[PATCH] upload-pack: Optionally allow fetching reachable sha1

[Fredrik Medley <fredrik.medley@gmail.com>]

For you who don't remember the email discussion, look through the references.

Since before, it is allowed to ask for a sha1, but most git servers refuse
the request[1]. This patch is based on a suggested location for
implementation[2] which has been updated according to ideas in the reply[3].

[1] http://thread.gmane.org/gmane.comp.version-control.git/257809
[2] http://thread.gmane.org/gmane.comp.version-control.git/258002
[3] http://thread.gmane.org/gmane.comp.version-control.git/258080


With uploadpack.allowreachablesha1inwant configuration option set,
"git fetch" can make a request with a "want" line that names an object
that has not been advertised (likely to have been obtained out of band or
from a submodule pointer). Only objects reachable from the branch tips,
hidden by transfer.hiderefs or not, will be processed.

Signed-off-by: Fredrik Medley <fredrik.medley@gmail.com>
---
 Documentation/config.txt |  6 ++++++
 fetch-pack.c             |  9 ++++++--
 t/t5516-fetch-push.sh    | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
 upload-pack.c            | 13 +++++++++---
 4 files changed, 78 insertions(+), 5 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 2e5ceaf..76cd713 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2538,6 +2538,12 @@ uploadpack.allowtipsha1inwant::
 	of a hidden ref (by default, such a request is rejected).
 	see also `uploadpack.hideRefs`.
 
+uploadpack.allowreachablesha1inwant::
+	Allow `upload-pack` to accept a fetch request that asks for an
+	object that is reachable from any ref tip. However, note that
+	calculating	object reachability is computationally expensive.
+	Defaults to `false`.
+
 uploadpack.keepAlive::
 	When `upload-pack` has started `pack-objects`, there may be a
 	quiet period while `pack-objects` prepares the pack. Normally
diff --git a/fetch-pack.c b/fetch-pack.c
index 48526aa..fb01b6c 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -43,7 +43,7 @@ static int marked;
 #define MAX_IN_VAIN 256
 
 static struct prio_queue rev_list = { compare_commits_by_commit_date };
-static int non_common_revs, multi_ack, use_sideband, allow_tip_sha1_in_want;
+static int non_common_revs, multi_ack, use_sideband, allow_tip_sha1_in_want, allow_reachable_sha1_in_want;
 
 static void rev_list_push(struct commit *commit, int mark)
 {
@@ -542,7 +542,7 @@ static void filter_refs(struct fetch_pack_args *args,
 	}
 
 	/* Append unmatched requests to the list */
-	if (allow_tip_sha1_in_want) {
+	if (allow_tip_sha1_in_want || allow_reachable_sha1_in_want) {
 		for (i = 0; i < nr_sought; i++) {
 			unsigned char sha1[20];
 
@@ -823,6 +823,11 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 			fprintf(stderr, "Server supports allow-tip-sha1-in-want\n");
 		allow_tip_sha1_in_want = 1;
 	}
+	if (server_supports("allow-reachable-sha1-in-want")) {
+		if (args->verbose)
+			fprintf(stderr, "Server supports allow-reachable-sha1-in-want\n");
+		allow_reachable_sha1_in_want = 1;
+	}
 	if (!server_supports("thin-pack"))
 		args->use_thin_pack = 0;
 	if (!server_supports("no-progress"))
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index 8a5f236..01fabfb 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1120,6 +1120,61 @@ test_expect_success 'fetch exact SHA1' '
 	)
 '
 
