1 files changed, 14 insertions, 1 deletions
diff --git a/c/ping.c b/c/ping.c
index f8d5bf7..8671318 100644
--- a/c/ping.c
+++ b/c/ping.c
@@ -14,6 +14,19 @@ static void put_ip(unsigned char *ip) {
     for (i = 0; i < 4; i++) { putu(ip[i]); if (i < 3) putc('.'); }
 }
 
+/* wait up to ~2s for an echo reply without blocking in the kernel: a lost
+   reply (some hosts rate-limit ICMP) must cost one "timeout" line, not
+   minutes wedged inside net_recv's pump-counted wait. */
+static unsigned char wait_reply(unsigned char s) {
+    unsigned char t, r;
+    for (t = 0; t < 40; t++) {
+        r = net_recv_nb(s, rbuf, (unsigned char)sizeof(rbuf));
+        if (r != 0xFE) return r;       /* reply (or error) */
+        msleep(50);
+    }
+    return 0xFF;                       /* ~2s with no reply */
+}
+
 void main(void) {
     char *arg;
     unsigned char s, seq, got = 0, i;
@@ -35,7 +48,7 @@ void main(void) {
     puts("PING "); put_ip(dst); nl();
     for (seq = 1; seq <= 4; seq++) {
         net_send(s, payload, 4);
-        if (net_recv(s, rbuf, (unsigned char)sizeof(rbuf)) != 0xFF) {
+        if (wait_reply(s) != 0xFF) {
             got++;
             puts("  reply from "); put_ip(dst); puts(" seq="); putu(seq); nl();
         } else {