Adding upstream version 6.0.4-dfsg.upstream/6.0.4-dfsgupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3104 insertions, 0 deletions

diff --git a/src/VBox/Runtime/r3/socket.cpp b/src/VBox/Runtime/r3/socket.cpp
new file mode 100644
index 00000000..8c875832
--- /dev/null
+++ b/src/VBox/Runtime/r3/socket.cpp
@@ -0,0 +1,3104 @@
+/* $Id: socket.cpp $ */
+/** @file
+ * IPRT - Network Sockets.
+ */
+
+/*
+ * Copyright (C) 2006-2019 Oracle Corporation
+ *
+ * This file is part of VirtualBox Open Source Edition (OSE), as
+ * available from http://www.virtualbox.org. This file is free software;
+ * you can redistribute it and/or modify it under the terms of the GNU
+ * General Public License (GPL) as published by the Free Software
+ * Foundation, in version 2 as it comes in the "COPYING" file of the
+ * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
+ * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
+ *
+ * The contents of this file may alternatively be used under the terms
+ * of the Common Development and Distribution License Version 1.0
+ * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
+ * VirtualBox OSE distribution, in which case the provisions of the
+ * CDDL are applicable instead of those of the GPL.
+ *
+ * You may elect to license modified versions of this file under the
+ * terms and conditions of either the GPL or the CDDL or both.
+ */
+
+
+/*********************************************************************************************************************************
+*   Header Files                                                                                                                 *
+*********************************************************************************************************************************/
+#ifdef RT_OS_WINDOWS
+# include <iprt/win/winsock2.h>
+# include <iprt/win/ws2tcpip.h>
+#else /* !RT_OS_WINDOWS */
+# include <errno.h>
+# include <sys/select.h>
+# include <sys/stat.h>
+# include <sys/socket.h>
+# include <netinet/in.h>
+# include <netinet/tcp.h>
+# include <arpa/inet.h>
+# ifdef IPRT_WITH_TCPIP_V6
+#  include <netinet6/in6.h>
+# endif
+# include <sys/un.h>
+# include <netdb.h>
+# include <unistd.h>
+# include <fcntl.h>
+# include <sys/uio.h>
+#endif /* !RT_OS_WINDOWS */
+#include <limits.h>
+
+#include "internal/iprt.h"
+#include <iprt/socket.h>
+
+#include <iprt/alloca.h>
+#include <iprt/asm.h>
+#include <iprt/assert.h>
+#include <iprt/ctype.h>
+#include <iprt/err.h>
+#include <iprt/mempool.h>
+#include <iprt/poll.h>
+#include <iprt/string.h>
+#include <iprt/thread.h>
+#include <iprt/time.h>
+#include <iprt/mem.h>
+#include <iprt/sg.h>
+#include <iprt/log.h>
+
+#include "internal/magics.h"
+#include "internal/socket.h"
+#include "internal/string.h"
+#ifdef RT_OS_WINDOWS
+# include "win/internal-r3-win.h"
+#endif
+
+
+/*********************************************************************************************************************************
+*   Defined Constants And Macros                                                                                                 *
+*********************************************************************************************************************************/
+/* non-standard linux stuff (it seems). */
+#ifndef MSG_NOSIGNAL
+# define MSG_NOSIGNAL           0
+#endif
+
+/* Windows has different names for SHUT_XXX. */
+#ifndef SHUT_RDWR
+# ifdef SD_BOTH
+#  define SHUT_RDWR             SD_BOTH
+# else
+#  define SHUT_RDWR             2
+# endif
+#endif
+#ifndef SHUT_WR
+# ifdef SD_SEND
+#  define SHUT_WR               SD_SEND
+# else
+#  define SHUT_WR               1
+# endif
+#endif
+#ifndef SHUT_RD
+# ifdef SD_RECEIVE
+#  define SHUT_RD               SD_RECEIVE
+# else
+#  define SHUT_RD               0
+# endif
+#endif
+
+/* fixup backlevel OSes. */
+#if defined(RT_OS_OS2) || defined(RT_OS_WINDOWS)
+# define socklen_t              int
+#endif
+
+/** How many pending connection. */
+#define RTTCP_SERVER_BACKLOG    10
+
+/* Limit read and write sizes on Windows and OS/2. */
+#ifdef RT_OS_WINDOWS
+# define RTSOCKET_MAX_WRITE     (INT_MAX / 2)
+# define RTSOCKET_MAX_READ      (INT_MAX / 2)
+#elif defined(RT_OS_OS2)
+# define RTSOCKET_MAX_WRITE     0x10000
+# define RTSOCKET_MAX_READ      0x10000
+#endif
+
+
+/*********************************************************************************************************************************
+*   Structures and Typedefs                                                                                                      *
+*********************************************************************************************************************************/
+/**
+ * Socket handle data.
+ *
+ * This is mainly required for implementing RTPollSet on Windows.
+ */
+typedef struct RTSOCKETINT
+{
+    /** Magic number (RTSOCKET_MAGIC). */
+    uint32_t            u32Magic;
+    /** Exclusive user count.
+     * This is used to prevent two threads from accessing the handle concurrently.
+     * It can be higher than 1 if this handle is reference multiple times in a
+     * polling set (Windows). */
+    uint32_t volatile   cUsers;
+    /** The native socket handle. */
+    RTSOCKETNATIVE      hNative;
+    /** Indicates whether the handle has been closed or not. */
+    bool volatile       fClosed;
+    /** Indicates whether the socket is operating in blocking or non-blocking mode
+     * currently. */
+    bool                fBlocking;
+#if defined(RT_OS_WINDOWS) || defined(RT_OS_OS2)
+    /** The pollset currently polling this socket.  This is NIL if no one is
+     * polling. */
+    RTPOLLSET           hPollSet;
+#endif
+#ifdef RT_OS_WINDOWS
+    /** The event semaphore we've associated with the socket handle.
+     * This is WSA_INVALID_EVENT if not done. */
+    WSAEVENT            hEvent;
+    /** The events we're polling for. */
+    uint32_t            fPollEvts;
+    /** The events we're currently subscribing to with WSAEventSelect.
+     * This is ZERO if we're currently not subscribing to anything. */
+    uint32_t            fSubscribedEvts;
+    /** Saved events which are only posted once and events harvested for
+     * sockets entered multiple times into to a poll set.   Imagine a scenario where
+     * you have a RTPOLL_EVT_READ entry and RTPOLL_EVT_ERROR entry.  The READ
+     * condition can be triggered between checking the READ entry and the ERROR
+     * entry, and we don't want to drop the READ, so we store it here and make sure
+     * the event is signalled.
+     *
+     * The RTPOLL_EVT_ERROR is inconsistenly sticky at the momemnt... */
+    uint32_t            fEventsSaved;
+    /** Set if fEventsSaved contains harvested events (used to avoid multiple
+     *  calls to rtSocketPollCheck on the same socket during rtSocketPollDone). */
+    bool                fHarvestedEvents;
+    /** Set if we're using the polling fallback. */
+    bool                fPollFallback;
+    /** Set if the fallback polling is active (event not set). */
+    bool volatile       fPollFallbackActive;
+    /** Set to shut down the fallback polling thread. */
+    bool volatile       fPollFallbackShutdown;
+    /** Socket use to wake up the select thread. */
+    RTSOCKETNATIVE      hPollFallbackNotifyW;
+    /** Socket the select thread always waits on. */
+    RTSOCKETNATIVE      hPollFallbackNotifyR;
+    /** The fallback polling thread. */
+    RTTHREAD            hPollFallbackThread;
+#endif /* RT_OS_WINDOWS */
+} RTSOCKETINT;
+
+
+/**
+ * Address union used internally for things like getpeername and getsockname.
+ */
+typedef union RTSOCKADDRUNION
+{
+    struct sockaddr     Addr;
+    struct sockaddr_in  IPv4;
+#ifdef IPRT_WITH_TCPIP_V6
+    struct sockaddr_in6 IPv6;
+#endif
+} RTSOCKADDRUNION;
+
+
+/*********************************************************************************************************************************
+*   Global Variables                                                                                                             *
+*********************************************************************************************************************************/
+#ifdef RT_OS_WINDOWS
+/** Indicates that we've successfully initialized winsock.  */
+static uint32_t volatile g_uWinSockInitedVersion = 0;
+#endif
+
+
+/*********************************************************************************************************************************
+*   Internal Functions                                                                                                           *
+*********************************************************************************************************************************/
+#ifdef RT_OS_WINDOWS
+static void rtSocketPokePollFallbackThread(RTSOCKETINT *pThis);
+#endif
+
+
+
+#ifdef RT_OS_WINDOWS
+/**
+ * Initializes winsock for the process.
+ *
+ * @returns IPRT status code.
+ */
+static int rtSocketInitWinsock(void)
+{
+    if (g_uWinSockInitedVersion != 0)
+        return VINF_SUCCESS;
+
+    if (   !g_pfnWSAGetLastError
+        || !g_pfnWSAStartup
+        || !g_pfnsocket
+        || !g_pfnclosesocket)
+        return VERR_NET_INIT_FAILED;
+
+    /*
+     * Initialize winsock. Try with 2.2 and back down till we get something that works.
+     */
+    static const WORD s_awVersions[] =
+    {
+        MAKEWORD(2, 2),
+        MAKEWORD(2, 1),
+        MAKEWORD(2, 0),
+        MAKEWORD(1, 1),
+        MAKEWORD(1, 0),
+    };
+    for (uint32_t i = 0; i < RT_ELEMENTS(s_awVersions); i++)
+    {
+        WSADATA     wsaData;
+        RT_ZERO(wsaData);
+        int rcWsa = g_pfnWSAStartup(s_awVersions[i], &wsaData);
+        if (rcWsa == 0)
+        {
+            /* AssertMsg(wsaData.wVersion >= s_awVersions[i]); - triggers with winsock 1.1 */
+            ASMAtomicWriteU32(&g_uWinSockInitedVersion, wsaData.wVersion);
+            return VINF_SUCCESS;
+        }
+        AssertLogRelMsg(rcWsa == WSAVERNOTSUPPORTED, ("rcWsa=%d (winsock version %#x)\n", rcWsa, s_awVersions[i]));
+    }
+    LogRel(("Failed to init winsock!\n"));
+    return VERR_NET_INIT_FAILED;
+}
+#endif
+
+
+/**
+ * Get the last error as an iprt status code.
+ *
+ * @returns IPRT status code.
+ */
+DECLINLINE(int) rtSocketError(void)
+{
+#ifdef RT_OS_WINDOWS
+    if (g_pfnWSAGetLastError)
+        return RTErrConvertFromWin32(g_pfnWSAGetLastError());
+    return VERR_NET_IO_ERROR;
+#else
+    return RTErrConvertFromErrno(errno);
+#endif
+}
+
+
+/**
+ * Resets the last error.
+ */
+DECLINLINE(void) rtSocketErrorReset(void)
+{
+#ifdef RT_OS_WINDOWS
+    if (g_pfnWSASetLastError)
+        g_pfnWSASetLastError(0);
+#else
+    errno = 0;
+#endif
+}
+
+
+/**
+ * Get the last resolver error as an iprt status code.
+ *
+ * @returns iprt status code.
+ */
+DECLHIDDEN(int) rtSocketResolverError(void)
+{
+#ifdef RT_OS_WINDOWS
+    if (g_pfnWSAGetLastError)
+        return RTErrConvertFromWin32(g_pfnWSAGetLastError());
+    return VERR_UNRESOLVED_ERROR;
+#else
+    switch (h_errno)
+    {
+        case HOST_NOT_FOUND:
+            return VERR_NET_HOST_NOT_FOUND;
+        case NO_DATA:
+            return VERR_NET_ADDRESS_NOT_AVAILABLE;
+        case NO_RECOVERY:
+            return VERR_IO_GEN_FAILURE;
+        case TRY_AGAIN:
+            return VERR_TRY_AGAIN;
+
+        default:
+            AssertLogRelMsgFailed(("Unhandled error %u\n", h_errno));
+            return VERR_UNRESOLVED_ERROR;
+    }
+#endif
+}
+
+
+/**
+ * Converts from a native socket address to a generic IPRT network address.
+ *
+ * @returns IPRT status code.
+ * @param   pSrc                The source address.
+ * @param   cbSrc               The size of the source address.
+ * @param   pAddr               Where to return the generic IPRT network
+ *                              address.
+ */
+static int rtSocketNetAddrFromAddr(RTSOCKADDRUNION const *pSrc, size_t cbSrc, PRTNETADDR pAddr)
+{
+    /*
+     * Convert the address.
+     */
+    if (   cbSrc == sizeof(struct sockaddr_in)
+        && pSrc->Addr.sa_family == AF_INET)
+    {
+        RT_ZERO(*pAddr);
+        pAddr->enmType      = RTNETADDRTYPE_IPV4;
+        pAddr->uPort        = RT_N2H_U16(pSrc->IPv4.sin_port);
+        pAddr->uAddr.IPv4.u = pSrc->IPv4.sin_addr.s_addr;
+    }
+#ifdef IPRT_WITH_TCPIP_V6
+    else if (   cbSrc == sizeof(struct sockaddr_in6)
+             && pSrc->Addr.sa_family == AF_INET6)
+    {
+        RT_ZERO(*pAddr);
+        pAddr->enmType            = RTNETADDRTYPE_IPV6;
+        pAddr->uPort              = RT_N2H_U16(pSrc->IPv6.sin6_port);
+        pAddr->uAddr.IPv6.au32[0] = pSrc->IPv6.sin6_addr.s6_addr32[0];
+        pAddr->uAddr.IPv6.au32[1] = pSrc->IPv6.sin6_addr.s6_addr32[1];
+        pAddr->uAddr.IPv6.au32[2] = pSrc->IPv6.sin6_addr.s6_addr32[2];
+        pAddr->uAddr.IPv6.au32[3] = pSrc->IPv6.sin6_addr.s6_addr32[3];
+    }
+#endif
+    else
+        return VERR_NET_ADDRESS_FAMILY_NOT_SUPPORTED;
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Converts from a generic IPRT network address to a native socket address.
