path: root/lib/select.c

/* Emulation for select(2)
   Contributed by Paolo Bonzini.

   Copyright 2008-2023 Free Software Foundation, Inc.

   This file is part of gnulib.

   This file 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.

   This file 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 program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include <sys/select.h>

#if defined _WIN32 && ! defined __CYGWIN__
/* Native Windows.  */

#include <alloca.h>
#include <assert.h>
#include <sys/types.h>
#include <errno.h>
#include <limits.h>

#include <winsock2.h>
#include <windows.h>
#include <io.h>
#include <stdio.h>
#include <conio.h>
#include <time.h>

/* Get the overridden 'struct timeval'.  */
#include <sys/time.h>

#if GNULIB_MSVC_NOTHROW
# include "msvc-nothrow.h"
#else
# include <io.h>
#endif

#undef select

/* Don't assume that UNICODE is not defined.  */
#undef GetModuleHandle
#define GetModuleHandle GetModuleHandleA
#undef PeekConsoleInput
#define PeekConsoleInput PeekConsoleInputA
#undef CreateEvent
#define CreateEvent CreateEventA
#undef PeekMessage
#define PeekMessage PeekMessageA
#undef DispatchMessage
#define DispatchMessage DispatchMessageA

/* Avoid warnings from gcc -Wcast-function-type.  */
#define GetProcAddress \
  (void *) GetProcAddress

struct bitset {
  unsigned char in[FD_SETSIZE / CHAR_BIT];
  unsigned char out[FD_SETSIZE / CHAR_BIT];
};

/* Declare data structures for ntdll functions.  */
typedef struct _FILE_PIPE_LOCAL_INFORMATION {
  ULONG NamedPipeType;
  ULONG NamedPipeConfiguration;
  ULONG MaximumInstances;
  ULONG CurrentInstances;
  ULONG InboundQuota;
  ULONG ReadDataAvailable;
  ULONG OutboundQuota;
  ULONG WriteQuotaAvailable;
  ULONG NamedPipeState;
  ULONG NamedPipeEnd;
} FILE_PIPE_LOCAL_INFORMATION, *PFILE_PIPE_LOCAL_INFORMATION;

typedef struct _IO_STATUS_BLOCK
{
  union {
    DWORD Status;
    PVOID Pointer;
  } u;
  ULONG_PTR Information;
} IO_STATUS_BLOCK, *PIO_STATUS_BLOCK;

typedef enum _FILE_INFORMATION_CLASS {
  FilePipeLocalInformation = 24
} FILE_INFORMATION_CLASS, *PFILE_INFORMATION_CLASS;

typedef DWORD (WINAPI *PNtQueryInformationFile)
         (HANDLE, IO_STATUS_BLOCK *, VOID *, ULONG, FILE_INFORMATION_CLASS);

#ifndef PIPE_BUF
#define PIPE_BUF        512
#endif

static BOOL IsConsoleHandle (HANDLE h)
{
  DWORD mode;
  return GetConsoleMode (h, &mode) != 0;
}

static BOOL
IsSocketHandle (HANDLE h)
{
  WSANETWORKEVENTS ev;

  if (IsConsoleHandle (h))
    return FALSE;

  /* Under Wine, it seems that getsockopt returns 0 for pipes too.
     WSAEnumNetworkEvents instead distinguishes the two correctly.  */
  ev.lNetworkEvents = 0xDEADBEEF;
  WSAEnumNetworkEvents ((SOCKET) h, NULL, &ev);
  return ev.lNetworkEvents != 0xDEADBEEF;
}

/* Compute output fd_sets for libc descriptor FD (whose Windows handle is
   H).  */

static int
windows_poll_handle (HANDLE h, int fd,
                     struct bitset *rbits,
                     struct bitset *wbits,
                     struct bitset *xbits)
{
  BOOL read, write, except;
  int i, ret;
  INPUT_RECORD *irbuffer;
  DWORD avail, nbuffer;
  BOOL bRet;
  IO_STATUS_BLOCK iosb;
  FILE_PIPE_LOCAL_INFORMATION fpli;
  static PNtQueryInformationFile NtQueryInformationFile;
  static BOOL once_only;

  read = write = except = FALSE;
  switch (GetFileType (h))
    {
    case FILE_TYPE_DISK:
      read = TRUE;
      write = TRUE;
      break;

    case FILE_TYPE_PIPE:
      if (!once_only)
        {
          NtQueryInformationFile = (PNtQueryInformationFile)
            GetProcAddress (GetModuleHandle ("ntdll.dll"),
                            "NtQueryInformationFile");
          once_only = TRUE;
        }