+for configallowtipsha1inwant in true false
+do
+	test_expect_success "shallow fetch reachable SHA1 (but not a ref), allowtipsha1inwant=$configallowtipsha1inwant" '
+		mk_empty testrepo &&
+		(
+			cd testrepo &&
+			git config uploadpack.allowtipsha1inwant $configallowtipsha1inwant &&
+			git commit --allow-empty -m foo &&
+			git commit --allow-empty -m bar
+		) &&
+		SHA1=`git --git-dir=testrepo/.git rev-parse HEAD^` &&
+		mk_empty shallow &&
+		(
+			cd shallow &&
+			test_must_fail git fetch --depth=1 ../testrepo/.git $SHA1 &&
+			git --git-dir=../testrepo/.git config uploadpack.allowreachablesha1inwant true &&
+			git fetch --depth=1 ../testrepo/.git $SHA1 &&
+			git cat-file commit $SHA1 >/dev/null
+		)
+	'
+
+	test_expect_success "deny fetch unreachable SHA1, allowtipsha1inwant=$configallowtipsha1inwant" '
+		mk_empty testrepo &&
+		(
+			cd testrepo &&
+			git config uploadpack.allowtipsha1inwant $configallowtipsha1inwant &&
+			git commit --allow-empty -m foo &&
+			git commit --allow-empty -m bar &&
+			git commit --allow-empty -m xyz
+		)
+		SHA1_1=`git --git-dir=testrepo/.git rev-parse HEAD^^` &&
+		SHA1_2=`git --git-dir=testrepo/.git rev-parse HEAD^` &&
+		SHA1_3=`git --git-dir=testrepo/.git rev-parse HEAD` &&
+		(
+			cd testrepo &&
+			git reset --hard $SHA1_2 &&
+			git cat-file commit $SHA1_3 >/dev/null &&
+			git cat-file commit $SHA1_3 >/dev/null
+		) &&
+		mk_empty shallow &&
+		(
+			cd shallow &&
+			test_must_fail git fetch ../testrepo/.git $SHA1_3 &&
+			test_must_fail git fetch ../testrepo/.git $SHA1_1 &&
+			git --git-dir=../testrepo/.git config uploadpack.allowreachablesha1inwant true &&
+			git fetch ../testrepo/.git $SHA1_1 &&
+			git cat-file commit $SHA1_1 >/dev/null &&
+			test_must_fail git cat-file commit $SHA1_2 >/dev/null &&
+			git fetch ../testrepo/.git $SHA1_2 &&
+			git cat-file commit $SHA1_2 >/dev/null &&
+			test_must_fail git fetch ../testrepo/.git $SHA1_3
+		)
+	'
+done
+
 test_expect_success 'fetch follows tags by default' '
 	mk_test testrepo heads/master &&
 	rm -fr src dst &&
diff --git a/upload-pack.c b/upload-pack.c
index aa84576..2e704d6 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -36,6 +36,7 @@ static int no_done;
 static int use_thin_pack, use_ofs_delta, use_include_tag;
 static int no_progress, daemon_mode;
 static int allow_tip_sha1_in_want;
+static int allow_reachable_sha1_in_want;
 static int shallow_nr;
 static struct object_array have_obj;
 static struct object_array want_obj;
@@ -443,7 +444,7 @@ static int get_common_commits(void)
 static int is_our_ref(struct object *o)
 {
 	return o->flags &
-		((allow_tip_sha1_in_want ? HIDDEN_REF : 0) | OUR_REF);
+		(((allow_tip_sha1_in_want || allow_reachable_sha1_in_want) ? HIDDEN_REF : 0) | OUR_REF);
 }
 
 static void check_non_tip(void)
@@ -456,8 +457,11 @@ static void check_non_tip(void)
 	char namebuf[42]; /* ^ + SHA-1 + LF */
 	int i;
 
-	/* In the normal in-process case non-tip request can never happen */
-	if (!stateless_rpc)
+	/*
+	 * In the normal in-process case without
+	 * uploadpack.allowreachablesha1inwant, non-tip requests can never happen.
+	 */
+	if (!stateless_rpc && !allow_reachable_sha1_in_want)
 		goto error;
 
 	cmd.argv = argv;
@@ -728,6 +732,7 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 			     sha1_to_hex(sha1), refname_nons,
 			     0, capabilities,
 			     allow_tip_sha1_in_want ? " allow-tip-sha1-in-want" : "",
+			     allow_reachable_sha1_in_want ? " allow-reachable-sha1-in-want" : "",
 			     stateless_rpc ? " no-done" : "",
 			     symref_info.buf,
 			     git_user_agent_sanitized());
@@ -789,6 +794,8 @@ static int upload_pack_config(const char *var, const char *value, void *unused)
 {
 	if (!strcmp("uploadpack.allowtipsha1inwant", var))
 		allow_tip_sha1_in_want = git_config_bool(var, value);
+	else if (!strcmp("uploadpack.allowreachablesha1inwant", var))
+		allow_reachable_sha1_in_want = git_config_bool(var, value);
 	else if (!strcmp("uploadpack.keepalive", var)) {
 		keepalive = git_config_int(var, value);
 		if (!keepalive)
-- 
1.9.1