+ *
+ * @returns IPRT status code.
+ * @param   pAddr               Pointer to the generic IPRT network address.
+ * @param   pDst                The source address.
+ * @param   cbDst               The size of the source address.
+ * @param   pcbAddr             Where to store the size of the returned address.
+ *                              Optional
+ */
+static int rtSocketAddrFromNetAddr(PCRTNETADDR pAddr, RTSOCKADDRUNION *pDst, size_t cbDst, int *pcbAddr)
+{
+    RT_BZERO(pDst, cbDst);
+    if (   pAddr->enmType == RTNETADDRTYPE_IPV4
+        && cbDst >= sizeof(struct sockaddr_in))
+    {
+        pDst->Addr.sa_family       = AF_INET;
+        pDst->IPv4.sin_port        = RT_H2N_U16(pAddr->uPort);
+        pDst->IPv4.sin_addr.s_addr = pAddr->uAddr.IPv4.u;
+        if (pcbAddr)
+            *pcbAddr = sizeof(pDst->IPv4);
+    }
+#ifdef IPRT_WITH_TCPIP_V6
+    else if (   pAddr->enmType == RTNETADDRTYPE_IPV6
+             && cbDst >= sizeof(struct sockaddr_in6))
+    {
+        pDst->Addr.sa_family              = AF_INET6;
+        pDst->IPv6.sin6_port              = RT_H2N_U16(pAddr->uPort);
+        pSrc->IPv6.sin6_addr.s6_addr32[0] = pAddr->uAddr.IPv6.au32[0];
+        pSrc->IPv6.sin6_addr.s6_addr32[1] = pAddr->uAddr.IPv6.au32[1];
+        pSrc->IPv6.sin6_addr.s6_addr32[2] = pAddr->uAddr.IPv6.au32[2];
+        pSrc->IPv6.sin6_addr.s6_addr32[3] = pAddr->uAddr.IPv6.au32[3];
+        if (pcbAddr)
+            *pcbAddr = sizeof(pDst->IPv6);
+    }
+#endif
+    else
+        return VERR_NET_ADDRESS_FAMILY_NOT_SUPPORTED;
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Tries to lock the socket for exclusive usage by the calling thread.
+ *
+ * Call rtSocketUnlock() to unlock.
+ *
+ * @returns @c true if locked, @c false if not.
+ * @param   pThis               The socket structure.
+ */
+DECLINLINE(bool) rtSocketTryLock(RTSOCKETINT *pThis)
+{
+    return ASMAtomicCmpXchgU32(&pThis->cUsers, 1, 0);
+}
+
+
+/**
+ * Unlocks the socket.
+ *
+ * @param   pThis               The socket structure.
+ */
+DECLINLINE(void) rtSocketUnlock(RTSOCKETINT *pThis)
+{
+    ASMAtomicCmpXchgU32(&pThis->cUsers, 0, 1);
+}
+
+
+/**
+ * The slow path of rtSocketSwitchBlockingMode that does the actual switching.
+ *
+ * @returns IPRT status code.
+ * @param   pThis               The socket structure.
+ * @param   fBlocking           The desired mode of operation.
+ * @remarks Do not call directly.
+ */
+static int rtSocketSwitchBlockingModeSlow(RTSOCKETINT *pThis, bool fBlocking)
+{
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnioctlsocket, VERR_NET_NOT_UNSUPPORTED);
+    u_long uBlocking = fBlocking ? 0 : 1;
+    if (g_pfnioctlsocket(pThis->hNative, FIONBIO, &uBlocking))
+        return rtSocketError();
+
+#else
+    int fFlags = fcntl(pThis->hNative, F_GETFL, 0);
+    if (fFlags == -1)
+        return rtSocketError();
+
+    if (fBlocking)
+        fFlags &= ~O_NONBLOCK;
+    else
+        fFlags |= O_NONBLOCK;
+    if (fcntl(pThis->hNative, F_SETFL, fFlags) == -1)
+       return rtSocketError();
+#endif
+
+    pThis->fBlocking = fBlocking;
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Switches the socket to the desired blocking mode if necessary.
+ *
+ * The socket must be locked.
+ *
+ * @returns IPRT status code.
+ * @param   pThis               The socket structure.
+ * @param   fBlocking           The desired mode of operation.
+ */
+DECLINLINE(int) rtSocketSwitchBlockingMode(RTSOCKETINT *pThis, bool fBlocking)
+{
+    if (pThis->fBlocking != fBlocking)
+        return rtSocketSwitchBlockingModeSlow(pThis, fBlocking);
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Creates an IPRT socket handle for a native one.
+ *
+ * @returns IPRT status code.
+ * @param   ppSocket        Where to return the IPRT socket handle.
+ * @param   hNative         The native handle.
+ */
+DECLHIDDEN(int) rtSocketCreateForNative(RTSOCKETINT **ppSocket, RTSOCKETNATIVE hNative)
+{
+    RTSOCKETINT *pThis = (RTSOCKETINT *)RTMemPoolAlloc(RTMEMPOOL_DEFAULT, sizeof(*pThis));
+    if (!pThis)
+        return VERR_NO_MEMORY;
+    pThis->u32Magic         = RTSOCKET_MAGIC;
+    pThis->cUsers           = 0;
+    pThis->hNative          = hNative;
+    pThis->fClosed          = false;
+    pThis->fBlocking        = true;
+#if defined(RT_OS_WINDOWS) || defined(RT_OS_OS2)
+    pThis->hPollSet         = NIL_RTPOLLSET;
+#endif
+#ifdef RT_OS_WINDOWS
+    pThis->hEvent                   = WSA_INVALID_EVENT;
+    pThis->fPollEvts                = 0;
+    pThis->fSubscribedEvts          = 0;
+    pThis->fEventsSaved             = 0;
+    pThis->fHarvestedEvents         = false;
+    pThis->fPollFallback            = g_uWinSockInitedVersion < MAKEWORD(2, 0)
+                                   || g_pfnWSACreateEvent == NULL
+                                   || g_pfnWSACloseEvent == NULL
+                                   || g_pfnWSAEventSelect == NULL
+                                   || g_pfnWSAEnumNetworkEvents == NULL;
+    pThis->fPollFallbackActive      = false;
+    pThis->fPollFallbackShutdown    = false;
+    pThis->hPollFallbackNotifyR     = NIL_RTSOCKETNATIVE;
+    pThis->hPollFallbackNotifyW     = NIL_RTSOCKETNATIVE;
+    pThis->hPollFallbackThread      = NIL_RTTHREAD;
+#endif
+    *ppSocket = pThis;
+    return VINF_SUCCESS;
+}
+
+
+RTDECL(int) RTSocketFromNative(PRTSOCKET phSocket, RTHCINTPTR uNative)
+{
+    AssertReturn(uNative != NIL_RTSOCKETNATIVE, VERR_INVALID_PARAMETER);
+#ifndef RT_OS_WINDOWS
+    AssertReturn(uNative >= 0, VERR_INVALID_PARAMETER);
+#endif
+    AssertPtrReturn(phSocket, VERR_INVALID_POINTER);
+    return rtSocketCreateForNative(phSocket, uNative);
+}
+
+
+/**
+ * Wrapper around socket().
+ *
+ * @returns IPRT status code.
+ * @param   phSocket            Where to store the handle to the socket on
+ *                              success.
+ * @param   iDomain             The protocol family (PF_XXX).
+ * @param   iType               The socket type (SOCK_XXX).
+ * @param   iProtocol           Socket parameter, usually 0.
+ */
+DECLHIDDEN(int) rtSocketCreate(PRTSOCKET phSocket, int iDomain, int iType, int iProtocol)
+{
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnsocket, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnclosesocket, VERR_NET_NOT_UNSUPPORTED);
+
+    /* Initialize WinSock. */
+    int rc2 = rtSocketInitWinsock();
+    if (RT_FAILURE(rc2))
+        return rc2;
+#endif
+
+    /*
+     * Create the socket.
+     */
+#ifdef RT_OS_WINDOWS
+    RTSOCKETNATIVE hNative = g_pfnsocket(iDomain, iType, iProtocol);
+#else
+    RTSOCKETNATIVE hNative = socket(iDomain, iType, iProtocol);
+#endif
+    if (hNative == NIL_RTSOCKETNATIVE)
+        return rtSocketError();
+
+    /*
+     * Wrap it.
+     */
+    int rc = rtSocketCreateForNative(phSocket, hNative);
+    if (RT_FAILURE(rc))
+    {
+#ifdef RT_OS_WINDOWS
+        g_pfnclosesocket(hNative);
+#else
+        close(hNative);
+#endif
+    }
+    return rc;
+}
+
+
+/**
+ * Wrapper around socketpair() for creating a local TCP connection.
+ *
+ * @returns IPRT status code.
+ * @param   phServer            Where to return the first native socket.
+ * @param   phClient            Where to return the second native socket.
+ */
+static int rtSocketCreateNativeTcpPair(RTSOCKETNATIVE *phServer, RTSOCKETNATIVE *phClient)
+{
+#ifdef RT_OS_WINDOWS
+    /*
+     * Initialize WinSock and make sure we got the necessary APIs.
+     */
+    int rc = rtSocketInitWinsock();
+    if (RT_FAILURE(rc))
+        return rc;
+    AssertReturn(g_pfnsocket, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnclosesocket, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnsetsockopt, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnbind, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfngetsockname, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnlisten, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnaccept, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnconnect, VERR_NET_NOT_UNSUPPORTED);
+
+    /*
+     * Create the "server" listen socket and the "client" socket.
+     */
+    RTSOCKETNATIVE hListener = g_pfnsocket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if (hListener == NIL_RTSOCKETNATIVE)
+        return rtSocketError();
+    RTSOCKETNATIVE hClient = g_pfnsocket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if (hClient != NIL_RTSOCKETNATIVE)
+    {
+
+        /*
+         * We let WinSock choose a port number when we bind.
+         */
+        union
+        {
+            struct sockaddr_in  Ip;
+            struct sockaddr     Generic;
+        } uAddr;
+        RT_ZERO(uAddr);
+        uAddr.Ip.sin_family      = AF_INET;
+        uAddr.Ip.sin_addr.s_addr = RT_H2N_U32_C(INADDR_LOOPBACK);
+        //uAddr.Ip.sin_port      = 0;
+        int fReuse = 1;
+        rc = g_pfnsetsockopt(hListener, SOL_SOCKET, SO_REUSEADDR, (const char *)&fReuse, sizeof(fReuse));
+        if (rc == 0)
+        {
+            rc = g_pfnbind(hListener, &uAddr.Generic, sizeof(uAddr.Ip));
+            if (rc == 0)
+            {
+                /*
+                 * Get the address the client should connect to.  According to the docs,
+                 * we cannot assume that getsockname sets the IP and family.
+                 */
+                RT_ZERO(uAddr);
+                int cbAddr = sizeof(uAddr.Ip);
+                rc = g_pfngetsockname(hListener, &uAddr.Generic, &cbAddr);
+                if (rc == 0)
+                {
+                    uAddr.Ip.sin_family      = AF_INET;
+                    uAddr.Ip.sin_addr.s_addr = RT_H2N_U32_C(INADDR_LOOPBACK);
+
+                    /*
+                     * Listen, connect and accept.
+                     */
+                    rc = g_pfnlisten(hListener, 1 /*cBacklog*/);
+                    if (rc == 0)
+                    {
+                        rc = g_pfnconnect(hClient, &uAddr.Generic, sizeof(uAddr.Ip));
+                        if (rc == 0)
+                        {
+                            RTSOCKETNATIVE hServer = g_pfnaccept(hListener, NULL, NULL);
+                            if (hServer != NIL_RTSOCKETNATIVE)
+                            {
+                                g_pfnclosesocket(hListener);
+
+                                /*
+                                 * Done!
+                                 */
+                                *phServer = hServer;
+                                *phClient = hClient;
+                                return VINF_SUCCESS;
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        rc = rtSocketError();
+        g_pfnclosesocket(hClient);
+    }
+    else
+        rc = rtSocketError();
+    g_pfnclosesocket(hListener);
+    return rc;
+
+#else
+    /*
+     * Got socket pair, so use it.
+     * Note! This isn't TCP per se, but it should fool the users.
+     */
+    int aSockets[2] = { -1, -1 };
+    if (socketpair(AF_LOCAL, SOCK_STREAM, 0, aSockets) == 0)
+    {
+        *phServer = aSockets[0];
+        *phClient = aSockets[1];
+        return VINF_SUCCESS;
+    }
+    return rtSocketError();
+#endif
+}
+
+
+/**
+ * Worker for RTTcpCreatePair.
+ *
+ * @returns IPRT status code.
+ * @param   phServer            Where to return the "server" side of the pair.
+ * @param   phClient            Where to return the "client" side of the pair.
+ * @note    There is no server or client side, but we gotta call it something.
