groupsock/GroupsockHelper.cpp

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/**********
This library is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the
Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.)

This library is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
more details.

You should have received a copy of the GNU Lesser General Public License
along with this library; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
**********/
// "mTunnel" multicast access service
// Copyright (c) 1996-2010 Live Networks, Inc.  All rights reserved.
// Helper routines to implement 'group sockets'
// Implementation

#include "GroupsockHelper.hh"

#if defined(__WIN32__) || defined(_WIN32)
#include <time.h>
extern "C" int initializeWinsockIfNecessary();
#else
#include <stdarg.h>
#include <time.h>
#include <fcntl.h>
#define initializeWinsockIfNecessary() 1
#endif
#include <stdio.h>

// By default, use INADDR_ANY for the sending and receiving interfaces:
netAddressBits SendingInterfaceAddr = INADDR_ANY;
netAddressBits ReceivingInterfaceAddr = INADDR_ANY;

static void socketErr(UsageEnvironment& env, char const* errorMsg) {
        env.setResultErrMsg(errorMsg);
}

static int reuseFlag = 1;

NoReuse::NoReuse() {
  reuseFlag = 0;
}

NoReuse::~NoReuse() {
  reuseFlag = 1;
}

int setupDatagramSocket(UsageEnvironment& env, Port port) {
  if (!initializeWinsockIfNecessary()) {
    socketErr(env, "Failed to initialize 'winsock': ");
    return -1;
  }

  int newSocket = socket(AF_INET, SOCK_DGRAM, 0);
  if (newSocket < 0) {
    socketErr(env, "unable to create datagram socket: ");
    return newSocket;
  }

  if (setsockopt(newSocket, SOL_SOCKET, SO_REUSEADDR,
                 (const char*)&reuseFlag, sizeof reuseFlag) < 0) {
    socketErr(env, "setsockopt(SO_REUSEADDR) error: ");
    closeSocket(newSocket);
    return -1;
  }

#if defined(__WIN32__) || defined(_WIN32)
  // Windoze doesn't properly handle SO_REUSEPORT or IP_MULTICAST_LOOP
#else
#ifdef SO_REUSEPORT
  if (setsockopt(newSocket, SOL_SOCKET, SO_REUSEPORT,
                 (const char*)&reuseFlag, sizeof reuseFlag) < 0) {
    socketErr(env, "setsockopt(SO_REUSEPORT) error: ");
    closeSocket(newSocket);
    return -1;
  }
#endif

#ifdef IP_MULTICAST_LOOP
  const u_int8_t loop = 1;
  if (setsockopt(newSocket, IPPROTO_IP, IP_MULTICAST_LOOP,
                 (const char*)&loop, sizeof loop) < 0) {
    socketErr(env, "setsockopt(IP_MULTICAST_LOOP) error: ");
    closeSocket(newSocket);
    return -1;
  }
#endif
#endif

  // Note: Windoze requires binding, even if the port number is 0
  netAddressBits addr = INADDR_ANY;
#if defined(__WIN32__) || defined(_WIN32)
#else
  if (port.num() != 0 || ReceivingInterfaceAddr != INADDR_ANY) {
#endif
    if (port.num() == 0) addr = ReceivingInterfaceAddr;
    MAKE_SOCKADDR_IN(name, addr, port.num());
    if (bind(newSocket, (struct sockaddr*)&name, sizeof name) != 0) {
      char tmpBuffer[100];
      sprintf(tmpBuffer, "bind() error (port number: %d): ",
              ntohs(port.num()));
      socketErr(env, tmpBuffer);
      closeSocket(newSocket);
      return -1;
    }
#if defined(__WIN32__) || defined(_WIN32)
#else
  }
#endif

  // Set the sending interface for multicasts, if it's not the default:
  if (SendingInterfaceAddr != INADDR_ANY) {
    struct in_addr addr;
    addr.s_addr = SendingInterfaceAddr;

    if (setsockopt(newSocket, IPPROTO_IP, IP_MULTICAST_IF,
                   (const char*)&addr, sizeof addr) < 0) {
      socketErr(env, "error setting outgoing multicast interface: ");
      closeSocket(newSocket);
      return -1;
    }
  }

  return newSocket;
}

Boolean makeSocketNonBlocking(int sock) {
#if defined(__WIN32__) || defined(_WIN32) || defined(IMN_PIM)
  unsigned long arg = 1;
  return ioctlsocket(sock, FIONBIO, &arg) == 0;
#elif defined(VXWORKS)
  int arg = 1;
  return ioctl(sock, FIONBIO, (int)&arg) == 0;
#else
  int curFlags = fcntl(sock, F_GETFL, 0);
  return fcntl(sock, F_SETFL, curFlags|O_NONBLOCK) >= 0;
#endif
}

