Improved detection of bad/invalid signer keys.

[gnupg.git] / common / iobuf.c

/* iobuf.c  -  File Handling for OpenPGP.
 * Copyright (C) 1998, 1999, 2000, 2001, 2003, 2004, 2006,
 *               2007, 2008, 2009  Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GnuPG 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#ifdef HAVE_W32_SYSTEM
# include <windows.h>
#endif
#ifdef __riscos__
# include <kernel.h>
# include <swis.h>
#endif /* __riscos__ */

#include "util.h"
#include "sysutils.h"
#include "iobuf.h"

/*-- Begin configurable part.  --*/

/* The size of the internal buffers. 
   NOTE: If you change this value you MUST also adjust the regression
   test "armored_key_8192" in armor.test! */
#define IOBUF_BUFFER_SIZE  8192

/* We don't want to use the STDIO based backend.  If you change this
   be aware that there is no fsync support for the stdio backend.  */
#undef FILE_FILTER_USES_STDIO

/*-- End configurable part.  --*/


/* Under W32 the default is to use the setmode call.  Define a macro
   which allows us to enable this call.  */
#ifdef HAVE_W32_SYSTEM
# define USE_SETMODE 1
#endif /*HAVE_W32_SYSTEM*/


/* Definition of constants and macros used by our file filter
   implementation.  What we define here are 3 macros to make the
   appropriate calls:

   my_fileno 
     Is expanded to fileno(a) if using a stdion backend and to a if we
     are using the low-level backend.

   my_fopen 
     Is defined to fopen for the stdio backend and to direct_open if
     we are using the low-evel backend.

   my_fopen_ro 
     Is defined to fopen for the stdio backend and to fd_cache_open if
     we are using the low-evel backend.

   fp_or_fd_t
     Is the type we use for the backend stream or file descriptor.

   INVALID_FP, FILEP_OR_FD_FOR_STDIN, FILEP_OR_FD_FOR_STDOUT
     Are macros defined depending on the used backend.

*/
#ifdef FILE_FILTER_USES_STDIO
# define my_fileno(a)     fileno ((a))
# define my_fopen_ro(a,b) fopen ((a),(b))
# define my_fopen(a,b)    fopen ((a),(b))
  typedef FILE *fp_or_fd_t;
# define INVALID_FP              NULL
# define FILEP_OR_FD_FOR_STDIN   (stdin)
# define FILEP_OR_FD_FOR_STDOUT  (stdout)
#else /*!FILE_FILTER_USES_STDIO*/
# define my_fopen_ro(a,b) fd_cache_open ((a),(b))
# define my_fopen(a,b)    direct_open ((a),(b))
# ifdef HAVE_W32_SYSTEM
   /* (We assume that a HANDLE first into an int.)  */
#  define my_fileno(a)  ((int)(a))
   typedef HANDLE fp_or_fd_t;
#  define INVALID_FP             ((HANDLE)-1)
#  define FILEP_OR_FD_FOR_STDIN  (GetStdHandle (STD_INPUT_HANDLE))
#  define FILEP_OR_FD_FOR_STDOUT (GetStdHandle (STD_OUTPUT_HANDLE))
#  undef USE_SETMODE
# else /*!HAVE_W32_SYSTEM*/
#  define my_fileno(a)  (a)
   typedef int fp_or_fd_t;
#  define INVALID_FP             (-1)
#  define FILEP_OR_FD_FOR_STDIN  (0)
#  define FILEP_OR_FD_FOR_STDOUT (1)
# endif /*!HAVE_W32_SYSTEM*/
#endif /*!FILE_FILTER_USES_STDIO*/

/* The context used by the file filter.  */
typedef struct
{
  fp_or_fd_t fp;       /* Open file pointer or handle.  */
  int keep_open; 
  int no_cache;
  int eof_seen;
  int print_only_name; /* Flags indicating that fname is not a real file.  */
  char fname[1];       /* Name of the file.  */
}
file_filter_ctx_t;


/* If we are not using stdio as the backend we make use of a "close
   cache".  */
#ifndef FILE_FILTER_USES_STDIO
struct close_cache_s
{
  struct close_cache_s *next;
  fp_or_fd_t fp;
  char fname[1];
};
typedef struct close_cache_s *close_cache_t;
static close_cache_t close_cache;
#endif /*!FILE_FILTER_USES_STDIO*/



#ifdef HAVE_W32_SYSTEM
typedef struct
{
  int sock;
  int keep_open;
  int no_cache;
  int eof_seen;
  int print_only_name;  /* Flag indicating that fname is not a real file.  */
  char fname[1];        /* Name of the file */
}
sock_filter_ctx_t;
#endif /*HAVE_W32_SYSTEM*/

/* The first partial length header block must be of size 512
 * to make it easier (and efficienter) we use a min. block size of 512
 * for all chunks (but the last one) */
#define OP_MIN_PARTIAL_CHUNK      512
#define OP_MIN_PARTIAL_CHUNK_2POW 9

/* The context we use for the block filter (used to handle OpenPGP
   length information header).  */
typedef struct
{
  int use;
  size_t size;
  size_t count;
  int partial;     /* 1 = partial header, 2 in last partial packet.  */
  char *buffer;    /* Used for partial header.  */
  size_t buflen;   /* Used size of buffer.  */
  int first_c;     /* First character of a partial header (which is > 0).  */
  int eof;
}
block_filter_ctx_t;


/* Global flag to tell whether special file names are enabled.  See
   gpg.c for an explanation of these file names.  FIXME: it does not
   belong into the iobuf subsystem. */
static int special_names_enabled;

/* Local prototypes.  */
static int underflow (iobuf_t a);
static int translate_file_handle (int fd, int for_write);


\f
#ifndef FILE_FILTER_USES_STDIO
/* This is a replacement for strcmp.  Under W32 it does not
   distinguish between backslash and slash.  */
static int
fd_cache_strcmp (const char *a, const char *b)
{
#ifdef HAVE_DOSISH_SYSTEM
  for (; *a && *b; a++, b++)
    {
      if (*a != *b && !((*a == '/' && *b == '\\') 
                        || (*a == '\\' && *b == '/')) )
        break;
    }
  return *(const unsigned char *)a - *(const unsigned char *)b;
#else
  return strcmp (a, b);
#endif
}

/*
 * Invalidate (i.e. close) a cached iobuf
 */
static int
fd_cache_invalidate (const char *fname)
{
  close_cache_t cc;
  int rc = 0;

  assert (fname);
  if (DBG_IOBUF)
    log_debug ("fd_cache_invalidate (%s)\n", fname);

  for (cc = close_cache; cc; cc = cc->next)
    {
      if (cc->fp != INVALID_FP && !fd_cache_strcmp (cc->fname, fname))
        {
          if (DBG_IOBUF)
            log_debug ("                did (%s)\n", cc->fname);
#ifdef HAVE_W32_SYSTEM
          if (!CloseHandle (cc->fp))
            rc = -1;
#else
          rc = close (cc->fp);
#endif
          cc->fp = INVALID_FP;
        }
    }
  return rc;
}