+ */
+DECLHIDDEN(int) rtSocketCreateTcpPair(RTSOCKET *phServer, RTSOCKET *phClient)
+{
+    RTSOCKETNATIVE hServer = NIL_RTSOCKETNATIVE;
+    RTSOCKETNATIVE hClient = NIL_RTSOCKETNATIVE;
+    int rc = rtSocketCreateNativeTcpPair(&hServer, &hClient);
+    if (RT_SUCCESS(rc))
+    {
+        rc = rtSocketCreateForNative(phServer, hServer);
+        if (RT_SUCCESS(rc))
+        {
+            rc = rtSocketCreateForNative(phClient, hClient);
+            if (RT_SUCCESS(rc))
+                return VINF_SUCCESS;
+            RTSocketRelease(*phServer);
+        }
+        else
+        {
+#ifdef RT_OS_WINDOWS
+            g_pfnclosesocket(hServer);
+#else
+            close(hServer);
+#endif
+        }
+#ifdef RT_OS_WINDOWS
+        g_pfnclosesocket(hClient);
+#else
+        close(hClient);
+#endif
+    }
+
+    *phServer = NIL_RTSOCKET;
+    *phClient = NIL_RTSOCKET;
+    return rc;
+}
+
+
+RTDECL(uint32_t) RTSocketRetain(RTSOCKET hSocket)
+{
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, UINT32_MAX);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, UINT32_MAX);
+    return RTMemPoolRetain(pThis);
+}
+
+
+/**
+ * Worker for RTSocketRelease and RTSocketClose.
+ *
+ * @returns IPRT status code.
+ * @param   pThis               The socket handle instance data.
+ * @param   fDestroy            Whether we're reaching ref count zero.
+ */
+static int rtSocketCloseIt(RTSOCKETINT *pThis, bool fDestroy)
+{
+    /*
+     * Invalidate the handle structure on destroy.
+     */
+    if (fDestroy)
+    {
+        Assert(ASMAtomicReadU32(&pThis->u32Magic) == RTSOCKET_MAGIC);
+        ASMAtomicWriteU32(&pThis->u32Magic, RTSOCKET_MAGIC_DEAD);
+    }
+
+    int rc = VINF_SUCCESS;
+    if (ASMAtomicCmpXchgBool(&pThis->fClosed, true, false))
+    {
+#ifdef RT_OS_WINDOWS
+        /*
+         * Poke the polling thread if active and give it a small chance to stop.
+         */
+        if (   pThis->fPollFallback
+            && pThis->hPollFallbackThread != NIL_RTTHREAD)
+        {
+            ASMAtomicWriteBool(&pThis->fPollFallbackShutdown, true);
+            rtSocketPokePollFallbackThread(pThis);
+            int rc2 = RTThreadWait(pThis->hPollFallbackThread, RT_MS_1SEC, NULL);
+            if (RT_SUCCESS(rc2))
+                pThis->hPollFallbackThread = NIL_RTTHREAD;
+        }
+#endif
+
+        /*
+         * Close the native handle.
+         */
+        RTSOCKETNATIVE hNative = pThis->hNative;
+        if (hNative != NIL_RTSOCKETNATIVE)
+        {
+            pThis->hNative = NIL_RTSOCKETNATIVE;
+
+#ifdef RT_OS_WINDOWS
+            AssertReturn(g_pfnclosesocket, VERR_NET_NOT_UNSUPPORTED);
+            if (g_pfnclosesocket(hNative))
+#else
+            if (close(hNative))
+#endif
+            {
+                rc = rtSocketError();
+#ifdef RT_OS_WINDOWS
+                AssertMsgFailed(("closesocket(%p) -> %Rrc\n", (uintptr_t)hNative, rc));
+#else
+                AssertMsgFailed(("close(%d) -> %Rrc\n", hNative, rc));
+#endif
+            }
+        }
+
+#ifdef RT_OS_WINDOWS
+        /*
+         * Windows specific polling cleanup.
+         */
+        WSAEVENT hEvent = pThis->hEvent;
+        if (hEvent != WSA_INVALID_EVENT)
+        {
+            pThis->hEvent = WSA_INVALID_EVENT;
+            if (!pThis->fPollFallback)
+            {
+                Assert(g_pfnWSACloseEvent);
+                if (g_pfnWSACloseEvent)
+                    g_pfnWSACloseEvent(hEvent);
+            }
+            else
+                CloseHandle(hEvent);
+        }
+
+        if (pThis->fPollFallback)
+        {
+            if (pThis->hPollFallbackNotifyW != NIL_RTSOCKETNATIVE)
+            {
+                g_pfnclosesocket(pThis->hPollFallbackNotifyW);
+                pThis->hPollFallbackNotifyW = NIL_RTSOCKETNATIVE;
+            }
+
+            if (pThis->hPollFallbackThread != NIL_RTTHREAD)
+            {
+                int rc2 = RTThreadWait(pThis->hPollFallbackThread, RT_MS_1MIN / 2, NULL);
+                AssertRC(rc2);
+                pThis->hPollFallbackThread = NIL_RTTHREAD;
+            }
+
+            if (pThis->hPollFallbackNotifyR != NIL_RTSOCKETNATIVE)
+            {
+                g_pfnclosesocket(pThis->hPollFallbackNotifyR);
+                pThis->hPollFallbackNotifyR = NIL_RTSOCKETNATIVE;
+            }
+        }
+#endif
+    }
+
+    return rc;
+}
+
+
+RTDECL(uint32_t) RTSocketRelease(RTSOCKET hSocket)
+{
+    RTSOCKETINT *pThis = hSocket;
+    if (pThis == NIL_RTSOCKET)
+        return 0;
+    AssertPtrReturn(pThis, UINT32_MAX);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, UINT32_MAX);
+
+    /* get the refcount without killing it... */
+    uint32_t cRefs = RTMemPoolRefCount(pThis);
+    AssertReturn(cRefs != UINT32_MAX, UINT32_MAX);
+    if (cRefs == 1)
+        rtSocketCloseIt(pThis, true);
+
+    return RTMemPoolRelease(RTMEMPOOL_DEFAULT, pThis);
+}
+
+
+RTDECL(int) RTSocketClose(RTSOCKET hSocket)
+{
+    RTSOCKETINT *pThis = hSocket;
+    if (pThis == NIL_RTSOCKET)
+        return VINF_SUCCESS;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+
+    uint32_t cRefs = RTMemPoolRefCount(pThis);
+    AssertReturn(cRefs != UINT32_MAX, UINT32_MAX);
+
+    int rc = rtSocketCloseIt(pThis, cRefs == 1);
+
+    RTMemPoolRelease(RTMEMPOOL_DEFAULT, pThis);
+    return rc;
+}
+
+
+RTDECL(RTHCUINTPTR) RTSocketToNative(RTSOCKET hSocket)
+{
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, RTHCUINTPTR_MAX);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, RTHCUINTPTR_MAX);
+    return (RTHCUINTPTR)pThis->hNative;
+}
+
+
+RTDECL(int) RTSocketSetInheritance(RTSOCKET hSocket, bool fInheritable)
+{
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(RTMemPoolRefCount(pThis) >= (pThis->cUsers ? 2U : 1U), VERR_CALLER_NO_REFERENCE);
+
+    int rc = VINF_SUCCESS;
+#ifdef RT_OS_WINDOWS
+    if (!SetHandleInformation((HANDLE)pThis->hNative, HANDLE_FLAG_INHERIT, fInheritable ? HANDLE_FLAG_INHERIT : 0))
+        rc = RTErrConvertFromWin32(GetLastError());
+#else
+    if (fcntl(pThis->hNative, F_SETFD, fInheritable ? 0 : FD_CLOEXEC) < 0)
+        rc = RTErrConvertFromErrno(errno);
+#endif
+
+    return rc;
+}
+
+
+static bool rtSocketIsIPv4Numerical(const char *pszAddress, PRTNETADDRIPV4 pAddr)
+{
+
+    /* Empty address resolves to the INADDR_ANY address (good for bind). */
+    if (!pszAddress || !*pszAddress)
+    {
+        pAddr->u = INADDR_ANY;
+        return true;
+    }
+
+    /* Four quads? */
+    char *psz = (char *)pszAddress;
+    for (int i = 0; i < 4; i++)
+    {
+        uint8_t u8;
+        int rc = RTStrToUInt8Ex(psz, &psz, 0, &u8);
+        if (rc != VINF_SUCCESS && rc != VWRN_TRAILING_CHARS)
+            return false;
+        if (*psz != (i < 3 ? '.' : '\0'))
+            return false;
+        psz++;
+
+        pAddr->au8[i] = u8;             /* big endian */
+    }
+
+    return true;
+}
+
+RTDECL(int) RTSocketParseInetAddress(const char *pszAddress, unsigned uPort, PRTNETADDR pAddr)
+{
+    int rc;
+
+    /*
+     * Validate input.
+     */
+    AssertReturn(uPort > 0, VERR_INVALID_PARAMETER);
+    AssertPtrNullReturn(pszAddress, VERR_INVALID_POINTER);
+
+    /*
+     * Resolve the address. Pretty crude at the moment, but we have to make
+     * sure to not ask the NT 4 gethostbyname about an IPv4 address as it may
+     * give a wrong answer.
+     */
+    /** @todo this only supports IPv4, and IPv6 support needs to be added.
+     * It probably needs to be converted to getaddrinfo(). */
+    RTNETADDRIPV4 IPv4Quad;
+    if (rtSocketIsIPv4Numerical(pszAddress, &IPv4Quad))
+    {
+        Log3(("rtSocketIsIPv4Numerical: %s -> %#x (%RTnaipv4)\n", pszAddress, IPv4Quad.u, IPv4Quad));
+        RT_ZERO(*pAddr);
+        pAddr->enmType      = RTNETADDRTYPE_IPV4;
+        pAddr->uPort        = uPort;
+        pAddr->uAddr.IPv4   = IPv4Quad;
+        return VINF_SUCCESS;
+    }
+
+#ifdef RT_OS_WINDOWS
+    /* Initialize WinSock and check version before we call gethostbyname. */
+    if (!g_pfngethostbyname)
+        return VERR_NET_NOT_UNSUPPORTED;
+
+    int rc2 = rtSocketInitWinsock();
+    if (RT_FAILURE(rc2))
+        return rc2;
+
+# define gethostbyname g_pfngethostbyname
+#endif
+
+    struct hostent *pHostEnt;
+    pHostEnt = gethostbyname(pszAddress);
+    if (!pHostEnt)
+    {
+        rc = rtSocketResolverError();
+        AssertMsgFailed(("Could not resolve '%s', rc=%Rrc\n", pszAddress, rc));
+        return rc;
+    }
+
+    if (pHostEnt->h_addrtype == AF_INET)
+    {
+        RT_ZERO(*pAddr);
+        pAddr->enmType      = RTNETADDRTYPE_IPV4;
+        pAddr->uPort        = uPort;
+        pAddr->uAddr.IPv4.u = ((struct in_addr *)pHostEnt->h_addr)->s_addr;
+        Log3(("gethostbyname: %s -> %#x (%RTnaipv4)\n", pszAddress, pAddr->uAddr.IPv4.u, pAddr->uAddr.IPv4));
+    }
+    else
+        return VERR_NET_ADDRESS_FAMILY_NOT_SUPPORTED;
+
+#ifdef RT_OS_WINDOWS
+# undef gethostbyname
+#endif
+    return VINF_SUCCESS;
+}
+
+
+/*
+ * New function to allow both ipv4 and ipv6 addresses to be resolved.
+ * Breaks compatibility with windows before 2000.
+ */
+RTDECL(int) RTSocketQueryAddressStr(const char *pszHost, char *pszResult, size_t *pcbResult, PRTNETADDRTYPE penmAddrType)
+{
+    AssertPtrReturn(pszHost, VERR_INVALID_POINTER);
+    AssertPtrReturn(pcbResult, VERR_INVALID_POINTER);
+    AssertPtrNullReturn(penmAddrType, VERR_INVALID_POINTER);
+    AssertPtrNullReturn(pszResult, VERR_INVALID_POINTER);
+
+#if defined(RT_OS_OS2) || defined(RT_OS_WINDOWS) /** @todo dynamically resolve the APIs not present in NT4! */
+    return VERR_NOT_SUPPORTED;
+
+#else
+    int rc;
+    if (*pcbResult < 16)
+        return VERR_NET_ADDRESS_NOT_AVAILABLE;
+
+    /* Setup the hint. */
+    struct addrinfo grHints;
+    RT_ZERO(grHints);
+    grHints.ai_socktype = 0;
+    grHints.ai_flags    = 0;
+    grHints.ai_protocol = 0;
+    grHints.ai_family   = AF_UNSPEC;
+    if (penmAddrType)
+    {
+        switch (*penmAddrType)
+        {
+            case RTNETADDRTYPE_INVALID:
+                /*grHints.ai_family = AF_UNSPEC;*/
+                break;
+            case RTNETADDRTYPE_IPV4:
+                grHints.ai_family = AF_INET;
+                break;
+            case RTNETADDRTYPE_IPV6:
+                grHints.ai_family = AF_INET6;
+                break;
+            default:
+                AssertFailedReturn(VERR_INVALID_PARAMETER);
+        }
+    }
+
+# ifdef RT_OS_WINDOWS
+    /*
+     * Winsock2 init
+     */
+    if (   !g_pfngetaddrinfo
+        || !g_pfnfreeaddrinfo)
+        return VERR_NET_NOT_UNSUPPORTED;
+
+    int rc2 = rtSocketInitWinsock();
+    if (RT_FAILURE(rc2))
+        return rc2;
+
+#  define getaddrinfo  g_pfngetaddrinfo
+#  define freeaddrinfo g_pfnfreeaddrinfo
+# endif
+
+    /** @todo r=bird: getaddrinfo and freeaddrinfo breaks the additions on NT4. */
+    struct addrinfo *pgrResults = NULL;
+    rc = getaddrinfo(pszHost, "", &grHints, &pgrResults);
+    if (rc != 0)
+        return VERR_NET_ADDRESS_NOT_AVAILABLE;
+
+    // return data
+    // on multiple matches return only the first one
+
+    if (!pgrResults)
+        return VERR_NET_ADDRESS_NOT_AVAILABLE;
+
+    struct addrinfo const *pgrResult = pgrResults->ai_next;
+    if (!pgrResult)
+    {
+        freeaddrinfo(pgrResults);
+        return VERR_NET_ADDRESS_NOT_AVAILABLE;
+    }
+
+    RTNETADDRTYPE   enmAddrType = RTNETADDRTYPE_INVALID;
+    size_t          cchIpAddress;
+    char            szIpAddress[48];
+    if (pgrResult->ai_family == AF_INET)
+    {
+        struct sockaddr_in const *pgrSa = (struct sockaddr_in const *)pgrResult->ai_addr;
+        cchIpAddress = RTStrPrintf(szIpAddress, sizeof(szIpAddress),
+                                   "%RTnaipv4", pgrSa->sin_addr.s_addr);
+        Assert(cchIpAddress >= 7 && cchIpAddress < sizeof(szIpAddress) - 1);
+        enmAddrType = RTNETADDRTYPE_IPV4;
+        rc = VINF_SUCCESS;
+    }
+    else if (pgrResult->ai_family == AF_INET6)
+    {
+        struct sockaddr_in6 const *pgrSa6 = (struct sockaddr_in6 const *)pgrResult->ai_addr;
+        cchIpAddress = RTStrPrintf(szIpAddress, sizeof(szIpAddress),
+                                   "%RTnaipv6", (PRTNETADDRIPV6)&pgrSa6->sin6_addr);
+        enmAddrType = RTNETADDRTYPE_IPV6;
+        rc = VINF_SUCCESS;
+    }
+    else
+    {
+        rc = VERR_NET_ADDRESS_NOT_AVAILABLE;
+        szIpAddress[0] = '\0';
+        cchIpAddress = 0;
+    }
+    freeaddrinfo(pgrResults);
+
+    /*
+     * Copy out the result.
