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tclWinSock.c

/*
 * tclWinSock.c --
 *
 *    This file contains Windows-specific socket related code.
 *
 * Copyright (c) 1995-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclWinSock.c,v 1.61 2007/12/13 15:28:44 dgp Exp $
 */

#include "tclWinInt.h"

/*
 * Support for control over sockets' KEEPALIVE and NODELAY behavior is
 * currently disabled.
 */

#undef TCL_FEATURE_KEEPALIVE_NAGLE

/*
 * Make sure to remove the redirection defines set in tclWinPort.h that is in
 * use in other sections of the core, except for us.
 */

#undef getservbyname
#undef getsockopt
#undef ntohs
#undef setsockopt

/*
 * The following variable is used to tell whether this module has been
 * initialized.  If 1, initialization of sockets was successful, if -1 then
 * socket initialization failed (WSAStartup failed).
 */

static int initialized = 0;
TCL_DECLARE_MUTEX(socketMutex)

/*
 * The following variable holds the network name of this host.
 */

static TclInitProcessGlobalValueProc InitializeHostName;
static ProcessGlobalValue hostName = {
    0, 0, NULL, NULL, InitializeHostName, NULL, NULL
};

/*
 * The following defines declare the messages used on socket windows.
 */

#define SOCKET_MESSAGE      WM_USER+1
#define SOCKET_SELECT       WM_USER+2
#define SOCKET_TERMINATE    WM_USER+3
#define SELECT              TRUE
#define UNSELECT      FALSE

/*
 * The following structure is used to store the data associated with each
 * socket.
 */

typedef struct SocketInfo {
    Tcl_Channel channel;      /* Channel associated with this socket. */
    SOCKET socket;            /* Windows SOCKET handle. */
    int flags;                /* Bit field comprised of the flags described
                         * below. */
    int watchEvents;          /* OR'ed combination of FD_READ, FD_WRITE,
                         * FD_CLOSE, FD_ACCEPT and FD_CONNECT that
                         * indicate which events are interesting. */
    int readyEvents;          /* OR'ed combination of FD_READ, FD_WRITE,
                         * FD_CLOSE, FD_ACCEPT and FD_CONNECT that
                         * indicate which events have occurred. */
    int selectEvents;         /* OR'ed combination of FD_READ, FD_WRITE,
                         * FD_CLOSE, FD_ACCEPT and FD_CONNECT that
                         * indicate which events are currently being
                         * selected. */
    int acceptEventCount;     /* Count of the current number of FD_ACCEPTs
                         * that have arrived and not yet processed. */
    Tcl_TcpAcceptProc *acceptProc;
                        /* Proc to call on accept. */
    ClientData acceptProcData;      /* The data for the accept proc. */
    int lastError;            /* Error code from last message. */
    struct SocketInfo *nextPtr;     /* The next socket on the per-thread socket
                         * list. */
} SocketInfo;

/*
 * The following structure is what is added to the Tcl event queue when a
 * socket event occurs.
 */

typedef struct SocketEvent {
    Tcl_Event header;         /* Information that is standard for all
                         * events. */
    SOCKET socket;            /* Socket descriptor that is ready. Used to
                         * find the SocketInfo structure for the file
                         * (can't point directly to the SocketInfo
                         * structure because it could go away while
                         * the event is queued). */
} SocketEvent;

/*
 * This defines the minimum buffersize maintained by the kernel.
 */

#define TCP_BUFFER_SIZE 4096

/*
 * The following macros may be used to set the flags field of a SocketInfo
 * structure.
 */

#define SOCKET_ASYNC          (1<<0)      /* The socket is in blocking mode. */
#define SOCKET_EOF            (1<<1)      /* A zero read happened on the
                               * socket. */
#define SOCKET_ASYNC_CONNECT  (1<<2)      /* This socket uses async connect. */
#define SOCKET_PENDING        (1<<3)      /* A message has been sent for this
                               * socket */

typedef struct ThreadSpecificData {
    HWND hwnd;                /* Handle to window for socket messages. */
    HANDLE socketThread;      /* Thread handling the window */
    Tcl_ThreadId threadId;    /* Parent thread. */
    HANDLE readyEvent;        /* Event indicating that a socket event is
                         * ready. Also used to indicate that the
                         * socketThread has been initialized and has
                         * started. */
    HANDLE socketListLock;    /* Win32 Event to lock the socketList */
    SocketInfo *socketList;   /* Every open socket in this thread has an
                         * entry on this list. */
} ThreadSpecificData;

static Tcl_ThreadDataKey dataKey;
static WNDCLASS windowClass;

/*
 * Static functions defined in this file.
 */

static SocketInfo *     CreateSocket(Tcl_Interp *interp, int port,
                      const char *host, int server, const char *myaddr,
                      int myport, int async);
static int        CreateSocketAddress(LPSOCKADDR_IN sockaddrPtr,
                      const char *host, int port);
static void       InitSockets(void);
static SocketInfo *     NewSocketInfo(SOCKET socket);
static void       SocketExitHandler(ClientData clientData);
static LRESULT CALLBACK SocketProc(HWND hwnd, UINT message, WPARAM wParam,
                      LPARAM lParam);
static int        SocketsEnabled(void);
static void       TcpAccept(SocketInfo *infoPtr);
static int        WaitForSocketEvent(SocketInfo *infoPtr, int events,
                      int *errorCodePtr);
static DWORD WINAPI     SocketThread(LPVOID arg);
static void       TcpThreadActionProc(ClientData instanceData,
                      int action);

static Tcl_EventCheckProc     SocketCheckProc;
static Tcl_EventProc          SocketEventProc;
static Tcl_EventSetupProc     SocketSetupProc;
static Tcl_DriverBlockModeProc      TcpBlockProc;
static Tcl_DriverCloseProc    TcpCloseProc;
static Tcl_DriverSetOptionProc      TcpSetOptionProc;
static Tcl_DriverGetOptionProc      TcpGetOptionProc;
static Tcl_DriverInputProc    TcpInputProc;
static Tcl_DriverOutputProc   TcpOutputProc;
static Tcl_DriverWatchProc    TcpWatchProc;
static Tcl_DriverGetHandleProc      TcpGetHandleProc;

/*
 * This structure describes the channel type structure for TCP socket
 * based IO.
 */

static Tcl_ChannelType tcpChannelType = {
    "tcp",            /* Type name. */
    TCL_CHANNEL_VERSION_5,  /* v5 channel */
    TcpCloseProc,     /* Close proc. */
    TcpInputProc,     /* Input proc. */
    TcpOutputProc,          /* Output proc. */
    NULL,             /* Seek proc. */
    TcpSetOptionProc,       /* Set option proc. */
    TcpGetOptionProc,       /* Get option proc. */
    TcpWatchProc,     /* Set up notifier to watch this channel. */
    TcpGetHandleProc,       /* Get an OS handle from channel. */
    NULL,             /* close2proc. */
    TcpBlockProc,     /* Set socket into (non-)blocking mode. */
    NULL,             /* flush proc. */
    NULL,             /* handler proc. */
    NULL,             /* wide seek proc */
    TcpThreadActionProc,    /* thread action proc */
    NULL,             /* truncate */
};

/*
 *----------------------------------------------------------------------
 *
 * InitSockets --
 *
 *    Initialize the socket module.  If winsock startup is successful,
 *    registers the event window for the socket notifier code.
 *
 *    Assumes socketMutex is held.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Initializes winsock, registers a new window class and creates a
 *    window for use in asynchronous socket notification.
 *
 *----------------------------------------------------------------------
 */

static void
InitSockets(void)
{
    DWORD id;
    WSADATA wsaData;
    DWORD err;
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
          TclThreadDataKeyGet(&dataKey);

    if (!initialized) {
      initialized = 1;
      Tcl_CreateExitHandler(SocketExitHandler, (ClientData) NULL);

      /*
       * Create the async notification window with a new class. We must
       * create a new class to avoid a Windows 95 bug that causes us to get
       * the wrong message number for socket events if the message window is
       * a subclass of a static control.
       */

      windowClass.style = 0;
      windowClass.cbClsExtra = 0;
      windowClass.cbWndExtra = 0;
      windowClass.hInstance = TclWinGetTclInstance();
      windowClass.hbrBackground = NULL;
      windowClass.lpszMenuName = NULL;
      windowClass.lpszClassName = "TclSocket";
      windowClass.lpfnWndProc = SocketProc;
      windowClass.hIcon = NULL;
      windowClass.hCursor = NULL;

      if (!RegisterClassA(&windowClass)) {
          TclWinConvertError(GetLastError());
          goto initFailure;
      }

      /*
       * Initialize the winsock library and check the interface version
       * actually loaded. We only ask for the 1.1 interface and do require
       * that it not be less than 1.1.
       */