      if (PeekNamedPipe (h, NULL, 0, NULL, &avail, NULL) != 0)
        {
          if (avail)
            read = TRUE;
        }
      else if (GetLastError () == ERROR_BROKEN_PIPE)
        ;

      else
        {
          /* It was the write-end of the pipe.  Check if it is writable.
             If NtQueryInformationFile fails, optimistically assume the pipe is
             writable.  This could happen on Windows 9x, where
             NtQueryInformationFile is not available, or if we inherit a pipe
             that doesn't permit FILE_READ_ATTRIBUTES access on the write end
             (I think this should not happen since Windows XP SP2; WINE seems
             fine too).  Otherwise, ensure that enough space is available for
             atomic writes.  */
          memset (&iosb, 0, sizeof (iosb));
          memset (&fpli, 0, sizeof (fpli));

          if (!NtQueryInformationFile
              || NtQueryInformationFile (h, &iosb, &fpli, sizeof (fpli),
                                         FilePipeLocalInformation)
              || fpli.WriteQuotaAvailable >= PIPE_BUF
              || (fpli.OutboundQuota < PIPE_BUF &&
                  fpli.WriteQuotaAvailable == fpli.OutboundQuota))
            write = TRUE;
        }
      break;

    case FILE_TYPE_CHAR:
      write = TRUE;
      if (!(rbits->in[fd / CHAR_BIT] & (1 << (fd & (CHAR_BIT - 1)))))
        break;

      ret = WaitForSingleObject (h, 0);
      if (ret == WAIT_OBJECT_0)
        {
          if (!IsConsoleHandle (h))
            {
              read = TRUE;
              break;
            }

          nbuffer = avail = 0;
          bRet = GetNumberOfConsoleInputEvents (h, &nbuffer);

          /* Screen buffers handles are filtered earlier.  */
          assert (bRet);
          if (nbuffer == 0)
            {
              except = TRUE;
              break;
            }

          irbuffer = (INPUT_RECORD *) alloca (nbuffer * sizeof (INPUT_RECORD));
          bRet = PeekConsoleInput (h, irbuffer, nbuffer, &avail);
          if (!bRet || avail == 0)
            {
              except = TRUE;
              break;
            }

          for (i = 0; i < avail; i++)
            if (irbuffer[i].EventType == KEY_EVENT)
              read = TRUE;
        }
      break;

    default:
      ret = WaitForSingleObject (h, 0);
      write = TRUE;
      if (ret == WAIT_OBJECT_0)
        read = TRUE;

      break;
    }

  ret = 0;
  if (read && (rbits->in[fd / CHAR_BIT] & (1 << (fd & (CHAR_BIT - 1)))))
    {
      rbits->out[fd / CHAR_BIT] |= (1 << (fd & (CHAR_BIT - 1)));
      ret++;
    }

  if (write && (wbits->in[fd / CHAR_BIT] & (1 << (fd & (CHAR_BIT - 1)))))
    {
      wbits->out[fd / CHAR_BIT] |= (1 << (fd & (CHAR_BIT - 1)));
      ret++;
    }

  if (except && (xbits->in[fd / CHAR_BIT] & (1 << (fd & (CHAR_BIT - 1)))))
    {
      xbits->out[fd / CHAR_BIT] |= (1 << (fd & (CHAR_BIT - 1)));
      ret++;
    }

  return ret;
}

int
rpl_select (int nfds, fd_set *rfds, fd_set *wfds, fd_set *xfds,
            struct timeval *timeout)
#undef timeval
{
  static struct timeval tv0;
  static HANDLE hEvent;
  HANDLE h, handle_array[FD_SETSIZE + 2];
  fd_set handle_rfds, handle_wfds, handle_xfds;
  struct bitset rbits, wbits, xbits;
  unsigned char anyfds_in[FD_SETSIZE / CHAR_BIT];
  DWORD ret, wait_timeout, nhandles, nsock, nbuffer;
  MSG msg;
  int i, fd, rc;
  clock_t tend;

  if (nfds > FD_SETSIZE)
    nfds = FD_SETSIZE;

  if (!timeout)
    wait_timeout = INFINITE;
  else
    {
      wait_timeout = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;

      /* select is also used as a portable usleep.  */
      if (!rfds && !wfds && !xfds)
        {
          Sleep (wait_timeout);
          return 0;
        }
    }

  if (!hEvent)
    hEvent = CreateEvent (NULL, FALSE, FALSE, NULL);

  handle_array[0] = hEvent;
  nhandles = 1;
  nsock = 0;