+     */
+    size_t const cbResult = *pcbResult;
+    *pcbResult = cchIpAddress + 1;
+    if (cchIpAddress < cbResult)
+        memcpy(pszResult, szIpAddress, cchIpAddress + 1);
+    else
+    {
+        RT_BZERO(pszResult, cbResult);
+        if (RT_SUCCESS(rc))
+            rc = VERR_BUFFER_OVERFLOW;
+    }
+    if (penmAddrType && RT_SUCCESS(rc))
+        *penmAddrType = enmAddrType;
+    return rc;
+
+# ifdef RT_OS_WINDOWS
+#  undef getaddrinfo
+#  undef freeaddrinfo
+# endif
+#endif /* !RT_OS_OS2 */
+}
+
+
+RTDECL(int) RTSocketRead(RTSOCKET hSocket, void *pvBuffer, size_t cbBuffer, size_t *pcbRead)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(cbBuffer > 0, VERR_INVALID_PARAMETER);
+    AssertPtr(pvBuffer);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnrecv, VERR_NET_NOT_UNSUPPORTED);
+# define recv g_pfnrecv
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, true /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /*
+     * Read loop.
+     * If pcbRead is NULL we have to fill the entire buffer!
+     */
+    size_t  cbRead   = 0;
+    size_t  cbToRead = cbBuffer;
+    for (;;)
+    {
+        rtSocketErrorReset();
+#ifdef RTSOCKET_MAX_READ
+        int    cbNow = cbToRead >= RTSOCKET_MAX_READ ? RTSOCKET_MAX_READ : (int)cbToRead;
+#else
+        size_t cbNow = cbToRead;
+#endif
+        ssize_t cbBytesRead = recv(pThis->hNative, (char *)pvBuffer + cbRead, cbNow, MSG_NOSIGNAL);
+        if (cbBytesRead <= 0)
+        {
+            rc = rtSocketError();
+            Assert(RT_FAILURE_NP(rc) || cbBytesRead == 0);
+            if (RT_SUCCESS_NP(rc))
+            {
+                if (!pcbRead)
+                    rc = VERR_NET_SHUTDOWN;
+                else
+                {
+                    *pcbRead = 0;
+                    rc = VINF_SUCCESS;
+                }
+            }
+            break;
+        }
+        if (pcbRead)
+        {
+            /* return partial data */
+            *pcbRead = cbBytesRead;
+            break;
+        }
+
+        /* read more? */
+        cbRead += cbBytesRead;
+        if (cbRead == cbBuffer)
+            break;
+
+        /* next */
+        cbToRead = cbBuffer - cbRead;
+    }
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef recv
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketReadFrom(RTSOCKET hSocket, void *pvBuffer, size_t cbBuffer, size_t *pcbRead, PRTNETADDR pSrcAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(cbBuffer > 0, VERR_INVALID_PARAMETER);
+    AssertPtr(pvBuffer);
+    AssertPtr(pcbRead);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnrecvfrom, VERR_NET_NOT_UNSUPPORTED);
+# define recvfrom g_pfnrecvfrom
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, true /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /*
+     * Read data.
+     */
+    size_t  cbRead   = 0;
+    size_t  cbToRead = cbBuffer;
+    rtSocketErrorReset();
+    RTSOCKADDRUNION u;
+#ifdef RTSOCKET_MAX_READ
+    int       cbNow  = cbToRead >= RTSOCKET_MAX_READ ? RTSOCKET_MAX_READ : (int)cbToRead;
+    int       cbAddr = sizeof(u);
+#else
+    size_t    cbNow  = cbToRead;
+    socklen_t cbAddr = sizeof(u);
+#endif
+    ssize_t cbBytesRead = recvfrom(pThis->hNative, (char *)pvBuffer + cbRead, cbNow, MSG_NOSIGNAL, &u.Addr, &cbAddr);
+    if (cbBytesRead <= 0)
+    {
+        rc = rtSocketError();
+        Assert(RT_FAILURE_NP(rc) || cbBytesRead == 0);
+        if (RT_SUCCESS_NP(rc))
+        {
+            *pcbRead = 0;
+            rc = VINF_SUCCESS;
+        }
+    }
+    else
+    {
+        if (pSrcAddr)
+            rc = rtSocketNetAddrFromAddr(&u, cbAddr, pSrcAddr);
+        *pcbRead = cbBytesRead;
+    }
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef recvfrom
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketWrite(RTSOCKET hSocket, const void *pvBuffer, size_t cbBuffer)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnsend, VERR_NET_NOT_UNSUPPORTED);
+# define send g_pfnsend
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, true /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /*
+     * Try write all at once.
+     */
+#ifdef RTSOCKET_MAX_WRITE
+    int     cbNow     = cbBuffer >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbBuffer;
+#else
+    size_t  cbNow     = cbBuffer >= SSIZE_MAX   ? SSIZE_MAX   :      cbBuffer;
+#endif
+    ssize_t cbWritten = send(pThis->hNative, (const char *)pvBuffer, cbNow, MSG_NOSIGNAL);
+    if (RT_LIKELY((size_t)cbWritten == cbBuffer && cbWritten >= 0))
+        rc = VINF_SUCCESS;
+    else if (cbWritten < 0)
+        rc = rtSocketError();
+    else
+    {
+        /*
+         * Unfinished business, write the remainder of the request.  Must ignore
+         * VERR_INTERRUPTED here if we've managed to send something.
+         */
+        size_t cbSentSoFar = 0;
+        for (;;)
+        {
+            /* advance */
+            cbBuffer    -= (size_t)cbWritten;
+            if (!cbBuffer)
+                break;
+            cbSentSoFar += (size_t)cbWritten;
+            pvBuffer     = (char const *)pvBuffer + cbWritten;
+
+            /* send */
+#ifdef RTSOCKET_MAX_WRITE
+            cbNow = cbBuffer >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbBuffer;
+#else
+            cbNow = cbBuffer >= SSIZE_MAX   ? SSIZE_MAX   :      cbBuffer;
+#endif
+            cbWritten = send(pThis->hNative, (const char *)pvBuffer, cbNow, MSG_NOSIGNAL);
+            if (cbWritten >= 0)
+                AssertMsg(cbBuffer >= (size_t)cbWritten, ("Wrote more than we requested!!! cbWritten=%zu cbBuffer=%zu rtSocketError()=%d\n",
+                                                          cbWritten, cbBuffer, rtSocketError()));
+            else
+            {
+                rc = rtSocketError();
+                if (rc != VERR_INTERNAL_ERROR || cbSentSoFar == 0)
+                    break;
+                cbWritten = 0;
+                rc = VINF_SUCCESS;
+            }
+        }
+    }
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef send
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketWriteTo(RTSOCKET hSocket, const void *pvBuffer, size_t cbBuffer, PCRTNETADDR pAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnsendto, VERR_NET_NOT_UNSUPPORTED);
+# define sendto g_pfnsendto
+#endif
+
+    /* no locking since UDP reads may be done concurrently to writes, and
+     * this is the normal use case of this code. */
+
+    int rc = rtSocketSwitchBlockingMode(pThis, true /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /* Figure out destination address. */
+    struct sockaddr *pSA = NULL;
+#ifdef RT_OS_WINDOWS
+    int cbSA = 0;
+#else
+    socklen_t cbSA = 0;
+#endif
+    RTSOCKADDRUNION u;
+    if (pAddr)
+    {
+        rc = rtSocketAddrFromNetAddr(pAddr, &u, sizeof(u), NULL);
+        if (RT_FAILURE(rc))
+            return rc;
+        pSA = &u.Addr;
+        cbSA = sizeof(u);
+    }
+
+    /*
+     * Must write all at once, otherwise it is a failure.
+     */
+#ifdef RT_OS_WINDOWS
+    int     cbNow     = cbBuffer >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbBuffer;
+#else
+    size_t  cbNow     = cbBuffer >= SSIZE_MAX   ? SSIZE_MAX   :      cbBuffer;
+#endif
+    ssize_t cbWritten = sendto(pThis->hNative, (const char *)pvBuffer, cbNow, MSG_NOSIGNAL, pSA, cbSA);
+    if (RT_LIKELY((size_t)cbWritten == cbBuffer && cbWritten >= 0))
+        rc = VINF_SUCCESS;
+    else if (cbWritten < 0)
+        rc = rtSocketError();
+    else
+        rc = VERR_TOO_MUCH_DATA;
+
+    /// @todo rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef sendto
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketWriteToNB(RTSOCKET hSocket, const void *pvBuffer, size_t cbBuffer, PCRTNETADDR pAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnsendto, VERR_NET_NOT_UNSUPPORTED);
+# define sendto g_pfnsendto
+#endif
+
+    /* no locking since UDP reads may be done concurrently to writes, and
+     * this is the normal use case of this code. */
+
+    int rc = rtSocketSwitchBlockingMode(pThis, false /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /* Figure out destination address. */
+    struct sockaddr *pSA = NULL;
+#ifdef RT_OS_WINDOWS
+    int cbSA = 0;
+#else
+    socklen_t cbSA = 0;
+#endif
+    RTSOCKADDRUNION u;
+    if (pAddr)
+    {
+        rc = rtSocketAddrFromNetAddr(pAddr, &u, sizeof(u), NULL);
+        if (RT_FAILURE(rc))
+            return rc;
+        pSA = &u.Addr;
+        cbSA = sizeof(u);
+    }
+
+    /*
+     * Must write all at once, otherwise it is a failure.
+     */
+#ifdef RT_OS_WINDOWS
+    int     cbNow     = cbBuffer >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbBuffer;
+#else
+    size_t  cbNow     = cbBuffer >= SSIZE_MAX   ? SSIZE_MAX   :      cbBuffer;
+#endif
+    ssize_t cbWritten = sendto(pThis->hNative, (const char *)pvBuffer, cbNow, MSG_NOSIGNAL, pSA, cbSA);
+    if (RT_LIKELY((size_t)cbWritten == cbBuffer && cbWritten >= 0))
+        rc = VINF_SUCCESS;
+    else if (cbWritten < 0)
+        rc = rtSocketError();
+    else
+        rc = VERR_TOO_MUCH_DATA;
+
+    /// @todo rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef sendto
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSgWrite(RTSOCKET hSocket, PCRTSGBUF pSgBuf)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertPtrReturn(pSgBuf, VERR_INVALID_PARAMETER);
+    AssertReturn(pSgBuf->cSegs > 0, VERR_INVALID_PARAMETER);
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, true /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /*
+     * Construct message descriptor (translate pSgBuf) and send it.
