fetch-pack: Implement no-done capability

If enabled on the connection "multi_ack_detailed no-done" as a
pair allows the remote upload-pack process to send a PACK down
to the client as soon as a "ACK %s ready" message was also sent.

Over git:// and ssh:// where a bi-directional stream is in place
this has very little difference over the classical version that
waits for the client to send a "done\n" line by itself.  It does
slightly reduce the latency involved to start the pack stream as
there is one less round-trip from client->server required.

Over smart HTTP this avoids needing to send a final RPC that has
all of the prior common objects.  Instead the server is able to
return a pack as soon as its ready to.  For many common users the
smart HTTP fetch is now just 2 requests: GET .../info/refs, and
a POST .../git-upload-pack to not only negotiate but also receive
the pack stream.  Only users who have more than 32 local unshared
commits with the remote will need additional requests to negotiate
a common merge base.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index 5173dc9aadbbb481188c2df61abeab39a20a0a91..59fbda522b7ba0ce4308aa85fac1a7b1b51c1550 100644 (file)
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -14,6 +14,7 @@ static int transfer_unpack_limit = -1;
 static int fetch_unpack_limit = -1;
 static int unpack_limit = 100;
 static int prefer_ofs_delta = 1;
+static int no_done = 0;
 static struct fetch_pack_args args = {
        /* .uploadpack = */ "git-upload-pack",
 };
@@ -225,6 +226,7 @@ static int find_common(int fd[2], unsigned char *result_sha1,
        const unsigned char *sha1;
        unsigned in_vain = 0;
        int got_continue = 0;
+       int got_ready = 0;
        struct strbuf req_buf = STRBUF_INIT;
        size_t state_len = 0;
 
@@ -262,6 +264,7 @@ static int find_common(int fd[2], unsigned char *result_sha1,
                        struct strbuf c = STRBUF_INIT;
                        if (multi_ack == 2)     strbuf_addstr(&c, " multi_ack_detailed");
                        if (multi_ack == 1)     strbuf_addstr(&c, " multi_ack");
+                       if (no_done)            strbuf_addstr(&c, " no-done");
                        if (use_sideband == 2)  strbuf_addstr(&c, " side-band-64k");
                        if (use_sideband == 1)  strbuf_addstr(&c, " side-band");
                        if (args.use_thin_pack) strbuf_addstr(&c, " thin-pack");
@@ -379,8 +382,10 @@ static int find_common(int fd[2], unsigned char *result_sha1,
                                        retval = 0;
                                        in_vain = 0;
                                        got_continue = 1;
-                                       if (ack == ACK_ready)
+                                       if (ack == ACK_ready) {
                                                rev_list = NULL;
+                                               got_ready = 1;
+                                       }
                                        break;
                                        }
                                }
@@ -394,8 +399,10 @@ static int find_common(int fd[2], unsigned char *result_sha1,
                }
        }
 done:
-       packet_buf_write(&req_buf, "done\n");
-       send_request(fd[1], &req_buf);
+       if (!got_ready || !no_done) {
+               packet_buf_write(&req_buf, "done\n");
+               send_request(fd[1], &req_buf);
+       }
        if (args.verbose)
                fprintf(stderr, "done\n");
        if (retval != 0) {
@@ -698,6 +705,11 @@ static struct ref *do_fetch_pack(int fd[2],
                if (args.verbose)
                        fprintf(stderr, "Server supports multi_ack_detailed\n");
                multi_ack = 2;
+               if (server_supports("no-done")) {
+                       if (args.verbose)
+                               fprintf(stderr, "Server supports no-done\n");
+                       no_done = 1;
+               }
        }
        else if (server_supports("multi_ack")) {
                if (args.verbose)