#define WSA_VERSION_MAJOR 1
#define WSA_VERSION_MINOR 1
#define WSA_VERSION_REQD  MAKEWORD(WSA_VERSION_MAJOR, WSA_VERSION_MINOR)

      err = WSAStartup((WORD)WSA_VERSION_REQD, &wsaData);
      if (err != 0) {
          TclWinConvertWSAError(err);
          goto initFailure;
      }

      /*
       * Note the byte positions are swapped for the comparison, so that
       * 0x0002 (2.0, MAKEWORD(2,0)) doesn't look less than 0x0101 (1.1).
       * We want the comparison to be 0x0200 < 0x0101.
       */

      if (MAKEWORD(HIBYTE(wsaData.wVersion), LOBYTE(wsaData.wVersion))
            < MAKEWORD(WSA_VERSION_MINOR, WSA_VERSION_MAJOR)) {
          TclWinConvertWSAError(WSAVERNOTSUPPORTED);
          WSACleanup();
          goto initFailure;
      }

#undef WSA_VERSION_REQD
#undef WSA_VERSION_MAJOR
#undef WSA_VERSION_MINOR
    }

    /*
     * Check for per-thread initialization.
     */

    if (tsdPtr == NULL) {
      tsdPtr = TCL_TSD_INIT(&dataKey);
      tsdPtr->socketList = NULL;
      tsdPtr->hwnd       = NULL;
      tsdPtr->threadId   = Tcl_GetCurrentThread();
      tsdPtr->readyEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
      if (tsdPtr->readyEvent == NULL) {
          goto initFailure;
      }
      tsdPtr->socketListLock = CreateEvent(NULL, FALSE, TRUE, NULL);
      if (tsdPtr->socketListLock == NULL) {
          goto initFailure;
      }
      tsdPtr->socketThread = CreateThread(NULL, 256, SocketThread, tsdPtr,
            0, &id);
      if (tsdPtr->socketThread == NULL) {
          goto initFailure;
      }

      SetThreadPriority(tsdPtr->socketThread, THREAD_PRIORITY_HIGHEST);

      /*
       * Wait for the thread to signal when the window has been created and
       * if it is ready to go.
       */

      WaitForSingleObject(tsdPtr->readyEvent, INFINITE);

      if (tsdPtr->hwnd == NULL) {
          goto initFailure; /* Trouble creating the window */
      }

      Tcl_CreateEventSource(SocketSetupProc, SocketCheckProc, NULL);
    }
    return;

  initFailure:
    TclpFinalizeSockets();
    initialized = -1;
    return;
}

/*
 *----------------------------------------------------------------------
 *
 * SocketsEnabled --
 *
 *    Check that the WinSock was successfully initialized.
 *
 * Results:
 *    1 if it is.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

    /* ARGSUSED */
static int
SocketsEnabled(void)
{
    int enabled;
    Tcl_MutexLock(&socketMutex);
    enabled = (initialized == 1);
    Tcl_MutexUnlock(&socketMutex);
    return enabled;
}


/*
 *----------------------------------------------------------------------
 *
 * SocketExitHandler --
 *
 *    Callback invoked during exit clean up to delete the socket
 *    communication window and to release the WinSock DLL.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

    /* ARGSUSED */
static void
SocketExitHandler(
    ClientData clientData)          /* Not used. */
{
    Tcl_MutexLock(&socketMutex);
    /*
     * Make sure the socket event handling window is cleaned-up for, at
     * most, this thread.
     */

    TclpFinalizeSockets();
    UnregisterClass("TclSocket", TclWinGetTclInstance());
    WSACleanup();
    initialized = 0;
    Tcl_MutexUnlock(&socketMutex);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpFinalizeSockets --
 *
 *    This function is called from Tcl_FinalizeThread to finalize the
 *    platform specific socket subsystem. Also, it may be called from within
 *    this module to cleanup the state if unable to initialize the sockets
 *    subsystem.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Deletes the event source and destroys the socket thread.
 *
 *----------------------------------------------------------------------
 */

void
TclpFinalizeSockets(void)
{
    ThreadSpecificData *tsdPtr;

    tsdPtr = (ThreadSpecificData *) TclThreadDataKeyGet(&dataKey);
    if (tsdPtr != NULL) {
      if (tsdPtr->socketThread != NULL) {
          if (tsdPtr->hwnd != NULL) {
            PostMessage(tsdPtr->hwnd, SOCKET_TERMINATE, 0, 0);

            /*
             * Wait for the thread to exit. This ensures that we are
             * completely cleaned up before we leave this function.
             */

            WaitForSingleObject(tsdPtr->readyEvent, INFINITE);
            tsdPtr->hwnd = NULL;
          }
          CloseHandle(tsdPtr->socketThread);
          tsdPtr->socketThread = NULL;
      }
      if (tsdPtr->readyEvent != NULL) {
          CloseHandle(tsdPtr->readyEvent);
          tsdPtr->readyEvent = NULL;
      }
      if (tsdPtr->socketListLock != NULL) {
          CloseHandle(tsdPtr->socketListLock);
          tsdPtr->socketListLock = NULL;
      }
      Tcl_DeleteEventSource(SocketSetupProc, SocketCheckProc, NULL);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclpHasSockets --
 *
 *    This function determines whether sockets are available on the current
 *    system and returns an error in interp if they are not. Note that
 *    interp may be NULL.
 *
 * Results:
 *    Returns TCL_OK if the system supports sockets, or TCL_ERROR with an
 *    error in interp (if non-NULL).
 *
 * Side effects:
 *    If not already prepared, initializes the TSD structure and socket
 *    message handling thread associated to the calling thread for the
 *    subsystem of the driver.
 *
 *----------------------------------------------------------------------
 */

int
TclpHasSockets(
    Tcl_Interp *interp)       /* Where to write an error message if sockets
                         * are not present, or NULL if no such message
                         * is to be written. */
{
    Tcl_MutexLock(&socketMutex);
    InitSockets();
    Tcl_MutexUnlock(&socketMutex);

    if (SocketsEnabled()) {
      return TCL_OK;
    }
    if (interp != NULL) {
      Tcl_AppendResult(interp, "sockets are not available on this system",
            NULL);
    }
    return TCL_ERROR;
}

/*
 *----------------------------------------------------------------------
 *
 * SocketSetupProc --
 *
 *    This function is invoked before Tcl_DoOneEvent blocks waiting for an
 *    event.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Adjusts the block time if needed.
 *
 *----------------------------------------------------------------------
 */

void
SocketSetupProc(
    ClientData data,          /* Not used. */
    int flags)                /* Event flags as passed to Tcl_DoOneEvent. */
{
    SocketInfo *infoPtr;
    Tcl_Time blockTime = { 0, 0 };
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if (!(flags & TCL_FILE_EVENTS)) {
      return;
    }

    /*
     * Check to see if there is a ready socket.  If so, poll.
     */

    WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
    for (infoPtr = tsdPtr->socketList; infoPtr != NULL;
          infoPtr = infoPtr->nextPtr) {
      if (infoPtr->readyEvents & infoPtr->watchEvents) {
          Tcl_SetMaxBlockTime(&blockTime);
          break;
      }
    }
    SetEvent(tsdPtr->socketListLock);
}

/*
 *----------------------------------------------------------------------
 *
 * SocketCheckProc --
 *
 *    This function is called by Tcl_DoOneEvent to check the socket event
 *    source for events.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    May queue an event.
 *
 *----------------------------------------------------------------------
 */

static void
SocketCheckProc(
    ClientData data,          /* Not used. */
    int flags)                /* Event flags as passed to Tcl_DoOneEvent. */
{
    SocketInfo *infoPtr;
    SocketEvent *evPtr;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if (!(flags & TCL_FILE_EVENTS)) {
      return;
    }

    /*
     * Queue events for any ready sockets that don't already have events
     * queued (caused by persistent states that won't generate WinSock
     * events).
     */

    WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
    for (infoPtr = tsdPtr->socketList; infoPtr != NULL;
          infoPtr = infoPtr->nextPtr) {
      if ((infoPtr->readyEvents & infoPtr->watchEvents)
            && !(infoPtr->flags & SOCKET_PENDING)) {
          infoPtr->flags |= SOCKET_PENDING;
          evPtr = (SocketEvent *) ckalloc(sizeof(SocketEvent));
          evPtr->header.proc = SocketEventProc;
          evPtr->socket = infoPtr->socket;
          Tcl_QueueEvent((Tcl_Event *) evPtr, TCL_QUEUE_TAIL);
      }
    }
    SetEvent(tsdPtr->socketListLock);
}

