First call to splice should not block while writing to pipe.

In certain condition, if the second call to splice does not write a full
packet, the first call to splice can block since the pipe is full, to prevent
this condition, we never block while writing to the pipe.

proxy.c

@@ -265,9 +265,9 @@ void forward_data(int source_sock, int destination_sock) {
         exit(EXIT_FAILURE);
     }
 
-    while ((n = splice(source_sock, NULL, buf_pipe[WRITE], NULL, BUF_SIZE, SPLICE_F_MOVE)) > 0) {
-        if (splice(buf_pipe[READ], NULL, destination_sock, NULL, n, SPLICE_F_MOVE) < 0) {
-            perror("splice");
+    while ((n = splice(source_sock, NULL, buf_pipe[WRITE], NULL, SSIZE_MAX, SPLICE_F_NONBLOCK|SPLICE_F_MOVE)) > 0) {
+        if (splice(buf_pipe[READ], NULL, destination_sock, NULL, SSIZE_MAX, SPLICE_F_MOVE) < 0) {
+            perror("write");
             exit(EXIT_FAILURE);
         }
     }
@@ -279,6 +279,9 @@ void forward_data(int source_sock, int destination_sock) {
     }
 #endif
 
+    if (n < 0)
+        perror("read");
+
 #ifdef USE_SPLICE
     close(buf_pipe[0]);
     close(buf_pipe[1]);