct child_process po = CHILD_PROCESS_INIT;
FILE *po_in;
int i;

i = 4;
@ -97,21 +95,22 @@ static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, stru
* We feed the pack-objects we just spawned with revision
* parameters by writing to the pipe.
*/
po_in = xfdopen(po.in, "w");
for (i = 0; i < extra->nr; i++)
if (!feed_object(extra->sha1[i], po.in, 1))
break;
feed_object(extra->sha1[i], po_in, 1);

while (refs) {
if (!is_null_oid(&refs->old_oid) &&
!feed_object(refs->old_oid.hash, po.in, 1))
break;
if (!is_null_oid(&refs->new_oid) &&
!feed_object(refs->new_oid.hash, po.in, 0))
break;
if (!is_null_oid(&refs->old_oid))
feed_object(refs->old_oid.hash, po_in, 1);
if (!is_null_oid(&refs->new_oid))
feed_object(refs->new_oid.hash, po_in, 0);
refs = refs->next;
}

close(po.in);
fflush(po_in);
if (ferror(po_in))
die_errno("error writing to pack-objects");
fclose(po_in);

if (args->stateless_rpc) {
char *buf = xmalloc(LARGE_PACKET_MAX);