There are several uses of the magic number "line+45" when
parsing ACK lines from the server, and it's rather unclear
why 45 is the correct number. We can make this more clear by
keeping a running pointer as we parse, using skip_prefix to
jump past the first "ACK ", then adding 40 to jump past
get_sha1_hex (which is still magical, but hopefully 40 is
less magical to readers of git code).

Note that this actually puts us at line+44. The original
required some character between the sha1 and further ACK
flags (it is supposed to be a space, but we never enforced
that). We start our search for flags at line+44, which
meanas we are slightly more liberal than the old code.

Signed-off-by: Jeff King <>
I actually think we could tighten this even more and drop the strstrs,
too, like:

  arg += 40;
  if (*arg++ != ' ')
        return ACK;
  if (!strcmp(arg, "continue"))
        return ACK_continue;

and so on. But I wasn't sure if there was a reason for the use of
strstr. According to pack-protocol.txt, we would only get one at a time,
and always with a single space between them.

 fetch-pack.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index 3de3bd5..72ec520 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -189,20 +189,23 @@ static enum ack_type get_ack(int fd, unsigned char 
        int len;
        char *line = packet_read_line(fd, &len);
+       const char *arg;
        if (!len)
                die("git fetch-pack: expected ACK/NAK, got EOF");
        if (!strcmp(line, "NAK"))
                return NAK;
-       if (starts_with(line, "ACK ")) {
-               if (!get_sha1_hex(line+4, result_sha1)) {
-                       if (len < 45)
+       if (skip_prefix(line, "ACK ", &arg)) {
+               if (!get_sha1_hex(arg, result_sha1)) {
+                       arg += 40;
+                       len -= arg - line;
+                       if (len < 1)
                                return ACK;
-                       if (strstr(line+45, "continue"))
+                       if (strstr(arg, "continue"))
                                return ACK_continue;
-                       if (strstr(line+45, "common"))
+                       if (strstr(arg, "common"))
                                return ACK_common;
-                       if (strstr(line+45, "ready"))
+                       if (strstr(arg, "ready"))
                                return ACK_ready;
                        return ACK;

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