closingd: Ensure proper closing of TCP socket.

Fixes: #1457

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;
+}