  /* Copy descriptors to bitsets.  At the same time, eliminate
     bits in the "wrong" direction for console input buffers
     and screen buffers, because screen buffers are waitable
     and they will block until a character is available.  */
  memset (&rbits, 0, sizeof (rbits));
  memset (&wbits, 0, sizeof (wbits));
  memset (&xbits, 0, sizeof (xbits));
  memset (anyfds_in, 0, sizeof (anyfds_in));
  if (rfds)
    for (i = 0; i < rfds->fd_count; i++)
      {
        fd = rfds->fd_array[i];
        h = (HANDLE) _get_osfhandle (fd);
        if (IsConsoleHandle (h)
            && !GetNumberOfConsoleInputEvents (h, &nbuffer))
          continue;

        rbits.in[fd / CHAR_BIT] |= 1 << (fd & (CHAR_BIT - 1));
        anyfds_in[fd / CHAR_BIT] |= 1 << (fd & (CHAR_BIT - 1));
      }
  else
    rfds = (fd_set *) alloca (sizeof (fd_set));

  if (wfds)
    for (i = 0; i < wfds->fd_count; i++)
      {
        fd = wfds->fd_array[i];
        h = (HANDLE) _get_osfhandle (fd);
        if (IsConsoleHandle (h)
            && GetNumberOfConsoleInputEvents (h, &nbuffer))
          continue;

        wbits.in[fd / CHAR_BIT] |= 1 << (fd & (CHAR_BIT - 1));
        anyfds_in[fd / CHAR_BIT] |= 1 << (fd & (CHAR_BIT - 1));
      }
  else
    wfds = (fd_set *) alloca (sizeof (fd_set));

  if (xfds)
    for (i = 0; i < xfds->fd_count; i++)
      {
        fd = xfds->fd_array[i];
        xbits.in[fd / CHAR_BIT] |= 1 << (fd & (CHAR_BIT - 1));
        anyfds_in[fd / CHAR_BIT] |= 1 << (fd & (CHAR_BIT - 1));
      }
  else
    xfds = (fd_set *) alloca (sizeof (fd_set));

  /* Zero all the fd_sets, including the application's.  */
  FD_ZERO (rfds);
  FD_ZERO (wfds);
  FD_ZERO (xfds);
  FD_ZERO (&handle_rfds);
  FD_ZERO (&handle_wfds);
  FD_ZERO (&handle_xfds);

  /* Classify handles.  Create fd sets for sockets, poll the others. */
  for (i = 0; i < nfds; i++)
    {
      if ((anyfds_in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) == 0)
        continue;

      h = (HANDLE) _get_osfhandle (i);
      if (!h)
        {
          errno = EBADF;
          return -1;
        }

      if (IsSocketHandle (h))
        {
          int requested = FD_CLOSE;

          /* See above; socket handles are mapped onto select, but we
             need to map descriptors to handles.  */
          if (rbits.in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
            {
              requested |= FD_READ | FD_ACCEPT;
              FD_SET ((SOCKET) h, rfds);
              FD_SET ((SOCKET) h, &handle_rfds);
            }
          if (wbits.in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
            {
              requested |= FD_WRITE | FD_CONNECT;
              FD_SET ((SOCKET) h, wfds);
              FD_SET ((SOCKET) h, &handle_wfds);
            }
          if (xbits.in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
            {
              requested |= FD_OOB;
              FD_SET ((SOCKET) h, xfds);
              FD_SET ((SOCKET) h, &handle_xfds);
            }

          WSAEventSelect ((SOCKET) h, hEvent, requested);
          nsock++;
        }
      else
        {
          handle_array[nhandles++] = h;

          /* Poll now.  If we get an event, do not wait below.  */
          if (wait_timeout != 0
              && windows_poll_handle (h, i, &rbits, &wbits, &xbits))
            wait_timeout = 0;
        }
    }

  /* Place a sentinel at the end of the array.  */
  handle_array[nhandles] = NULL;

  /* When will the waiting period expire?  */
  if (wait_timeout != INFINITE)
    tend = clock () + wait_timeout;

restart:
  if (wait_timeout == 0 || nsock == 0)
    rc = 0;
  else
    {
      /* See if we need to wait in the loop below.  If any select is ready,
         do MsgWaitForMultipleObjects anyway to dispatch messages, but
         no need to call select again.  */
      rc = select (0, &handle_rfds, &handle_wfds, &handle_xfds, &tv0);
      if (rc == 0)
        {
          /* Restore the fd_sets for the other select we do below.  */
          memcpy (&handle_rfds, rfds, sizeof (fd_set));
          memcpy (&handle_wfds, wfds, sizeof (fd_set));
          memcpy (&handle_xfds, xfds, sizeof (fd_set));
        }
      else
        wait_timeout = 0;
    }