/*
 *----------------------------------------------------------------------
 *
 * SocketEventProc --
 *
 *    This function is called by Tcl_ServiceEvent when a socket event
 *    reaches the front of the event queue. This function is responsible for
 *    notifying the generic channel code.
 *
 * Results:
 *    Returns 1 if the event was handled, meaning it should be removed from
 *    the queue. Returns 0 if the event was not handled, meaning it should
 *    stay on the queue. The only time the event isn't handled is if the
 *    TCL_FILE_EVENTS flag bit isn't set.
 *
 * Side effects:
 *    Whatever the channel callback functions do.
 *
 *----------------------------------------------------------------------
 */

static int
SocketEventProc(
    Tcl_Event *evPtr,         /* Event to service. */
    int flags)                /* Flags that indicate what events to handle,
                         * such as TCL_FILE_EVENTS. */
{
    SocketInfo *infoPtr;
    SocketEvent *eventPtr = (SocketEvent *) evPtr;
    int mask = 0;
    int events;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if (!(flags & TCL_FILE_EVENTS)) {
      return 0;
    }

    /*
     * Find the specified socket on the socket list.
     */

    WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
    for (infoPtr = tsdPtr->socketList; infoPtr != NULL;
          infoPtr = infoPtr->nextPtr) {
      if (infoPtr->socket == eventPtr->socket) {
          break;
      }
    }
    SetEvent(tsdPtr->socketListLock);

    /*
     * Discard events that have gone stale.
     */

    if (!infoPtr) {
      return 1;
    }

    infoPtr->flags &= ~SOCKET_PENDING;

    /*
     * Handle connection requests directly.
     */

    if (infoPtr->readyEvents & FD_ACCEPT) {
      TcpAccept(infoPtr);
      return 1;
    }

    /*
     * Mask off unwanted events and compute the read/write mask so we can
     * notify the channel.
     */

    events = infoPtr->readyEvents & infoPtr->watchEvents;

    if (events & FD_CLOSE) {
      /*
       * If the socket was closed and the channel is still interested in
       * read events, then we need to ensure that we keep polling for this
       * event until someone does something with the channel. Note that we
       * do this before calling Tcl_NotifyChannel so we don't have to watch
       * out for the channel being deleted out from under us. This may cause
       * a redundant trip through the event loop, but it's simpler than
       * trying to do unwind protection.
       */

      Tcl_Time blockTime = { 0, 0 };
      Tcl_SetMaxBlockTime(&blockTime);
      mask |= TCL_READABLE|TCL_WRITABLE;
    } else if (events & FD_READ) {
      fd_set readFds;
      struct timeval timeout;

      /*
       * We must check to see if data is really available, since someone
       * could have consumed the data in the meantime. Turn off async
       * notification so select will work correctly. If the socket is still
       * readable, notify the channel driver, otherwise reset the async
       * select handler and keep waiting.
       */

      SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
            (WPARAM) UNSELECT, (LPARAM) infoPtr);

      FD_ZERO(&readFds);
      FD_SET(infoPtr->socket, &readFds);
      timeout.tv_usec = 0;
      timeout.tv_sec = 0;

      if (select(0, &readFds, NULL, NULL, &timeout) != 0) {
          mask |= TCL_READABLE;
      } else {
          infoPtr->readyEvents &= ~(FD_READ);
          SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
                (WPARAM) SELECT, (LPARAM) infoPtr);
      }
    }
    if (events & (FD_WRITE | FD_CONNECT)) {
      mask |= TCL_WRITABLE;
      if (events & FD_CONNECT && infoPtr->lastError != NO_ERROR) {
          /*
           * Connect errors should also fire the readable handler.
           */

          mask |= TCL_READABLE;
      }
    }

    if (mask) {
      Tcl_NotifyChannel(infoPtr->channel, mask);
    }
    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpBlockProc --
 *
 *    Sets a socket into blocking or non-blocking mode.
 *
 * Results:
 *    0 if successful, errno if there was an error.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
TcpBlockProc(
    ClientData instanceData,  /* The socket to block/un-block. */
    int mode)                 /* TCL_MODE_BLOCKING or
                         * TCL_MODE_NONBLOCKING. */
{
    SocketInfo *infoPtr = (SocketInfo *) instanceData;

    if (mode == TCL_MODE_NONBLOCKING) {
      infoPtr->flags |= SOCKET_ASYNC;
    } else {
      infoPtr->flags &= ~(SOCKET_ASYNC);
    }
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpCloseProc --
 *
 *    This function is called by the generic IO level to perform channel
 *    type specific cleanup on a socket based channel when the channel is
 *    closed.
 *
 * Results:
 *    0 if successful, the value of errno if failed.
 *
 * Side effects:
 *    Closes the socket.
 *
 *----------------------------------------------------------------------
 */

    /* ARGSUSED */
static int
TcpCloseProc(
    ClientData instanceData,  /* The socket to close. */
    Tcl_Interp *interp)       /* Unused. */
{
    SocketInfo *infoPtr = (SocketInfo *) instanceData;
    /* TIP #218 */
    int errorCode = 0;
    /* ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey); */

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (SocketsEnabled()) {
      /*
       * Clean up the OS socket handle. The default Windows setting for a
       * socket is SO_DONTLINGER, which does a graceful shutdown in the
       * background.
       */

      if (closesocket(infoPtr->socket) == SOCKET_ERROR) {
          TclWinConvertWSAError((DWORD) WSAGetLastError());
          errorCode = Tcl_GetErrno();
      }
    }

    /*
     * TIP #218. Removed the code removing the structure from the global
     * socket list. This is now done by the thread action callbacks, and only
     * there. This happens before this code is called. We can free without
     * fear of damaging the list.
     */

    ckfree((char *) infoPtr);
    return errorCode;
}

/*
 *----------------------------------------------------------------------
 *
 * NewSocketInfo --
 *
 *    This function allocates and initializes a new SocketInfo structure.
 *
 * Results:
 *    Returns a newly allocated SocketInfo.
 *
 * Side effects:
 *    None, except for allocation of memory.
 *
 *----------------------------------------------------------------------
 */

static SocketInfo *
NewSocketInfo(
    SOCKET socket)
{
    SocketInfo *infoPtr;
    /* ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey); */

    infoPtr = (SocketInfo *) ckalloc((unsigned) sizeof(SocketInfo));
    infoPtr->channel = 0;
    infoPtr->socket = socket;
    infoPtr->flags = 0;
    infoPtr->watchEvents = 0;
    infoPtr->readyEvents = 0;
    infoPtr->selectEvents = 0;
    infoPtr->acceptEventCount = 0;
    infoPtr->acceptProc = NULL;
    infoPtr->acceptProcData = NULL;
    infoPtr->lastError = 0;

    /*
     * TIP #218. Removed the code inserting the new structure into the global
     * list. This is now handled in the thread action callbacks, and only
     * there.
     */

    infoPtr->nextPtr = NULL;

    return infoPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * CreateSocket --
 *
 *    This function opens a new socket and initializes the SocketInfo
 *    structure.
 *
 * Results:
 *    Returns a new SocketInfo, or NULL with an error in interp.
 *
 * Side effects:
 *    None, except for allocation of memory.
 *
 *----------------------------------------------------------------------
 */

static SocketInfo *
CreateSocket(
    Tcl_Interp *interp,       /* For error reporting; can be NULL. */
    int port,                 /* Port number to open. */
    const char *host,         /* Name of host on which to open port. */
    int server,               /* 1 if socket should be a server socket, else
                         * 0 for a client socket. */
    const char *myaddr,       /* Optional client-side address */
    int myport,               /* Optional client-side port */
    int async)                /* If nonzero, connect client socket
                         * asynchronously. */
{
    u_long flag = 1;          /* Indicates nonblocking mode. */
    int asyncConnect = 0;     /* Will be 1 if async connect is in
                         * progress. */
    SOCKADDR_IN sockaddr;     /* Socket address */
    SOCKADDR_IN mysockaddr;   /* Socket address for client */
    SOCKET sock = INVALID_SOCKET;
    SocketInfo *infoPtr;      /* The returned value. */
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
          TclThreadDataKeyGet(&dataKey);

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      return NULL;
    }

    if (!CreateSocketAddress(&sockaddr, host, port)) {
      goto error;
    }
    if ((myaddr != NULL || myport != 0) &&
          !CreateSocketAddress(&mysockaddr, myaddr, myport)) {
      goto error;
    }

    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == INVALID_SOCKET) {
      goto error;
    }

    /*
     * Win-NT has a misfeature that sockets are inherited in child processes
     * by default. Turn off the inherit bit.
     */

    SetHandleInformation((HANDLE) sock, HANDLE_FLAG_INHERIT, 0);

