push: receiver end advertises refs from alternate repositories

Earlier, when pushing into a repository that borrows from alternate object
stores, we followed the longstanding design decision not to trust refs in
the alternate repository that houses the object store we are borrowing
from.  If your public repository is borrowing from Linus's public
repository, you pushed into it long time ago, and now when you try to push
your updated history that is in sync with more recent history from Linus,
you will end up sending not just your own development, but also the
changes you acquired through Linus's tree, even though the objects needed
for the latter already exists at the receiving end.  This is because the
receiving end does not advertise that the objects only reachable from the
borrowed repository (i.e. Linus's) are already available there.

This solves the issue by making the receiving end advertise refs from
borrowed repositories.  They are not sent with their true names but with a
phoney name ".have" to make sure that the old senders will safely ignore
them (otherwise, the old senders will misbehave, trying to push matching
refs, and mirror push that deletes refs that only exist at the receiving
end).

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-receive-pack.c b/builtin-receive-pack.c
index 6d6027ead17b86519d69c3dfc9b98c01e916d277..45e3cd90fd476cdb0a32e5de27739b18e060e031 100644 (file)
--- a/builtin-receive-pack.c
+++ b/builtin-receive-pack.c
@@ -6,6 +6,8 @@
 #include "exec_cmd.h"
 #include "commit.h"
 #include "object.h"
+#include "remote.h"
+#include "transport.h"
 
 static const char receive_pack_usage[] = "git-receive-pack <git-dir>";
 
@@ -462,6 +464,40 @@ static int delete_only(struct command *cmd)
        return 1;
 }
 
+static int add_refs_from_alternate(struct alternate_object_database *e, void *unused)
+{
+       char *other = xstrdup(make_absolute_path(e->base));
+       size_t len = strlen(other);
+       struct remote *remote;
+       struct transport *transport;
+       const struct ref *extra;
+
+       while (other[len-1] == '/')
+               other[--len] = '\0';
+       if (len < 8 || memcmp(other + len - 8, "/objects", 8))
+               return 0;
+       /* Is this a git repository with refs? */
+       memcpy(other + len - 8, "/refs", 6);
+       if (!is_directory(other))
+               return 0;
+       other[len - 8] = '\0';
+       remote = remote_get(other);
+       transport = transport_get(remote, other);
+       for (extra = transport_get_remote_refs(transport);
+            extra;
+            extra = extra->next) {
+               add_extra_ref(".have", extra->old_sha1, 0);
+       }
+       transport_disconnect(transport);
+       free(other);
+       return 0;
+}
+
+static void add_alternate_refs(void)
+{
+       foreach_alt_odb(add_refs_from_alternate, NULL);
+}
+
 int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 {
        int i;
@@ -497,7 +533,9 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
        else if (0 <= receive_unpack_limit)
                unpack_limit = receive_unpack_limit;
 
+       add_alternate_refs();
        write_head_info();
+       clear_extra_refs();
 
        /* EOF */
        packet_flush(1);

diff --git a/cache.h b/cache.h
index 98a742122dbacbb39fa104cdfe909a9a884ed7b6..99af83a0479ef472078afcd288b1f6ba6283a2f0 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -641,6 +641,8 @@ extern struct alternate_object_database {
 } *alt_odb_list;
 extern void prepare_alt_odb(void);
 extern void add_to_alternates_file(const char *reference);
+typedef int alt_odb_fn(struct alternate_object_database *, void *);
+extern void foreach_alt_odb(alt_odb_fn, void*);
 
 struct pack_window {
        struct pack_window *next;

diff --git a/sha1_file.c b/sha1_file.c
index ae550e89c0942bb9e34b252b653c40e869a074a4..12be17b5dace07a2ca71613e4e9093cdb77492ac 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -393,6 +393,16 @@ void add_to_alternates_file(const char *reference)
                link_alt_odb_entries(alt, alt + strlen(alt), '\n', NULL, 0);
 }
 
+void foreach_alt_odb(alt_odb_fn fn, void *cb)
+{
+       struct alternate_object_database *ent;
+
+       prepare_alt_odb();
+       for (ent = alt_odb_list; ent; ent = ent->next)
+               if (fn(ent, cb))
+                       return;
+}
+
 void prepare_alt_odb(void)
 {
        const char *alt;