sio: implement getsockname wrapper

SWIM wants to allow to bind to zero ports so as the kernel could
choose any free port automatically. It is needed mainly for
tests.

Zero port means that a real port is known only after bind() has
called, and getsockname() should be used to get it. SWIM uses sio
library for such lowlevel API. This is why that function is added
to sio.

Needed for #3234

src/lib/core/sio.c

@@ -293,6 +293,16 @@ sio_getpeername(int fd, struct sockaddr *addr, socklen_t *addrlen)
 	return 0;
 }
 
+int
+sio_getsockname(int fd, struct sockaddr *addr, socklen_t *addrlen)
+{
+	if (getsockname(fd, addr, addrlen) < 0) {
+		diag_set(SocketError, sio_socketname(fd), "getsockname");
+		return -1;
+	}
+	return 0;
+}
+
 const char *
 sio_strfaddr(const struct sockaddr *addr, socklen_t addrlen)
 {

src/lib/core/sio.h

@@ -86,6 +86,21 @@ sio_strfaddr(const struct sockaddr *addr, socklen_t addrlen);
 int
 sio_getpeername(int fd, struct sockaddr *addr, socklen_t *addrlen);
 
+/**
+ * Fill @a addr with a real address currently bound to @a fd
+ * socket.
+ *
+ * @param fd Socket.
+ * @param[out] addr An address structure to fill.
+ * @param[in][out] addlen On input it is a size of @a addr as a
+ *                 buffer. On output it becomes a size of a new
+ *                 content of @a addr.
+ * @retval 0 Success.
+ * @retval -1 Error.
+ */
+int
+sio_getsockname(int fd, struct sockaddr *addr, socklen_t *addrlen);
+
 /**
  * Advance write position in the iovec array
  * based on its current value and the number of

test/unit/sio.c

@@ -78,6 +78,26 @@ check_uri_to_addr(void)
 	footer();
 }
 
+static void
+check_auto_bind(void)
+{
+	header();
+	plan(3);
+
+	struct sockaddr_in addr;
+	socklen_t addrlen = sizeof(addr);
+	sio_uri_to_addr("127.0.0.1:0", (struct sockaddr *) &addr);
+	int fd = sio_socket(AF_INET, SOCK_STREAM, 0);
+	is(sio_bind(fd, (struct sockaddr *) &addr, sizeof(addr)), 0,
+	   "bind to 0 works");
+	is(sio_getsockname(fd, (struct sockaddr *) &addr, &addrlen), 0,
+	   "getsockname works on 0 bind");
+	isnt(addr.sin_port, 0, "a real port is returned");
+
+	check_plan();
+	footer();
+}
+
 int
 main(void)
 {
@@ -85,8 +105,9 @@ main(void)
 	fiber_init(fiber_c_invoke);
 
 	header();
-	plan(1);
+	plan(2);
 	check_uri_to_addr();
+	check_auto_bind();
 	int rc = check_plan();
 	footer();
 

test/unit/sio.result

 	*** main ***
-1..1
+1..2
 	*** check_uri_to_addr ***
     1..18
     ok 1 - invalid uri is detected
@@ -22,4 +22,11 @@
     ok 18 - invalid IP
 ok 1 - subtests
 	*** check_uri_to_addr: done ***
+	*** check_auto_bind ***
+    1..3
+    ok 1 - bind to 0 works
+    ok 2 - getsockname works on 0 bind
+    ok 3 - a real port is returned
+ok 2 - subtests
+	*** check_auto_bind: done ***
 	*** main: done ***