Boolean makeSocketBlocking(int sock) {
#if defined(__WIN32__) || defined(_WIN32) || defined(IMN_PIM)
  unsigned long arg = 0;
  return ioctlsocket(sock, FIONBIO, &arg) == 0;
#elif defined(VXWORKS)
  int arg = 0;
  return ioctl(sock, FIONBIO, (int)&arg) == 0;
#else
  int curFlags = fcntl(sock, F_GETFL, 0);
  return fcntl(sock, F_SETFL, curFlags&(~O_NONBLOCK)) >= 0;
#endif
}

int setupStreamSocket(UsageEnvironment& env,
                      Port port, Boolean makeNonBlocking) {
  if (!initializeWinsockIfNecessary()) {
    socketErr(env, "Failed to initialize 'winsock': ");
    return -1;
  }

  int newSocket = socket(AF_INET, SOCK_STREAM, 0);
  if (newSocket < 0) {
    socketErr(env, "unable to create stream socket: ");
    return newSocket;
  }

  if (setsockopt(newSocket, SOL_SOCKET, SO_REUSEADDR,
                 (const char*)&reuseFlag, sizeof reuseFlag) < 0) {
    socketErr(env, "setsockopt(SO_REUSEADDR) error: ");
    closeSocket(newSocket);
    return -1;
  }

  // SO_REUSEPORT doesn't really make sense for TCP sockets, so we
  // normally don't set them.  However, if you really want to do this
  // #define REUSE_FOR_TCP
#ifdef REUSE_FOR_TCP
#if defined(__WIN32__) || defined(_WIN32)
  // Windoze doesn't properly handle SO_REUSEPORT
#else
#ifdef SO_REUSEPORT
  if (setsockopt(newSocket, SOL_SOCKET, SO_REUSEPORT,
                 (const char*)&reuseFlag, sizeof reuseFlag) < 0) {
    socketErr(env, "setsockopt(SO_REUSEPORT) error: ");
    closeSocket(newSocket);
    return -1;
  }
#endif
#endif
#endif

  // Note: Windoze requires binding, even if the port number is 0
#if defined(__WIN32__) || defined(_WIN32)
#else
  if (port.num() != 0 || ReceivingInterfaceAddr != INADDR_ANY) {
#endif
    MAKE_SOCKADDR_IN(name, ReceivingInterfaceAddr, port.num());
    if (bind(newSocket, (struct sockaddr*)&name, sizeof name) != 0) {
      char tmpBuffer[100];
      sprintf(tmpBuffer, "bind() error (port number: %d): ",
              ntohs(port.num()));
      socketErr(env, tmpBuffer);
      closeSocket(newSocket);
      return -1;
    }
#if defined(__WIN32__) || defined(_WIN32)
#else
  }
#endif

  if (makeNonBlocking) {
    if (!makeSocketNonBlocking(newSocket)) {
      socketErr(env, "failed to make non-blocking: ");
      closeSocket(newSocket);
      return -1;
    }
  }

  return newSocket;
}

int readSocket(UsageEnvironment& env,
               int socket, unsigned char* buffer, unsigned bufferSize,
               struct sockaddr_in& fromAddress) {
  SOCKLEN_T addressSize = sizeof fromAddress;
  int bytesRead = recvfrom(socket, (char*)buffer, bufferSize, 0,
                           (struct sockaddr*)&fromAddress,
                           &addressSize);
  if (bytesRead < 0) {
    //##### HACK to work around bugs in Linux and Windows:
    int err = env.getErrno();
    if (err == 111 /*ECONNREFUSED (Linux)*/
#if defined(__WIN32__) || defined(_WIN32)
        // What a piece of crap Windows is.  Sometimes
        // recvfrom() returns -1, but with an 'errno' of 0.
        // This appears not to be a real error; just treat
        // it as if it were a read of zero bytes, and hope
        // we don't have to do anything else to 'reset'
        // this alleged error:
        || err == 0 || err == EWOULDBLOCK
#else
        || err == EAGAIN
#endif
        || err == 113 /*EHOSTUNREACH (Linux)*/) { // Why does Linux return this for datagram sock?
      fromAddress.sin_addr.s_addr = 0;
      return 0;
    }
    //##### END HACK
    socketErr(env, "recvfrom() error: ");
  }

