[PATCH v3 8/9] promisor-remote: change promisor_remote_reply()'s signature

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

The `promisor_remote_reply()` function performs two tasks:
1. It uses filter_promisor_remote() to parse the server's
   "promisor-remote" advertisement and to mark accepted remotes in the
   repository configuration.
2. It assembles a reply string containing the accepted remote names to
   send back to the server.

In a following commit, the fetch-pack logic will need to trigger the
side effect (1) to ensure the repository state is correct, but it will
not need to send a reply (2).

To avoid assembling a reply string when it is not needed, let's change
the signature of promisor_remote_reply(). It will now return `void` and
accept a second `char **accepted_out` argument. Only if that argument
is not NULL will a reply string be assembled and returned back to the
caller via that argument.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 connect.c         |  3 ++-
 promisor-remote.c | 24 +++++++++++++-----------
 promisor-remote.h | 10 +++++-----
 3 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/connect.c b/connect.c
index c6f76e3082..a02583a102 100644
--- a/connect.c
+++ b/connect.c
@@ -505,7 +505,8 @@ static void send_capabilities(int fd_out, struct packet_reader *reader)
 		reader->hash_algo = &hash_algos[GIT_HASH_SHA1_LEGACY];
 	}
 	if (server_feature_v2("promisor-remote", &promisor_remote_info)) {
-		char *reply = promisor_remote_reply(promisor_remote_info);
+		char *reply;
+		promisor_remote_reply(promisor_remote_info, &reply);
 		if (reply) {
 			packet_write_fmt(fd_out, "promisor-remote=%s", reply);
 			free(reply);
diff --git a/promisor-remote.c b/promisor-remote.c
index f3bafb7731..96fa215b06 100644
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -920,25 +920,27 @@ static void filter_promisor_remote(struct repository *repo,
 	}
 }
 
-char *promisor_remote_reply(const char *info)
+void promisor_remote_reply(const char *info, char **accepted_out)
 {
 	struct strvec accepted = STRVEC_INIT;
-	struct strbuf reply = STRBUF_INIT;
 
 	filter_promisor_remote(the_repository, &accepted, info);
 
-	if (!accepted.nr)
-		return NULL;
-
-	for (size_t i = 0; i < accepted.nr; i++) {
-		if (i)
-			strbuf_addch(&reply, ';');
-		strbuf_addstr_urlencode(&reply, accepted.v[i], allow_unsanitized);
+	if (accepted_out) {
+		if (accepted.nr) {
+			struct strbuf reply = STRBUF_INIT;
+			for (size_t i = 0; i < accepted.nr; i++) {
+				if (i)
+					strbuf_addch(&reply, ';');
+				strbuf_addstr_urlencode(&reply, accepted.v[i], allow_unsanitized);
+			}
+			*accepted_out = strbuf_detach(&reply, NULL);
+		} else {
+			*accepted_out = NULL;
+		}
 	}
 
 	strvec_clear(&accepted);
-
-	return strbuf_detach(&reply, NULL);
 }
 
 void mark_promisor_remotes_as_accepted(struct repository *r, const char *remotes)
diff --git a/promisor-remote.h b/promisor-remote.h
index d227299fd0..3d4d2de018 100644
--- a/promisor-remote.h
+++ b/promisor-remote.h
@@ -49,12 +49,12 @@ char *promisor_remote_info(struct repository *repo);
 /*
  * Prepare a reply to a "promisor-remote" advertisement from a server.
  * Check the value of "promisor.acceptfromserver" and maybe the
- * configured promisor remotes, if any, to prepare the reply.
- * Return value is NULL if no promisor remote from the server
- * is accepted. Otherwise it contains the names of the accepted promisor
- * remotes separated by ';'. See gitprotocol-v2(5).
+ * configured promisor remotes, if any, to prepare the reply. If the
+ * `accepted_out` argument is not NULL, it is set to either NULL or to
+ * the names of the accepted promisor remotes separated by ';' if
+ * any. See gitprotocol-v2(5).
  */
-char *promisor_remote_reply(const char *info);
+void promisor_remote_reply(const char *info, char **accepted_out);
 
 /*
  * Set the 'accepted' flag for some promisor remotes. Useful on the
-- 
2.53.0.70.g3d1fd9d397.dirty