/* Try to sync changes to the disk.  This is to avoid data loss during
   a system crash in write/close/rename cycle on some file
   systems.  */
static int
fd_cache_synchronize (const char *fname)
{
  int err = 0;

#ifdef HAVE_FSYNC
  close_cache_t cc;

  if (DBG_IOBUF)
    log_debug ("fd_cache_synchronize (%s)\n", fname);

  for (cc=close_cache; cc; cc = cc->next )
    {
      if (cc->fp != INVALID_FP && !fd_cache_strcmp (cc->fname, fname))
        {
          if (DBG_IOBUF)
            log_debug ("                 did (%s)\n", cc->fname);

          err = fsync (cc->fp);
        }
    }
#else
  (void)fname;
#endif /*HAVE_FSYNC*/

  return err;
}


static fp_or_fd_t
direct_open (const char *fname, const char *mode)
{
#ifdef HAVE_W32_SYSTEM
  unsigned long da, cd, sm;
  HANDLE hfile;

  /* Note, that we do not handle all mode combinations */

  /* According to the ReactOS source it seems that open() of the
   * standard MSW32 crt does open the file in shared mode which is
   * something new for MS applications ;-)
   */
  if (strchr (mode, '+'))
    {
      if (fd_cache_invalidate (fname))
        return INVALID_FP;
      da = GENERIC_READ | GENERIC_WRITE;
      cd = OPEN_EXISTING;
      sm = FILE_SHARE_READ | FILE_SHARE_WRITE;
    }
  else if (strchr (mode, 'w'))
    {
      if (fd_cache_invalidate (fname))
        return INVALID_FP;
      da = GENERIC_WRITE;
      cd = CREATE_ALWAYS;
      sm = FILE_SHARE_WRITE;
    }
  else
    {
      da = GENERIC_READ;
      cd = OPEN_EXISTING;
      sm = FILE_SHARE_READ;
    }

  hfile = CreateFile (fname, da, sm, NULL, cd, FILE_ATTRIBUTE_NORMAL, NULL);
  return hfile;
#else /*!HAVE_W32_SYSTEM*/
  int oflag;
  int cflag = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;

  /* Note, that we do not handle all mode combinations */
  if (strchr (mode, '+'))
    {
      if (fd_cache_invalidate (fname))
        return INVALID_FP;
      oflag = O_RDWR;
    }
  else if (strchr (mode, 'w'))
    {
      if (fd_cache_invalidate (fname))
        return INVALID_FP;
      oflag = O_WRONLY | O_CREAT | O_TRUNC;
    }
  else
    {
      oflag = O_RDONLY;
    }
#ifdef O_BINARY
  if (strchr (mode, 'b'))
    oflag |= O_BINARY;
#endif
  /* No we need to distinguish between POSIX and RISC OS.  */
#ifndef __riscos__
  return open (fname, oflag, cflag);
#else
  {
    struct stat buf;
    int rc = stat (fname, &buf);

    /* Don't allow iobufs on directories */
    if (!rc && S_ISDIR (buf.st_mode) && !S_ISREG (buf.st_mode))
      return __set_errno (EISDIR);
    else
      return open (fname, oflag, cflag);
  }
#endif
#endif /*!HAVE_W32_SYSTEM*/
}


/*
 * Instead of closing an FD we keep it open and cache it for later reuse 
 * Note that this caching strategy only works if the process does not chdir.
 */
static void
fd_cache_close (const char *fname, fp_or_fd_t fp)
{
  close_cache_t cc;

  assert (fp);
  if (!fname || !*fname)
    {
#ifdef HAVE_W32_SYSTEM
      CloseHandle (fp);
#else
      close (fp);
#endif
      if (DBG_IOBUF)
        log_debug ("fd_cache_close (%d) real\n", (int)fp);
      return;
    }
  /* try to reuse a slot */
  for (cc = close_cache; cc; cc = cc->next)
    {
      if (cc->fp == INVALID_FP && !fd_cache_strcmp (cc->fname, fname))
        {
          cc->fp = fp;
          if (DBG_IOBUF)
            log_debug ("fd_cache_close (%s) used existing slot\n", fname);
          return;
        }
    }
  /* add a new one */
  if (DBG_IOBUF)
    log_debug ("fd_cache_close (%s) new slot created\n", fname);
  cc = xcalloc (1, sizeof *cc + strlen (fname));
  strcpy (cc->fname, fname);
  cc->fp = fp;
  cc->next = close_cache;
  close_cache = cc;
}

/*
 * Do an direct_open on FNAME but first try to reuse one from the fd_cache
 */
static fp_or_fd_t
fd_cache_open (const char *fname, const char *mode)
{
  close_cache_t cc;

  assert (fname);
  for (cc = close_cache; cc; cc = cc->next)
    {
      if (cc->fp != INVALID_FP && !fd_cache_strcmp (cc->fname, fname))
        {
          fp_or_fd_t fp = cc->fp;
          cc->fp = INVALID_FP;
          if (DBG_IOBUF)
            log_debug ("fd_cache_open (%s) using cached fp\n", fname);
#ifdef HAVE_W32_SYSTEM
          if (SetFilePointer (fp, 0, NULL, FILE_BEGIN) == 0xffffffff)
            {
              log_error ("rewind file failed on handle %p: ec=%d\n",
                         fp, (int) GetLastError ());
              fp = INVALID_FP;
            }
#else
          if (lseek (fp, 0, SEEK_SET) == (off_t) - 1)
            {
              log_error ("can't rewind fd %d: %s\n", fp, strerror (errno));
              fp = INVALID_FP;
            }
#endif
          return fp;
        }
    }
  if (DBG_IOBUF)
    log_debug ("fd_cache_open (%s) not cached\n", fname);
  return direct_open (fname, mode);
}

#endif /*FILE_FILTER_USES_STDIO */


/****************
 * Read data from a file into buf which has an allocated length of *LEN.
 * return the number of read bytes in *LEN. OPAQUE is the FILE * of
 * the stream. A is not used.
 * control may be:
 * IOBUFCTRL_INIT: called just before the function is linked into the
 *                 list of function. This can be used to prepare internal
 *                 data structures of the function.
 * IOBUFCTRL_FREE: called just before the function is removed from the
 *                  list of functions and can be used to release internal
 *                  data structures or close a file etc.
 * IOBUFCTRL_UNDERFLOW: called by iobuf_underflow to fill the buffer
 *                  with new stuff. *RET_LEN is the available size of the
 *                  buffer, and should be set to the number of bytes
 *                  which were put into the buffer. The function
 *                  returns 0 to indicate success, -1 on EOF and
 *                  GPG_ERR_xxxxx for other errors.
 *
 * IOBUFCTRL_FLUSH: called by iobuf_flush() to write out the collected stuff.
 *                  *RET_LAN is the number of bytes in BUF.
 *
 * IOBUFCTRL_CANCEL: send to all filters on behalf of iobuf_cancel.  The
 *                  filter may take appropriate action on this message.
 */
static int
file_filter (void *opaque, int control, iobuf_t chain, byte * buf,
             size_t * ret_len)
{
  file_filter_ctx_t *a = opaque;
  fp_or_fd_t f = a->fp;
  size_t size = *ret_len;
  size_t nbytes = 0;
  int rc = 0;