  return bytesRead;
}

Boolean writeSocket(UsageEnvironment& env,
                    int socket, struct in_addr address, Port port,
                    u_int8_t ttlArg,
                    unsigned char* buffer, unsigned bufferSize) {
        do {
                if (ttlArg != 0) {
                        // Before sending, set the socket's TTL:
#if defined(__WIN32__) || defined(_WIN32)
#define TTL_TYPE int
#else
#define TTL_TYPE u_int8_t
#endif
                        TTL_TYPE ttl = (TTL_TYPE)ttlArg;
                        if (setsockopt(socket, IPPROTO_IP, IP_MULTICAST_TTL,
                                       (const char*)&ttl, sizeof ttl) < 0) {
                                socketErr(env, "setsockopt(IP_MULTICAST_TTL) error: ");
                                break;
                        }
                }

                MAKE_SOCKADDR_IN(dest, address.s_addr, port.num());
                int bytesSent = sendto(socket, (char*)buffer, bufferSize, 0,
                                       (struct sockaddr*)&dest, sizeof dest);
                if (bytesSent != (int)bufferSize) {
                        char tmpBuf[100];
                        sprintf(tmpBuf, "writeSocket(%d), sendTo() error: wrote %d bytes instead of %u: ", socket, bytesSent, bufferSize);
                        socketErr(env, tmpBuf);
                        break;
                }

                return True;
        } while (0);

        return False;
}

static unsigned getBufferSize(UsageEnvironment& env, int bufOptName,
                              int socket) {
  unsigned curSize;
  SOCKLEN_T sizeSize = sizeof curSize;
  if (getsockopt(socket, SOL_SOCKET, bufOptName,
                 (char*)&curSize, &sizeSize) < 0) {
    socketErr(env, "getBufferSize() error: ");
    return 0;
  }

  return curSize;
}
unsigned getSendBufferSize(UsageEnvironment& env, int socket) {
  return getBufferSize(env, SO_SNDBUF, socket);
}
unsigned getReceiveBufferSize(UsageEnvironment& env, int socket) {
  return getBufferSize(env, SO_RCVBUF, socket);
}

static unsigned setBufferTo(UsageEnvironment& env, int bufOptName,
                            int socket, unsigned requestedSize) {
  SOCKLEN_T sizeSize = sizeof requestedSize;
  setsockopt(socket, SOL_SOCKET, bufOptName, (char*)&requestedSize, sizeSize);

  // Get and return the actual, resulting buffer size:
  return getBufferSize(env, bufOptName, socket);
}
unsigned setSendBufferTo(UsageEnvironment& env,
                         int socket, unsigned requestedSize) {
        return setBufferTo(env, SO_SNDBUF, socket, requestedSize);
}
unsigned setReceiveBufferTo(UsageEnvironment& env,
                            int socket, unsigned requestedSize) {
        return setBufferTo(env, SO_RCVBUF, socket, requestedSize);
}

static unsigned increaseBufferTo(UsageEnvironment& env, int bufOptName,
                                 int socket, unsigned requestedSize) {
  // First, get the current buffer size.  If it's already at least
  // as big as what we're requesting, do nothing.
  unsigned curSize = getBufferSize(env, bufOptName, socket);

  // Next, try to increase the buffer to the requested size,
  // or to some smaller size, if that's not possible:
  while (requestedSize > curSize) {
    SOCKLEN_T sizeSize = sizeof requestedSize;
    if (setsockopt(socket, SOL_SOCKET, bufOptName,
                   (char*)&requestedSize, sizeSize) >= 0) {
      // success
      return requestedSize;
    }
    requestedSize = (requestedSize+curSize)/2;
  }

  return getBufferSize(env, bufOptName, socket);
}
unsigned increaseSendBufferTo(UsageEnvironment& env,
                              int socket, unsigned requestedSize) {
  return increaseBufferTo(env, SO_SNDBUF, socket, requestedSize);
}
unsigned increaseReceiveBufferTo(UsageEnvironment& env,
                                 int socket, unsigned requestedSize) {
  return increaseBufferTo(env, SO_RCVBUF, socket, requestedSize);
}