+     */
+    rc = VERR_NO_TMP_MEMORY;
+#ifdef RT_OS_WINDOWS
+    if (g_pfnWSASend)
+    {
+        AssertCompileSize(WSABUF, sizeof(RTSGSEG));
+        AssertCompileMemberSize(WSABUF, buf, RT_SIZEOFMEMB(RTSGSEG, pvSeg));
+
+        LPWSABUF paMsg = (LPWSABUF)RTMemTmpAllocZ(pSgBuf->cSegs * sizeof(WSABUF));
+        if (paMsg)
+        {
+            for (unsigned i = 0; i < pSgBuf->cSegs; i++)
+            {
+                paMsg[i].buf = (char *)pSgBuf->paSegs[i].pvSeg;
+                paMsg[i].len = (u_long)pSgBuf->paSegs[i].cbSeg;
+            }
+
+            DWORD dwSent;
+            int hrc = g_pfnWSASend(pThis->hNative, paMsg, pSgBuf->cSegs, &dwSent, MSG_NOSIGNAL, NULL, NULL);
+            if (!hrc)
+                rc = VINF_SUCCESS;
+    /** @todo check for incomplete writes */
+            else
+                rc = rtSocketError();
+
+            RTMemTmpFree(paMsg);
+        }
+    }
+    else if (g_pfnsend)
+    {
+        rc = VINF_SUCCESS;
+        for (uint32_t iSeg = 0; iSeg < pSgBuf->cSegs; iSeg++)
+        {
+            uint8_t const *pbSeg = (uint8_t const *)pSgBuf->paSegs[iSeg].pvSeg;
+            size_t         cbSeg = pSgBuf->paSegs[iSeg].cbSeg;
+            int            cbNow;
+            ssize_t        cbWritten;
+            for (;;)
+            {
+                cbNow = cbSeg >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbSeg;
+                cbWritten = g_pfnsend(pThis->hNative, (const char *)pbSeg, cbNow, MSG_NOSIGNAL);
+                if ((size_t)cbWritten >= cbSeg || cbWritten < 0)
+                    break;
+                pbSeg += cbWritten;
+                cbSeg -= cbWritten;
+            }
+            if (cbWritten < 0)
+            {
+                rc = rtSocketError();
+                break;
+            }
+        }
+    }
+    else
+        rc = VERR_NET_NOT_UNSUPPORTED;
+
+#else  /* !RT_OS_WINDOWS */
+    AssertCompileSize(struct iovec, sizeof(RTSGSEG));
+    AssertCompileMemberSize(struct iovec, iov_base, RT_SIZEOFMEMB(RTSGSEG, pvSeg));
+    AssertCompileMemberSize(struct iovec, iov_len,  RT_SIZEOFMEMB(RTSGSEG, cbSeg));
+
+    struct iovec *paMsg = (struct iovec *)RTMemTmpAllocZ(pSgBuf->cSegs * sizeof(struct iovec));
+    if (paMsg)
+    {
+        for (unsigned i = 0; i < pSgBuf->cSegs; i++)
+        {
+            paMsg[i].iov_base = pSgBuf->paSegs[i].pvSeg;
+            paMsg[i].iov_len  = pSgBuf->paSegs[i].cbSeg;
+        }
+
+        struct msghdr msgHdr;
+        RT_ZERO(msgHdr);
+        msgHdr.msg_iov    = paMsg;
+        msgHdr.msg_iovlen = pSgBuf->cSegs;
+        ssize_t cbWritten = sendmsg(pThis->hNative, &msgHdr, MSG_NOSIGNAL);
+        if (RT_LIKELY(cbWritten >= 0))
+            rc = VINF_SUCCESS;
+/** @todo check for incomplete writes */
+        else
+            rc = rtSocketError();
+
+        RTMemTmpFree(paMsg);
+    }
+#endif /* !RT_OS_WINDOWS */
+
+    rtSocketUnlock(pThis);
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSgWriteL(RTSOCKET hSocket, size_t cSegs, ...)
+{
+    va_list va;
+    va_start(va, cSegs);
+    int rc = RTSocketSgWriteLV(hSocket, cSegs, va);
+    va_end(va);
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSgWriteLV(RTSOCKET hSocket, size_t cSegs, va_list va)
+{
+    /*
+     * Set up a S/G segment array + buffer on the stack and pass it
+     * on to RTSocketSgWrite.
+     */
+    Assert(cSegs <= 16);
+    PRTSGSEG paSegs = (PRTSGSEG)alloca(cSegs * sizeof(RTSGSEG));
+    AssertReturn(paSegs, VERR_NO_TMP_MEMORY);
+    for (size_t i = 0; i < cSegs; i++)
+    {
+        paSegs[i].pvSeg = va_arg(va, void *);
+        paSegs[i].cbSeg = va_arg(va, size_t);
+    }
+
+    RTSGBUF SgBuf;
+    RTSgBufInit(&SgBuf, paSegs, cSegs);
+    return RTSocketSgWrite(hSocket, &SgBuf);
+}
+
+
+RTDECL(int) RTSocketReadNB(RTSOCKET hSocket, void *pvBuffer, size_t cbBuffer, size_t *pcbRead)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(cbBuffer > 0, VERR_INVALID_PARAMETER);
+    AssertPtr(pvBuffer);
+    AssertPtrReturn(pcbRead, VERR_INVALID_PARAMETER);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnrecv, VERR_NET_NOT_UNSUPPORTED);
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, false /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    rtSocketErrorReset();
+#ifdef RTSOCKET_MAX_READ
+    int    cbNow = cbBuffer >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbBuffer;
+#else
+    size_t cbNow = cbBuffer;
+#endif
+
+#ifdef RT_OS_WINDOWS
+    int cbRead = g_pfnrecv(pThis->hNative, (char *)pvBuffer, cbNow, MSG_NOSIGNAL);
+    if (cbRead >= 0)
+    {
+        *pcbRead = cbRead;
+        rc = VINF_SUCCESS;
+    }
+    else
+    {
+        rc = rtSocketError();
+        if (rc == VERR_TRY_AGAIN)
+        {
+            *pcbRead = 0;
+            rc = VINF_TRY_AGAIN;
+        }
+    }
+
+#else
+    ssize_t cbRead = recv(pThis->hNative, pvBuffer, cbNow, MSG_NOSIGNAL);
+    if (cbRead >= 0)
+        *pcbRead = cbRead;
+    else if (   errno == EAGAIN
+# ifdef EWOULDBLOCK
+#  if EWOULDBLOCK != EAGAIN
+             || errno == EWOULDBLOCK
+#  endif
+# endif
+             )
+    {
+        *pcbRead = 0;
+        rc = VINF_TRY_AGAIN;
+    }
+    else
+        rc = rtSocketError();
+#endif
+
+    rtSocketUnlock(pThis);
+    return rc;
+}
+
+
+RTDECL(int) RTSocketWriteNB(RTSOCKET hSocket, const void *pvBuffer, size_t cbBuffer, size_t *pcbWritten)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertPtrReturn(pcbWritten, VERR_INVALID_PARAMETER);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnsend, VERR_NET_NOT_UNSUPPORTED);
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, false /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    rtSocketErrorReset();
+#ifdef RT_OS_WINDOWS
+# ifdef RTSOCKET_MAX_WRITE
+    int    cbNow = cbBuffer >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbBuffer;
+# else
+    size_t cbNow = cbBuffer;
+# endif
+    int cbWritten = g_pfnsend(pThis->hNative, (const char *)pvBuffer, cbNow, MSG_NOSIGNAL);
+    if (cbWritten >= 0)
+    {
+        *pcbWritten = cbWritten;
+        rc = VINF_SUCCESS;
+    }
+    else
+    {
+        rc = rtSocketError();
+        if (rc == VERR_TRY_AGAIN)
+        {
+            *pcbWritten = 0;
+            rc = VINF_TRY_AGAIN;
+        }
+    }
+#else
+    ssize_t cbWritten = send(pThis->hNative, pvBuffer, cbBuffer, MSG_NOSIGNAL);
+    if (cbWritten >= 0)
+        *pcbWritten = cbWritten;
+    else if (   errno == EAGAIN
+# ifdef EWOULDBLOCK
+#  if EWOULDBLOCK != EAGAIN
+             || errno == EWOULDBLOCK
+#  endif
+# endif
+            )
+    {
+        *pcbWritten = 0;
+        rc = VINF_TRY_AGAIN;
+    }
+    else
+        rc = rtSocketError();
+#endif
+
+    rtSocketUnlock(pThis);
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSgWriteNB(RTSOCKET hSocket, PCRTSGBUF pSgBuf, size_t *pcbWritten)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertPtrReturn(pSgBuf, VERR_INVALID_PARAMETER);
+    AssertPtrReturn(pcbWritten, VERR_INVALID_PARAMETER);
+    AssertReturn(pSgBuf->cSegs > 0, VERR_INVALID_PARAMETER);
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = rtSocketSwitchBlockingMode(pThis, false /* fBlocking */);
+    if (RT_FAILURE(rc))
+        return rc;
+
+    unsigned cSegsToSend = 0;
+    rc = VERR_NO_TMP_MEMORY;
+#ifdef RT_OS_WINDOWS
+    if (g_pfnWSASend)
+    {
+        LPWSABUF paMsg = NULL;
+        RTSgBufMapToNative(paMsg, pSgBuf, WSABUF, buf, char *, len, u_long, cSegsToSend);
+        if (paMsg)
+        {
+            DWORD dwSent = 0;
+            int hrc = g_pfnWSASend(pThis->hNative, paMsg, cSegsToSend, &dwSent, MSG_NOSIGNAL, NULL, NULL);
+            if (!hrc)
+                rc = VINF_SUCCESS;
+            else
+                rc = rtSocketError();
+
+            *pcbWritten = dwSent;
+
+            RTMemTmpFree(paMsg);
+        }
+    }
+    else if (g_pfnsend)
+    {
+        size_t cbWrittenTotal = 0;
+        rc = VINF_SUCCESS;
+        for (uint32_t iSeg = 0; iSeg < pSgBuf->cSegs; iSeg++)
+        {
+            uint8_t const *pbSeg = (uint8_t const *)pSgBuf->paSegs[iSeg].pvSeg;
+            size_t         cbSeg = pSgBuf->paSegs[iSeg].cbSeg;
+            int            cbNow;
+            ssize_t        cbWritten;
+            for (;;)
+            {
+                cbNow = cbSeg >= RTSOCKET_MAX_WRITE ? RTSOCKET_MAX_WRITE : (int)cbSeg;
+                cbWritten = g_pfnsend(pThis->hNative, (const char *)pbSeg, cbNow, MSG_NOSIGNAL);
+                if ((size_t)cbWritten >= cbSeg || cbWritten < 0)
+                    break;
+                cbWrittenTotal += cbWrittenTotal;
+                pbSeg += cbWritten;
+                cbSeg -= cbWritten;
+            }
+            if (cbWritten < 0)
+            {
+                rc = rtSocketError();
+                break;
+            }
+            if (cbWritten != cbNow)
+                break;
+        }
+        *pcbWritten = cbWrittenTotal;
+    }
+    else
+        rc = VERR_NET_NOT_UNSUPPORTED;
+
+#else  /* !RT_OS_WINDOWS */
+    struct iovec *paMsg = NULL;
+
+    RTSgBufMapToNative(paMsg, pSgBuf, struct iovec, iov_base, void *, iov_len, size_t, cSegsToSend);
+    if (paMsg)
+    {
+        struct msghdr msgHdr;
+        RT_ZERO(msgHdr);
+        msgHdr.msg_iov    = paMsg;
+        msgHdr.msg_iovlen = cSegsToSend;
+        ssize_t cbWritten = sendmsg(pThis->hNative, &msgHdr, MSG_NOSIGNAL);
+        if (RT_LIKELY(cbWritten >= 0))
+        {
+            rc = VINF_SUCCESS;
+            *pcbWritten = cbWritten;
+        }
+        else
+            rc = rtSocketError();
+
+        RTMemTmpFree(paMsg);
+    }
+#endif /* !RT_OS_WINDOWS */
+
+    rtSocketUnlock(pThis);
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSgWriteLNB(RTSOCKET hSocket, size_t cSegs, size_t *pcbWritten, ...)
+{
+    va_list va;
+    va_start(va, pcbWritten);
+    int rc = RTSocketSgWriteLVNB(hSocket, cSegs, pcbWritten, va);
+    va_end(va);
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSgWriteLVNB(RTSOCKET hSocket, size_t cSegs, size_t *pcbWritten, va_list va)
+{
+    /*
+     * Set up a S/G segment array + buffer on the stack and pass it
+     * on to RTSocketSgWrite.
+     */
+    Assert(cSegs <= 16);
+    PRTSGSEG paSegs = (PRTSGSEG)alloca(cSegs * sizeof(RTSGSEG));
+    AssertReturn(paSegs, VERR_NO_TMP_MEMORY);
+    for (size_t i = 0; i < cSegs; i++)
+    {
+        paSegs[i].pvSeg = va_arg(va, void *);
+        paSegs[i].cbSeg = va_arg(va, size_t);
+    }
+
+    RTSGBUF SgBuf;
+    RTSgBufInit(&SgBuf, paSegs, cSegs);
+    return RTSocketSgWriteNB(hSocket, &SgBuf, pcbWritten);
+}
+
+
+RTDECL(int) RTSocketSelectOne(RTSOCKET hSocket, RTMSINTERVAL cMillies)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(RTMemPoolRefCount(pThis) >= (pThis->cUsers ? 2U : 1U), VERR_CALLER_NO_REFERENCE);
+    int const fdMax = (int)pThis->hNative + 1;
+    AssertReturn((RTSOCKETNATIVE)(fdMax - 1) == pThis->hNative, VERR_INTERNAL_ERROR_5);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnselect, VERR_NET_NOT_UNSUPPORTED);
+# define select g_pfnselect
+#endif
+
+    /*
+     * Set up the file descriptor sets and do the select.
+     */
+    fd_set fdsetR;
+    FD_ZERO(&fdsetR);
+    FD_SET(pThis->hNative, &fdsetR);
+
+    fd_set fdsetE = fdsetR;
+
+    int rc;
+    if (cMillies == RT_INDEFINITE_WAIT)
+        rc = select(fdMax, &fdsetR, NULL, &fdsetE, NULL);
+    else
+    {
+        struct timeval timeout;
+        timeout.tv_sec = cMillies / 1000;
+        timeout.tv_usec = (cMillies % 1000) * 1000;
+        rc = select(fdMax, &fdsetR, NULL, &fdsetE, &timeout);
+    }
+    if (rc > 0)
+        rc = VINF_SUCCESS;
+    else if (rc == 0)
+        rc = VERR_TIMEOUT;
+    else
+        rc = rtSocketError();
+
+#ifdef RT_OS_WINDOWS
+# undef select
+#endif
+    return rc;
+}
+
+
+/**
+ * Internal worker for RTSocketSelectOneEx and rtSocketPollCheck (fallback)
+ *
+ * @returns IPRT status code
+ * @param   pThis               The socket (valid).
