gvfs-helper: expose gvfs/objects GET and POST semantics

Expose the differences in the semantics of GET and POST for
the "gvfs/objects" API:

    HTTP GET: fetches a single loose object over the network.
              When a commit object is requested, it just returns
	      the single object.

    HTTP POST: fetches a batch of objects over the network.
               When the oid-set contains a commit object, all
	       referenced trees are also included in the response.

gvfs-helper is updated to take "get" and "post" command line options.
the gvfs-helper "server" mode is updated to take "objects.get" and
"objects.post" verbs.

For convenience, the "get" option and the "objects.get" verb
do allow more than one object to be requested.  gvfs-helper will
automatically issue a series of (single object) HTTP GET requests
and creating a series of loose objects.

The "post" option and the "objects.post" verb will perform bulk
object fetching using the batch-size chunking.  Individual HTTP
POST requests containing more than one object will be created
as a packfile.  A HTTP POST for a single object will create a
loose object.

This commit also contains some refactoring to eliminate the
assumption that POST is always associated with packfiles.

In gvfs-helper-client.c, gh_client__get_immediate() now uses the
"objects.get" verb and ignores any currently queued objects.

In gvfs-helper-client.c, the OIDSET built by gh_client__queue_oid()
is only processed when gh_client__drain_queue() is called.  The queue
is processed using the "object.post" verb.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: jeffhostetler

gvfs-helper-client.c

@@ -17,7 +17,6 @@
 
 static struct oidset gh_client__oidset_queued = OIDSET_INIT;
 static unsigned long gh_client__oidset_count;
-static int gh_client__includes_immediate;
 
 struct gh_server__process {
 	struct subprocess_entry subprocess; /* must be first */
@@ -28,13 +27,20 @@ static int gh_server__subprocess_map_initialized;
 static struct hashmap gh_server__subprocess_map;
 static struct odb_source *gh_client__chosen_odb;
 
-#define CAP_GET      (1u<<1)
+/*
+ * The "objects" capability has 2 verbs: "get" and "post".
+ */
+#define CAP_OBJECTS      (1u<<1)
+#define CAP_OBJECTS_NAME "objects"
+
+#define CAP_OBJECTS__VERB_GET1_NAME "get"
+#define CAP_OBJECTS__VERB_POST_NAME "post"
 
 static int gh_client__start_fn(struct subprocess_entry *subprocess)
 {
 	static int versions[] = {1, 0};
 	static struct subprocess_capability capabilities[] = {
-		{ "get", CAP_GET },
+		{ CAP_OBJECTS_NAME, CAP_OBJECTS },
 		{ NULL, 0 }
 	};
 
@@ -46,14 +52,16 @@ static int gh_client__start_fn(struct subprocess_entry *subprocess)
 }
 
 /*
- * Send:
+ * Send the queued OIDs in the OIDSET to gvfs-helper for it to
+ * fetch from the cache-server or main Git server using "/gvfs/objects"
+ * POST semantics.
  *
- *     get LF
+ *     objects.post LF
  *     (<hex-oid> LF)*
  *     <flush>
  *
  */
-static int gh_client__get__send_command(struct child_process *process)
+static int gh_client__send__objects_post(struct child_process *process)
 {
 	struct oidset_iter iter;
 	struct object_id *oid;
@@ -64,7 +72,9 @@ static int gh_client__get__send_command(struct child_process *process)
 	 * so that we don't have to.
 	 */
 
-	err = packet_write_fmt_gently(process->in, "get\n");
+	err = packet_write_fmt_gently(
+		process->in,
+		(CAP_OBJECTS_NAME "." CAP_OBJECTS__VERB_POST_NAME "\n"));
 	if (err)
 		return err;
 
@@ -83,6 +93,46 @@ static int gh_client__get__send_command(struct child_process *process)
 	return 0;
 }
 