Boolean socketJoinGroup(UsageEnvironment& env, int socket,
                        netAddressBits groupAddress){
  if (!IsMulticastAddress(groupAddress)) return True; // ignore this case

  struct ip_mreq imr;
  imr.imr_multiaddr.s_addr = groupAddress;
  imr.imr_interface.s_addr = ReceivingInterfaceAddr;
  if (setsockopt(socket, IPPROTO_IP, IP_ADD_MEMBERSHIP,
                 (const char*)&imr, sizeof (struct ip_mreq)) < 0) {
#if defined(__WIN32__) || defined(_WIN32)
    if (env.getErrno() != 0) {
      // That piece-of-shit toy operating system (Windows) sometimes lies
      // about setsockopt() failing!
#endif
      socketErr(env, "setsockopt(IP_ADD_MEMBERSHIP) error: ");
      return False;
#if defined(__WIN32__) || defined(_WIN32)
    }
#endif
  }

  return True;
}

Boolean socketLeaveGroup(UsageEnvironment&, int socket,
                         netAddressBits groupAddress) {
  if (!IsMulticastAddress(groupAddress)) return True; // ignore this case

  struct ip_mreq imr;
  imr.imr_multiaddr.s_addr = groupAddress;
  imr.imr_interface.s_addr = ReceivingInterfaceAddr;
  if (setsockopt(socket, IPPROTO_IP, IP_DROP_MEMBERSHIP,
                 (const char*)&imr, sizeof (struct ip_mreq)) < 0) {
    return False;
  }

  return True;
}

// The source-specific join/leave operations require special setsockopt()
// commands, and a special structure (ip_mreq_source).  If the include files
// didn't define these, we do so here:
#if !defined(IP_ADD_SOURCE_MEMBERSHIP)
struct ip_mreq_source {
  struct  in_addr imr_multiaddr;  /* IP multicast address of group */
  struct  in_addr imr_sourceaddr; /* IP address of source */
  struct  in_addr imr_interface;  /* local IP address of interface */
};
#endif

#ifndef IP_ADD_SOURCE_MEMBERSHIP

#ifdef LINUX
#define IP_ADD_SOURCE_MEMBERSHIP   39
#define IP_DROP_SOURCE_MEMBERSHIP 40
#else
#define IP_ADD_SOURCE_MEMBERSHIP   25
#define IP_DROP_SOURCE_MEMBERSHIP 26
#endif

#endif

Boolean socketJoinGroupSSM(UsageEnvironment& env, int socket,
                           netAddressBits groupAddress,
                           netAddressBits sourceFilterAddr) {
  if (!IsMulticastAddress(groupAddress)) return True; // ignore this case

  struct ip_mreq_source imr;
  imr.imr_multiaddr.s_addr = groupAddress;
  imr.imr_sourceaddr.s_addr = sourceFilterAddr;
  imr.imr_interface.s_addr = ReceivingInterfaceAddr;
  if (setsockopt(socket, IPPROTO_IP, IP_ADD_SOURCE_MEMBERSHIP,
                 (const char*)&imr, sizeof (struct ip_mreq_source)) < 0) {
    socketErr(env, "setsockopt(IP_ADD_SOURCE_MEMBERSHIP) error: ");
    return False;
  }

  return True;
}

Boolean socketLeaveGroupSSM(UsageEnvironment& /*env*/, int socket,
                            netAddressBits groupAddress,
                            netAddressBits sourceFilterAddr) {
  if (!IsMulticastAddress(groupAddress)) return True; // ignore this case

  struct ip_mreq_source imr;
  imr.imr_multiaddr.s_addr = groupAddress;
  imr.imr_sourceaddr.s_addr = sourceFilterAddr;
  imr.imr_interface.s_addr = ReceivingInterfaceAddr;
  if (setsockopt(socket, IPPROTO_IP, IP_DROP_SOURCE_MEMBERSHIP,
                 (const char*)&imr, sizeof (struct ip_mreq_source)) < 0) {
    return False;
  }

  return True;
}

static Boolean getSourcePort0(int socket, portNumBits& resultPortNum/*host order*/) {
  sockaddr_in test; test.sin_port = 0;
  SOCKLEN_T len = sizeof test;
  if (getsockname(socket, (struct sockaddr*)&test, &len) < 0) return False;