    /*
     * Set kernel space buffering
     */

    TclSockMinimumBuffers((int) sock, TCP_BUFFER_SIZE);

    if (server) {
      /*
       * Bind to the specified port. Note that we must not call setsockopt
       * with SO_REUSEADDR because Microsoft allows addresses to be reused
       * even if they are still in use.
       *
       * Bind should not be affected by the socket having already been set
       * into nonblocking mode. If there is trouble, this is one place to
       * look for bugs.
       */

      if (bind(sock, (SOCKADDR *) &sockaddr, sizeof(SOCKADDR_IN))
            == SOCKET_ERROR) {
          goto error;
      }

      /*
       * Set the maximum number of pending connect requests to the max value
       * allowed on each platform (Win32 and Win32s may be different, and
       * there may be differences between TCP/IP stacks).
       */

      if (listen(sock, SOMAXCONN) == SOCKET_ERROR) {
          goto error;
      }

      /*
       * Add this socket to the global list of sockets.
       */

      infoPtr = NewSocketInfo(sock);

      /*
       * Set up the select mask for connection request events.
       */

      infoPtr->selectEvents = FD_ACCEPT;
      infoPtr->watchEvents |= FD_ACCEPT;

    } else {
      /*
       * Try to bind to a local port, if specified.
       */

      if (myaddr != NULL || myport != 0) {
          if (bind(sock, (SOCKADDR *) &mysockaddr, sizeof(SOCKADDR_IN))
                == SOCKET_ERROR) {
            goto error;
          }
      }

      /*
       * Set the socket into nonblocking mode if the connect should be done
       * in the background.
       */

      if (async) {
          if (ioctlsocket(sock, (long) FIONBIO, &flag) == SOCKET_ERROR) {
            goto error;
          }
      }

      /*
       * Attempt to connect to the remote socket.
       */

      if (connect(sock, (SOCKADDR *) &sockaddr,
            sizeof(SOCKADDR_IN)) == SOCKET_ERROR) {
          TclWinConvertWSAError((DWORD) WSAGetLastError());
          if (Tcl_GetErrno() != EWOULDBLOCK) {
            goto error;
          }

          /*
           * The connection is progressing in the background.
           */

          asyncConnect = 1;
      }

      /*
       * Add this socket to the global list of sockets.
       */

      infoPtr = NewSocketInfo(sock);

      /*
       * Set up the select mask for read/write events. If the connect
       * attempt has not completed, include connect events.
       */

      infoPtr->selectEvents = FD_READ | FD_WRITE | FD_CLOSE;
      if (asyncConnect) {
          infoPtr->flags |= SOCKET_ASYNC_CONNECT;
          infoPtr->selectEvents |= FD_CONNECT;
      }
    }

    /*
     * Register for interest in events in the select mask. Note that this
     * automatically places the socket into non-blocking mode.
     */

    ioctlsocket(sock, (long) FIONBIO, &flag);
    SendMessage(tsdPtr->hwnd, SOCKET_SELECT, (WPARAM) SELECT, (LPARAM) infoPtr);

    return infoPtr;

  error:
    TclWinConvertWSAError((DWORD) WSAGetLastError());
    if (interp != NULL) {
      Tcl_AppendResult(interp, "couldn't open socket: ",
            Tcl_PosixError(interp), NULL);
    }
    if (sock != INVALID_SOCKET) {
      closesocket(sock);
    }
    return NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * CreateSocketAddress --
 *
 *    This function initializes a sockaddr structure for a host and port.
 *
 * Results:
 *    1 if the host was valid, 0 if the host could not be converted to an IP
 *    address.
 *
 * Side effects:
 *    Fills in the *sockaddrPtr structure.
 *
 *----------------------------------------------------------------------
 */

static int
CreateSocketAddress(
    LPSOCKADDR_IN sockaddrPtr,      /* Socket address */
    const char *host,         /* Host. NULL implies INADDR_ANY */
    int port)                 /* Port number */
{
    struct hostent *hostent;  /* Host database entry */
    struct in_addr addr;      /* For 64/32 bit madness */

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      Tcl_SetErrno(EFAULT);
      return 0;
    }

    ZeroMemory(sockaddrPtr, sizeof(SOCKADDR_IN));
    sockaddrPtr->sin_family = AF_INET;
    sockaddrPtr->sin_port = htons((u_short) (port & 0xFFFF));
    if (host == NULL) {
      addr.s_addr = INADDR_ANY;
    } else {
      addr.s_addr = inet_addr(host);
      if (addr.s_addr == INADDR_NONE) {
          hostent = gethostbyname(host);
          if (hostent != NULL) {
            memcpy(&addr, hostent->h_addr, (size_t) hostent->h_length);
          } else {
#ifdef      EHOSTUNREACH
            Tcl_SetErrno(EHOSTUNREACH);
#else
#ifdef ENXIO
            Tcl_SetErrno(ENXIO);
#endif
#endif
            return 0;   /* Error. */
          }
      }
    }

    /*
     * NOTE: On 64 bit machines the assignment below is rumored to not do the
     * right thing. Please report errors related to this if you observe
     * incorrect behavior on 64 bit machines such as DEC Alphas. Should we
     * modify this code to do an explicit memcpy?
     */

    sockaddrPtr->sin_addr.s_addr = addr.s_addr;
    return 1;                 /* Success. */
}

/*
 *----------------------------------------------------------------------
 *
 * WaitForSocketEvent --
 *
 *    Waits until one of the specified events occurs on a socket.
 *
 * Results:
 *    Returns 1 on success or 0 on failure, with an error code in
 *    errorCodePtr.
 *
 * Side effects:
 *    Processes socket events off the system queue.
 *
 *----------------------------------------------------------------------
 */

static int
WaitForSocketEvent(
    SocketInfo *infoPtr,      /* Information about this socket. */
    int events,               /* Events to look for. */
    int *errorCodePtr)        /* Where to store errors? */
{
    int result = 1;
    int oldMode;
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
          TclThreadDataKeyGet(&dataKey);

    /*
     * Be sure to disable event servicing so we are truly modal.
     */

    oldMode = Tcl_SetServiceMode(TCL_SERVICE_NONE);

    /*
     * Reset WSAAsyncSelect so we have a fresh set of events pending.
     */

    SendMessage(tsdPtr->hwnd, SOCKET_SELECT, (WPARAM) UNSELECT,
          (LPARAM) infoPtr);

    SendMessage(tsdPtr->hwnd, SOCKET_SELECT, (WPARAM) SELECT,
          (LPARAM) infoPtr);

    while (1) {
      if (infoPtr->lastError) {
          *errorCodePtr = infoPtr->lastError;
          result = 0;
          break;
      } else if (infoPtr->readyEvents & events) {
          break;
      } else if (infoPtr->flags & SOCKET_ASYNC) {
          *errorCodePtr = EWOULDBLOCK;
          result = 0;
          break;
      }

      /*
       * Wait until something happens.
       */

      WaitForSingleObject(tsdPtr->readyEvent, INFINITE);
    }

    (void) Tcl_SetServiceMode(oldMode);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_OpenTcpClient --
 *
 *    Opens a TCP client socket and creates a channel around it.
 *
 * Results:
 *    The channel or NULL if failed. An error message is returned in the
 *    interpreter on failure.
 *
 * Side effects:
 *    Opens a client socket and creates a new channel.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_OpenTcpClient(
    Tcl_Interp *interp,       /* For error reporting; can be NULL. */
    int port,                 /* Port number to open. */
    const char *host,         /* Host on which to open port. */
    const char *myaddr,       /* Client-side address */
    int myport,               /* Client-side port */
    int async)                /* If nonzero, should connect client socket
                         * asynchronously. */
{
    SocketInfo *infoPtr;
    char channelName[16 + TCL_INTEGER_SPACE];

    if (TclpHasSockets(interp) != TCL_OK) {
      return NULL;
    }

    /*
     * Create a new client socket and wrap it in a channel.
     */

    infoPtr = CreateSocket(interp, port, host, 0, myaddr, myport, async);
    if (infoPtr == NULL) {
      return NULL;
    }

    wsprintfA(channelName, "sock%d", infoPtr->socket);

    infoPtr->channel = Tcl_CreateChannel(&tcpChannelType, channelName,
          (ClientData) infoPtr, (TCL_READABLE | TCL_WRITABLE));
    if (Tcl_SetChannelOption(interp, infoPtr->channel, "-translation",
          "auto crlf") == TCL_ERROR) {
      Tcl_Close((Tcl_Interp *) NULL, infoPtr->channel);
      return (Tcl_Channel) NULL;
    }
    if (Tcl_SetChannelOption(NULL, infoPtr->channel, "-eofchar", "")
          == TCL_ERROR) {
      Tcl_Close((Tcl_Interp *) NULL, infoPtr->channel);
      return (Tcl_Channel) NULL;
    }
    return infoPtr->channel;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_MakeTcpClientChannel --
 *
 *    Creates a Tcl_Channel from an existing client TCP socket.
 *
 * Results:
 *    The Tcl_Channel wrapped around the preexisting TCP socket.
 *
 * Side effects:
 *    None.
 *
 * NOTE: Code contributed by Mark Diekhans (markd@grizzly.com)
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_MakeTcpClientChannel(
    ClientData sock)          /* The socket to wrap up into a channel. */
{
    SocketInfo *infoPtr;
    char channelName[16 + TCL_INTEGER_SPACE];
    ThreadSpecificData *tsdPtr;

    if (TclpHasSockets(NULL) != TCL_OK) {
      return NULL;
    }

    tsdPtr = (ThreadSpecificData *)TclThreadDataKeyGet(&dataKey);

