gluon-neighbour-info: avoid recv() with NULL buffer (#2323)

Calling functions like recv() with a NULL buffer is not explicitly
allowed by the POSIX standard, so it must be avoided to be portable
across different libc implementations. Allocate an initial buffer before
handling requests, and also pass this buffer to the peek recv() call.

Fixes: 531937cf ("gluon-neighbour-info: fix broken output with large results")

package/gluon-neighbour-info/src/gluon-neighbour-info.c

@@ -95,7 +95,7 @@ ssize_t recvtimeout(int socket, char **recvbuffer, size_t *recvbuffer_len,
 
 	setsockopt(socket, SOL_SOCKET, SO_RCVTIMEO, &timeout_left, sizeof(timeout_left));
 
-	recvlen = recv(socket, NULL, 0, MSG_PEEK | MSG_TRUNC);
+	recvlen = recv(socket, *recvbuffer, 0, MSG_PEEK | MSG_TRUNC);
 	if (recvlen < 0)
 		return recvlen;
 
@@ -269,6 +269,8 @@ int main(int argc, char **argv) {
 		fflush(stdout);
 	}
 
+	resize_recvbuffer(&recvbuffer, &recvbuffer_len, 8192);
+
 	do {
 		ret = request(sock, &recvbuffer, &recvbuffer_len, &client_addr,
 			      request_string, sse, timeout, max_count);