lightningd/msg_queue: support queueing/dequeueing of fds.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/msg_queue.c

@@ -1,4 +1,7 @@
+#include <assert.h>
+#include <ccan/take/take.h>
 #include <lightningd/msg_queue.h>
+#include <wire/wire.h>
 
 void msg_queue_init(struct msg_queue *q, const tal_t *ctx)
 {
@@ -6,7 +9,7 @@ void msg_queue_init(struct msg_queue *q, const tal_t *ctx)
 	q->ctx = ctx;
 }
 
-void msg_enqueue(struct msg_queue *q, const u8 *add)
+static void do_enqueue(struct msg_queue *q, const u8 *add)
 {
 	size_t n = tal_count(q->q);
 	tal_resize(&q->q, n+1);
@@ -16,6 +19,20 @@ void msg_enqueue(struct msg_queue *q, const u8 *add)
 	io_wake(q);
 }
 
+void msg_enqueue(struct msg_queue *q, const u8 *add)
+{
+	assert(fromwire_peektype(add) != MSG_PASS_FD);
+	do_enqueue(q, add);
+}
+
+void msg_enqueue_fd(struct msg_queue *q, int fd)
+{
+	u8 *fdmsg = tal_arr(q->ctx, u8, 0);
+	towire_u16(&fdmsg, MSG_PASS_FD);
+	towire_u32(&fdmsg, fd);
+	do_enqueue(q, take(fdmsg));
+}
+
 const u8 *msg_dequeue(struct msg_queue *q)
 {
 	size_t n = tal_count(q->q);
@@ -29,3 +46,14 @@ const u8 *msg_dequeue(struct msg_queue *q)
 	tal_resize(&q->q, n-1);
 	return msg;
 }
+
+int msg_is_fd(const u8 *msg)
+{
+	const u8 *p = msg + sizeof(u16);
+	size_t len = tal_count(msg) - sizeof(u16);
+
+	if (fromwire_peektype(msg) != MSG_PASS_FD)
+		return -1;
+
+	return fromwire_u32(&p, &len);
+}

lightningd/msg_queue.h

@@ -5,6 +5,9 @@
 #include <ccan/io/io.h>
 #include <ccan/short_types/short_types.h>
 
+/* Reserved type used to indicate we're actually passing an fd. */
+#define MSG_PASS_FD 0xFFFF
+
 struct msg_queue {
 	const u8 **q;
 	const tal_t *ctx;
@@ -12,10 +15,18 @@ struct msg_queue {
 
 void msg_queue_init(struct msg_queue *q, const tal_t *ctx);
 
+/* If add is taken(), freed after sending. */
 void msg_enqueue(struct msg_queue *q, const u8 *add);
 
+/* Fd is closed after sending. */
+void msg_enqueue_fd(struct msg_queue *q, int fd);
+
+/* Returns NULL if nothing to do. */
 const u8 *msg_dequeue(struct msg_queue *q);
 
+/* Returns -1 if not an fd: close after sending. */
+int msg_is_fd(const u8 *msg);
+
 #define msg_queue_wait(conn, q, next, arg) \
 	io_out_wait((conn), (q), (next), (arg))