Make inter-packet delay configurable via --delay-ms

README.md

@@ -79,6 +79,7 @@ If your platform isn't covered, see [Building from Source](#building-from-source
 | `--bind-port` | `33333`    | 1..65535 | Local port to bind on |
 | `--mtu`       | `1500`     | 64..65507 | Max packet size in bytes |
 | `--ttl`       | `15`       | > 0 | Seconds of silence before giving up |
+| `--delay-ms`  | `20`       | ≥ 0 | Pause between successive packets (use `0` for loopback / tests) |
 | `-h, --help`  | —          | — | Print help |
 | `--version`   | —          | — | Print version |
 

src/Config.cpp

@@ -2,9 +2,10 @@
 
 std::string fileName;
 
-int mtu     = 0;
-int ttl     = 0;
-int ttl_max = 0;
+int mtu      = 0;
+int ttl      = 0;
+int ttl_max  = 0;
+int delay_ms = 0;
 
 SOCKET _socket;
 

src/Config.hpp

@@ -13,6 +13,8 @@ extern int mtu;     // Max packet size to send and receive
 extern int ttl;     // Current wait time for new packages before shutting down
 extern int ttl_max; // Maximum wait time for new packages before shutting down
 
+extern int delay_ms; // Inter-packet pause when blasting parts / RESENDs
+
 extern SOCKET _socket;
 
 extern SOCKADDR_IN server_address;

src/Main.cpp

@@ -38,6 +38,7 @@ int main(int argc, char* argv[]) {
         ("bind-port",  "Local port to bind on",                 cxxopts::value<int>()->default_value("33333"))
         ("mtu",        "MTU packet",                            cxxopts::value<int>()->default_value("1500"))
         ("ttl",        "Time to live",                          cxxopts::value<int>()->default_value("15"))
+        ("delay-ms",   "Delay between successive packets, ms",  cxxopts::value<int>()->default_value("20"))
         ("h,help",     "Print help")
         ("version",    "Print version");
 
@@ -64,6 +65,7 @@ int main(int argc, char* argv[]) {
     int parsed_ttl       = result["ttl"].as<int>();
     int parsed_port      = result["port"].as<int>();
     int parsed_bind_port = result["bind-port"].as<int>();
+    int parsed_delay_ms  = result["delay-ms"].as<int>();
 
     if (parsed_mtu < 64 || parsed_mtu > 65507) {
         std::cerr << "Error: --mtu must be between 64 and 65507" << std::endl;
@@ -81,6 +83,10 @@ int main(int argc, char* argv[]) {
         std::cerr << "Error: --bind-port must be between 1 and 65535" << std::endl;
         return 1;
     }
+    if (parsed_delay_ms < 0) {
+        std::cerr << "Error: --delay-ms must be 0 or greater" << std::endl;
+        return 1;
+    }
 
     const std::string type = result["type"].as<std::string>();
     if (type != "sender" && type != "receiver") {
@@ -102,6 +108,7 @@ int main(int argc, char* argv[]) {
     mtu      = parsed_mtu;
     ttl      = parsed_ttl;
     ttl_max  = parsed_ttl;
+    delay_ms = parsed_delay_ms;
     fileName = result["file"].as<std::string>();
 
     _socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);

src/Receiver.cpp

@@ -59,7 +59,7 @@ void checkParts() {
             sendto(_socket, buffer, 10, 0, reinterpret_cast<sockaddr*>(&broadcast_address),
                    sizeof(broadcast_address));
             std::cout << "Request part of file with index " << index << std::endl;
-            std::this_thread::sleep_for(20ms);
+            if (delay_ms > 0) std::this_thread::sleep_for(std::chrono::milliseconds(delay_ms));
         }
 
         SOCKADDR_IN sender_address;

src/Sender.cpp

@@ -113,7 +113,7 @@ void run() {
     for (size_t part_index = 0; part_index < total_parts; ++part_index) {
         sent_part.insert({ part_index, 0 });
         sendPart(part_index);
-        std::this_thread::sleep_for(20ms);
+        if (delay_ms > 0) std::this_thread::sleep_for(std::chrono::milliseconds(delay_ms));
     }
 
     snprintf(buffer, 7, "FINISH");

tests/e2e.sh

@@ -38,9 +38,12 @@ run_test() {
     dd if=/dev/urandom of="$src" bs=1024 count="$size_kb" status=none
 
     # Receiver listens on $recv_port, sends RESEND back to $send_port (sender's bind).
+    # --delay-ms 0 removes the inter-packet pause that the protocol uses on real
+    # LANs to avoid overrunning receivers; on loopback it just slows tests down.
     echo "==> [$label] starting receiver (bind=$recv_port, target=$send_port)"
     "$BINARY" --type receiver --file "$dst" --broadcast 127.0.0.1 \
               --bind-port "$recv_port" --port "$send_port" --ttl "$recv_ttl" \
+              --delay-ms 0 \
         > "$recv_log" 2>&1 &
     local recv_pid=$!
 
@@ -51,6 +54,7 @@ run_test() {
     echo "==> [$label] starting sender (bind=$send_port, target=$recv_port)"
     if ! "$BINARY" --type sender --file "$src" --broadcast 127.0.0.1 \
                    --bind-port "$send_port" --port "$recv_port" --ttl "$send_ttl" \
+                   --delay-ms 0 \
             > "$send_log" 2>&1; then
         echo "FAIL: [$label] sender exited non-zero"
         echo "--- sender log:"; cat "$send_log"
@@ -90,11 +94,11 @@ run_test() {
 
 # Args: label, size_kb, recv_bind_port, send_bind_port, recv_ttl, send_ttl
 #
-# Small file: 50 KiB -> ~35 parts at default MTU 1500, ~0.7s transfer.
-run_test "small" 50    33401 33402 5  3
+# Small file: 50 KiB -> ~35 parts at default MTU 1500.
+run_test "small" 50    33401 33402 3 1
 
-# Large file: 2 MiB -> ~1400 parts at default MTU 1500, ~28s transfer.
-run_test "large" 2048  33403 33404 60 30
+# Large file: 2 MiB -> ~1400 parts at default MTU 1500.
+run_test "large" 2048  33403 33404 3 1
 
 echo
 echo "All E2E tests passed."