6 files changed, 39 insertions, 29 deletions
diff --git a/src/network/socket/qnativesocketengine.cpp b/src/network/socket/qnativesocketengine.cpp
index 3f7c0d94e1..03395a37f0 100644
--- a/src/network/socket/qnativesocketengine.cpp
+++ b/src/network/socket/qnativesocketengine.cpp
@@ -1162,6 +1162,7 @@ bool QNativeSocketEngine::waitForReadOrWrite(bool *readyToRead, bool *readyToWri
     return ret > 0;
 }
 
+#if 0   // currently unused
 /*!
     Returns the size of the operating system's socket receive
     buffer. Depending on the operating system, this size may be
@@ -1220,7 +1221,7 @@ void QNativeSocketEngine::setSendBufferSize(qint64 size)
     Q_CHECK_VALID_SOCKETLAYER(QNativeSocketEngine::setSendBufferSize(), Q_VOID);
     setOption(SendBufferSocketOption, size);
 }
-
+#endif
 
 /*!
     Sets the option \a option to the value \a value.
diff --git a/src/network/socket/qnativesocketengine_p.h b/src/network/socket/qnativesocketengine_p.h
index bfea824bcb..aa61b74823 100644
--- a/src/network/socket/qnativesocketengine_p.h
+++ b/src/network/socket/qnativesocketengine_p.h
@@ -166,11 +166,13 @@ public:
     qint64 writeDatagram(const char *data, qint64 len, const QIpPacketHeader &) override;
     qint64 bytesToWrite() const override;
 
+#if 0   // currently unused
     qint64 receiveBufferSize() const;
     void setReceiveBufferSize(qint64 bufferSize);
 
     qint64 sendBufferSize() const;
     void setSendBufferSize(qint64 bufferSize);
+#endif
 
     int option(SocketOption option) const override;
     bool setOption(SocketOption option, int value) override;
diff --git a/src/network/socket/qnativesocketengine_unix.cpp b/src/network/socket/qnativesocketengine_unix.cpp
index a8f756dc31..cb0a521360 100644
--- a/src/network/socket/qnativesocketengine_unix.cpp
+++ b/src/network/socket/qnativesocketengine_unix.cpp
@@ -829,18 +829,10 @@ qint64 QNativeSocketEnginePrivate::nativeBytesAvailable() const
 
 bool QNativeSocketEnginePrivate::nativeHasPendingDatagrams() const
 {
-    // Create a sockaddr struct and reset its port number.
-    qt_sockaddr storage;
-    QT_SOCKLEN_T storageSize = sizeof(storage);
-    memset(&storage, 0, storageSize);
-
-    // Peek 1 bytes into the next message. The size of the message may
-    // well be 0, so we can't check recvfrom's return value.
+    // Peek 1 bytes into the next message.
     ssize_t readBytes;
-    do {
-        char c;
-        readBytes = ::recvfrom(socketDescriptor, &c, 1, MSG_PEEK, &storage.a, &storageSize);
-    } while (readBytes == -1 && errno == EINTR);
+    char c;
+    EINTR_LOOP(readBytes, ::recv(socketDescriptor, &c, 1, MSG_PEEK));
 
     // If there's no error, or if our buffer was too small, there must be a
     // pending datagram.
@@ -868,22 +860,42 @@ qint64 QNativeSocketEnginePrivate::nativePendingDatagramSize() const
     if (recvResult != -1)
         recvResult = value;
 #else
-    QVarLengthArray<char, 8192> udpMessagePeekBuffer(8192);
+    // We need to grow the buffer to fit the entire datagram.
+    // We start at 1500 bytes (the MTU for Ethernet V2), which should catch
+    // almost all uses (effective MTU for UDP under IPv4 is 1468), except
+    // for localhost datagrams and those reassembled by the IP layer.
+    char udpMessagePeekBuffer[1500];
+    struct msghdr msg;
+    struct iovec vec;
+
+    memset(&msg, 0, sizeof(msg));
+    msg.msg_iov = &vec;
+    msg.msg_iovlen = 1;
+    vec.iov_base = udpMessagePeekBuffer;
+    vec.iov_len = sizeof(udpMessagePeekBuffer);
 
     for (;;) {
         // the data written to udpMessagePeekBuffer is discarded, so
         // this function is still reentrant although it might not look
         // so.
-        recvResult = ::recv(socketDescriptor, udpMessagePeekBuffer.data(),
-            udpMessagePeekBuffer.size(), MSG_PEEK);
+        recvResult = ::recvmsg(socketDescriptor, &msg, MSG_PEEK);
         if (recvResult == -1 && errno == EINTR)
             continue;
 
