[PATCH v4] fetch-pack: always allow fetching of literal SHA1s

[Jonathan Tan <jonathantanmy@google.com>]

fetch-pack, when fetching a literal SHA-1 from a server that is not
configured with uploadpack.allowtipsha1inwant (or similar), always
returns an error message of the form "Server does not allow request for
unadvertised object %s". However, it is sometimes the case that such
object is advertised. This situation would occur, for example, if a user
or a script was provided a SHA-1 instead of a branch or tag name for
fetching, and wanted to invoke "git fetch" or "git fetch-pack" using
that SHA-1.

Teach fetch-pack to also check the SHA-1s of the refs in the received
ref advertisement if a literal SHA-1 was given by the user.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---

Thanks, peff. I've incorporated your suggestions - I don't feel very
strongly about this, but I guess it's worthwhile to avoid the quadratic
behavior if we can.

Also incorporated Jonathan Nieder's suggestion about the placement of
the last line. The relevant function is also factored out (following
peff's suggestion).
---
 fetch-pack.c          | 36 +++++++++++++++++++++++++++++++++++-
 t/t5500-fetch-pack.sh | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index afb8b0502..1adb1a6c2 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -15,6 +15,7 @@
 #include "version.h"
 #include "prio-queue.h"
 #include "sha1-array.h"
+#include "oidset.h"
 
 static int transfer_unpack_limit = -1;
 static int fetch_unpack_limit = -1;
@@ -592,13 +593,22 @@ static void mark_recent_complete_commits(struct fetch_pack_args *args,
 	}
 }
 
+static void add_refs_to_oidset(struct oidset *oids, const struct ref *refs)
+{
+	for (; refs; refs = refs->next)
+		oidset_insert(oids, &refs->old_oid);
+}
+
 static void filter_refs(struct fetch_pack_args *args,
 			struct ref **refs,
 			struct ref **sought, int nr_sought)
 {
 	struct ref *newlist = NULL;
 	struct ref **newtail = &newlist;
+	struct ref *unmatched = NULL;
 	struct ref *ref, *next;
+	struct oidset tip_oids = OIDSET_INIT;
+	int tip_oids_initialized = 0;
 	int i;
 
 	i = 0;
@@ -631,13 +641,15 @@ static void filter_refs(struct fetch_pack_args *args,
 			ref->next = NULL;
 			newtail = &ref->next;
 		} else {
-			free(ref);
+			ref->next = unmatched;
+			unmatched = ref;
 		}
 	}
 
 	/* Append unmatched requests to the list */
 	for (i = 0; i < nr_sought; i++) {
 		unsigned char sha1[20];
+		int can_append = 0;
 
 		ref = sought[i];
 		if (ref->match_status != REF_NOT_MATCHED)
@@ -649,6 +661,21 @@ static void filter_refs(struct fetch_pack_args *args,
 
 		if ((allow_unadvertised_object_request &
 		    (ALLOW_TIP_SHA1 | ALLOW_REACHABLE_SHA1))) {
+			can_append = 1;
+		} else {
+			if (!tip_oids_initialized) {
+				/*
+				 * Check all refs, including those already
+				 * matched
+				 */
+				add_refs_to_oidset(&tip_oids, unmatched);
+				add_refs_to_oidset(&tip_oids, newlist);
+				tip_oids_initialized = 1;
+			}
+			can_append = oidset_contains(&tip_oids, &ref->old_oid);
+		}
+
+		if (can_append) {
 			ref->match_status = REF_MATCHED;
 			*newtail = copy_ref(ref);
 			newtail = &(*newtail)->next;
@@ -656,6 +683,13 @@ static void filter_refs(struct fetch_pack_args *args,
 			ref->match_status = REF_UNADVERTISED_NOT_ALLOWED;
 		}
 	}
+
+	oidset_clear(&tip_oids);
+	for (ref = unmatched; ref; ref = next) {
+		next = ref->next;
+		free(ref);
+	}
+
 	*refs = newlist;
 }
 
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index b5865b385..80a1a3239 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -547,6 +547,41 @@ test_expect_success 'fetch-pack can fetch a raw sha1' '
 	git fetch-pack hidden $(git -C hidden rev-parse refs/hidden/one)
 '
 
+test_expect_success 'fetch-pack can fetch a raw sha1 that is advertised as a ref' '
+	rm -rf server client &&
+	git init server &&
+	test_commit -C server 1 &&
+
+	git init client &&
+	git -C client fetch-pack ../server \
+		$(git -C server rev-parse refs/heads/master)
+'
+
+test_expect_success 'fetch-pack can fetch a raw sha1 overlapping a named ref' '
+	rm -rf server client &&
+	git init server &&
+	test_commit -C server 1 &&
+	test_commit -C server 2 &&
+
+	git init client &&
+	git -C client fetch-pack ../server \
+		$(git -C server rev-parse refs/tags/1) refs/tags/1
+'
+
+test_expect_success 'fetch-pack cannot fetch a raw sha1 that is not advertised as a ref' '
+	rm -rf server &&
+
+	git init server &&
+	test_commit -C server 5 &&
+	git -C server tag -d 5 &&
+	test_commit -C server 6 &&
+
+	git init client &&
+	test_must_fail git -C client fetch-pack ../server \
+		$(git -C server rev-parse refs/heads/master^) 2>err &&
+	test_i18ngrep "Server does not allow request for unadvertised object" err
+'
+
 check_prot_path () {
 	cat >expected <<-EOF &&
 	Diag: url=$1
-- 
2.13.0.rc2.291.g57267f2277-goog