    /*
     * Set kernel space buffering and non-blocking.
     */

    TclSockMinimumBuffers((int) sock, TCP_BUFFER_SIZE);

    infoPtr = NewSocketInfo((SOCKET) sock);

    /*
     * Start watching for read/write events on the socket.
     */

    infoPtr->selectEvents = FD_READ | FD_CLOSE | FD_WRITE;
    SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
          (WPARAM) SELECT, (LPARAM) infoPtr);

    wsprintfA(channelName, "sock%d", infoPtr->socket);
    infoPtr->channel = Tcl_CreateChannel(&tcpChannelType, channelName,
          (ClientData) infoPtr, (TCL_READABLE | TCL_WRITABLE));
    Tcl_SetChannelOption(NULL, infoPtr->channel, "-translation", "auto crlf");
    return infoPtr->channel;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_OpenTcpServer --
 *
 *    Opens a TCP server socket and creates a channel around it.
 *
 * Results:
 *    The channel or NULL if failed. An error message is returned in the
 *    interpreter on failure.
 *
 * Side effects:
 *    Opens a server socket and creates a new channel.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_OpenTcpServer(
    Tcl_Interp *interp,       /* For error reporting - may be NULL. */
    int port,                 /* Port number to open. */
    const char *host,         /* Name of local host. */
    Tcl_TcpAcceptProc *acceptProc,
                        /* Callback for accepting connections from new
                         * clients. */
    ClientData acceptProcData)      /* Data for the callback. */
{
    SocketInfo *infoPtr;
    char channelName[16 + TCL_INTEGER_SPACE];

    if (TclpHasSockets(interp) != TCL_OK) {
      return NULL;
    }

    /*
     * Create a new client socket and wrap it in a channel.
     */

    infoPtr = CreateSocket(interp, port, host, 1, NULL, 0, 0);
    if (infoPtr == NULL) {
      return NULL;
    }

    infoPtr->acceptProc = acceptProc;
    infoPtr->acceptProcData = acceptProcData;

    wsprintfA(channelName, "sock%d", infoPtr->socket);

    infoPtr->channel = Tcl_CreateChannel(&tcpChannelType, channelName,
          (ClientData) infoPtr, 0);
    if (Tcl_SetChannelOption(interp, infoPtr->channel, "-eofchar", "")
          == TCL_ERROR) {
      Tcl_Close((Tcl_Interp *) NULL, infoPtr->channel);
      return (Tcl_Channel) NULL;
    }

    return infoPtr->channel;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpAccept --
 *
 *    Accept a TCP socket connection. This is called by SocketEventProc and
 *    it in turns calls the registered accept function.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Invokes the accept proc which may invoke arbitrary Tcl code.
 *
 *----------------------------------------------------------------------
 */

static void
TcpAccept(
    SocketInfo *infoPtr)      /* Socket to accept. */
{
    SOCKET newSocket;
    SocketInfo *newInfoPtr;
    SOCKADDR_IN addr;
    int len;
    char channelName[16 + TCL_INTEGER_SPACE];
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
          TclThreadDataKeyGet(&dataKey);

    /*
     * Accept the incoming connection request.
     */

    len = sizeof(SOCKADDR_IN);

    newSocket = accept(infoPtr->socket, (SOCKADDR *)&addr,
          &len);

    /*
     * Clear the ready mask so we can detect the next connection request. Note
     * that connection requests are level triggered, so if there is a request
     * already pending, a new event will be generated.
     */

    if (newSocket == INVALID_SOCKET) {
      infoPtr->acceptEventCount = 0;
      infoPtr->readyEvents &= ~(FD_ACCEPT);
      return;
    }

    /*
     * It is possible that more than one FD_ACCEPT has been sent, so an extra
     * count must be kept. Decrement the count, and reset the readyEvent bit
     * if the count is no longer > 0.
     */

    infoPtr->acceptEventCount--;

    if (infoPtr->acceptEventCount <= 0) {
      infoPtr->readyEvents &= ~(FD_ACCEPT);
    }

    /*
     * Win-NT has a misfeature that sockets are inherited in child processes
     * by default. Turn off the inherit bit.
     */

    SetHandleInformation((HANDLE) newSocket, HANDLE_FLAG_INHERIT, 0);

    /*
     * Add this socket to the global list of sockets.
     */

    newInfoPtr = NewSocketInfo(newSocket);

    /*
     * Select on read/write events and create the channel.
     */

    newInfoPtr->selectEvents = (FD_READ | FD_WRITE | FD_CLOSE);
    SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
          (WPARAM) SELECT, (LPARAM) newInfoPtr);

    wsprintfA(channelName, "sock%d", newInfoPtr->socket);
    newInfoPtr->channel = Tcl_CreateChannel(&tcpChannelType, channelName,
          (ClientData) newInfoPtr, (TCL_READABLE | TCL_WRITABLE));
    if (Tcl_SetChannelOption(NULL, newInfoPtr->channel, "-translation",
          "auto crlf") == TCL_ERROR) {
      Tcl_Close((Tcl_Interp *) NULL, newInfoPtr->channel);
      return;
    }
    if (Tcl_SetChannelOption(NULL, newInfoPtr->channel, "-eofchar", "")
          == TCL_ERROR) {
      Tcl_Close((Tcl_Interp *) NULL, newInfoPtr->channel);
      return;
    }

    /*
     * Invoke the accept callback function.
     */

    if (infoPtr->acceptProc != NULL) {
      (infoPtr->acceptProc) (infoPtr->acceptProcData, newInfoPtr->channel,
            inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TcpInputProc --
 *
 *    This function is called by the generic IO level to read data from a
 *    socket based channel.
 *
 * Results:
 *    The number of bytes read or -1 on error.
 *
 * Side effects:
 *    Consumes input from the socket.
 *
 *----------------------------------------------------------------------
 */

static int
TcpInputProc(
    ClientData instanceData,  /* The socket state. */
    char *buf,                /* Where to store data. */
    int toRead,               /* Maximum number of bytes to read. */
    int *errorCodePtr)        /* Where to store error codes. */
{
    SocketInfo *infoPtr = (SocketInfo *) instanceData;
    int bytesRead;
    DWORD error;
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
          TclThreadDataKeyGet(&dataKey);

    *errorCodePtr = 0;

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      *errorCodePtr = EFAULT;
      return -1;
    }

    /*
     * First check to see if EOF was already detected, to prevent calling the
     * socket stack after the first time EOF is detected.
     */

    if (infoPtr->flags & SOCKET_EOF) {
      return 0;
    }

    /*
     * Check to see if the socket is connected before trying to read.
     */

    if ((infoPtr->flags & SOCKET_ASYNC_CONNECT)
          && !WaitForSocketEvent(infoPtr, FD_CONNECT, errorCodePtr)) {
      return -1;
    }

    /*
     * No EOF, and it is connected, so try to read more from the socket. Note
     * that we clear the FD_READ bit because read events are level triggered
     * so a new event will be generated if there is still data available to be
     * read. We have to simulate blocking behavior here since we are always
     * using non-blocking sockets.
     */

    while (1) {
      SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
            (WPARAM) UNSELECT, (LPARAM) infoPtr);
      bytesRead = recv(infoPtr->socket, buf, toRead, 0);
      infoPtr->readyEvents &= ~(FD_READ);

      /*
       * Check for end-of-file condition or successful read.
       */

      if (bytesRead == 0) {
          infoPtr->flags |= SOCKET_EOF;
      }
      if (bytesRead != SOCKET_ERROR) {
          break;
      }

      /*
       * If an error occurs after the FD_CLOSE has arrived, then ignore the
       * error and report an EOF.
       */

      if (infoPtr->readyEvents & FD_CLOSE) {
          infoPtr->flags |= SOCKET_EOF;
          bytesRead = 0;
          break;
      }