  (void)chain; /* Not used.  */

#ifdef FILE_FILTER_USES_STDIO
  if (control == IOBUFCTRL_UNDERFLOW)
    {
      assert (size);  /* We need a buffer. */
      if (feof (f))
        { 
          /* On terminals you could easily read as many EOFs as you
             call fread() or fgetc() repeatly.  Every call will block
             until you press CTRL-D. So we catch this case before we
             call fread() again.  */
          rc = -1;              
          *ret_len = 0;         
        }
      else
        {
          clearerr (f);
          nbytes = fread (buf, 1, size, f);
          if (feof (f) && !nbytes)
            {
              rc = -1;  /* Okay: we can return EOF now. */
            }
          else if (ferror (f) && errno != EPIPE)
            {
              rc = gpg_error_from_syserror ();
              log_error ("%s: read error: %s\n", a->fname, strerror (errno));
            }
          *ret_len = nbytes;
        }
    }
  else if (control == IOBUFCTRL_FLUSH)
    {
      if (size)
        {
          clearerr (f);
          nbytes = fwrite (buf, 1, size, f);
          if (ferror (f))
            {
              rc = gpg_error_from_syserror ();
              log_error ("%s: write error: %s\n", a->fname, strerror (errno));
            }
        }
      *ret_len = nbytes;
    }
  else if (control == IOBUFCTRL_INIT)
    {
      a->keep_open = a->no_cache = 0;
    }
  else if (control == IOBUFCTRL_DESC)
    {
      *(char **) buf = "file_filter";
    }
  else if (control == IOBUFCTRL_FREE)
    {
      if (f != stdin && f != stdout)
        {
          if (DBG_IOBUF)
            log_debug ("%s: close fd %d\n", a->fname, fileno (f));
          if (!a->keep_open)
            fclose (f);
        }
      f = NULL;
      xfree (a); /* We can free our context now. */
    }
#else /* !stdio implementation */

  if (control == IOBUFCTRL_UNDERFLOW)
    {
      assert (size); /* We need a buffer.  */
      if (a->eof_seen)
        {
          rc = -1;
          *ret_len = 0;
        }
      else
        {
#ifdef HAVE_W32_SYSTEM
          unsigned long nread;

          nbytes = 0;
          if (!ReadFile (f, buf, size, &nread, NULL))
            {
              int ec = (int) GetLastError ();
              if (ec != ERROR_BROKEN_PIPE)
                {
                  rc = gpg_error_from_errno (ec);
                  log_error ("%s: read error: ec=%d\n", a->fname, ec);
                }
            }
          else if (!nread)
            {
              a->eof_seen = 1;
              rc = -1;
            }
          else
            {
              nbytes = nread;
            }

#else

          int n;

          nbytes = 0;
          do
            {
              n = read (f, buf, size);
            }
          while (n == -1 && errno == EINTR);
          if (n == -1)
            {                   /* error */
              if (errno != EPIPE)
                {
                  rc = gpg_error_from_syserror ();
                  log_error ("%s: read error: %s\n",
                             a->fname, strerror (errno));
                }
            }
          else if (!n)
            {                   /* eof */
              a->eof_seen = 1;
              rc = -1;
            }
          else
            {
              nbytes = n;
            }
#endif
          *ret_len = nbytes;
        }
    }
  else if (control == IOBUFCTRL_FLUSH)
    {
      if (size)
        {
#ifdef HAVE_W32_SYSTEM
          byte *p = buf;
          unsigned long n;

          nbytes = size;
          do
            {
              if (size && !WriteFile (f, p, nbytes, &n, NULL))
                {
                  int ec = (int) GetLastError ();
                  rc = gpg_error_from_errno (ec);
                  log_error ("%s: write error: ec=%d\n", a->fname, ec);
                  break;
                }
              p += n;
              nbytes -= n;
            }
          while (nbytes);
          nbytes = p - buf;
#else
          byte *p = buf;
          int n;

          nbytes = size;
          do
            {
              do
                {
                  n = write (f, p, nbytes);
                }
              while (n == -1 && errno == EINTR);
              if (n > 0)
                {
                  p += n;
                  nbytes -= n;
                }
            }
          while (n != -1 && nbytes);
          if (n == -1)
            {
              rc = gpg_error_from_syserror ();
              log_error ("%s: write error: %s\n", a->fname, strerror (errno));
            }
          nbytes = p - buf;
#endif
        }
      *ret_len = nbytes;
    }
  else if (control == IOBUFCTRL_INIT)
    {
      a->eof_seen = 0;
      a->keep_open = 0;
      a->no_cache = 0;
    }
  else if (control == IOBUFCTRL_DESC)
    {
      *(char **) buf = "file_filter(fd)";
    }
  else if (control == IOBUFCTRL_FREE)
    {
#ifdef HAVE_W32_SYSTEM
      if (f != FILEP_OR_FD_FOR_STDIN && f != FILEP_OR_FD_FOR_STDOUT)
        {
          if (DBG_IOBUF)
            log_debug ("%s: close handle %p\n", a->fname, f);
          if (!a->keep_open)
            fd_cache_close (a->no_cache ? NULL : a->fname, f);
        }
#else
      if ((int) f != 0 && (int) f != 1)
        {
          if (DBG_IOBUF)
            log_debug ("%s: close fd %d\n", a->fname, f);
          if (!a->keep_open)
            fd_cache_close (a->no_cache ? NULL : a->fname, f);
        }
      f = INVALID_FP;
#endif
      xfree (a); /* We can free our context now. */
    }
#endif /* !stdio implementation. */
  return rc;
}


#ifdef HAVE_W32_SYSTEM
/* Because network sockets are special objects under Lose32 we have to
   use a dedicated filter for them. */
static int
sock_filter (void *opaque, int control, iobuf_t chain, byte * buf,
             size_t * ret_len)
{
  sock_filter_ctx_t *a = opaque;
  size_t size = *ret_len;
  size_t nbytes = 0;
  int rc = 0;

  (void)chain;

  if (control == IOBUFCTRL_UNDERFLOW)
    {
      assert (size);            /* need a buffer */
      if (a->eof_seen)
        {
          rc = -1;
          *ret_len = 0;
        }
      else
        {
          int nread;

          nread = recv (a->sock, buf, size, 0);
          if (nread == SOCKET_ERROR)
            {
              int ec = (int) WSAGetLastError ();
              rc = gpg_error_from_errno (ec);
              log_error ("socket read error: ec=%d\n", ec);
            }
          else if (!nread)
            {
              a->eof_seen = 1;
              rc = -1;
            }
          else
            {
              nbytes = nread;
            }
          *ret_len = nbytes;
        }
    }
  else if (control == IOBUFCTRL_FLUSH)
    {
      if (size)
        {
          byte *p = buf;
          int n;

          nbytes = size;
          do
            {
              n = send (a->sock, p, nbytes, 0);
              if (n == SOCKET_ERROR)
                {
                  int ec = (int) WSAGetLastError ();
                  rc = gpg_error_from_errno (ec);
                  log_error ("socket write error: ec=%d\n", ec);
                  break;
                }
              p += n;
              nbytes -= n;
            }
          while (nbytes);
          nbytes = p - buf;
        }
      *ret_len = nbytes;
    }
  else if (control == IOBUFCTRL_INIT)
    {
      a->eof_seen = 0;
      a->keep_open = 0;
      a->no_cache = 0;
    }
  else if (control == IOBUFCTRL_DESC)
    {
      *(char **) buf = "sock_filter";
    }
  else if (control == IOBUFCTRL_FREE)
    {
      if (!a->keep_open)
        closesocket (a->sock);
      xfree (a);                /* we can free our context now */
    }
  return rc;
}
#endif /*HAVE_W32_SYSTEM*/