+/*
+ * Send the given OID to gvfs-helper for it to fetch from the
+ * cache-server or main Git server using "/gvfs/objects" GET
+ * semantics.
+ *
+ * This ignores any queued OIDs.
+ *
+ *     objects.get LF
+ *     <hex-oid> LF
+ *     <flush>
+ *
+ */
+static int gh_client__send__objects_get(struct child_process *process,
+					const struct object_id *oid)
+{
+	int err;
+
+	/*
+	 * We assume that all of the packet_ routines call error()
+	 * so that we don't have to.
+	 */
+
+	err = packet_write_fmt_gently(
+		process->in,
+		(CAP_OBJECTS_NAME "." CAP_OBJECTS__VERB_GET1_NAME "\n"));
+	if (err)
+		return err;
+
+	err = packet_write_fmt_gently(process->in, "%s\n",
+				      oid_to_hex(oid));
+	if (err)
+		return err;
+
+	err = packet_flush_gently(process->in);
+	if (err)
+		return err;
+
+	return 0;
+}
+
 /*
  * Update the loose object cache to include the newly created
  * object.
@@ -131,7 +181,7 @@ static void gh_client__update_packed_git(const char *line)
 }
 
 /*
- * We expect:
+ * Both CAP_OBJECTS verbs return the same format response:
  *
  *    <odb>
  *    <data>*
@@ -162,7 +212,7 @@ static void gh_client__update_packed_git(const char *line)
  * grouped with a queued request for a blob.  The tree-walk *might* be
  * able to continue and let the 404 blob be handled later.
  */
-static int gh_client__get__receive_response(
+static int gh_client__objects__receive_response(
 	struct child_process *process,
 	enum gh_client__created *p_ghc,
 	int *p_nr_loose, int *p_nr_packfile)
@@ -241,17 +291,12 @@ static void gh_client__choose_odb(void)
 	}
 }
 
-static int gh_client__get(enum gh_client__created *p_ghc)
+static struct gh_server__process *gh_client__find_long_running_process(
+	unsigned int cap_needed)
 {
 	struct gh_server__process *entry;
-	struct child_process *process;
 	struct strvec argv = STRVEC_INIT;
 	struct strbuf quoted = STRBUF_INIT;
-	int nr_loose = 0;
-	int nr_packfile = 0;
-	int err = 0;
-
-	trace2_region_enter("gh-client", "get", the_repository);
 
 	gh_client__choose_odb();
 
@@ -267,6 +312,11 @@ static int gh_client__get(enum gh_client__created *p_ghc)
 
 	sq_quote_argv_pretty(&quoted, argv.v);
 
+	/*
+	 * Find an existing long-running process with the above command
+	 * line -or- create a new long-running process for this and
+	 * subsequent 'get' requests.
+	 */
 	if (!gh_server__subprocess_map_initialized) {
 		gh_server__subprocess_map_initialized = 1;
 		hashmap_init(&gh_server__subprocess_map,
@@ -280,70 +330,24 @@ static int gh_client__get(enum gh_client__created *p_ghc)
 		entry = xmalloc(sizeof(*entry));
 		entry->supported_capabilities = 0;
 
-		err = subprocess_start_strvec(
-			&gh_server__subprocess_map, &entry->subprocess, 1,
-			&argv, gh_client__start_fn);
-		if (err) {
-			free(entry);
-			goto leave_region;
-		}
+		if (subprocess_start_strvec(&gh_server__subprocess_map,
+					  &entry->subprocess, 1,
+					  &argv, gh_client__start_fn))
+			FREE_AND_NULL(entry);
 	}
 
-	process = &entry->subprocess.process;
-
-	if (!(CAP_GET & entry->supported_capabilities)) {
-		error("gvfs-helper: does not support GET");
-		subprocess_stop(&gh_server__subprocess_map,
-				(struct subprocess_entry *)entry);
-		free(entry);
-		err = -1;
-		goto leave_region;
-	}
-
-	sigchain_push(SIGPIPE, SIG_IGN);
-
-	err = gh_client__get__send_command(process);
-	if (!err)
-		err = gh_client__get__receive_response(process, p_ghc,
-						 &nr_loose, &nr_packfile);
-
-	sigchain_pop(SIGPIPE);
-
-	if (err) {
+	if (entry &&
+	    (entry->supported_capabilities & cap_needed) != cap_needed) {
+		error("gvfs-helper: does not support needed capabilities");
 		subprocess_stop(&gh_server__subprocess_map,
 				(struct subprocess_entry *)entry);
-		free(entry);
+		FREE_AND_NULL(entry);
 	}
 
-leave_region:
 	strvec_clear(&argv);
 	strbuf_release(&quoted);
 