+ * @param   fEvents             The events to select for.
+ * @param   pfEvents            Where to return the events.
+ * @param   cMillies            How long to select for, in milliseconds.
+ */
+static int rtSocketSelectOneEx(RTSOCKET pThis, uint32_t fEvents, uint32_t *pfEvents, RTMSINTERVAL cMillies)
+{
+    RTSOCKETNATIVE hNative = pThis->hNative;
+    if (hNative == NIL_RTSOCKETNATIVE)
+    {
+        /* Socket is already closed? Possible we raced someone calling rtSocketCloseIt.
+           Should we return a different status code? */
+        *pfEvents = RTSOCKET_EVT_ERROR;
+        return VINF_SUCCESS;
+    }
+
+    int const fdMax = (int)hNative + 1;
+    AssertReturn((RTSOCKETNATIVE)(fdMax - 1) == hNative, VERR_INTERNAL_ERROR_5);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnselect, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfn__WSAFDIsSet, VERR_NET_NOT_UNSUPPORTED);
+# define select         g_pfnselect
+# define __WSAFDIsSet   g_pfn__WSAFDIsSet
+#endif
+
+    *pfEvents = 0;
+
+    /*
+     * Set up the file descriptor sets and do the select.
+     */
+    fd_set fdsetR;
+    fd_set fdsetW;
+    fd_set fdsetE;
+    FD_ZERO(&fdsetR);
+    FD_ZERO(&fdsetW);
+    FD_ZERO(&fdsetE);
+
+    if (fEvents & RTSOCKET_EVT_READ)
+        FD_SET(hNative, &fdsetR);
+    if (fEvents & RTSOCKET_EVT_WRITE)
+        FD_SET(hNative, &fdsetW);
+    if (fEvents & RTSOCKET_EVT_ERROR)
+        FD_SET(hNative, &fdsetE);
+
+    int rc;
+    if (cMillies == RT_INDEFINITE_WAIT)
+        rc = select(fdMax, &fdsetR, &fdsetW, &fdsetE, NULL);
+    else
+    {
+        struct timeval timeout;
+        timeout.tv_sec = cMillies / 1000;
+        timeout.tv_usec = (cMillies % 1000) * 1000;
+        rc = select(fdMax, &fdsetR, &fdsetW, &fdsetE, &timeout);
+    }
+    if (rc > 0)
+    {
+        if (pThis->hNative == hNative)
+        {
+            if (FD_ISSET(hNative, &fdsetR))
+                *pfEvents |= RTSOCKET_EVT_READ;
+            if (FD_ISSET(hNative, &fdsetW))
+                *pfEvents |= RTSOCKET_EVT_WRITE;
+            if (FD_ISSET(hNative, &fdsetE))
+                *pfEvents |= RTSOCKET_EVT_ERROR;
+            rc = VINF_SUCCESS;
+        }
+        else
+        {
+            /* Socket was closed while we waited (rtSocketCloseIt).  Different status code? */
+            *pfEvents = RTSOCKET_EVT_ERROR;
+            rc = VINF_SUCCESS;
+        }
+    }
+    else if (rc == 0)
+        rc = VERR_TIMEOUT;
+    else
+        rc = rtSocketError();
+
+#ifdef RT_OS_WINDOWS
+# undef select
+# undef __WSAFDIsSet
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketSelectOneEx(RTSOCKET hSocket, uint32_t fEvents, uint32_t *pfEvents, RTMSINTERVAL cMillies)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertPtrReturn(pfEvents, VERR_INVALID_PARAMETER);
+    AssertReturn(!(fEvents & ~RTSOCKET_EVT_VALID_MASK), VERR_INVALID_PARAMETER);
+    AssertReturn(RTMemPoolRefCount(pThis) >= (pThis->cUsers ? 2U : 1U), VERR_CALLER_NO_REFERENCE);
+
+    return rtSocketSelectOneEx(pThis, fEvents, pfEvents, cMillies);
+}
+
+
+RTDECL(int) RTSocketShutdown(RTSOCKET hSocket, bool fRead, bool fWrite)
+{
+    /*
+     * Validate input, don't lock it because we might want to interrupt a call
+     * active on a different thread.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(RTMemPoolRefCount(pThis) >= (pThis->cUsers ? 2U : 1U), VERR_CALLER_NO_REFERENCE);
+    AssertReturn(fRead || fWrite, VERR_INVALID_PARAMETER);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnshutdown, VERR_NET_NOT_UNSUPPORTED);
+# define shutdown g_pfnshutdown
+#endif
+
+    /*
+     * Do the job.
+     */
+    int rc = VINF_SUCCESS;
+    int fHow;
+    if (fRead && fWrite)
+        fHow = SHUT_RDWR;
+    else if (fRead)
+        fHow = SHUT_RD;
+    else
+        fHow = SHUT_WR;
+    if (shutdown(pThis->hNative, fHow) == -1)
+        rc = rtSocketError();
+
+#ifdef RT_OS_WINDOWS
+# undef shutdown
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketGetLocalAddress(RTSOCKET hSocket, PRTNETADDR pAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(RTMemPoolRefCount(pThis) >= (pThis->cUsers ? 2U : 1U), VERR_CALLER_NO_REFERENCE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfngetsockname, VERR_NET_NOT_UNSUPPORTED);
+# define getsockname g_pfngetsockname
+#endif
+
+    /*
+     * Get the address and convert it.
+     */
+    int             rc;
+    RTSOCKADDRUNION u;
+#ifdef RT_OS_WINDOWS
+    int             cbAddr = sizeof(u);
+#else
+    socklen_t       cbAddr = sizeof(u);
+#endif
+    RT_ZERO(u);
+    if (getsockname(pThis->hNative, &u.Addr, &cbAddr) == 0)
+        rc = rtSocketNetAddrFromAddr(&u, cbAddr, pAddr);
+    else
+        rc = rtSocketError();
+
+#ifdef RT_OS_WINDOWS
+# undef getsockname
+#endif
+    return rc;
+}
+
+
+RTDECL(int) RTSocketGetPeerAddress(RTSOCKET hSocket, PRTNETADDR pAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertReturn(RTMemPoolRefCount(pThis) >= (pThis->cUsers ? 2U : 1U), VERR_CALLER_NO_REFERENCE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfngetpeername, VERR_NET_NOT_UNSUPPORTED);
+# define getpeername g_pfngetpeername
+#endif
+
+    /*
+     * Get the address and convert it.
+     */
+    int             rc;
+    RTSOCKADDRUNION u;
+#ifdef RT_OS_WINDOWS
+    int             cbAddr = sizeof(u);
+#else
+    socklen_t       cbAddr = sizeof(u);
+#endif
+    RT_ZERO(u);
+    if (getpeername(pThis->hNative, &u.Addr, &cbAddr) == 0)
+        rc = rtSocketNetAddrFromAddr(&u, cbAddr, pAddr);
+    else
+        rc = rtSocketError();
+
+#ifdef RT_OS_WINDOWS
+# undef getpeername
+#endif
+    return rc;
+}
+
+
+
+/**
+ * Wrapper around bind.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   pAddr               The address to bind to.
+ */
+DECLHIDDEN(int) rtSocketBind(RTSOCKET hSocket, PCRTNETADDR pAddr)
+{
+    RTSOCKADDRUNION u;
+    int             cbAddr;
+    int rc = rtSocketAddrFromNetAddr(pAddr, &u, sizeof(u), &cbAddr);
+    if (RT_SUCCESS(rc))
+        rc = rtSocketBindRawAddr(hSocket, &u.Addr, cbAddr);
+    return rc;
+}
+
+
+/**
+ * Very thin wrapper around bind.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   pvAddr              The address to bind to (struct sockaddr and
+ *                              friends).
+ * @param   cbAddr              The size of the address.
+ */
+DECLHIDDEN(int) rtSocketBindRawAddr(RTSOCKET hSocket, void const *pvAddr, size_t cbAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+    AssertPtrReturn(pvAddr, VERR_INVALID_POINTER);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnbind, VERR_NET_NOT_UNSUPPORTED);
+# define bind g_pfnbind
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc;
+    if (bind(pThis->hNative, (struct sockaddr const *)pvAddr, (int)cbAddr) == 0)
+        rc = VINF_SUCCESS;
+    else
+        rc = rtSocketError();
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef bind
+#endif
+    return rc;
+}
+
+
+
+/**
+ * Wrapper around listen.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   cMaxPending         The max number of pending connections.
+ */
+DECLHIDDEN(int) rtSocketListen(RTSOCKET hSocket, int cMaxPending)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnlisten, VERR_NET_NOT_UNSUPPORTED);
+# define listen g_pfnlisten
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = VINF_SUCCESS;
+    if (listen(pThis->hNative, cMaxPending) != 0)
+        rc = rtSocketError();
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef listen
+#endif
+    return rc;
+}
+
+
+/**
+ * Wrapper around accept.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   phClient            Where to return the client socket handle on
+ *                              success.
+ * @param   pAddr               Where to return the client address.
+ * @param   pcbAddr             On input this gives the size buffer size of what
+ *                              @a pAddr point to.  On return this contains the
+ *                              size of what's stored at @a pAddr.
+ */
+DECLHIDDEN(int) rtSocketAccept(RTSOCKET hSocket, PRTSOCKET phClient, struct sockaddr *pAddr, size_t *pcbAddr)
+{
+    /*
+     * Validate input.
+     * Only lock the socket temporarily while we get the native handle, so that
+     * we can safely shutdown and destroy the socket from a different thread.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnaccept, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnclosesocket, VERR_NET_NOT_UNSUPPORTED);
+# define accept g_pfnaccept
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    /*
+     * Call accept().
+     */
+    rtSocketErrorReset();
+    int         rc      = VINF_SUCCESS;
+#ifdef RT_OS_WINDOWS
+    int         cbAddr  = (int)*pcbAddr;
+#else
+    socklen_t   cbAddr  = *pcbAddr;
+#endif
+    RTSOCKETNATIVE hNativeClient = accept(pThis->hNative, pAddr, &cbAddr);
+    if (hNativeClient != NIL_RTSOCKETNATIVE)
+    {
+        *pcbAddr = cbAddr;
+
+        /*
+         * Wrap the client socket.
+         */
+        rc = rtSocketCreateForNative(phClient, hNativeClient);
+        if (RT_FAILURE(rc))
+        {
+#ifdef RT_OS_WINDOWS
+            g_pfnclosesocket(hNativeClient);
+#else
+            close(hNativeClient);
+#endif
+        }
+    }
+    else
+        rc = rtSocketError();
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef accept
+#endif
+    return rc;
+}
+
+
+/**
+ * Wrapper around connect.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   pAddr               The socket address to connect to.
+ * @param   cMillies            Number of milliseconds to wait for the connect attempt to complete.
+ *                              Use RT_INDEFINITE_WAIT to wait for ever.
+ *                              Use RT_TCPCLIENTCONNECT_DEFAULT_WAIT to wait for the default time
+ *                              configured on the running system.
+ */
+DECLHIDDEN(int) rtSocketConnect(RTSOCKET hSocket, PCRTNETADDR pAddr, RTMSINTERVAL cMillies)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnconnect, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfnselect, VERR_NET_NOT_UNSUPPORTED);
+    AssertReturn(g_pfngetsockopt, VERR_NET_NOT_UNSUPPORTED);
+# define connect        g_pfnconnect
+# define select         g_pfnselect
+# define getsockopt     g_pfngetsockopt
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    RTSOCKADDRUNION u;
+    int             cbAddr;
+    int rc = rtSocketAddrFromNetAddr(pAddr, &u, sizeof(u), &cbAddr);
+    if (RT_SUCCESS(rc))
+    {
+        if (cMillies == RT_SOCKETCONNECT_DEFAULT_WAIT)
+        {
+            if (connect(pThis->hNative, &u.Addr, cbAddr) != 0)
+                rc = rtSocketError();
+        }
+        else
+        {
+            /*
+             * Switch the socket to nonblocking mode, initiate the connect
+             * and wait for the socket to become writable or until the timeout
+             * expires.