-        if (recvResult != (ssize_t) udpMessagePeekBuffer.size())
+        // was the result truncated?
+        if ((msg.msg_flags & MSG_TRUNC) == 0)
             break;
 
-        udpMessagePeekBuffer.resize(udpMessagePeekBuffer.size() * 2);
+        // grow by 16 times
+        msg.msg_iovlen *= 16;
+        if (msg.msg_iov != &vec)
+            delete[] msg.msg_iov;
+        msg.msg_iov = new struct iovec[msg.msg_iovlen];
+        std::fill_n(msg.msg_iov, msg.msg_iovlen, vec);
     }
+
+    if (msg.msg_iov != &vec)
+        delete[] msg.msg_iov;
 #endif
 
 #if defined (QNATIVESOCKETENGINE_DEBUG)
diff --git a/src/network/socket/qnativesocketengine_win.cpp b/src/network/socket/qnativesocketengine_win.cpp
index e21bf29d4b..7556bb98f4 100644
--- a/src/network/socket/qnativesocketengine_win.cpp
+++ b/src/network/socket/qnativesocketengine_win.cpp
@@ -1146,10 +1146,10 @@ qint64 QNativeSocketEnginePrivate::nativePendingDatagramSize() const
     DWORD bufferCount = 5;
     WSABUF * buf = 0;
     for (;;) {
-        // the data written to udpMessagePeekBuffer is discarded, so
-        // this function is still reentrant although it might not look
-        // so.
-        static char udpMessagePeekBuffer[8192];
+        // We start at 1500 bytes (the MTU for Ethernet V2), which should catch
+        // almost all uses (effective MTU for UDP under IPv4 is 1468), except
+        // for localhost datagrams and those reassembled by the IP layer.
+        char udpMessagePeekBuffer[1500];
 
         buf = new WSABUF[bufferCount];
         for (DWORD i=0; i<bufferCount; i++) {
diff --git a/src/network/socket/qsocks5socketengine.cpp b/src/network/socket/qsocks5socketengine.cpp
index 64bbdedcfd..a07ea65046 100644
--- a/src/network/socket/qsocks5socketengine.cpp
+++ b/src/network/socket/qsocks5socketengine.cpp
@@ -39,8 +39,6 @@
 
 #include "qsocks5socketengine_p.h"
 
-#ifndef QT_NO_SOCKS5
-
 #include "qtcpsocket.h"
 #include "qudpsocket.h"
 #include "qtcpserver.h"
@@ -1938,6 +1936,4 @@ QAbstractSocketEngine *QSocks5SocketEngineHandler::createSocketEngine(qintptr so
     return 0;
 }
 
-#endif // QT_NO_SOCKS5
-
 QT_END_NAMESPACE
diff --git a/src/network/socket/qsocks5socketengine_p.h b/src/network/socket/qsocks5socketengine_p.h
index 38139b065f..1942eff4ca 100644
--- a/src/network/socket/qsocks5socketengine_p.h
+++ b/src/network/socket/qsocks5socketengine_p.h
@@ -55,9 +55,9 @@
 #include "qabstractsocketengine_p.h"
 #include "qnetworkproxy.h"
 
-QT_BEGIN_NAMESPACE
+QT_REQUIRE_CONFIG(socks5);
 
-#ifndef QT_NO_SOCKS5
+QT_BEGIN_NAMESPACE
 
 class QSocks5SocketEnginePrivate;
 
@@ -291,7 +291,6 @@ public:
     virtual QAbstractSocketEngine *createSocketEngine(qintptr socketDescriptor, QObject *parent) override;
 };
 
-
 QT_END_NAMESPACE
-#endif // QT_NO_SOCKS5
+
 #endif // QSOCKS5SOCKETENGINE_H