-	trace2_data_intmax("gh-client", the_repository,
-			   "get/immediate", gh_client__includes_immediate);
-
-	trace2_data_intmax("gh-client", the_repository,
-			   "get/nr_objects", gh_client__oidset_count);
-
-	if (nr_loose)
-		trace2_data_intmax("gh-client", the_repository,
-				   "get/nr_loose", nr_loose);
-
-	if (nr_packfile)
-		trace2_data_intmax("gh-client", the_repository,
-				   "get/nr_packfile", nr_packfile);
-
-	if (err)
-		trace2_data_intmax("gh-client", the_repository,
-				   "get/error", err);
-
-	trace2_region_leave("gh-client", "get", the_repository);
-
-	oidset_clear(&gh_client__oidset_queued);
-	gh_client__oidset_count = 0;
-	gh_client__includes_immediate = 0;
-
-	return err;
+	return entry;
 }
 
 void gh_client__queue_oid(const struct object_id *oid)
@@ -370,27 +374,97 @@ void gh_client__queue_oid_array(const struct object_id *oids, int oid_nr)
 		gh_client__queue_oid(&oids[k]);
 }
 
+/*
+ * Bulk fetch all of the queued OIDs in the OIDSET.
+ */
 int gh_client__drain_queue(enum gh_client__created *p_ghc)
 {
+	struct gh_server__process *entry;
+	struct child_process *process;
+	int nr_loose = 0;
+	int nr_packfile = 0;
+	int err = 0;
+
 	*p_ghc = GHC__CREATED__NOTHING;
 
 	if (!gh_client__oidset_count)
 		return 0;
 
-	return gh_client__get(p_ghc);
+	entry = gh_client__find_long_running_process(CAP_OBJECTS);
+	if (!entry)
+		return -1;
+
+	trace2_region_enter("gh-client", "objects/post", the_repository);
+
+	process = &entry->subprocess.process;
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	err = gh_client__send__objects_post(process);
+	if (!err)
+		err = gh_client__objects__receive_response(
+			process, p_ghc, &nr_loose, &nr_packfile);
+
+	sigchain_pop(SIGPIPE);
+
+	if (err) {
+		subprocess_stop(&gh_server__subprocess_map,
+				(struct subprocess_entry *)entry);
+		FREE_AND_NULL(entry);
+	}
+
+	trace2_data_intmax("gh-client", the_repository,
+			   "objects/post/nr_objects", gh_client__oidset_count);
+	trace2_region_leave("gh-client", "objects/post", the_repository);
+
+	oidset_clear(&gh_client__oidset_queued);
+	gh_client__oidset_count = 0;
+
+	return err;
 }
+
+/*
+ * Get exactly 1 object immediately.
+ * Ignore any queued objects.
+ */
 int gh_client__get_immediate(const struct object_id *oid,
 			     enum gh_client__created *p_ghc)
 {
-	gh_client__includes_immediate = 1;
+	struct gh_server__process *entry;
+	struct child_process *process;
+	int nr_loose = 0;
+	int nr_packfile = 0;
+	int err = 0;
 
 	// TODO consider removing this trace2.  it is useful for interactive
 	// TODO debugging, but may generate way too much noise for a data
 	// TODO event.
 	trace2_printf("gh_client__get_immediate: %s", oid_to_hex(oid));
 
-	if (!oidset_insert(&gh_client__oidset_queued, oid))
-		gh_client__oidset_count++;
+	entry = gh_client__find_long_running_process(CAP_OBJECTS);
+	if (!entry)
+		return -1;
+
+	trace2_region_enter("gh-client", "objects/get", the_repository);
 
-	return gh_client__drain_queue(p_ghc);
+	process = &entry->subprocess.process;
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	err = gh_client__send__objects_get(process, oid);
+	if (!err)
+		err = gh_client__objects__receive_response(
+			process, p_ghc, &nr_loose, &nr_packfile);
+
+	sigchain_pop(SIGPIPE);
+
+	if (err) {
+		subprocess_stop(&gh_server__subprocess_map,
+				(struct subprocess_entry *)entry);
+		FREE_AND_NULL(entry);
+	}
+
+	trace2_region_leave("gh-client", "objects/get", the_repository);
+
+	return err;
 }