      /*
       * Check for error condition or underflow in non-blocking case.
       */

      error = WSAGetLastError();
      if ((infoPtr->flags & SOCKET_ASYNC) || (error != WSAEWOULDBLOCK)) {
          TclWinConvertWSAError(error);
          *errorCodePtr = Tcl_GetErrno();
          bytesRead = -1;
          break;
      }

      /*
       * In the blocking case, wait until the file becomes readable or
       * closed and try again.
       */

      if (!WaitForSocketEvent(infoPtr, FD_READ|FD_CLOSE, errorCodePtr)) {
          bytesRead = -1;
          break;
      }
    }

    SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
          (WPARAM) SELECT, (LPARAM) infoPtr);

    return bytesRead;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpOutputProc --
 *
 *    This function is called by the generic IO level to write data to a
 *    socket based channel.
 *
 * Results:
 *    The number of bytes written or -1 on failure.
 *
 * Side effects:
 *    Produces output on the socket.
 *
 *----------------------------------------------------------------------
 */

static int
TcpOutputProc(
    ClientData instanceData,  /* The socket state. */
    const char *buf,          /* Where to get data. */
    int toWrite,        /* Maximum number of bytes to write. */
    int *errorCodePtr)        /* Where to store error codes. */
{
    SocketInfo *infoPtr = (SocketInfo *) instanceData;
    int bytesWritten;
    DWORD error;
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
          TclThreadDataKeyGet(&dataKey);

    *errorCodePtr = 0;

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      *errorCodePtr = EFAULT;
      return -1;
    }

    /*
     * Check to see if the socket is connected before trying to write.
     */

    if ((infoPtr->flags & SOCKET_ASYNC_CONNECT)
          && !WaitForSocketEvent(infoPtr, FD_CONNECT, errorCodePtr)) {
      return -1;
    }

    while (1) {
      SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
            (WPARAM) UNSELECT, (LPARAM) infoPtr);

      bytesWritten = send(infoPtr->socket, buf, toWrite, 0);
      if (bytesWritten != SOCKET_ERROR) {
          /*
           * Since Windows won't generate a new write event until we hit an
           * overflow condition, we need to force the event loop to poll
           * until the condition changes.
           */

          if (infoPtr->watchEvents & FD_WRITE) {
            Tcl_Time blockTime = { 0, 0 };
            Tcl_SetMaxBlockTime(&blockTime);
          }
          break;
      }

      /*
       * Check for error condition or overflow. In the event of overflow, we
       * need to clear the FD_WRITE flag so we can detect the next writable
       * event. Note that Windows only sends a new writable event after a
       * send fails with WSAEWOULDBLOCK.
       */

      error = WSAGetLastError();
      if (error == WSAEWOULDBLOCK) {
          infoPtr->readyEvents &= ~(FD_WRITE);
          if (infoPtr->flags & SOCKET_ASYNC) {
            *errorCodePtr = EWOULDBLOCK;
            bytesWritten = -1;
            break;
          }
      } else {
          TclWinConvertWSAError(error);
          *errorCodePtr = Tcl_GetErrno();
          bytesWritten = -1;
          break;
      }

      /*
       * In the blocking case, wait until the file becomes writable or
       * closed and try again.
       */

      if (!WaitForSocketEvent(infoPtr, FD_WRITE|FD_CLOSE, errorCodePtr)) {
          bytesWritten = -1;
          break;
      }
    }

    SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
          (WPARAM) SELECT, (LPARAM) infoPtr);

    return bytesWritten;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpSetOptionProc --
 *
 *    Sets Tcp channel specific options.
 *
 * Results:
 *    None, unless an error happens.
 *
 * Side effects:
 *    Changes attributes of the socket at the system level.
 *
 *----------------------------------------------------------------------
 */

static int
TcpSetOptionProc(
    ClientData instanceData,  /* Socket state. */
    Tcl_Interp *interp,       /* For error reporting - can be NULL. */
    const char *optionName,   /* Name of the option to set. */
    const char *value)        /* New value for option. */
{
    SocketInfo *infoPtr;
    SOCKET sock;

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      if (interp) {
          Tcl_AppendResult(interp, "winsock is not initialized", NULL);
      }
      return TCL_ERROR;
    }

    infoPtr = (SocketInfo *) instanceData;
    sock = infoPtr->socket;

#ifdef TCL_FEATURE_KEEPALIVE_NAGLE
    if (!stricmp(optionName, "-keepalive")) {
      BOOL val = FALSE;
      int boolVar, rtn;

      if (Tcl_GetBoolean(interp, value, &boolVar) != TCL_OK) {
          return TCL_ERROR;
      }
      if (boolVar) {
          val = TRUE;
      }
      rtn = setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE,
            (const char *) &val, sizeof(BOOL));
      if (rtn != 0) {
          TclWinConvertWSAError(WSAGetLastError());
          if (interp) {
            Tcl_AppendResult(interp, "couldn't set socket option: ",
                  Tcl_PosixError(interp), NULL);
          }
          return TCL_ERROR;
      }
      return TCL_OK;
    } else if (!stricmp(optionName, "-nagle")) {
      BOOL val = FALSE;
      int boolVar, rtn;

      if (Tcl_GetBoolean(interp, value, &boolVar) != TCL_OK) {
          return TCL_ERROR;
      }
      if (!boolVar) {
          val = TRUE;
      }
      rtn = setsockopt(sock, IPPROTO_TCP, TCP_NODELAY,
            (const char *) &val, sizeof(BOOL));
      if (rtn != 0) {
          TclWinConvertWSAError(WSAGetLastError());
          if (interp) {
            Tcl_AppendResult(interp, "couldn't set socket option: ",
                  Tcl_PosixError(interp), NULL);
          }
          return TCL_ERROR;
      }
      return TCL_OK;
    }

    return Tcl_BadChannelOption(interp, optionName, "keepalive nagle");
#else
    return Tcl_BadChannelOption(interp, optionName, "");
#endif /*TCL_FEATURE_KEEPALIVE_NAGLE*/
}

/*
 *----------------------------------------------------------------------
 *
 * TcpGetOptionProc --
 *
 *    Computes an option value for a TCP socket based channel, or a list of
 *    all options and their values.
 *
 *    Note: This code is based on code contributed by John Haxby.
 *
 * Results:
 *    A standard Tcl result. The value of the specified option or a list of
 *    all options and their values is returned in the supplied DString.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
TcpGetOptionProc(
    ClientData instanceData,  /* Socket state. */
    Tcl_Interp *interp,       /* For error reporting - can be NULL */
    const char *optionName,   /* Name of the option to retrieve the value
                         * for, or NULL to get all options and their
                         * values. */
    Tcl_DString *dsPtr)       /* Where to store the computed value;
                         * initialized by caller. */
{
    SocketInfo *infoPtr;
    SOCKADDR_IN sockname;
    SOCKADDR_IN peername;
    struct hostent *hostEntPtr;
    SOCKET sock;
    int size = sizeof(SOCKADDR_IN);
    size_t len = 0;
    char buf[TCL_INTEGER_SPACE];

    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      if (interp) {
          Tcl_AppendResult(interp, "winsock is not initialized", NULL);
      }
      return TCL_ERROR;
    }

    infoPtr = (SocketInfo *) instanceData;
    sock = (int) infoPtr->socket;
    if (optionName != NULL) {
      len = strlen(optionName);
    }

    if ((len > 1) && (optionName[1] == 'e') &&
          (strncmp(optionName, "-error", len) == 0)) {
      int optlen;
      DWORD err;
      int ret;

      optlen = sizeof(int);
      ret = TclWinGetSockOpt((int)sock, SOL_SOCKET, SO_ERROR,
            (char *)&err, &optlen);
      if (ret == SOCKET_ERROR) {
          err = WSAGetLastError();
      }
      if (err) {
          TclWinConvertWSAError(err);
          Tcl_DStringAppend(dsPtr, Tcl_ErrnoMsg(Tcl_GetErrno()), -1);
      }
      return TCL_OK;
    }

    if ((len == 0) || ((len > 1) && (optionName[1] == 'p') &&
          (strncmp(optionName, "-peername", len) == 0))) {
      if (getpeername(sock, (LPSOCKADDR) &peername, &size) == 0) {
          if (len == 0) {
            Tcl_DStringAppendElement(dsPtr, "-peername");
            Tcl_DStringStartSublist(dsPtr);
          }
          Tcl_DStringAppendElement(dsPtr, inet_ntoa(peername.sin_addr));

