closingd: Ensure proper closing of TCP socket.

Fixes: #1457

closingd/Makefile

@@ -60,6 +60,7 @@ CLOSINGD_COMMON_OBJS :=				\
 	common/permute_tx.o			\
 	common/ping.o				\
 	common/read_peer_msg.o			\
+	common/socket_close.o			\
 	common/status.o				\
 	common/status_wire.o			\
 	common/subdaemon.o			\

closingd/closing.c

@@ -9,6 +9,7 @@
 #include <common/peer_billboard.h>
 #include <common/peer_failed.h>
 #include <common/read_peer_msg.h>
+#include <common/socket_close.h>
 #include <common/status.h>
 #include <common/subdaemon.h>
 #include <common/type_to_string.h>
@@ -581,6 +582,11 @@ int main(int argc, char *argv[])
 		       offer[LOCAL]);
 
 	/* We're done! */
+	/* Properly close the channel first. */
+	if (!socket_close(PEER_FD))
+		status_unusual("Closing and draining peerfd gave error: %s",
+			       strerror(errno));
+	/* Sending the below will kill us! */
 	wire_sync_write(REQ_FD,	take(towire_closing_complete(NULL)));
 	tal_free(ctx);
 	daemon_shutdown();

common/Makefile

@@ -33,6 +33,7 @@ COMMON_SRC_NOGEN :=				\
 	common/ping.c				\
 	common/pseudorand.c			\
 	common/read_peer_msg.c			\
+	common/socket_close.c			\
 	common/sphinx.c				\
 	common/status.c				\
 	common/status_wire.c			\

common/socket_close.c

@@ -0,0 +1,47 @@
+#include "socket_close.h"
+#include <ccan/noerr/noerr.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+/*
+Simplified (minus all the error checks):
+
+	shutdown(fd, SHUT_WR);
+	for (;;) {
+		char unused[64]
+		sys_res = read(fd, unused, 64);
+		if (sys_res == 0)
+			break;
+	}
+	close(fd);
+*/
+
+bool socket_close(int fd)
+{
+	char unused[64];
+	int sys_res;
+
+	sys_res = shutdown(fd, SHUT_WR);
+	if (sys_res < 0) {
+		close_noerr(fd);
+		return false;
+	}
+
+	for (;;) {
+		do {
+			sys_res = read(fd, unused, sizeof(unused));
+		} while (sys_res < 0 && errno == EINTR);
+		if (sys_res < 0) {
+			close_noerr(fd);
+			return false;
+		}
+		if (sys_res == 0)
+			break;
+	}
+
+	if (close(fd) < 0)
+		return false;
+	else
+		return true;
+}

common/socket_close.h

@@ -0,0 +1,23 @@
+/* common/socket_close - Properly close a socket,
+ * ensuring that any data we write just before
+ * the close has been transmitted to the other
+ * side, and ignoring any data the other side
+ * has sent at the time the close was started.
+ *
+ * Reference:
+ *
+ * http://ia800504.us.archive.org/3/items/TheUltimateSo_lingerPageOrWhyIsMyTcpNotReliable/the-ultimate-so_linger-page-or-why-is-my-tcp-not-reliable.html
+ */
+#ifndef LIGHTNING_COMMON_SOCKET_CLOSE_H
+#define LIGHTNING_COMMON_SOCKET_CLOSE_H
+#include "config.h"
+#include <stdbool.h>
+
+/* Return false if something failed, true if
+ * nothing failed.
+ * If something failed, error is stored in
+ * `errno.
+ */
+bool socket_close(int fd);
+
+#endif /* LIGHTNING_COMMON_SOCKET_CLOSE_H */