fetch-pack: give up after getting too many "ack continue"

If your repository have more roots than the remote repository
you ask an object for, the remote upload-pack keeps responding
"ack continue" until it fills up its received-have buffer
(currently 256 entries).  Usually this is not a problem because
the requester stops traversing the ancestry chain from the commit
it gets "ack continue" for, but this mechanism does not work as
a roadblock when it traverses down the path to the root the
other side does not have.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/fetch-pack.c b/fetch-pack.c
index 8daa93d..8371348 100644 (file)
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -18,6 +18,12 @@ static const char *exec = "git-upload-pack";
 #define SEEN           (1U << 3)
 #define POPPED         (1U << 4)
 
+/*
+ * After sending this many "have"s if we do not get any new ACK , we
+ * give up traversing our history.
+ */
+#define MAX_IN_VAIN 256
+
 static struct commit_list *rev_list = NULL;
 static int non_common_revs = 0, multi_ack = 0, use_thin_pack = 0;
 
@@ -134,6 +140,8 @@ static int find_common(int fd[2], unsigned char *result_sha1,
        int fetching;
        int count = 0, flushes = 0, retval;
        const unsigned char *sha1;
+       unsigned in_vain = 0;
+       int got_continue = 0;
 
        for_each_ref(rev_list_insert_ref);
 
@@ -172,6 +180,7 @@ static int find_common(int fd[2], unsigned char *result_sha1,
                packet_write(fd[1], "have %s\n", sha1_to_hex(sha1));
                if (verbose)
                        fprintf(stderr, "have %s\n", sha1_to_hex(sha1));
+               in_vain++;
                if (!(31 & ++count)) {
                        int ack;
 
@@ -200,9 +209,16 @@ static int find_common(int fd[2], unsigned char *result_sha1,
                                                lookup_commit(result_sha1);
                                        mark_common(commit, 0, 1);
                                        retval = 0;
+                                       in_vain = 0;
+                                       got_continue = 1;
                                }
                        } while (ack);
                        flushes--;
+                       if (got_continue && MAX_IN_VAIN < in_vain) {
+                               if (verbose)
+                                       fprintf(stderr, "giving up\n");
+                               break; /* give up */
+                       }
                }
        }
 done: