[PATCH v2 15/36] external-odb: add 'get_direct' support

[Christian Couder <christian.couder@gmail.com>]

This implements the 'get_direct' capability/instruction that makes
it possible for external odb helper scripts to pass blobs to Git
by directly writing them as loose objects files.

It is better to call this a "direct" mode rather than a "fault-in"
mode as we could have the same kind of mechanism to "put" objects
into an external odb, where the odb helper would access blobs it
wants to send to an external odb directly from files, but it
would be strange to call that a fault-in mode too.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 external-odb.c |  3 ++-
 odb-helper.c   | 20 +++++++++++++++++---
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/external-odb.c b/external-odb.c
index c3d90f39fb..192b09e843 100644
--- a/external-odb.c
+++ b/external-odb.c
@@ -138,7 +138,8 @@ int external_odb_get_object(const unsigned char *sha1)
 		int ret;
 		int fd;
 
-		if (!odb_helper_has_object(o, sha1))
+		if (!(o->supported_capabilities & ODB_HELPER_CAP_GET_RAW_OBJ) &&
+		    !(o->supported_capabilities & ODB_HELPER_CAP_GET_GIT_OBJ))
 			continue;
 
 		fd = create_object_tmpfile(&tmpfile, pathbuf.buf);
diff --git a/odb-helper.c b/odb-helper.c
index 7e5eab94cf..30cfe689de 100644
--- a/odb-helper.c
+++ b/odb-helper.c
@@ -336,14 +336,28 @@ int odb_helper_get_object(struct odb_helper *o, const unsigned char *sha1,
 int odb_helper_get_direct(struct odb_helper *o,
 			  const unsigned char *sha1)
 {
-	int res = 0;
 	uint64_t start = getnanotime();
 
-	fetch_object(o->dealer, sha1);
+	if (o->type == ODB_HELPER_GIT_REMOTE) {
+		fetch_object(o->dealer, sha1);
+	} else {
+		struct odb_helper_object *obj;
+		struct odb_helper_cmd cmd;
+
+		obj = odb_helper_lookup(o, sha1);
+		if (!obj)
+			return -1;
+
+		if (odb_helper_start(o, &cmd, "get_direct %s", sha1_to_hex(sha1)) < 0)
+			return -1;
+
+		if (odb_helper_finish(o, &cmd))
+			return -1;
+	}
 
 	trace_performance_since(start, "odb_helper_get_direct");
 
-	return res;
+	return 0;
 }
 
 int odb_helper_get_many_direct(struct odb_helper *o,
-- 
2.17.0.rc0.37.g8f476fabe9