/****************
 * This is used to implement the block write mode.
 * Block reading is done on a byte by byte basis in readbyte(),
 * without a filter
 */
static int
block_filter (void *opaque, int control, iobuf_t chain, byte * buffer,
              size_t * ret_len)
{
  block_filter_ctx_t *a = opaque;
  char *buf = (char *)buffer;
  size_t size = *ret_len;
  int c, needed, rc = 0;
  char *p;

  if (control == IOBUFCTRL_UNDERFLOW)
    {
      size_t n = 0;

      p = buf;
      assert (size);            /* need a buffer */
      if (a->eof)               /* don't read any further */
        rc = -1;
      while (!rc && size)
        {
          if (!a->size)
            {                   /* get the length bytes */
              if (a->partial == 2)
                {
                  a->eof = 1;
                  if (!n)
                    rc = -1;
                  break;
                }
              else if (a->partial)
                {
                  /* These OpenPGP introduced huffman like encoded length
                   * bytes are really a mess :-( */
                  if (a->first_c)
                    {
                      c = a->first_c;
                      a->first_c = 0;
                    }
                  else if ((c = iobuf_get (chain)) == -1)
                    {
                      log_error ("block_filter: 1st length byte missing\n");
                      rc = GPG_ERR_BAD_DATA;
                      break;
                    }
                  if (c < 192)
                    {
                      a->size = c;
                      a->partial = 2;
                      if (!a->size)
                        {
                          a->eof = 1;
                          if (!n)
                            rc = -1;
                          break;
                        }
                    }
                  else if (c < 224)
                    {
                      a->size = (c - 192) * 256;
                      if ((c = iobuf_get (chain)) == -1)
                        {
                          log_error
                            ("block_filter: 2nd length byte missing\n");
                          rc = GPG_ERR_BAD_DATA;
                          break;
                        }
                      a->size += c + 192;
                      a->partial = 2;
                      if (!a->size)
                        {
                          a->eof = 1;
                          if (!n)
                            rc = -1;
                          break;
                        }
                    }
                  else if (c == 255)
                    {
                      a->size = iobuf_get (chain) << 24;
                      a->size |= iobuf_get (chain) << 16;
                      a->size |= iobuf_get (chain) << 8;
                      if ((c = iobuf_get (chain)) == -1)
                        {
                          log_error ("block_filter: invalid 4 byte length\n");
                          rc = GPG_ERR_BAD_DATA;
                          break;
                        }
                      a->size |= c;
                      a->partial = 2;
                      if (!a->size)
                        {
                          a->eof = 1;
                          if (!n)
                            rc = -1;
                          break;
                        }
                    }
                  else
                    { /* Next partial body length. */
                      a->size = 1 << (c & 0x1f);
                    }
                  /*  log_debug("partial: ctx=%p c=%02x size=%u\n", a, c, a->size); */
                }
              else
                BUG (); 
            }

          while (!rc && size && a->size)
            {
              needed = size < a->size ? size : a->size;
              c = iobuf_read (chain, p, needed);
              if (c < needed)
                {
                  if (c == -1)
                    c = 0;
                  log_error
                    ("block_filter %p: read error (size=%lu,a->size=%lu)\n",
                     a, (ulong) size + c, (ulong) a->size + c);
                  rc = GPG_ERR_BAD_DATA;
                }
              else
                {
                  size -= c;
                  a->size -= c;
                  p += c;
                  n += c;
                }
            }
        }
      *ret_len = n;
    }
  else if (control == IOBUFCTRL_FLUSH)
    {
      if (a->partial)
        {                       /* the complicated openpgp scheme */
          size_t blen, n, nbytes = size + a->buflen;

          assert (a->buflen <= OP_MIN_PARTIAL_CHUNK);
          if (nbytes < OP_MIN_PARTIAL_CHUNK)
            {
              /* not enough to write a partial block out; so we store it */
              if (!a->buffer)
                a->buffer = xmalloc (OP_MIN_PARTIAL_CHUNK);
              memcpy (a->buffer + a->buflen, buf, size);
              a->buflen += size;
            }
          else
            {                   /* okay, we can write out something */
              /* do this in a loop to use the most efficient block lengths */
              p = buf;
              do
                {
                  /* find the best matching block length - this is limited
                   * by the size of the internal buffering */
                  for (blen = OP_MIN_PARTIAL_CHUNK * 2,
                       c = OP_MIN_PARTIAL_CHUNK_2POW + 1; blen <= nbytes;
                       blen *= 2, c++)
                    ;
                  blen /= 2;
                  c--;
                  /* write the partial length header */
                  assert (c <= 0x1f);   /*;-) */
                  c |= 0xe0;
                  iobuf_put (chain, c);
                  if ((n = a->buflen))
                    {           /* write stuff from the buffer */
                      assert (n == OP_MIN_PARTIAL_CHUNK);
                      if (iobuf_write (chain, a->buffer, n))
                        rc = gpg_error_from_syserror ();
                      a->buflen = 0;
                      nbytes -= n;
                    }
                  if ((n = nbytes) > blen)
                    n = blen;
                  if (n && iobuf_write (chain, p, n))
                    rc = gpg_error_from_syserror ();
                  p += n;
                  nbytes -= n;
                }
              while (!rc && nbytes >= OP_MIN_PARTIAL_CHUNK);
              /* store the rest in the buffer */
              if (!rc && nbytes)
                {
                  assert (!a->buflen);
                  assert (nbytes < OP_MIN_PARTIAL_CHUNK);
                  if (!a->buffer)
                    a->buffer = xmalloc (OP_MIN_PARTIAL_CHUNK);
                  memcpy (a->buffer, p, nbytes);
                  a->buflen = nbytes;
                }
            }
        }
      else
        BUG ();
    }
  else if (control == IOBUFCTRL_INIT)
    {
      if (DBG_IOBUF)
        log_debug ("init block_filter %p\n", a);
      if (a->partial)
        a->count = 0;
      else if (a->use == 1)
        a->count = a->size = 0;
      else
        a->count = a->size;     /* force first length bytes */
      a->eof = 0;
      a->buffer = NULL;
      a->buflen = 0;
    }
  else if (control == IOBUFCTRL_DESC)
    {
      *(char **) buf = "block_filter";
    }
  else if (control == IOBUFCTRL_FREE)
    {
      if (a->use == 2)
        {                       /* write the end markers */
          if (a->partial)
            {
              u32 len;
              /* write out the remaining bytes without a partial header
               * the length of this header may be 0 - but if it is
               * the first block we are not allowed to use a partial header
               * and frankly we can't do so, because this length must be
               * a power of 2. This is _really_ complicated because we
               * have to check the possible length of a packet prior
               * to it's creation: a chain of filters becomes complicated
               * and we need a lot of code to handle compressed packets etc.
               *   :-(((((((
               */
              /* construct header */
              len = a->buflen;
              /*log_debug("partial: remaining length=%u\n", len ); */
              if (len < 192)
                rc = iobuf_put (chain, len);
              else if (len < 8384)
                {
                  if (!(rc = iobuf_put (chain, ((len - 192) / 256) + 192)))
                    rc = iobuf_put (chain, ((len - 192) % 256));
                }
              else
                {               /* use a 4 byte header */
                  if (!(rc = iobuf_put (chain, 0xff)))
                    if (!(rc = iobuf_put (chain, (len >> 24) & 0xff)))
                      if (!(rc = iobuf_put (chain, (len >> 16) & 0xff)))
                        if (!(rc = iobuf_put (chain, (len >> 8) & 0xff)))
                          rc = iobuf_put (chain, len & 0xff);
                }
              if (!rc && len)
                rc = iobuf_write (chain, a->buffer, len);
              if (rc)
                {
                  log_error ("block_filter: write error: %s\n",
                             strerror (errno));
                  rc = gpg_error_from_syserror ();
                }
              xfree (a->buffer);
              a->buffer = NULL;
              a->buflen = 0;
            }
          else
            BUG ();
        }
      else if (a->size)
        {
          log_error ("block_filter: pending bytes!\n");
        }
      if (DBG_IOBUF)
        log_debug ("free block_filter %p\n", a);
      xfree (a);                /* we can free our context now */
    }

