Async connection abstraction

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

lightningd/connection.h

@@ -0,0 +1,48 @@
+#ifndef LIGHTNING_LIGHTNINGD_CONNECTION_H
+#define LIGHTNING_LIGHTNINGD_CONNECTION_H
+
+#include "config.h"
+#include <ccan/io/io.h>
+#include <ccan/short_types/short_types.h>
+
+struct daemon_conn {
+	/* Context to tallocate all things from, possibly the
+	 * container of this connection. */
+	tal_t *ctx;
+
+	/* Last message we received */
+	u8 *msg_in;
+
+	/* Array of queued outgoing messages */
+	u8 **msg_out;
+
+	int conn_fd;
+	struct io_conn *conn;
+
+	/* Callback for incoming messages */
+	struct io_plan *(*daemon_conn_recv)(struct io_conn *conn, struct daemon_conn *);
+};
+
+/**
+ * daemon_conn_init - Initialize a new daemon connection
+ *
+ * @ctx: context to allocate from
+ * @dc: daemon_conn to initialize
+ * @fd: socket file descriptor to wrap
+ * @daemon_conn_recv: callback function to be called upon receiving a message
+ */
+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 *));
+/**
+ * daemon_conn_send - Enqueue an outgoing message to be sent
+ */
+void daemon_conn_send(struct daemon_conn *dc, u8 *msg);
+
+/**
+ * daemon_conn_read_next - Read the next message
+ */
+struct io_plan *daemon_conn_read_next(struct io_conn *conn,
+				      struct daemon_conn *dc);
+
+#endif /* LIGHTNING_LIGHTNINGD_CONNECTION_H */