[PATCH v2] upload-pack: use buffered I/O to talk to rev-list

[René Scharfe <l.s.r@xxxxxx>]

Like f0bca72dc77 (send-pack: use buffered I/O to talk to pack-objects,
2016-06-08), significantly reduce the number of system calls and
simplify the code for sending object IDs to rev-list by using stdio's
buffering.

Take care to handle errors immediately to get the correct error code,
and to flush the buffer explicitly before closing the stream in order to
catch any write errors for these last bytes.

Helped-by: Chris Torek <chris.torek@xxxxxxxxx>
Helped-by: Johannes Sixt <j6t@xxxxxxxx>
---
Changes since v1:
- Handle fprintf() errors immediately.
- Call ferror() and fflush() explicitly before calling fclose().
- Ignore fclose() errors, similar to the original code.
- Initialize the stream pointer and use a NULL check in the error
  handler to avoid a bogus compiler warning about it being used
  without initialization.

 upload-pack.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/upload-pack.c b/upload-pack.c
index 80ad9a38d81..811fdd47b58 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -603,9 +603,8 @@ static int do_reachable_revlist(struct child_process *cmd,
 		"rev-list", "--stdin", NULL,
 	};
 	struct object *o;
-	char namebuf[GIT_MAX_HEXSZ + 2]; /* ^ + hash + LF */
+	FILE *cmd_in = NULL;
 	int i;
-	const unsigned hexsz = the_hash_algo->hexsz;

 	cmd->argv = argv;
 	cmd->git_cmd = 1;
@@ -623,8 +622,8 @@ static int do_reachable_revlist(struct child_process *cmd,
 	if (start_command(cmd))
 		goto error;

-	namebuf[0] = '^';
-	namebuf[hexsz + 1] = '\n';
+	cmd_in = xfdopen(cmd->in, "w");
+
 	for (i = get_max_object_index(); 0 < i; ) {
 		o = get_indexed_object(--i);
 		if (!o)
@@ -633,11 +632,9 @@ static int do_reachable_revlist(struct child_process *cmd,
 			o->flags &= ~TMP_MARK;
 		if (!is_our_ref(o, allow_uor))
 			continue;
-		memcpy(namebuf + 1, oid_to_hex(&o->oid), hexsz);
-		if (write_in_full(cmd->in, namebuf, hexsz + 2) < 0)
+		if (fprintf(cmd_in, "^%s\n", oid_to_hex(&o->oid)) < 0)
 			goto error;
 	}
-	namebuf[hexsz] = '\n';
 	for (i = 0; i < src->nr; i++) {
 		o = src->objects[i].item;
 		if (is_our_ref(o, allow_uor)) {
@@ -647,11 +644,12 @@ static int do_reachable_revlist(struct child_process *cmd,
 		}
 		if (reachable && o->type == OBJ_COMMIT)
 			o->flags |= TMP_MARK;
-		memcpy(namebuf, oid_to_hex(&o->oid), hexsz);
-		if (write_in_full(cmd->in, namebuf, hexsz + 1) < 0)
+		if (fprintf(cmd_in, "%s\n", oid_to_hex(&o->oid)) < 0)
 			goto error;
 	}
-	close(cmd->in);
+	if (ferror(cmd_in) || fflush(cmd_in))
+		goto error;
+	fclose(cmd_in);
 	cmd->in = -1;
 	sigchain_pop(SIGPIPE);

@@ -660,8 +658,8 @@ static int do_reachable_revlist(struct child_process *cmd,
 error:
 	sigchain_pop(SIGPIPE);

-	if (cmd->in >= 0)
-		close(cmd->in);
+	if (cmd_in)
+		fclose(cmd_in);
 	if (cmd->out >= 0)
 		close(cmd->out);
 	return -1;
--
2.28.0