  return rc;
}


static void
print_chain (iobuf_t a)
{
  if (!DBG_IOBUF)
    return;
  for (; a; a = a->chain)
    {
      size_t dummy_len = 0;
      const char *desc = "[none]";

      if (a->filter)
        a->filter (a->filter_ov, IOBUFCTRL_DESC, NULL,
                   (byte *) & desc, &dummy_len);

      log_debug ("iobuf chain: %d.%d `%s' filter_eof=%d start=%d len=%d\n",
                 a->no, a->subno, desc?desc:"?", a->filter_eof,
                 (int) a->d.start, (int) a->d.len);
    }
}

int
iobuf_print_chain (iobuf_t a)
{
  print_chain (a);
  return 0;
}

/****************
 * Allocate a new io buffer, with no function assigned.
 * Use is the desired usage: 1 for input, 2 for output, 3 for temp buffer
 * BUFSIZE is a suggested buffer size.
 */
iobuf_t
iobuf_alloc (int use, size_t bufsize)
{
  iobuf_t a;
  static int number = 0;

  a = xcalloc (1, sizeof *a);
  a->use = use;
  a->d.buf = xmalloc (bufsize);
  a->d.size = bufsize;
  a->no = ++number;
  a->subno = 0;
  a->opaque = NULL;
  a->real_fname = NULL;
  return a;
}

int
iobuf_close (iobuf_t a)
{
  iobuf_t a2;
  size_t dummy_len = 0;
  int rc = 0;

  if (a && a->directfp)
    {
      fclose (a->directfp);
      xfree (a->real_fname);
      if (DBG_IOBUF)
        log_debug ("iobuf_close -> %p\n", a->directfp);
      return 0;
    }

  for (; a && !rc; a = a2)
    {
      a2 = a->chain;
      if (a->use == 2 && (rc = iobuf_flush (a)))
        log_error ("iobuf_flush failed on close: %s\n", gpg_strerror (rc));

      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: close `%s'\n", a->no, a->subno,
                   a->desc?a->desc:"?");
      if (a->filter && (rc = a->filter (a->filter_ov, IOBUFCTRL_FREE,
                                        a->chain, NULL, &dummy_len)))
        log_error ("IOBUFCTRL_FREE failed on close: %s\n", gpg_strerror (rc));
      xfree (a->real_fname);
      if (a->d.buf)
        {
          memset (a->d.buf, 0, a->d.size);      /* erase the buffer */
          xfree (a->d.buf);
        }
      xfree (a);
    }
  return rc;
}

int
iobuf_cancel (iobuf_t a)
{
  const char *s;
  iobuf_t a2;
  int rc;
#if defined(HAVE_W32_SYSTEM) || defined(__riscos__)
  char *remove_name = NULL;
#endif

  if (a && a->use == 2)
    {
      s = iobuf_get_real_fname (a);
      if (s && *s)
        {
#if defined(HAVE_W32_SYSTEM) || defined(__riscos__)
          remove_name = xstrdup (s);
#else
          remove (s);
#endif
        }
    }

  /* send a cancel message to all filters */
  for (a2 = a; a2; a2 = a2->chain)
    {
      size_t dummy;
      if (a2->filter)
        a2->filter (a2->filter_ov, IOBUFCTRL_CANCEL, a2->chain, NULL, &dummy);
    }

  rc = iobuf_close (a);
#if defined(HAVE_W32_SYSTEM) || defined(__riscos__)
  if (remove_name)
    {
      /* Argg, MSDOS does not allow to remove open files.  So
       * we have to do it here */
      remove (remove_name);
      xfree (remove_name);
    }
#endif
  return rc;
}


/****************
 * create a temporary iobuf, which can be used to collect stuff
 * in an iobuf and later be written by iobuf_write_temp() to another
 * iobuf.
 */
iobuf_t
iobuf_temp ()
{
  iobuf_t a;

  a = iobuf_alloc (3, IOBUF_BUFFER_SIZE);

  return a;
}

iobuf_t
iobuf_temp_with_content (const char *buffer, size_t length)
{
  iobuf_t a;

  a = iobuf_alloc (3, length);
  memcpy (a->d.buf, buffer, length);
  a->d.len = length;

  return a;
}

void
iobuf_enable_special_filenames (int yes)
{
  special_names_enabled = yes;
}


/* See whether the filename has the form "-&nnnn", where n is a
   non-zero number.  Returns this number or -1 if it is not the
   case.  */
static int
check_special_filename (const char *fname)
{
  if (special_names_enabled && fname && *fname == '-' && fname[1] == '&')
    {
      int i;

      fname += 2;
      for (i = 0; digitp (fname+i); i++)
        ;
      if (!fname[i])
        return atoi (fname);
    }
  return -1;
}


/* This fucntion returns true if FNAME indicates a PIPE (stdout or
   stderr) or a special file name if those are enabled. */
int
iobuf_is_pipe_filename (const char *fname)
{
  if (!fname || (*fname=='-' && !fname[1]) )
    return 1;
  return check_special_filename (fname) != -1;
}

