MINOR: mux: Add a new "avail_streams" method.

Add a new method for mux, avail_streams, that returns the number of streams
still available for a mux.
For the mux_pt, it'll return 1 if the connection is in idle, or 0. For
the H2 mux, it'll return the max number of streams allowed, minus the number
of streams currently in use.

include/types/connection.h

@@ -326,6 +326,7 @@ struct mux_ops {
 	void (*show_fd)(struct buffer *, struct connection *); /* append some data about connection into chunk for "show fd" */
 	int (*subscribe)(struct conn_stream *cs, int event_type, void *param); /* Subscribe to events, such as "being able to send" */
 	int (*unsubscribe)(struct conn_stream *cs, int event_type, void *param); /* Unsubscribe to events */
+	int (*avail_streams)(struct connection *conn); /* Returns the number of streams still available for a connection */
 	unsigned int flags;                           /* some flags characterizing the mux's capabilities (MX_FL_*) */
 	char name[8];                                 /* mux layer name, zero-terminated */
 };

src/mux_h2.c

@@ -339,6 +339,13 @@ static inline void h2_release_buf(struct h2c *h2c, struct buffer *bptr)
 	}
 }
 
+static int h2_avail_streams(struct connection *conn)
+{
+	struct h2c *h2c = conn->mux_ctx;
+
+	return (h2_settings_max_concurrent_streams - h2c->nb_streams);
+}
+
 
 /*****************************************************************/
 /* functions below are dedicated to the mux setup and management */
@@ -3793,6 +3800,7 @@ const struct mux_ops h2_ops = {
 	.attach = h2_attach,
 	.get_first_cs = h2_get_first_cs,
 	.detach = h2_detach,
+	.avail_streams = h2_avail_streams,
 	.shutr = h2_shutr,
 	.shutw = h2_shutw,
 	.show_fd = h2_show_fd,

src/mux_pt.c

@@ -163,6 +163,13 @@ static void mux_pt_detach(struct conn_stream *cs)
 	mux_pt_destroy(ctx);
 }
 
+static int mux_pt_avail_streams(struct connection *conn)
+{
+	struct mux_pt_ctx *ctx = conn->mux_ctx;
+
+	return (ctx->cs == NULL ? 1 : 0);
+}
+
 static void mux_pt_shutr(struct conn_stream *cs, enum cs_shr_mode mode)
 {
 	if (cs->flags & CS_FL_SHR)
@@ -261,6 +268,7 @@ const struct mux_ops mux_pt_ops = {
 	.attach = mux_pt_attach,
 	.get_first_cs = mux_pt_get_first_cs,
 	.detach = mux_pt_detach,
+	.avail_streams = mux_pt_avail_streams,
 	.shutr = mux_pt_shutr,
 	.shutw = mux_pt_shutw,
 	.flags = MX_FL_NONE,