+             */
+            rc = rtSocketSwitchBlockingMode(pThis, false /* fBlocking */);
+            if (RT_SUCCESS(rc))
+            {
+                if (connect(pThis->hNative, &u.Addr, cbAddr) != 0)
+                {
+                    rc = rtSocketError();
+                    if (rc == VERR_TRY_AGAIN || rc == VERR_NET_IN_PROGRESS)
+                    {
+                        int rcSock = 0;
+                        fd_set FdSetWriteable;
+                        struct timeval TvTimeout;
+
+                        TvTimeout.tv_sec = cMillies / RT_MS_1SEC;
+                        TvTimeout.tv_usec = (cMillies % RT_MS_1SEC) * RT_US_1MS;
+
+                        FD_ZERO(&FdSetWriteable);
+                        FD_SET(pThis->hNative, &FdSetWriteable);
+                        do
+                        {
+                            rcSock = select(pThis->hNative + 1, NULL, &FdSetWriteable, NULL,
+                                              cMillies == RT_INDEFINITE_WAIT || cMillies >= INT_MAX
+                                            ? NULL
+                                            : &TvTimeout);
+                            if (rcSock > 0)
+                            {
+                                int iSockError = 0;
+                                socklen_t cbSockOpt = sizeof(iSockError);
+                                rcSock = getsockopt(pThis->hNative, SOL_SOCKET, SO_ERROR, (char *)&iSockError, &cbSockOpt);
+                                if (rcSock == 0)
+                                {
+                                    if (iSockError == 0)
+                                        rc = VINF_SUCCESS;
+                                    else
+                                    {
+#ifdef RT_OS_WINDOWS
+                                        rc = RTErrConvertFromWin32(iSockError);
+#else
+                                        rc = RTErrConvertFromErrno(iSockError);
+#endif
+                                    }
+                                }
+                                else
+                                    rc = rtSocketError();
+                            }
+                            else if (rcSock == 0)
+                                rc = VERR_TIMEOUT;
+                            else
+                                rc = rtSocketError();
+                        } while (rc == VERR_INTERRUPTED);
+                    }
+                }
+
+                rtSocketSwitchBlockingMode(pThis, true /* fBlocking */);
+            }
+        }
+    }
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef connect
+# undef select
+# undef getsockopt
+#endif
+    return rc;
+}
+
+
+/**
+ * Wrapper around connect, raw address, no timeout.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   pvAddr              The raw socket address to connect to.
+ * @param   cbAddr              The size of the raw address.
+ */
+DECLHIDDEN(int) rtSocketConnectRaw(RTSOCKET hSocket, void const *pvAddr, size_t cbAddr)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnconnect, VERR_NET_NOT_UNSUPPORTED);
+# define connect        g_pfnconnect
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc;
+    if (connect(pThis->hNative, (const struct sockaddr *)pvAddr, (int)cbAddr) == 0)
+        rc = VINF_SUCCESS;
+    else
+        rc = rtSocketError();
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef connect
+#endif
+    return rc;
+}
+
+
+/**
+ * Wrapper around setsockopt.
+ *
+ * @returns IPRT status code.
+ * @param   hSocket             The socket handle.
+ * @param   iLevel              The protocol level, e.g. IPPORTO_TCP.
+ * @param   iOption             The option, e.g. TCP_NODELAY.
+ * @param   pvValue             The value buffer.
+ * @param   cbValue             The size of the value pointed to by pvValue.
+ */
+DECLHIDDEN(int) rtSocketSetOpt(RTSOCKET hSocket, int iLevel, int iOption, void const *pvValue, int cbValue)
+{
+    /*
+     * Validate input.
+     */
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(g_pfnsetsockopt, VERR_NET_NOT_UNSUPPORTED);
+# define setsockopt g_pfnsetsockopt
+#endif
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = VINF_SUCCESS;
+    if (setsockopt(pThis->hNative, iLevel, iOption, (const char *)pvValue, cbValue) != 0)
+        rc = rtSocketError();
+
+    rtSocketUnlock(pThis);
+#ifdef RT_OS_WINDOWS
+# undef setsockopt
+#endif
+    return rc;
+}
+
+
+/**
+ * Internal RTPollSetAdd helper that returns the handle that should be added to
+ * the pollset.
+ *
+ * @returns Valid handle on success, INVALID_HANDLE_VALUE on failure.
+ * @param   hSocket             The socket handle.
+ * @param   fEvents             The events we're polling for.
+ * @param   phNative            Where to put the primary handle.
+ */
+DECLHIDDEN(int) rtSocketPollGetHandle(RTSOCKET hSocket, uint32_t fEvents, PRTHCINTPTR phNative)
+{
+    RTSOCKETINT *pThis = hSocket;
+    RT_NOREF_PV(fEvents);
+    AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, VERR_INVALID_HANDLE);
+#ifdef RT_OS_WINDOWS
+    AssertReturn(rtSocketTryLock(pThis), VERR_CONCURRENT_ACCESS);
+
+    int rc = VINF_SUCCESS;
+    if (pThis->hEvent != WSA_INVALID_EVENT)
+        *phNative = (RTHCINTPTR)pThis->hEvent;
+    else if (g_pfnWSACreateEvent)
+    {
+        pThis->hEvent = g_pfnWSACreateEvent();
+        *phNative = (RTHCINTPTR)pThis->hEvent;
+        if (pThis->hEvent == WSA_INVALID_EVENT)
+            rc = rtSocketError();
+    }
+    else
+    {
+        AssertCompile(WSA_INVALID_EVENT == (WSAEVENT)NULL);
+        pThis->hEvent = CreateEventW(NULL, TRUE /*fManualReset*/, FALSE /*fInitialState*/,  NULL /*pwszName*/);
+        *phNative = (RTHCINTPTR)pThis->hEvent;
+        if (pThis->hEvent == WSA_INVALID_EVENT)
+            rc = RTErrConvertFromWin32(GetLastError());
+    }
+
+    rtSocketUnlock(pThis);
+    return rc;
+
+#else  /* !RT_OS_WINDOWS */
+    *phNative = (RTHCUINTPTR)pThis->hNative;
+    return VINF_SUCCESS;
+#endif /* !RT_OS_WINDOWS */
+}
+
+#ifdef RT_OS_WINDOWS
+
+/**
+ * Fallback poller thread.
+ *
+ * @returns VINF_SUCCESS.
+ * @param   hSelf               The thread handle.
+ * @param   pvUser              Socket instance data.
+ */
+static DECLCALLBACK(int) rtSocketPollFallbackThreadProc(RTTHREAD hSelf, void *pvUser)
+{
+    RTSOCKETINT *pThis = (RTSOCKETINT *)pvUser;
+    RT_NOREF(hSelf);
+# define __WSAFDIsSet g_pfn__WSAFDIsSet
+
+    /*
+     * The execution loop.
+     */
+    while (!ASMAtomicReadBool(&pThis->fPollFallbackShutdown))
+    {
+        /*
+         * Do the selecting (with a 15 second timeout because that seems like a good idea).
+         */
+        struct fd_set SetRead;
+        struct fd_set SetWrite;
+        struct fd_set SetXcpt;
+
+        FD_ZERO(&SetRead);
+        FD_ZERO(&SetWrite);
+        FD_ZERO(&SetXcpt);
+
+        FD_SET(pThis->hPollFallbackNotifyR, &SetRead);
+        FD_SET(pThis->hPollFallbackNotifyR, &SetXcpt);
+
+        bool     fActive = ASMAtomicReadBool(&pThis->fPollFallbackActive);
+        uint32_t fEvents;
+        if (!fActive)
+            fEvents = 0;
+        else
+        {
+            fEvents = ASMAtomicReadU32(&pThis->fSubscribedEvts);
+            if (fEvents & RTPOLL_EVT_READ)
+                FD_SET(pThis->hNative, &SetRead);
+            if (fEvents & RTPOLL_EVT_WRITE)
+                FD_SET(pThis->hNative, &SetWrite);
+            if (fEvents & RTPOLL_EVT_ERROR)
+                FD_SET(pThis->hNative, &SetXcpt);
+        }
+
+        struct timeval Timeout;
+        Timeout.tv_sec  = 15;
+        Timeout.tv_usec = 0;
+        int rc = g_pfnselect(INT_MAX /*ignored*/, &SetRead, &SetWrite, &SetXcpt, &Timeout);
+
+        /* Stop immediately if told to shut down. */
+        if (ASMAtomicReadBool(&pThis->fPollFallbackShutdown))
+            break;
+
+        /*
+         * Process the result.
+         */
+        if (rc > 0)
+        {
+            /* First the socket we're listening on. */
+            if (   fEvents
+                && (   FD_ISSET(pThis->hNative, &SetRead)
+                    || FD_ISSET(pThis->hNative, &SetWrite)
+                    || FD_ISSET(pThis->hNative, &SetXcpt)) )
+            {
+                ASMAtomicWriteBool(&pThis->fPollFallbackActive, false);
+                SetEvent(pThis->hEvent);
+            }
+
+            /* Then maintain the notification pipe.  (We only read one byte here
+               because we're overly paranoid wrt socket switching to blocking mode.) */
+            if (FD_ISSET(pThis->hPollFallbackNotifyR, &SetRead))
+            {
+                char chIgnored;
+                g_pfnrecv(pThis->hPollFallbackNotifyR, &chIgnored, sizeof(chIgnored), MSG_NOSIGNAL);
+            }
+        }
+        else
+            AssertMsg(rc == 0, ("%Rrc\n", rtSocketError()));
+    }
+
+# undef __WSAFDIsSet
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Pokes the fallback thread, making sure it gets out of whatever it's stuck in.
+ *
+ * @param   pThis               The socket handle.
+ */
+static void rtSocketPokePollFallbackThread(RTSOCKETINT *pThis)
+{
+    Assert(pThis->fPollFallback);
+    if (pThis->hPollFallbackThread != NIL_RTTHREAD)
+    {
+        int cbWritten = g_pfnsend(pThis->hPollFallbackNotifyW, "!", 1, MSG_NOSIGNAL);
+        AssertMsg(cbWritten == 1, ("cbWritten=%d err=%Rrc\n",  rtSocketError()));
+        RT_NOREF_PV(cbWritten);
+    }
+}
+
+
+/**
+ * Called by rtSocketPollStart to make the thread start selecting on the socket.
+ *
+ * @returns 0 on success, RTPOLL_EVT_ERROR on failure.
+ * @param   pThis               The socket handle.
+ */
+static uint32_t rtSocketPollFallbackStart(RTSOCKETINT *pThis)
+{
+    /*
+     * Reset the event and tell the thread to start selecting on the socket.
+     */
+    ResetEvent(pThis->hEvent);
+    ASMAtomicWriteBool(&pThis->fPollFallbackActive, true);
+
+    /*
+     * Wake up the thread the thread.
+     */
+    if (pThis->hPollFallbackThread != NIL_RTTHREAD)
+        rtSocketPokePollFallbackThread(pThis);
+    else
+    {
+        /*
+         * Not running, need to set it up and start it.
+         */
+        AssertLogRelReturn(pThis->hEvent != NULL && pThis->hEvent != INVALID_HANDLE_VALUE, RTPOLL_EVT_ERROR);
+
+        /* Create the notification socket pair. */
+        int rc;
+        if (pThis->hPollFallbackNotifyR == NIL_RTSOCKETNATIVE)
+        {
+            rc = rtSocketCreateNativeTcpPair(&pThis->hPollFallbackNotifyW, &pThis->hPollFallbackNotifyR);
+            AssertLogRelRCReturn(rc, RTPOLL_EVT_ERROR);
+
+            /* Make the read end non-blocking (not fatal). */
+            u_long fNonBlocking = 1;
+            rc = g_pfnioctlsocket(pThis->hPollFallbackNotifyR, FIONBIO, &fNonBlocking);
+            AssertLogRelMsg(rc == 0,  ("rc=%#x %Rrc\n", rc, rtSocketError()));
+        }
+
+        /* Finally, start the thread.  ASSUME we don't need too much stack. */
+        rc = RTThreadCreate(&pThis->hPollFallbackThread, rtSocketPollFallbackThreadProc, pThis,
+                            _128K, RTTHREADTYPE_IO, RTTHREADFLAGS_WAITABLE, "sockpoll");
+        AssertLogRelRCReturn(rc, RTPOLL_EVT_ERROR);
+    }
+    return 0;
+}
+
+
+/**
+ * Undos the harm done by WSAEventSelect.
+ *
+ * @returns IPRT status code.
+ * @param   pThis               The socket handle.
+ */
+static int rtSocketPollClearEventAndRestoreBlocking(RTSOCKETINT *pThis)
+{
+    int rc = VINF_SUCCESS;
+    if (pThis->fSubscribedEvts)
+    {
+        if (!pThis->fPollFallback)
+        {
+            Assert(g_pfnWSAEventSelect && g_pfnioctlsocket);
+            if (g_pfnWSAEventSelect && g_pfnioctlsocket)
+            {
+                if (g_pfnWSAEventSelect(pThis->hNative, WSA_INVALID_EVENT, 0) == 0)
+                {
+                    pThis->fSubscribedEvts = 0;
+
+                    /*
+                     * Switch back to blocking mode if that was the state before the
+                     * operation.
+                     */
+                    if (pThis->fBlocking)
+                    {
+                        u_long fNonBlocking = 0;
+                        int rc2 = g_pfnioctlsocket(pThis->hNative, FIONBIO, &fNonBlocking);
+                        if (rc2 != 0)
+                        {
+                            rc = rtSocketError();
+                            AssertMsgFailed(("%Rrc; rc2=%d\n", rc, rc2));
+                        }
+                    }
+                }
+                else
+                {
+                    rc = rtSocketError();
+                    AssertMsgFailed(("%Rrc\n", rc));
+                }
+            }
+            else
+            {
+                Assert(pThis->fPollFallback);
+                rc = VINF_SUCCESS;
+            }
+        }
+        /*
+         * Just clear the event mask as we never started waiting if we get here.
+         */
+        else
+            ASMAtomicWriteU32(&pThis->fSubscribedEvts, 0);
+    }
+    return rc;
+}
+
+
+/**
+ * Updates the mask of events we're subscribing to.
+ *
+ * @returns IPRT status code.
+ * @param   pThis               The socket handle.
+ * @param   fEvents             The events we want to subscribe to.