  resultPortNum = ntohs(test.sin_port);
  return True;
}

Boolean getSourcePort(UsageEnvironment& env, int socket, Port& port) {
  portNumBits portNum = 0;
  if (!getSourcePort0(socket, portNum) || portNum == 0) {
    // Hack - call bind(), then try again:
    MAKE_SOCKADDR_IN(name, INADDR_ANY, 0);
    bind(socket, (struct sockaddr*)&name, sizeof name);

    if (!getSourcePort0(socket, portNum) || portNum == 0) {
      socketErr(env, "getsockname() error: ");
      return False;
    }
  }

  port = Port(portNum);
  return True;
}

static Boolean badAddress(netAddressBits addr) {
  // Check for some possible erroneous addresses:
  netAddressBits hAddr = ntohl(addr);
  return (hAddr == 0x7F000001 /* 127.0.0.1 */
          || hAddr == 0
          || hAddr == (netAddressBits)(~0));
}

Boolean loopbackWorks = 1;

netAddressBits ourIPAddress(UsageEnvironment& env) {
  static netAddressBits ourAddress = 0;
  int sock = -1;
  struct in_addr testAddr;

  if (ourAddress == 0) {
    // We need to find our source address
    struct sockaddr_in fromAddr;
    fromAddr.sin_addr.s_addr = 0;

    // Get our address by sending a (0-TTL) multicast packet,
    // receiving it, and looking at the source address used.
    // (This is kinda bogus, but it provides the best guarantee
    // that other nodes will think our address is the same as we do.)
    do {
      loopbackWorks = 0; // until we learn otherwise

      testAddr.s_addr = our_inet_addr("228.67.43.91"); // arbitrary
      Port testPort(15947); // ditto

      sock = setupDatagramSocket(env, testPort);
      if (sock < 0) break;

      if (!socketJoinGroup(env, sock, testAddr.s_addr)) break;

      unsigned char testString[] = "hostIdTest";
      unsigned testStringLength = sizeof testString;

      if (!writeSocket(env, sock, testAddr, testPort, 0,
                       testString, testStringLength)) break;

      // Block until the socket is readable (with a 5-second timeout):
      fd_set rd_set;
      FD_ZERO(&rd_set);
      FD_SET((unsigned)sock, &rd_set);
      const unsigned numFds = sock+1;
      struct timeval timeout;
      timeout.tv_sec = 5;
      timeout.tv_usec = 0;
      int result = select(numFds, &rd_set, NULL, NULL, &timeout);
      if (result <= 0) break;

      unsigned char readBuffer[20];
      int bytesRead = readSocket(env, sock,
                                 readBuffer, sizeof readBuffer,
                                 fromAddr);
      if (bytesRead != (int)testStringLength
          || strncmp((char*)readBuffer, (char*)testString, testStringLength) != 0) {
        break;
      }

      loopbackWorks = 1;
    } while (0);

    if (!loopbackWorks) do {
      // We couldn't find our address using multicast loopback
      // so try instead to look it up directly.
      char hostname[100];
      hostname[0] = '\0';
      gethostname(hostname, sizeof hostname);
      if (hostname[0] == '\0') {
        env.setResultErrMsg("initial gethostname() failed");
        break;
      }

#if defined(VXWORKS)
#include <hostLib.h>
      if (ERROR == (ourAddress = hostGetByName( hostname ))) break;
#else
      struct hostent* hstent
        = (struct hostent*)gethostbyname(hostname);
      if (hstent == NULL || hstent->h_length != 4) {
        env.setResultErrMsg("initial gethostbyname() failed");
        break;
      }
      // Take the first address that's not bad
      // (This code, like many others, won't handle IPv6)
      netAddressBits addr = 0;
      for (unsigned i = 0; ; ++i) {
        char* addrPtr = hstent->h_addr_list[i];
        if (addrPtr == NULL) break;

        netAddressBits a = *(netAddressBits*)addrPtr;
        if (!badAddress(a)) {
          addr = a;
          break;
        }
      }
      if (addr != 0) {
        fromAddr.sin_addr.s_addr = addr;
      } else {
        env.setResultMsg("no address");
        break;
      }
    } while (0);

