Async connection abstraction

This is an attempt at unifying all the async connection handling into
a reusable module.

lightningd/connection.c

@@ -0,0 +1,69 @@
+#include "connection.h"
+#include <ccan/take/take.h>
+#include <wire/wire_io.h>
+
+static void daemon_conn_enqueue(struct daemon_conn *dc, u8 *msg)
+{
+	size_t n = tal_count(dc->msg_out);
+	tal_resize(&dc->msg_out, n + 1);
+	dc->msg_out[n] = tal_dup_arr(dc->ctx, u8, msg, tal_count(msg), 0);
+}
+
+static const u8 *daemon_conn_dequeue(struct daemon_conn *dc)
+{
+	const u8 *msg;
+	size_t n = tal_count(dc->msg_out);
+
+	if (n == 0)
+		return NULL;
+	msg = dc->msg_out[0];
+	memmove(dc->msg_out, dc->msg_out + 1, sizeof(dc->msg_in[0]) * (n-1));
+	tal_resize(&dc->msg_out, n-1);
+	return msg;
+}
+
+struct io_plan *daemon_conn_read_next(struct io_conn *conn,
+				      struct daemon_conn *dc)
+{
+	dc->msg_in = tal_free(dc->msg_in);
+	return io_read_wire(conn, dc->ctx, &dc->msg_in, dc->daemon_conn_recv,
+			    dc);
+}
+
+static struct io_plan *daemon_conn_write_next(struct io_conn *conn,
+				       struct daemon_conn *dc)
+{
+	const u8 *msg = daemon_conn_dequeue(dc);
+	if (msg) {
+		return io_write_wire(conn, take(msg), daemon_conn_write_next, dc);
+	} else {
+		return io_out_wait(conn, dc, daemon_conn_write_next, dc);
+	}
+}
+
+static struct io_plan *daemon_conn_start(struct io_conn *conn,
+					 struct daemon_conn *dc)
+{
+	dc->conn = conn;
+	return io_duplex(conn, daemon_conn_read_next(conn, dc),
+			 daemon_conn_write_next(conn, dc));
+}
+
+void daemon_conn_init(tal_t *ctx, struct daemon_conn *dc, int fd,
+		      struct io_plan *(*daemon_conn_recv)(struct io_conn *,
+							  struct daemon_conn *))
+{
+	dc->daemon_conn_recv = daemon_conn_recv;
+
+	dc->ctx = ctx;
+	dc->msg_in = NULL;
+	dc->msg_out = tal_arr(ctx, u8 *, 0);
+	dc->conn_fd = fd;
+	io_new_conn(ctx, fd, daemon_conn_start, dc);
+}
+
+void daemon_conn_send(struct daemon_conn *dc, u8 *msg)
+{
+	daemon_conn_enqueue(dc, msg);
+	io_wake(dc);
+}