Increase physical UDP receive and send buffers

node/Constants.hpp

@@ -739,9 +739,13 @@
 #define ZT_TRUST_EXPIRATION 600000
 
 /**
- * Desired buffer size for UDP sockets (used in service and osdep but defined here)
+ * Desired receive and send buffer sizes for physical UDP sockets.
+ *
+ * The additional capacity absorbs short bursts before ZeroTier's receive loop
+ * or the operating system's transmit path drains the socket.
  */
-#define ZT_UDP_DESIRED_BUF_SIZE 1048576
+#define ZT_UDP_DESIRED_RCVBUF_SIZE 4194304
+#define ZT_UDP_DESIRED_SNDBUF_SIZE 2097152
 
 /**
  * Desired / recommended min stack size for threads (used on some platforms to reset thread stack size)

osdep/Binder.hpp

@@ -449,7 +449,11 @@ class Binder {
 				++bi;
 			}
 			if (bi == _bindingCount) {
-				udps = phy.udpBind(reinterpret_cast<const struct sockaddr*>(&(ii->first)), (void*)0, ZT_UDP_DESIRED_BUF_SIZE);
+				udps = phy.udpBind(
+					reinterpret_cast<const struct sockaddr*>(&(ii->first)),
+					(void*)0,
+					ZT_UDP_DESIRED_RCVBUF_SIZE,
+					ZT_UDP_DESIRED_SNDBUF_SIZE);
 				if (udps) {
 #ifdef __LINUX__
 					// Bind Linux sockets to their device so routes that we manage do not override physical routes (wish all platforms had this!)

osdep/Phy.hpp

@@ -324,11 +324,12 @@ template <typename HANDLER_PTR_TYPE> class Phy {
 	 * Bind a UDP socket
 	 *
 	 * @param localAddress Local endpoint address and port
-	 * @param uptr Initial value of user pointer associated with this socket (default: NULL)
-	 * @param bufferSize Desired socket receive/send buffer size -- will set as close to this as possible (default: 0, leave alone)
+	 * @param uptr Initial value of user pointer associated with this socket
+	 * @param receiveBufferSize Desired socket receive buffer size -- will set as close to this as possible (0: leave alone)
+	 * @param sendBufferSize Desired socket send buffer size -- will set as close to this as possible (0: leave alone)
 	 * @return Socket or NULL on failure to bind
 	 */
-	inline PhySocket* udpBind(const struct sockaddr* localAddress, void* uptr = (void*)0, int bufferSize = 0)
+	inline PhySocket* udpBind(const struct sockaddr* localAddress, void* uptr, int receiveBufferSize, int sendBufferSize)
 	{
 		if (_socks.size() >= ZT_PHY_MAX_SOCKETS)
 			return (PhySocket*)0;
@@ -337,15 +338,17 @@ template <typename HANDLER_PTR_TYPE> class Phy {
 		if (! ZT_PHY_SOCKFD_VALID(s))
 			return (PhySocket*)0;
 
-		if (bufferSize > 0) {
-			int bs = bufferSize;
+		if (receiveBufferSize > 0) {
+			int bs = receiveBufferSize;
 			while (bs >= 65536) {
 				int tmpbs = bs;
 				if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, (const char*)&tmpbs, sizeof(tmpbs)) == 0)
 					break;
 				bs -= 4096;
 			}
-			bs = bufferSize;
+		}
+		if (sendBufferSize > 0) {
+			int bs = sendBufferSize;
 			while (bs >= 65536) {
 				int tmpbs = bs;
 				if (setsockopt(s, SOL_SOCKET, SO_SNDBUF, (const char*)&tmpbs, sizeof(tmpbs)) == 0)
@@ -447,6 +450,16 @@ template <typename HANDLER_PTR_TYPE> class Phy {
 		return (PhySocket*)&sws;
 	}
 
+	/**
+	 * Bind a UDP socket with one shared receive/send buffer size.
+	 *
+	 * This overload preserves the original API for existing callers.
+	 */
+	inline PhySocket* udpBind(const struct sockaddr* localAddress, void* uptr = (void*)0, int bufferSize = 0)
+	{
+		return udpBind(localAddress, uptr, bufferSize, bufferSize);
+	}
+
 	/**
 	 * Set the IP TTL for the next outgoing packet (for IPv4 UDP sockets only)
 	 *

selftest.cpp

@@ -1546,7 +1546,7 @@ static int testPhy()
 	testPhyInstance = new Phy<TestPhyHandlers*>(&testPhyHandlers, false, true);
 
 	std::cout << "[phy] Binding UDP listen socket to 127.0.0.1/60002... ";
-	PhySocket* udpListenSock = testPhyInstance->udpBind((const struct sockaddr*)&bindaddr);
+	PhySocket* udpListenSock = testPhyInstance->udpBind((const struct sockaddr*)&bindaddr, (void*)0, 262144, 131072);
 	if (! udpListenSock) {
 		std::cout << "FAILED." << std::endl;
 		return -1;