          if (peername.sin_addr.s_addr == 0) {
            hostEntPtr = NULL;
          } else {
            hostEntPtr = gethostbyaddr((char *) &(peername.sin_addr),
                  sizeof(peername.sin_addr), AF_INET);
          }
          if (hostEntPtr != NULL) {
            Tcl_DStringAppendElement(dsPtr, hostEntPtr->h_name);
          } else {
            Tcl_DStringAppendElement(dsPtr, inet_ntoa(peername.sin_addr));
          }
          TclFormatInt(buf, ntohs(peername.sin_port));
          Tcl_DStringAppendElement(dsPtr, buf);
          if (len == 0) {
            Tcl_DStringEndSublist(dsPtr);
          } else {
            return TCL_OK;
          }
      } else {
          /*
           * getpeername failed - but if we were asked for all the options
           * (len==0), don't flag an error at that point because it could be
           * an fconfigure request on a server socket (such sockets have no
           * peer). {Copied from unix/tclUnixChan.c}
           */

          if (len) {
            TclWinConvertWSAError((DWORD) WSAGetLastError());
            if (interp) {
                Tcl_AppendResult(interp, "can't get peername: ",
                      Tcl_PosixError(interp), NULL);
            }
            return TCL_ERROR;
          }
      }
    }

    if ((len == 0) || ((len > 1) && (optionName[1] == 's') &&
          (strncmp(optionName, "-sockname", len) == 0))) {
      if (getsockname(sock, (LPSOCKADDR) &sockname, &size) == 0) {
          if (len == 0) {
            Tcl_DStringAppendElement(dsPtr, "-sockname");
            Tcl_DStringStartSublist(dsPtr);
          }
          Tcl_DStringAppendElement(dsPtr, inet_ntoa(sockname.sin_addr));
          if (sockname.sin_addr.s_addr == 0) {
            hostEntPtr = NULL;
          } else {
            hostEntPtr = gethostbyaddr((char *) &(sockname.sin_addr),
                  sizeof(peername.sin_addr), AF_INET);
          }
          if (hostEntPtr != NULL) {
            Tcl_DStringAppendElement(dsPtr, hostEntPtr->h_name);
          } else {
            Tcl_DStringAppendElement(dsPtr, inet_ntoa(sockname.sin_addr));
          }
          TclFormatInt(buf, ntohs(sockname.sin_port));
          Tcl_DStringAppendElement(dsPtr, buf);
          if (len == 0) {
            Tcl_DStringEndSublist(dsPtr);
          } else {
            return TCL_OK;
          }
      } else {
          if (interp) {
            TclWinConvertWSAError((DWORD) WSAGetLastError());
            Tcl_AppendResult(interp, "can't get sockname: ",
                  Tcl_PosixError(interp), NULL);
          }
          return TCL_ERROR;
      }
    }

#ifdef TCL_FEATURE_KEEPALIVE_NAGLE
    if (len == 0 || !strncmp(optionName, "-keepalive", len)) {
      int optlen;
      BOOL opt = FALSE;

      if (len == 0) {
          Tcl_DStringAppendElement(dsPtr, "-keepalive");
      }
      optlen = sizeof(BOOL);
      getsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (char *)&opt, &optlen);
      if (opt) {
          Tcl_DStringAppendElement(dsPtr, "1");
      } else {
          Tcl_DStringAppendElement(dsPtr, "0");
      }
      if (len > 0) {
          return TCL_OK;
      }
    }

    if (len == 0 || !strncmp(optionName, "-nagle", len)) {
      int optlen;
      BOOL opt = FALSE;

      if (len == 0) {
          Tcl_DStringAppendElement(dsPtr, "-nagle");
      }
      optlen = sizeof(BOOL);
      getsockopt(sock, IPPROTO_TCP, TCP_NODELAY, (char *)&opt,
            &optlen);
      if (opt) {
          Tcl_DStringAppendElement(dsPtr, "0");
      } else {
          Tcl_DStringAppendElement(dsPtr, "1");
      }
      if (len > 0) {
          return TCL_OK;
      }
    }
#endif /*TCL_FEATURE_KEEPALIVE_NAGLE*/

    if (len > 0) {
#ifdef TCL_FEATURE_KEEPALIVE_NAGLE
      return Tcl_BadChannelOption(interp, optionName,
            "peername sockname keepalive nagle");
#else
      return Tcl_BadChannelOption(interp, optionName, "peername sockname");
#endif /*TCL_FEATURE_KEEPALIVE_NAGLE*/
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpWatchProc --
 *
 *    Informs the channel driver of the events that the generic channel code
 *    wishes to receive on this socket.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    May cause the notifier to poll if any of the specified conditions are
 *    already true.
 *
 *----------------------------------------------------------------------
 */

static void
TcpWatchProc(
    ClientData instanceData,  /* The socket state. */
    int mask)                 /* Events of interest; an OR-ed combination of
                         * TCL_READABLE, TCL_WRITABLE and
                         * TCL_EXCEPTION. */
{
    SocketInfo *infoPtr = (SocketInfo *) instanceData;

    /*
     * Update the watch events mask. Only if the socket is not a server
     * socket. Fix for SF Tcl Bug #557878.
     */

    if (!infoPtr->acceptProc) {
      infoPtr->watchEvents = 0;
      if (mask & TCL_READABLE) {
          infoPtr->watchEvents |= (FD_READ|FD_CLOSE|FD_ACCEPT);
      }
      if (mask & TCL_WRITABLE) {
          infoPtr->watchEvents |= (FD_WRITE|FD_CLOSE|FD_CONNECT);
      }

      /*
       * If there are any conditions already set, then tell the notifier to
       * poll rather than block.
       */

      if (infoPtr->readyEvents & infoPtr->watchEvents) {
          Tcl_Time blockTime = { 0, 0 };
          Tcl_SetMaxBlockTime(&blockTime);
      }
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TcpGetProc --
 *
 *    Called from Tcl_GetChannelHandle to retrieve an OS handle from inside
 *    a TCP socket based channel.
 *
 * Results:
 *    Returns TCL_OK with the socket in handlePtr.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
TcpGetHandleProc(
    ClientData instanceData,  /* The socket state. */
    int direction,            /* Not used. */
    ClientData *handlePtr)    /* Where to store the handle. */
{
    SocketInfo *statePtr = (SocketInfo *) instanceData;

    *handlePtr = (ClientData) statePtr->socket;
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * SocketThread --
 *
 *    Helper thread used to manage the socket event handling window.
 *
 * Results:
 *    1 if unable to create socket event window, 0 otherwise.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static DWORD WINAPI
SocketThread(
    LPVOID arg)
{
    MSG msg;
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)(arg);

    /*
     * Create a dummy window receiving socket events.
     */

    tsdPtr->hwnd = CreateWindow("TclSocket", "TclSocket",
          WS_TILED, 0, 0, 0, 0, NULL, NULL, windowClass.hInstance, arg);

    /*
     * Signalize thread creator that we are done creating the window.
     */

    SetEvent(tsdPtr->readyEvent);

    /*
     * If unable to create the window, exit this thread immediately.
     */

    if (tsdPtr->hwnd == NULL) {
      return 1;
    }

    /*
     * Process all messages on the socket window until WM_QUIT. This threads
     * exits only when instructed to do so by the call to
     * PostMessage(SOCKET_TERMINATE) in TclpFinalizeSockets().
     */

    while (GetMessage(&msg, NULL, 0, 0) > 0) {
      DispatchMessage(&msg);
    }

    /*
     * This releases waiters on thread exit in TclpFinalizeSockets()
     */

    SetEvent(tsdPtr->readyEvent);

    return msg.wParam;
}


/*
 *----------------------------------------------------------------------
 *
 * SocketProc --
 *
 *    This function is called when WSAAsyncSelect has been used to register
 *    interest in a socket event, and the event has occurred.
 *
 * Results:
 *    0 on success.
 *
 * Side effects:
 *    The flags for the given socket are updated to reflect the event that
 *    occured.
 *
 *----------------------------------------------------------------------
 */

static LRESULT CALLBACK
SocketProc(
    HWND hwnd,
    UINT message,
    WPARAM wParam,
    LPARAM lParam)
{
    int event, error;
    SOCKET socket;
    SocketInfo *infoPtr;
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
#ifdef _WIN64
          GetWindowLongPtr(hwnd, GWLP_USERDATA);
#else
          GetWindowLong(hwnd, GWL_USERDATA);
#endif

    switch (message) {
    default:
      return DefWindowProc(hwnd, message, wParam, lParam);
      break;

    case WM_CREATE:
      /*
       * Store the initial tsdPtr, it's from a different thread, so it's not
       * directly accessible, but needed.
       */

#ifdef _WIN64
      SetWindowLongPtr(hwnd, GWLP_USERDATA,
            (LONG_PTR) ((LPCREATESTRUCT)lParam)->lpCreateParams);
#else
      SetWindowLong(hwnd, GWL_USERDATA,
            (LONG) ((LPCREATESTRUCT)lParam)->lpCreateParams);
#endif
      break;

    case WM_DESTROY:
      PostQuitMessage(0);
      break;

    case SOCKET_MESSAGE:
      event = WSAGETSELECTEVENT(lParam);
      error = WSAGETSELECTERROR(lParam);
      socket = (SOCKET) wParam;