  /* How much is left to wait?  */
  if (wait_timeout != INFINITE)
    {
      clock_t tnow = clock ();
      if (tend >= tnow)
        wait_timeout = tend - tnow;
      else
        wait_timeout = 0;
    }

  for (;;)
    {
      ret = MsgWaitForMultipleObjects (nhandles, handle_array, FALSE,
                                       wait_timeout, QS_ALLINPUT);

      if (ret == WAIT_OBJECT_0 + nhandles)
        {
          /* new input of some other kind */
          BOOL bRet;
          while ((bRet = PeekMessage (&msg, NULL, 0, 0, PM_REMOVE)) != 0)
            {
              TranslateMessage (&msg);
              DispatchMessage (&msg);
            }
        }
      else
        break;
    }

  /* If we haven't done it yet, check the status of the sockets.  */
  if (rc == 0 && nsock > 0)
    rc = select (0, &handle_rfds, &handle_wfds, &handle_xfds, &tv0);

  if (nhandles > 1)
    {
      /* Count results that are not counted in the return value of select.  */
      nhandles = 1;
      for (i = 0; i < nfds; i++)
        {
          if ((anyfds_in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) == 0)
            continue;

          h = (HANDLE) _get_osfhandle (i);
          if (h == handle_array[nhandles])
            {
              /* Not a socket.  */
              nhandles++;
              windows_poll_handle (h, i, &rbits, &wbits, &xbits);
              if (rbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))
                  || wbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))
                  || xbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
                rc++;
            }
        }

      if (rc == 0
          && (wait_timeout == INFINITE
              /* If NHANDLES > 1, but no bits are set, it means we've
                 been told incorrectly that some handle was signaled.
                 This happens with anonymous pipes, which always cause
                 MsgWaitForMultipleObjects to exit immediately, but no
                 data is found ready to be read by windows_poll_handle.
                 To avoid a total failure (whereby we return zero and
                 don't wait at all), let's poll in a more busy loop.  */
              || (wait_timeout != 0 && nhandles > 1)))
        {
          /* Sleep 1 millisecond to avoid busy wait and retry with the
             original fd_sets.  */
          memcpy (&handle_rfds, rfds, sizeof (fd_set));
          memcpy (&handle_wfds, wfds, sizeof (fd_set));
          memcpy (&handle_xfds, xfds, sizeof (fd_set));
          SleepEx (1, TRUE);
          goto restart;
        }
      if (timeout && wait_timeout == 0 && rc == 0)
        timeout->tv_sec = timeout->tv_usec = 0;
    }

  /* Now fill in the results.  */
  FD_ZERO (rfds);
  FD_ZERO (wfds);
  FD_ZERO (xfds);
  nhandles = 1;
  for (i = 0; i < nfds; i++)
    {
      if ((anyfds_in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) == 0)
        continue;

      h = (HANDLE) _get_osfhandle (i);
      if (h != handle_array[nhandles])
        {
          /* Perform handle->descriptor mapping.  */
          SOCKET s = (SOCKET) h;
          WSAEventSelect (s, NULL, 0);
          if (FD_ISSET (s, &handle_rfds))
            FD_SET (i, rfds);
          if (FD_ISSET (s, &handle_wfds))
            FD_SET (i, wfds);
          if (FD_ISSET (s, &handle_xfds))
            FD_SET (i, xfds);
        }
      else
        {
          /* Not a socket.  */
          nhandles++;
          if (rbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
            FD_SET (i, rfds);
          if (wbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
            FD_SET (i, wfds);
          if (xbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))))
            FD_SET (i, xfds);
        }
    }

  return rc;
}

#else /* ! Native Windows.  */

#include <stddef.h> /* NULL */
#include <errno.h>
#include <unistd.h>

#undef select

int
rpl_select (int nfds, fd_set *rfds, fd_set *wfds, fd_set *xfds,
            struct timeval *timeout)
{
  int i;

  /* FreeBSD 8.2 has a bug: it does not always detect invalid fds.  */
  if (nfds < 0 || nfds > FD_SETSIZE)
    {
      errno = EINVAL;
      return -1;
    }
  for (i = 0; i < nfds; i++)
    {
      if (((rfds && FD_ISSET (i, rfds))
           || (wfds && FD_ISSET (i, wfds))
           || (xfds && FD_ISSET (i, xfds)))
          && dup2 (i, i) != i)
        return -1;
    }

  /* Interix 3.5 has a bug: it does not support nfds == 0.  */
  if (nfds == 0)
    {
      nfds = 1;
      rfds = NULL;
      wfds = NULL;
      xfds = NULL;
    }
  return select (nfds, rfds, wfds, xfds, timeout);
}

#endif