Set TCP_NODELAY on P2P sockets.

Nagle appears to be a significant contributor to latency now that the static
 sleeps are gone.  Most of our messages are relatively large compared to
 IP + TCP so I do not expect this to create enormous overhead.

This may also reduce traffic burstyness somewhat.

src/compat.h

@@ -38,6 +38,7 @@
 #include <sys/types.h>
 #include <net/if.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <ifaddrs.h>
 #include <limits.h>

src/net.cpp

@@ -963,6 +963,15 @@ static void AcceptConnection(const ListenSocket& hListenSocket) {
         return;
     }
 
+    // According to the internet TCP_NODELAY is not carried into accepted sockets
+    // on all platforms.  Set it again here just to be sure.
+    int set = 1;
+#ifdef WIN32
+    setsockopt(hSocket, IPPROTO_TCP, TCP_NODELAY, (const char*)&set, sizeof(int));
+#else
+    setsockopt(hSocket, IPPROTO_TCP, TCP_NODELAY, (void*)&set, sizeof(int));
+#endif
+
     if (CNode::IsBanned(addr) && !whitelisted)
     {
         LogPrintf("connection from %s dropped (banned)\n", addr.ToString());
@@ -1790,8 +1799,11 @@ bool BindListenPort(const CService &addrBind, string& strError, bool fWhiteliste
     // Allow binding if the port is still in TIME_WAIT state after
     // the program was closed and restarted.
     setsockopt(hListenSocket, SOL_SOCKET, SO_REUSEADDR, (void*)&nOne, sizeof(int));
+    // Disable Nagle's algorithm
+    setsockopt(hListenSocket, IPPROTO_TCP, TCP_NODELAY, (void*)&nOne, sizeof(int));
 #else
     setsockopt(hListenSocket, SOL_SOCKET, SO_REUSEADDR, (const char*)&nOne, sizeof(int));
+    setsockopt(hListenSocket, IPPROTO_TCP, TCP_NODELAY, (const char*)&nOne, sizeof(int));
 #endif
 
     // Set to non-blocking, incoming connections will also inherit this

src/netbase.cpp

@@ -444,12 +444,19 @@ bool static ConnectSocketDirectly(const CService &addrConnect, SOCKET& hSocketRe
     if (hSocket == INVALID_SOCKET)
         return false;
 
-#ifdef SO_NOSIGPIPE
     int set = 1;
+#ifdef SO_NOSIGPIPE
     // Different way of disabling SIGPIPE on BSD
     setsockopt(hSocket, SOL_SOCKET, SO_NOSIGPIPE, (void*)&set, sizeof(int));
 #endif
 
+    //Disable Nagle's algorithm
+#ifdef WIN32
+    setsockopt(hSocket, IPPROTO_TCP, TCP_NODELAY, (const char*)&set, sizeof(int));
+#else
+    setsockopt(hSocket, IPPROTO_TCP, TCP_NODELAY, (void*)&set, sizeof(int));
+#endif
+
     // Set to non-blocking
     if (!SetSocketNonBlocking(hSocket, true))
         return error("ConnectSocketDirectly: Setting socket to non-blocking failed, error %s\n", NetworkErrorString(WSAGetLastError()));