/****************
 * Create a head iobuf for reading from a file
 * returns: NULL if an error occures and sets errno
 */
iobuf_t
iobuf_open (const char *fname)
{
  iobuf_t a;
  fp_or_fd_t fp;
  file_filter_ctx_t *fcx;
  size_t len;
  int print_only = 0;
  int fd;

  if (!fname || (*fname == '-' && !fname[1]))
    {
      fp = FILEP_OR_FD_FOR_STDIN;
#ifdef USE_SETMODE
      setmode (my_fileno (fp), O_BINARY);
#endif
      fname = "[stdin]";
      print_only = 1;
    }
  else if ((fd = check_special_filename (fname)) != -1)
    return iobuf_fdopen (translate_file_handle (fd, 0), "rb");
  else if ((fp = my_fopen_ro (fname, "rb")) == INVALID_FP)
    return NULL;
  a = iobuf_alloc (1, IOBUF_BUFFER_SIZE);
  fcx = xmalloc (sizeof *fcx + strlen (fname));
  fcx->fp = fp;
  fcx->print_only_name = print_only;
  strcpy (fcx->fname, fname);
  if (!print_only)
    a->real_fname = xstrdup (fname);
  a->filter = file_filter;
  a->filter_ov = fcx;
  file_filter (fcx, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &len);
  file_filter (fcx, IOBUFCTRL_INIT, NULL, NULL, &len);
  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: open `%s' fd=%d\n",
               a->no, a->subno, fname, (int) my_fileno (fcx->fp));

  return a;
}

/****************
 * Create a head iobuf for reading from a file
 * returns: NULL if an error occures and sets errno
 */
iobuf_t
iobuf_fdopen (int fd, const char *mode)
{
  iobuf_t a;
  fp_or_fd_t fp;
  file_filter_ctx_t *fcx;
  size_t len;

#ifdef FILE_FILTER_USES_STDIO
  if (!(fp = fdopen (fd, mode)))
    return NULL;
#else
  fp = (fp_or_fd_t) fd;
#endif
  a = iobuf_alloc (strchr (mode, 'w') ? 2 : 1, IOBUF_BUFFER_SIZE);
  fcx = xmalloc (sizeof *fcx + 20);
  fcx->fp = fp;
  fcx->print_only_name = 1;
  sprintf (fcx->fname, "[fd %d]", fd);
  a->filter = file_filter;
  a->filter_ov = fcx;
  file_filter (fcx, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &len);
  file_filter (fcx, IOBUFCTRL_INIT, NULL, NULL, &len);
  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: fdopen `%s'\n", a->no, a->subno, fcx->fname);
  iobuf_ioctl (a, 3, 1, NULL);  /* disable fd caching */
  return a;
}


iobuf_t
iobuf_sockopen (int fd, const char *mode)
{
  iobuf_t a;
#ifdef HAVE_W32_SYSTEM
  sock_filter_ctx_t *scx;
  size_t len;

  a = iobuf_alloc (strchr (mode, 'w') ? 2 : 1, IOBUF_BUFFER_SIZE);
  scx = xmalloc (sizeof *scx + 25);
  scx->sock = fd;
  scx->print_only_name = 1;
  sprintf (scx->fname, "[sock %d]", fd);
  a->filter = sock_filter;
  a->filter_ov = scx;
  sock_filter (scx, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &len);
  sock_filter (scx, IOBUFCTRL_INIT, NULL, NULL, &len);
  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: sockopen `%s'\n", a->no, a->subno, scx->fname);
  iobuf_ioctl (a, 3, 1, NULL);  /* disable fd caching */
#else
  a = iobuf_fdopen (fd, mode);
#endif
  return a;
}

/****************
 * create an iobuf for writing to a file; the file will be created.
 */
iobuf_t
iobuf_create (const char *fname)
{
  iobuf_t a;
  fp_or_fd_t fp;
  file_filter_ctx_t *fcx;
  size_t len;
  int print_only = 0;
  int fd;

  if (!fname || (*fname == '-' && !fname[1]))
    {
      fp = FILEP_OR_FD_FOR_STDOUT;
#ifdef USE_SETMODE
      setmode (my_fileno (fp), O_BINARY);
#endif
      fname = "[stdout]";
      print_only = 1;
    }
  else if ((fd = check_special_filename (fname)) != -1)
    return iobuf_fdopen (translate_file_handle (fd, 1), "wb");
  else if ((fp = my_fopen (fname, "wb")) == INVALID_FP)
    return NULL;
  a = iobuf_alloc (2, IOBUF_BUFFER_SIZE);
  fcx = xmalloc (sizeof *fcx + strlen (fname));
  fcx->fp = fp;
  fcx->print_only_name = print_only;
  strcpy (fcx->fname, fname);
  if (!print_only)
    a->real_fname = xstrdup (fname);
  a->filter = file_filter;
  a->filter_ov = fcx;
  file_filter (fcx, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &len);
  file_filter (fcx, IOBUFCTRL_INIT, NULL, NULL, &len);
  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: create `%s'\n", a->no, a->subno,
               a->desc?a->desc:"?");

  return a;
}

/****************
 * append to an iobuf; if the file does not exist, create it.
 * cannot be used for stdout.
 * Note: This is not used.
 */
#if 0                           /* not used */
iobuf_t
iobuf_append (const char *fname)
{
  iobuf_t a;
  FILE *fp;
  file_filter_ctx_t *fcx;
  size_t len;

  if (!fname)
    return NULL;
  else if (!(fp = my_fopen (fname, "ab")))
    return NULL;
  a = iobuf_alloc (2, IOBUF_BUFFER_SIZE);
  fcx = m_alloc (sizeof *fcx + strlen (fname));
  fcx->fp = fp;
  strcpy (fcx->fname, fname);
  a->real_fname = m_strdup (fname);
  a->filter = file_filter;
  a->filter_ov = fcx;
  file_filter (fcx, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &len);
  file_filter (fcx, IOBUFCTRL_INIT, NULL, NULL, &len);
  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: append `%s'\n", a->no, a->subno,
               a->desc?a->desc:"?");

  return a;
}
#endif

iobuf_t
iobuf_openrw (const char *fname)
{
  iobuf_t a;
  fp_or_fd_t fp;
  file_filter_ctx_t *fcx;
  size_t len;

  if (!fname)
    return NULL;
  else if ((fp = my_fopen (fname, "r+b")) == INVALID_FP)
    return NULL;
  a = iobuf_alloc (2, IOBUF_BUFFER_SIZE);
  fcx = xmalloc (sizeof *fcx + strlen (fname));
  fcx->fp = fp;
  strcpy (fcx->fname, fname);
  a->real_fname = xstrdup (fname);
  a->filter = file_filter;
  a->filter_ov = fcx;
  file_filter (fcx, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &len);
  file_filter (fcx, IOBUFCTRL_INIT, NULL, NULL, &len);
  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: openrw `%s'\n", a->no, a->subno,
               a->desc?a->desc:"?");