    // Make sure we have a good address:
    netAddressBits from = fromAddr.sin_addr.s_addr;
    if (badAddress(from)) {
      char tmp[100];
      sprintf(tmp,
              "This computer has an invalid IP address: 0x%x",
              (netAddressBits)(ntohl(from)));
      env.setResultMsg(tmp);
      from = 0;
    }

    ourAddress = from;
#endif

    if (sock >= 0) {
      socketLeaveGroup(env, sock, testAddr.s_addr);
      closeSocket(sock);
    }

    // Use our newly-discovered IP address, and the current time,
    // to initialize the random number generator's seed:
    struct timeval timeNow;
    gettimeofday(&timeNow, NULL);
    unsigned seed = ourAddress^timeNow.tv_sec^timeNow.tv_usec;
    our_srandom(seed);
  }
  return ourAddress;
}

netAddressBits chooseRandomIPv4SSMAddress(UsageEnvironment& env) {
  // First, a hack to ensure that our random number generator is seeded:
  (void) ourIPAddress(env);

  // Choose a random address in the range [232.0.1.0, 232.255.255.255)
  // i.e., [0xE8000100, 0xE8FFFFFF)
  netAddressBits const first = 0xE8000100, lastPlus1 = 0xE8FFFFFF;
  netAddressBits const range = lastPlus1 - first;

  return htonl(first + ((netAddressBits)our_random())%range);
}

char const* timestampString() {
  struct timeval tvNow;
  gettimeofday(&tvNow, NULL);

#if !defined(_WIN32_WCE)
  static char timeString[9]; // holds hh:mm:ss plus trailing '\0'
  char const* ctimeResult = ctime((time_t*)&tvNow.tv_sec);
  char const* from = &ctimeResult[11];
  int i;
  for (i = 0; i < 8; ++i) {
    timeString[i] = from[i];
  }
  timeString[i] = '\0';
#else
  // WinCE apparently doesn't have "ctime()", so instead, construct
  // a timestamp string just using the integer and fractional parts
  // of "tvNow":
  static char timeString[50];
  sprintf(timeString, "%lu.%06ld", tvNow.tv_sec, tvNow.tv_usec);
#endif

  return (char const*)&timeString;
}

#if (defined(__WIN32__) || defined(_WIN32)) && !defined(IMN_PIM)
// For Windoze, we need to implement our own gettimeofday()
#if !defined(_WIN32_WCE)
#include <sys/timeb.h>
#endif

int gettimeofday(struct timeval* tp, int* /*tz*/) {
#if defined(_WIN32_WCE)
  /* FILETIME of Jan 1 1970 00:00:00. */
  static const unsigned __int64 epoch = 116444736000000000LL;

  FILETIME    file_time;
  SYSTEMTIME  system_time;
  ULARGE_INTEGER ularge;

  GetSystemTime(&system_time);
  SystemTimeToFileTime(&system_time, &file_time);
  ularge.LowPart = file_time.dwLowDateTime;
  ularge.HighPart = file_time.dwHighDateTime;

  tp->tv_sec = (long) ((ularge.QuadPart - epoch) / 10000000L);
  tp->tv_usec = (long) (system_time.wMilliseconds * 1000);
#else
  static LARGE_INTEGER tickFrequency, epochOffset;

  // For our first call, use "ftime()", so that we get a time with a proper epoch.
  // For subsequent calls, use "QueryPerformanceCount()", because it's more fine-grain.
  static Boolean isFirstCall = True;

  LARGE_INTEGER tickNow;
  QueryPerformanceCounter(&tickNow);

  if (isFirstCall) {
    struct timeb tb;
    ftime(&tb);
    tp->tv_sec = tb.time;
    tp->tv_usec = 1000*tb.millitm;

    // Also get our counter frequency:
    QueryPerformanceFrequency(&tickFrequency);

    // And compute an offset to add to subsequent counter times, so we get a proper epoch:
    epochOffset.QuadPart
      = tb.time*tickFrequency.QuadPart + (tb.millitm*tickFrequency.QuadPart)/1000 - tickNow.QuadPart;

    isFirstCall = False; // for next time
  } else {
    // Adjust our counter time so that we get a proper epoch:
    tickNow.QuadPart += epochOffset.QuadPart;

    tp->tv_sec = (long) (tickNow.QuadPart / tickFrequency.QuadPart);
    tp->tv_usec = (long) (((tickNow.QuadPart % tickFrequency.QuadPart) * 1000000L) / tickFrequency.QuadPart);
  }
#endif
  return 0;
}
#endif

---