From 63f846367ff63258c253e1c42fc43a24d4cdc460 Mon Sep 17 00:00:00 2001
From: Christian Hopps <chopps@labn.net>
Date: Thu, 12 Oct 2023 08:34:20 -0400
Subject: [PATCH] lib: msg: make short-circuit connections guaranteed

When short circuiting is requested the caller can count on that
being the connection type they get.

Signed-off-by: Christian Hopps <chopps@labn.net>
---
 lib/mgmt_msg.c | 19 +++++++++----------
 lib/mgmt_msg.h |  4 ++++
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/lib/mgmt_msg.c b/lib/mgmt_msg.c
index ee5c1008bd0c..16f6f0d526d7 100644
--- a/lib/mgmt_msg.c
+++ b/lib/mgmt_msg.c
@@ -634,7 +634,7 @@ static void msg_client_sched_connect(struct msg_client *client,
 				&client->conn_retry_tmr);
 }
 
-static bool msg_client_connect_short_circuit(struct msg_client *client)
+static int msg_client_connect_short_circuit(struct msg_client *client)
 {
 	struct msg_conn *server_conn;
 	struct msg_server *server;
@@ -647,11 +647,10 @@ static bool msg_client_connect_short_circuit(struct msg_client *client)
 		if (!strcmp(server->sopath, client->sopath))
 			break;
 	if (!server) {
-		MGMT_MSG_DBG(dbgtag,
-			     "no short-circuit connection available for %s",
+		MGMT_MSG_ERR(&client->conn.mstate,
+			     "no short-circuit server available for %s",
 			     client->sopath);
-
-		return false;
+		return -1;
 	}
 
 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets)) {
@@ -659,7 +658,7 @@ static bool msg_client_connect_short_circuit(struct msg_client *client)
 			&client->conn.mstate,
 			"socketpair failed trying to short-circuit connection on %s: %s",
 			client->sopath, safe_strerror(errno));
-		return false;
+		return -1;
 	}
 
 	/* client side */
@@ -687,7 +686,7 @@ static bool msg_client_connect_short_circuit(struct msg_client *client)
 		client->sopath, client->conn.mstate.idtag, client->conn.fd,
 		server_conn->mstate.idtag, server_conn->fd);
 
-	return true;
+	return 0;
 }
 
 
@@ -697,11 +696,12 @@ static void msg_client_connect(struct msg_client *client)
 	struct msg_conn *conn = &client->conn;
 	const char *dbgtag = conn->debug ? conn->mstate.idtag : NULL;
 
-	if (!client->short_circuit_ok ||
-	    !msg_client_connect_short_circuit(client))
+	if (!client->short_circuit_ok)
 		conn->fd =
 			mgmt_msg_connect(client->sopath, MSG_CONN_SEND_BUF_SIZE,
 					 MSG_CONN_RECV_BUF_SIZE, dbgtag);
+	else if (msg_client_connect_short_circuit(client))
+		conn->fd = -1;
 
 	if (conn->fd == -1)
 		/* retry the connection */
@@ -741,7 +741,6 @@ void msg_client_init(struct msg_client *client, struct event_loop *tm,
 	mgmt_msg_init(&conn->mstate, max_read_buf, max_write_buf, max_msg_sz,
 		      idtag);
 
-	/* XXX maybe just have client kick this off */
 	/* Start trying to connect to server */
 	msg_client_sched_connect(client, 0);
 }
diff --git a/lib/mgmt_msg.h b/lib/mgmt_msg.h
index dd7ae59f9162..3195d4a7fb07 100644
--- a/lib/mgmt_msg.h
+++ b/lib/mgmt_msg.h
@@ -136,6 +136,10 @@ struct msg_client {
 extern void msg_client_cleanup(struct msg_client *client);
 
 /*
+ * If `short_circuit_ok` is true, then the client-server connection will use a
+ * socketpair() rather than a unix-domain socket. This must be passed true if
+ * you wish to send messages short-circuit later.
+ *
  * `notify_disconnect` is not called when the user `msg_client_cleanup` is
  * called for a client which is currently connected. The socket is closed
  * but there is no notification.