use skip_prefix to avoid magic numbers

It's a common idiom to match a prefix and then skip past it
with a magic number, like:

  if (starts_with(foo, "bar"))
	  foo += 3;

This is easy to get wrong, since you have to count the
prefix string yourself, and there's no compiler check if the
string changes.  We can use skip_prefix to avoid the magic
numbers here.

Note that some of these conversions could be much shorter.
For example:

  if (starts_with(arg, "--foo=")) {
	  bar = arg + 6;
	  continue;
  }

could become:

  if (skip_prefix(arg, "--foo=", &bar))
	  continue;

However, I have left it as:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = v;
	  continue;
  }

to visually match nearby cases which need to actually
process the string. Like:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = atoi(v);
	  continue;
  }

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/fetch-pack.c b/fetch-pack.c
index eeee2bb..3de3bd5 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -319,18 +319,19 @@ static int find_common(struct fetch_pack_args *args,
 
 	if (args->depth > 0) {
 		char *line;
+		const char *arg;
 		unsigned char sha1[20];
 
 		send_request(args, fd[1], &req_buf);
 		while ((line = packet_read_line(fd[0], NULL))) {
-			if (starts_with(line, "shallow ")) {
-				if (get_sha1_hex(line + 8, sha1))
+			if (skip_prefix(line, "shallow ", &arg)) {
+				if (get_sha1_hex(arg, sha1))
 					die("invalid shallow line: %s", line);
 				register_shallow(sha1);
 				continue;
 			}
-			if (starts_with(line, "unshallow ")) {
-				if (get_sha1_hex(line + 10, sha1))
+			if (skip_prefix(line, "unshallow ", &arg)) {
+				if (get_sha1_hex(arg, sha1))
 					die("invalid unshallow line: %s", line);
 				if (!lookup_object(sha1))
 					die("object not found: %s", line);