  return a;
}


int
iobuf_ioctl (iobuf_t a, int cmd, int intval, void *ptrval)
{
  if (cmd == 1)
    {                           /* keep system filepointer/descriptor open */
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: ioctl `%s' keep=%d\n",
                   a ? a->no : -1, a ? a->subno : -1, 
                   a && a->desc ? a->desc : "?",
                   intval);
      for (; a; a = a->chain)
        if (!a->chain && a->filter == file_filter)
          {
            file_filter_ctx_t *b = a->filter_ov;
            b->keep_open = intval;
            return 0;
          }
#ifdef HAVE_W32_SYSTEM
        else if (!a->chain && a->filter == sock_filter)
          {
            sock_filter_ctx_t *b = a->filter_ov;
            b->keep_open = intval;
            return 0;
          }
#endif
    }
  else if (cmd == 2)
    {                           /* invalidate cache */
      if (DBG_IOBUF)
        log_debug ("iobuf-*.*: ioctl `%s' invalidate\n",
                   ptrval ? (char *) ptrval : "?");
      if (!a && !intval && ptrval)
        {
#ifndef FILE_FILTER_USES_STDIO
          if (fd_cache_invalidate (ptrval))
            return -1;
#endif
          return 0;
        }
    }
  else if (cmd == 3)
    {                           /* disallow/allow caching */
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: ioctl `%s' no_cache=%d\n",
                   a ? a->no : -1, a ? a->subno : -1, 
                   a && a->desc? a->desc : "?",
                   intval);
      for (; a; a = a->chain)
        if (!a->chain && a->filter == file_filter)
          {
            file_filter_ctx_t *b = a->filter_ov;
            b->no_cache = intval;
            return 0;
          }
#ifdef HAVE_W32_SYSTEM
        else if (!a->chain && a->filter == sock_filter)
          {
            sock_filter_ctx_t *b = a->filter_ov;
            b->no_cache = intval;
            return 0;
          }
#endif
    }
  else if (cmd == 4)
    {
      /* Do a fsync on the open fd and return any errors to the caller
         of iobuf_ioctl.  Note that we work on a file name here. */
      if (DBG_IOBUF)
        log_debug ("iobuf-*.*: ioctl `%s' fsync\n",
                   ptrval? (const char*)ptrval:"<null>");

        if (!a && !intval && ptrval)
          {
#ifndef FILE_FILTER_USES_STDIO
            return fd_cache_synchronize (ptrval);
#else
            return 0;
#endif
          }
      }


  return -1;
}


/****************
 * Register an i/o filter.
 */
int
iobuf_push_filter (iobuf_t a,
                   int (*f) (void *opaque, int control,
                             iobuf_t chain, byte * buf, size_t * len),
                   void *ov)
{
  return iobuf_push_filter2 (a, f, ov, 0);
}

int
iobuf_push_filter2 (iobuf_t a,
                    int (*f) (void *opaque, int control,
                              iobuf_t chain, byte * buf, size_t * len),
                    void *ov, int rel_ov)
{
  iobuf_t b;
  size_t dummy_len = 0;
  int rc = 0;

  if (a->directfp)
    BUG ();

  if (a->use == 2 && (rc = iobuf_flush (a)))
    return rc;
  /* make a copy of the current stream, so that
   * A is the new stream and B the original one.
   * The contents of the buffers are transferred to the
   * new stream.
   */
  b = xmalloc (sizeof *b);
  memcpy (b, a, sizeof *b);
  /* fixme: it is stupid to keep a copy of the name at every level
   * but we need the name somewhere because the name known by file_filter
   * may have been released when we need the name of the file */
  b->real_fname = a->real_fname ? xstrdup (a->real_fname) : NULL;
  /* remove the filter stuff from the new stream */
  a->filter = NULL;
  a->filter_ov = NULL;
  a->filter_ov_owner = 0;
  a->filter_eof = 0;
  if (a->use == 3)
    a->use = 2;                 /* make a write stream from a temp stream */

  if (a->use == 2)
    {                           /* allocate a fresh buffer for the
                                   original stream */
      b->d.buf = xmalloc (a->d.size);
      b->d.len = 0;
      b->d.start = 0;
    }
  else
    {                           /* allocate a fresh buffer for the new
                                   stream */
      a->d.buf = xmalloc (a->d.size);
      a->d.len = 0;
      a->d.start = 0;
    }
  /* disable nlimit for the new stream */
  a->ntotal = b->ntotal + b->nbytes;
  a->nlimit = a->nbytes = 0;
  a->nofast &= ~1;
  /* make a link from the new stream to the original stream */
  a->chain = b;
  a->opaque = b->opaque;

  /* setup the function on the new stream */
  a->filter = f;
  a->filter_ov = ov;
  a->filter_ov_owner = rel_ov;

  a->subno = b->subno + 1;
  f (ov, IOBUFCTRL_DESC, NULL, (byte *) & a->desc, &dummy_len);

  if (DBG_IOBUF)
    {
      log_debug ("iobuf-%d.%d: push `%s'\n", a->no, a->subno, 
                 a->desc?a->desc:"?");
      print_chain (a);
    }

  /* now we can initialize the new function if we have one */
  if (a->filter && (rc = a->filter (a->filter_ov, IOBUFCTRL_INIT, a->chain,
                                    NULL, &dummy_len)))
    log_error ("IOBUFCTRL_INIT failed: %s\n", gpg_strerror (rc));
  return rc;
}

/****************
 * Remove an i/o filter.
 */
static int
pop_filter (iobuf_t a, int (*f) (void *opaque, int control,
                               iobuf_t chain, byte * buf, size_t * len),
            void *ov)
{
  iobuf_t b;
  size_t dummy_len = 0;
  int rc = 0;

  if (a->directfp)
    BUG ();

  if (DBG_IOBUF)
    log_debug ("iobuf-%d.%d: pop `%s'\n", a->no, a->subno,
               a->desc?a->desc:"?");
  if (!a->filter)
    {                           /* this is simple */
      b = a->chain;
      assert (b);
      xfree (a->d.buf);
      xfree (a->real_fname);
      memcpy (a, b, sizeof *a);
      xfree (b);
      return 0;
    }
  for (b = a; b; b = b->chain)
    if (b->filter == f && (!ov || b->filter_ov == ov))
      break;
  if (!b)
    log_bug ("pop_filter(): filter function not found\n");

  /* flush this stream if it is an output stream */
  if (a->use == 2 && (rc = iobuf_flush (b)))
    {
      log_error ("iobuf_flush failed in pop_filter: %s\n", gpg_strerror (rc));
      return rc;
    }
  /* and tell the filter to free it self */
  if (b->filter && (rc = b->filter (b->filter_ov, IOBUFCTRL_FREE, b->chain,
                                    NULL, &dummy_len)))
    {
      log_error ("IOBUFCTRL_FREE failed: %s\n", gpg_strerror (rc));
      return rc;
    }
  if (b->filter_ov && b->filter_ov_owner)
    {
      xfree (b->filter_ov);
      b->filter_ov = NULL;
    }