      /*
       * Find the specified socket on the socket list and update its
       * eventState flag.
       */

      WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
      for (infoPtr = tsdPtr->socketList; infoPtr != NULL;
            infoPtr = infoPtr->nextPtr) {
          if (infoPtr->socket == socket) {
            /*
             * Update the socket state.
             *
             * A count of FD_ACCEPTS is stored, so if an FD_CLOSE event
             * happens, then clear the FD_ACCEPT count. Otherwise,
             * increment the count if the current event is an FD_ACCEPT.
             */

            if (event & FD_CLOSE) {
                infoPtr->acceptEventCount = 0;
                infoPtr->readyEvents &= ~(FD_WRITE|FD_ACCEPT);
            } else if (event & FD_ACCEPT) {
                infoPtr->acceptEventCount++;
            }

            if (event & FD_CONNECT) {
                /*
                 * The socket is now connected, clear the async connect
                 * flag.
                 */

                infoPtr->flags &= ~(SOCKET_ASYNC_CONNECT);

                /*
                 * Remember any error that occurred so we can report
                 * connection failures.
                 */

                if (error != ERROR_SUCCESS) {
                  TclWinConvertWSAError((DWORD) error);
                  infoPtr->lastError = Tcl_GetErrno();
                }
            }

            if (infoPtr->flags & SOCKET_ASYNC_CONNECT) {
                infoPtr->flags &= ~(SOCKET_ASYNC_CONNECT);
                if (error != ERROR_SUCCESS) {
                  TclWinConvertWSAError((DWORD) error);
                  infoPtr->lastError = Tcl_GetErrno();
                }
                infoPtr->readyEvents |= FD_WRITE;
            }
            infoPtr->readyEvents |= event;

            /*
             * Wake up the Main Thread.
             */

            SetEvent(tsdPtr->readyEvent);
            Tcl_ThreadAlert(tsdPtr->threadId);
            break;
          }
      }
      SetEvent(tsdPtr->socketListLock);
      break;

    case SOCKET_SELECT:
      infoPtr = (SocketInfo *) lParam;
      if (wParam == SELECT) {
          WSAAsyncSelect(infoPtr->socket, hwnd,
                SOCKET_MESSAGE, infoPtr->selectEvents);
      } else {
          /*
           * Clear the selection mask
           */

          WSAAsyncSelect(infoPtr->socket, hwnd, 0, 0);
      }
      break;

    case SOCKET_TERMINATE:
      DestroyWindow(hwnd);
      break;
    }

    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetHostName --
 *
 *    Returns the name of the local host.
 *
 * Results:
 *    A string containing the network name for this machine. The caller must
 *    not modify or free this string.
 *
 * Side effects:
 *    Caches the name to return for future calls.
 *
 *----------------------------------------------------------------------
 */

const char *
Tcl_GetHostName(void)
{
    return Tcl_GetString(TclGetProcessGlobalValue(&hostName));
}

/*
 *----------------------------------------------------------------------
 *
 * InitializeHostName --
 *
 *    This routine sets the process global value of the name of the local
 *    host on which the process is running.
 *
 * Results:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
InitializeHostName(
    char **valuePtr,
    int *lengthPtr,
    Tcl_Encoding *encodingPtr)
{
    WCHAR wbuf[MAX_COMPUTERNAME_LENGTH + 1];
    DWORD length = sizeof(wbuf) / sizeof(WCHAR);
    Tcl_DString ds;

    if ((*tclWinProcs->getComputerNameProc)(wbuf, &length) != 0) {
      /*
       * Convert string from native to UTF then change to lowercase.
       */

      Tcl_UtfToLower(Tcl_WinTCharToUtf((TCHAR *) wbuf, -1, &ds));

    } else {
      Tcl_DStringInit(&ds);
      if (TclpHasSockets(NULL) == TCL_OK) {
          /*
           * Buffer length of 255 copied slavishly from previous version of
           * this routine. Presumably there's a more "correct" macro value
           * for a properly sized buffer for a gethostname() call.
           * Maintainers are welcome to supply it.
           */

          Tcl_DString inDs;

          Tcl_DStringInit(&inDs);
          Tcl_DStringSetLength(&inDs, 255);
          if (gethostname(Tcl_DStringValue(&inDs),
                      Tcl_DStringLength(&inDs)) == 0) {
            Tcl_DStringSetLength(&ds, 0);
          } else {
            Tcl_ExternalToUtfDString(NULL,
                  Tcl_DStringValue(&inDs), -1, &ds);
          }
          Tcl_DStringFree(&inDs);
      }
    }

    *encodingPtr = Tcl_GetEncoding(NULL, "utf-8");
    *lengthPtr = Tcl_DStringLength(&ds);
    *valuePtr = ckalloc((unsigned int) (*lengthPtr)+1);
    memcpy(*valuePtr, Tcl_DStringValue(&ds), (size_t)(*lengthPtr)+1);
    Tcl_DStringFree(&ds);
}

/*
 *----------------------------------------------------------------------
 *
 * TclWinGetSockOpt, et al. --
 *
 *    These functions are wrappers that let us bind the WinSock API
 *    dynamically so we can run on systems that don't have the wsock32.dll.
 *    We need wrappers for these interfaces because they are called from the
 *    generic Tcl code.
 *
 * Results:
 *    As defined for each function.
 *
 * Side effects:
 *    As defined for each function.
 *
 *----------------------------------------------------------------------
 */

int
TclWinGetSockOpt(
    int s,
    int level,
    int optname,
    char * optval,
    int FAR *optlen)
{
    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      return SOCKET_ERROR;
    }

    return getsockopt((SOCKET)s, level, optname, optval, optlen);
}

int
TclWinSetSockOpt(
    int s,
    int level,
    int optname,
    const char * optval,
    int optlen)
{
    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      return SOCKET_ERROR;
    }

    return setsockopt((SOCKET)s, level, optname, optval, optlen);
}

u_short
TclWinNToHS(
    u_short netshort)
{
    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      return (u_short) -1;
    }

    return ntohs(netshort);
}

struct servent *
TclWinGetServByName(
    const char *name,
    const char *proto)
{
    /*
     * Check that WinSock is initialized; do not call it if not, to prevent
     * system crashes. This can happen at exit time if the exit handler for
     * WinSock ran before other exit handlers that want to use sockets.
     */

    if (!SocketsEnabled()) {
      return NULL;
    }

    return getservbyname(name, proto);
}

/*
 *----------------------------------------------------------------------
 *
 * TcpThreadActionProc --
 *
 *    Insert or remove any thread local refs to this channel.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Changes thread local list of valid channels.
 *
 *----------------------------------------------------------------------
 */

static void
TcpThreadActionProc(
    ClientData instanceData,
    int action)
{
    ThreadSpecificData *tsdPtr;
    SocketInfo *infoPtr = (SocketInfo *) instanceData;
    int notifyCmd;

    if (action == TCL_CHANNEL_THREAD_INSERT) {
      /*
       * Ensure that socket subsystem is initialized in this thread, or else
       * sockets will not work.
       */

      Tcl_MutexLock(&socketMutex);
      InitSockets();
      Tcl_MutexUnlock(&socketMutex);

      tsdPtr = TCL_TSD_INIT(&dataKey);

      WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
      infoPtr->nextPtr = tsdPtr->socketList;
      tsdPtr->socketList = infoPtr;
      SetEvent(tsdPtr->socketListLock);

      notifyCmd = SELECT;
    } else {
      SocketInfo **nextPtrPtr;
      int removed = 0;

      tsdPtr = TCL_TSD_INIT(&dataKey);

      /*
       * TIP #218, Bugfix: All access to socketList has to be protected by
       * the lock.
       */

      WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
      for (nextPtrPtr = &(tsdPtr->socketList); (*nextPtrPtr) != NULL;
            nextPtrPtr = &((*nextPtrPtr)->nextPtr)) {
          if ((*nextPtrPtr) == infoPtr) {
            (*nextPtrPtr) = infoPtr->nextPtr;
            removed = 1;
            break;
          }
      }
      SetEvent(tsdPtr->socketListLock);

      /*
       * This could happen if the channel was created in one thread and then
       * moved to another without updating the thread local data in each
       * thread.
       */

      if (!removed) {
          Tcl_Panic("file info ptr not on thread channel list");
      }

      notifyCmd = UNSELECT;
    }

    /*
     * Ensure that, or stop, notifications for the socket occur in this
     * thread.
     */

    SendMessage(tsdPtr->hwnd, SOCKET_SELECT,
          (WPARAM) notifyCmd, (LPARAM) infoPtr);
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */

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