+ */
+static int rtSocketPollUpdateEvents(RTSOCKETINT *pThis, uint32_t fEvents)
+{
+    if (!pThis->fPollFallback)
+    {
+        LONG fNetworkEvents = 0;
+        if (fEvents & RTPOLL_EVT_READ)
+            fNetworkEvents |= FD_READ;
+        if (fEvents & RTPOLL_EVT_WRITE)
+            fNetworkEvents |= FD_WRITE;
+        if (fEvents & RTPOLL_EVT_ERROR)
+            fNetworkEvents |= FD_CLOSE;
+        LogFlowFunc(("fNetworkEvents=%#x\n", fNetworkEvents));
+
+        if (g_pfnWSAEventSelect(pThis->hNative, pThis->hEvent, fNetworkEvents) == 0)
+        {
+            pThis->fSubscribedEvts = fEvents;
+            return VINF_SUCCESS;
+        }
+
+        int rc = rtSocketError();
+        AssertMsgFailed(("fNetworkEvents=%#x rc=%Rrc\n", fNetworkEvents, rtSocketError()));
+        return rc;
+    }
+
+    /*
+     * Update the events we're waiting for.  Caller will poke/start the thread. later
+     */
+    ASMAtomicWriteU32(&pThis->fSubscribedEvts, fEvents);
+    return VINF_SUCCESS;
+}
+
+#endif  /* RT_OS_WINDOWS */
+
+
+#if defined(RT_OS_WINDOWS) || defined(RT_OS_OS2)
+
+/**
+ * Checks for pending events.
+ *
+ * @returns Event mask or 0.
+ * @param   pThis               The socket handle.
+ * @param   fEvents             The desired events.
+ */
+static uint32_t rtSocketPollCheck(RTSOCKETINT *pThis, uint32_t fEvents)
+{
+    uint32_t fRetEvents = 0;
+
+    LogFlowFunc(("pThis=%#p fEvents=%#x\n", pThis, fEvents));
+
+# ifdef RT_OS_WINDOWS
+    /* Make sure WSAEnumNetworkEvents returns what we want. */
+    int rc = VINF_SUCCESS;
+    if ((pThis->fSubscribedEvts & fEvents) != fEvents)
+        rc = rtSocketPollUpdateEvents(pThis, pThis->fSubscribedEvts | fEvents);
+
+    if (!pThis->fPollFallback)
+    {
+        /* Atomically get pending events and reset the event semaphore. */
+        Assert(g_pfnWSAEnumNetworkEvents);
+        WSANETWORKEVENTS NetEvts;
+        RT_ZERO(NetEvts);
+        if (g_pfnWSAEnumNetworkEvents(pThis->hNative, pThis->hEvent, &NetEvts) == 0)
+        {
+            if (   (NetEvts.lNetworkEvents & FD_READ)
+                && NetEvts.iErrorCode[FD_READ_BIT] == 0)
+                fRetEvents |= RTPOLL_EVT_READ;
+
+            if (   (NetEvts.lNetworkEvents & FD_WRITE)
+                && NetEvts.iErrorCode[FD_WRITE_BIT] == 0)
+                fRetEvents |= RTPOLL_EVT_WRITE;
+
+            if (NetEvts.lNetworkEvents & FD_CLOSE)
+                fRetEvents |= RTPOLL_EVT_ERROR;
+            else
+                for (uint32_t i = 0; i < FD_MAX_EVENTS; i++)
+                    if (   (NetEvts.lNetworkEvents & (1L << i))
+                        && NetEvts.iErrorCode[i] != 0)
+                        fRetEvents |= RTPOLL_EVT_ERROR;
+
+            pThis->fEventsSaved = fRetEvents |= pThis->fEventsSaved;
+            fRetEvents &= fEvents | RTPOLL_EVT_ERROR;
+        }
+        else
+            rc = rtSocketError();
+    }
+
+    /* Fall back on select if we hit an error above or is using fallback polling. */
+    if (pThis->fPollFallback || RT_FAILURE(rc))
+    {
+        rc = rtSocketSelectOneEx(pThis, fEvents & RTPOLL_EVT_ERROR ? fEvents | RTPOLL_EVT_READ : fEvents, &fRetEvents, 0);
+        if (RT_SUCCESS(rc))
+        {
+            /* rtSocketSelectOneEx may return RTPOLL_EVT_READ on disconnect.  Use
+               getpeername to fix this. */
+            if ((fRetEvents & (RTPOLL_EVT_READ | RTPOLL_EVT_ERROR)) == RTPOLL_EVT_READ)
+            {
+# if 0 /* doens't work */
+                rtSocketErrorReset();
+                char chIgn;
+                rc = g_pfnrecv(pThis->hNative, &chIgn, 0, MSG_NOSIGNAL);
+                rc = rtSocketError();
+                if (RT_FAILURE(rc))
+                    fRetEvents |= RTPOLL_EVT_ERROR;
+
+                rc = g_pfnsend(pThis->hNative, &chIgn, 0, MSG_NOSIGNAL);
+                rc = rtSocketError();
+                if (RT_FAILURE(rc))
+                    fRetEvents |= RTPOLL_EVT_ERROR;
+
+                RTSOCKADDRUNION u;
+                int cbAddr = sizeof(u);
+                if (g_pfngetpeername(pThis->hNative, &u.Addr, &cbAddr) == SOCKET_ERROR)
+                    fRetEvents |= RTPOLL_EVT_ERROR;
+# endif
+                /* If no bytes are available, assume error condition. */
+                u_long cbAvail = 0;
+                rc = g_pfnioctlsocket(pThis->hNative, FIONREAD, &cbAvail);
+                if (rc == 0 && cbAvail == 0)
+                    fRetEvents |= RTPOLL_EVT_ERROR;
+            }
+            fRetEvents &= fEvents | RTPOLL_EVT_ERROR;
+        }
+        else if (rc == VERR_TIMEOUT)
+            fRetEvents = 0;
+        else
+            fRetEvents |= RTPOLL_EVT_ERROR;
+    }
+
+# else  /* RT_OS_OS2 */
+    int aFds[4] = { pThis->hNative, pThis->hNative, pThis->hNative, -1 };
+    int rc = os2_select(aFds, 1, 1, 1, 0);
+    if (rc > 0)
+    {
+        if (aFds[0] == pThis->hNative)
+            fRetEvents |= RTPOLL_EVT_READ;
+        if (aFds[1] == pThis->hNative)
+            fRetEvents |= RTPOLL_EVT_WRITE;
+        if (aFds[2] == pThis->hNative)
+            fRetEvents |= RTPOLL_EVT_ERROR;
+        fRetEvents &= fEvents;
+    }
+# endif /* RT_OS_OS2 */
+
+    LogFlowFunc(("fRetEvents=%#x\n", fRetEvents));
+    return fRetEvents;
+}
+
+
+/**
+ * Internal RTPoll helper that polls the socket handle and, if @a fNoWait is
+ * clear, starts whatever actions we've got running during the poll call.
+ *
+ * @returns 0 if no pending events, actions initiated if @a fNoWait is clear.
+ *          Event mask (in @a fEvents) and no actions if the handle is ready
+ *          already.
+ *          UINT32_MAX (asserted) if the socket handle is busy in I/O or a
+ *          different poll set.
+ *
+ * @param   hSocket             The socket handle.
+ * @param   hPollSet            The poll set handle (for access checks).
+ * @param   fEvents             The events we're polling for.
+ * @param   fFinalEntry         Set if this is the final entry for this handle
+ *                              in this poll set.  This can be used for dealing
+ *                              with duplicate entries.
+ * @param   fNoWait             Set if it's a zero-wait poll call.  Clear if
+ *                              we'll wait for an event to occur.
+ *
+ * @remarks There is a potential race wrt duplicate handles when @a fNoWait is
+ *          @c true, we don't currently care about that oddity...
+ */
+DECLHIDDEN(uint32_t) rtSocketPollStart(RTSOCKET hSocket, RTPOLLSET hPollSet, uint32_t fEvents, bool fFinalEntry, bool fNoWait)
+{
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, UINT32_MAX);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, UINT32_MAX);
+    /** @todo This isn't quite sane. Replace by critsect and open up concurrent
+     *        reads and writes! */
+    if (rtSocketTryLock(pThis))
+        pThis->hPollSet = hPollSet;
+    else
+    {
+        AssertReturn(pThis->hPollSet == hPollSet, UINT32_MAX);
+        ASMAtomicIncU32(&pThis->cUsers);
+    }
+
+    /* (rtSocketPollCheck will reset the event object). */
+# ifdef RT_OS_WINDOWS
+    uint32_t fRetEvents = pThis->fEventsSaved;
+    pThis->fEventsSaved = 0; /* Reset */
+    fRetEvents |= rtSocketPollCheck(pThis, fEvents);
+
+    if (   !fRetEvents
+        && !fNoWait)
+    {
+        pThis->fPollEvts |= fEvents;
+        if (fFinalEntry)
+        {
+            if (pThis->fSubscribedEvts != pThis->fPollEvts)
+            {
+                /** @todo seems like there might be a call to many here and that fPollEvts is
+                 *        totally unnecessary... (bird) */
+                int rc = rtSocketPollUpdateEvents(pThis, pThis->fPollEvts);
+                if (RT_FAILURE(rc))
+                {
+                    pThis->fPollEvts = 0;
+                    fRetEvents       = UINT32_MAX;
+                }
+            }
+
+            /* Make sure we don't block when there are events pending relevant to an earlier poll set entry. */
+            if (pThis->fEventsSaved && !pThis->fPollFallback && g_pfnWSASetEvent && fRetEvents == 0)
+                g_pfnWSASetEvent(pThis->hEvent);
+        }
+    }
+# else
+    uint32_t fRetEvents = rtSocketPollCheck(pThis, fEvents);
+# endif
+
+    if (fRetEvents || fNoWait)
+    {
+        if (pThis->cUsers == 1)
+        {
+# ifdef RT_OS_WINDOWS
+            pThis->fEventsSaved    &= RTPOLL_EVT_ERROR;
+            pThis->fHarvestedEvents = false;
+            rtSocketPollClearEventAndRestoreBlocking(pThis);
+# endif
+            pThis->hPollSet = NIL_RTPOLLSET;
+        }
+# ifdef RT_OS_WINDOWS
+        else
+            pThis->fHarvestedEvents = true;
+# endif
+        ASMAtomicDecU32(&pThis->cUsers);
+    }
+# ifdef RT_OS_WINDOWS
+    /*
+     * Kick the poller thread on if this is the final entry and we're in
+     * winsock 1.x fallback mode.
+     */
+    else if (pThis->fPollFallback && fFinalEntry)
+        fRetEvents = rtSocketPollFallbackStart(pThis);
+# endif
+
+    return fRetEvents;
+}
+
+
+/**
+ * Called after a WaitForMultipleObjects returned in order to check for pending
+ * events and stop whatever actions that rtSocketPollStart() initiated.
+ *
+ * @returns Event mask or 0.
+ *
+ * @param   hSocket             The socket handle.
+ * @param   fEvents             The events we're polling for.
+ * @param   fFinalEntry         Set if this is the final entry for this handle
+ *                              in this poll set.  This can be used for dealing
+ *                              with duplicate entries.  Only keep in mind that
+ *                              this method is called in reverse order, so the
+ *                              first call will have this set (when the entire
+ *                              set was processed).
+ * @param   fHarvestEvents      Set if we should check for pending events.
+ */
+DECLHIDDEN(uint32_t) rtSocketPollDone(RTSOCKET hSocket, uint32_t fEvents, bool fFinalEntry, bool fHarvestEvents)
+{
+    RTSOCKETINT *pThis = hSocket;
+    AssertPtrReturn(pThis, 0);
+    AssertReturn(pThis->u32Magic == RTSOCKET_MAGIC, 0);
+    Assert(pThis->cUsers > 0);
+    Assert(pThis->hPollSet != NIL_RTPOLLSET);
+    RT_NOREF_PV(fFinalEntry);
+
+# ifdef RT_OS_WINDOWS
+    /*
+     * Deactivate the poll thread if we're in winsock 1.x fallback poll mode.
+     */
+    if (   pThis->fPollFallback
+        && pThis->hPollFallbackThread != NIL_RTTHREAD)
+    {
+        ASMAtomicWriteU32(&pThis->fSubscribedEvts, 0);
+        if (ASMAtomicXchgBool(&pThis->fPollFallbackActive, false))
+            rtSocketPokePollFallbackThread(pThis);
+    }
+# endif
+
+    /*
+     * Harvest events and clear the event mask for the next round of polling.
+     */
+    uint32_t fRetEvents;
+# ifdef RT_OS_WINDOWS
+    if (!pThis->fPollFallback)
+    {
+        if (!pThis->fHarvestedEvents)
+        {
+            fRetEvents = rtSocketPollCheck(pThis, fEvents);
+            pThis->fHarvestedEvents = true;
+        }
+        else
+            fRetEvents = pThis->fEventsSaved;
+        if (fHarvestEvents)
+            fRetEvents &= fEvents;
+        else
+            fRetEvents = 0;
+        pThis->fPollEvts = 0;
+    }
+    else
+# endif
+    {
+        if (fHarvestEvents)
+            fRetEvents = rtSocketPollCheck(pThis, fEvents);
+        else
+            fRetEvents = 0;
+    }
+
+    /*
+     * Make the socket blocking again and unlock the handle.
+     */
+    if (pThis->cUsers == 1)
+    {
+# ifdef RT_OS_WINDOWS
+        pThis->fEventsSaved    &= RTPOLL_EVT_ERROR;
+        pThis->fHarvestedEvents = false;
+        rtSocketPollClearEventAndRestoreBlocking(pThis);
+# endif
+        pThis->hPollSet = NIL_RTPOLLSET;
+    }
+    ASMAtomicDecU32(&pThis->cUsers);
+    return fRetEvents;
+}
+
+#endif /* RT_OS_WINDOWS || RT_OS_OS2 */
+