Use select() + send().

prrt/time-protocol.h

@@ -113,15 +113,39 @@ static inline ssize_t _send(socket_t conn, const char *buf, size_t size)
     int written = 0;
     ssize_t n = 0;
     while (written < size) {
-        n = send(conn, buf, size - written, 0);
-        if (n < 0) {
-            _time();
-            printf("WRITE FAILED: %ld, errno: %d\n", n, errno);
-            printf("%s\n", buf - written);
-            return written;
+        fd_set wfds;
+        struct timeval tv;
+        int retval;
+        FD_ZERO(&wfds);
+        FD_SET(conn, &wfds);
+
+        tv.tv_sec = 1;
+        tv.tv_usec = 0;
+        retval = select(conn + 1, NULL, &wfds, NULL, &tv);
+        if (!FD_ISSET(conn, &wfds)) {
+            continue;
+        }
+
+        if (retval == -1) {
+            printf("Select failed: %d.\n", errno);
+            return -1;
+        } else if (retval > 0) {
+            n = send(conn, buf, size - written, 0);
+            if (n < 0) {
+                _time();
+                printf("RECEIVE FAILED: %ld, errno: %d\n, written %ld / %ld", n, errno, written, size);
+                printf("%s\n", buf - written);
+                return written;
+            }
+            if (n == 0) {
+                break;
+            }
+            written += n;
+            buf += n;
+        } else {
+            continue;
         }
-        written += n;
-        buf += n;
+
     }
     return written;
 }