  /* and see how to remove it */
  if (a == b && !b->chain)
    log_bug ("can't remove the last filter from the chain\n");
  else if (a == b)
    {                           /* remove the first iobuf from the chain */
      /* everything from b is copied to a. This is save because
       * a flush has been done on the to be removed entry
       */
      b = a->chain;
      xfree (a->d.buf);
      xfree (a->real_fname);
      memcpy (a, b, sizeof *a);
      xfree (b);
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: popped filter\n", a->no, a->subno);
    }
  else if (!b->chain)
    {                           /* remove the last iobuf from the chain */
      log_bug ("Ohh jeee, trying to remove a head filter\n");
    }
  else
    {                           /* remove an intermediate iobuf from the chain */
      log_bug ("Ohh jeee, trying to remove an intermediate filter\n");
    }

  return rc;
}


/****************
 * read underflow: read more bytes into the buffer and return
 * the first byte or -1 on EOF.
 */
static int
underflow (iobuf_t a)
{
  size_t len;
  int rc;

  assert (a->d.start == a->d.len);
  if (a->use == 3)
    return -1;                  /* EOF because a temp buffer can't do an underflow */

  if (a->filter_eof)
    {
      if (a->chain)
        {
          iobuf_t b = a->chain;
          if (DBG_IOBUF)
            log_debug ("iobuf-%d.%d: pop `%s' in underflow\n",
                       a->no, a->subno, a->desc?a->desc:"?");
          xfree (a->d.buf);
          xfree (a->real_fname);
          memcpy (a, b, sizeof *a);
          xfree (b);
          print_chain (a);
        }
      else
        a->filter_eof = 0;      /* for the top level filter */
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: underflow: eof (due to filter eof)\n",
                   a->no, a->subno);
      return -1;                /* return one(!) EOF */
    }
  if (a->error)
    {
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: error\n", a->no, a->subno);
      return -1;
    }

  if (a->directfp)
    {
      FILE *fp = a->directfp;

      len = fread (a->d.buf, 1, a->d.size, fp);
      if (len < a->d.size)
        {
          if (ferror (fp))
            a->error = gpg_error_from_syserror ();
        }
      a->d.len = len;
      a->d.start = 0;
      return len ? a->d.buf[a->d.start++] : -1;
    }


  if (a->filter)
    {
      len = a->d.size;
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: underflow: req=%lu\n",
                   a->no, a->subno, (ulong) len);
      rc = a->filter (a->filter_ov, IOBUFCTRL_UNDERFLOW, a->chain,
                      a->d.buf, &len);
      if (DBG_IOBUF)
        {
          log_debug ("iobuf-%d.%d: underflow: got=%lu rc=%d\n",
                     a->no, a->subno, (ulong) len, rc);
/*          if( a->no == 1 ) */
/*                   log_hexdump ("     data:", a->d.buf, len); */
        }
      if (a->use == 1 && rc == -1)
        {                       /* EOF: we can remove the filter */
          size_t dummy_len = 0;

          /* and tell the filter to free itself */
          if ((rc = a->filter (a->filter_ov, IOBUFCTRL_FREE, a->chain,
                               NULL, &dummy_len)))
            log_error ("IOBUFCTRL_FREE failed: %s\n", gpg_strerror (rc));
          if (a->filter_ov && a->filter_ov_owner)
            {
              xfree (a->filter_ov);
              a->filter_ov = NULL;
            }
          a->filter = NULL;
          a->desc = NULL;
          a->filter_ov = NULL;
          a->filter_eof = 1;
          if (!len && a->chain)
            {
              iobuf_t b = a->chain;
              if (DBG_IOBUF)
                log_debug ("iobuf-%d.%d: pop in underflow (!len)\n",
                           a->no, a->subno);
              xfree (a->d.buf);
              xfree (a->real_fname);
              memcpy (a, b, sizeof *a);
              xfree (b);
              print_chain (a);
            }
        }
      else if (rc)
        a->error = rc;

      if (!len)
        {
          if (DBG_IOBUF)
            log_debug ("iobuf-%d.%d: underflow: eof\n", a->no, a->subno);
          return -1;
        }
      a->d.len = len;
      a->d.start = 0;
      return a->d.buf[a->d.start++];
    }
  else
    {
      if (DBG_IOBUF)
        log_debug ("iobuf-%d.%d: underflow: eof (no filter)\n",
                   a->no, a->subno);
      return -1;                /* no filter; return EOF */
    }
}


int
iobuf_flush (iobuf_t a)
{
  size_t len;
  int rc;

  if (a->directfp)
    return 0;

  if (a->use == 3)
    {                           /* increase the temp buffer */
      unsigned char *newbuf;
      size_t newsize = a->d.size + IOBUF_BUFFER_SIZE;

      if (DBG_IOBUF)
        log_debug ("increasing temp iobuf from %lu to %lu\n",
                   (ulong) a->d.size, (ulong) newsize);
      newbuf = xmalloc (newsize);
      memcpy (newbuf, a->d.buf, a->d.len);
      xfree (a->d.buf);
      a->d.buf = newbuf;
      a->d.size = newsize;
      return 0;
    }
  else if (a->use != 2)
    log_bug ("flush on non-output iobuf\n");
  else if (!a->filter)
    log_bug ("iobuf_flush: no filter\n");
  len = a->d.len;
  rc = a->filter (a->filter_ov, IOBUFCTRL_FLUSH, a->chain, a->d.buf, &len);
  if (!rc && len != a->d.len)
    {
      log_info ("iobuf_flush did not write all!\n");
      rc = GPG_ERR_INTERNAL;
    }
  else if (rc)
    a->error = rc;
  a->d.len = 0;

  return rc;
}


/****************
 * Read a byte from the iobuf; returns -1 on EOF
 */
int
iobuf_readbyte (iobuf_t a)
{
  int c;

  if (a->nlimit && a->nbytes >= a->nlimit)
    return -1;                  /* forced EOF */

  if (a->d.start < a->d.len)
    {
      c = a->d.buf[a->d.start++];
    }
  else if ((c = underflow (a)) == -1)
    return -1;                  /* EOF */

  a->nbytes++;
  return c;
}


int
iobuf_read (iobuf_t a, void *buffer, unsigned int buflen)
{
  unsigned char *buf = (unsigned char *)buffer;
  int c, n;

  if (a->nlimit)
    {
      /* Handle special cases. */
      for (n = 0; n < buflen; n++)
        {
          if ((c = iobuf_readbyte (a)) == -1)
            {
              if (!n)
                return -1;      /* eof */
              break;
            }
          else if (buf)
            *buf = c;
          if (buf)
            buf++;
        }
      return n;
    }

  n = 0;
  do
    {
      if (n < buflen && a->d.start < a->d.len)
        {
          unsigned size = a->d.len - a->d.start;
          if (size > buflen - n)
            size = buflen - n;
          if (buf)
            memcpy (buf, a->d.buf + a->d.start, size);
          n += size;
          a->d.start += size;
          if (buf)
            buf += size;
        }
      if (n < buflen)
        {
          if ((c = underflow (a)) == -1)
            {
              a->nbytes += n;
              return n ? n : -1 /*EOF*/;
            }
          if (buf)
            *buf++ = c;
          n++;
        }
    }
  while (n < buflen);
  a->nbytes += n;
  return n;
}



/****************
 * Have a look at the iobuf.
 * NOTE: This only works in special cases.
 */
int
iobuf_peek (iobuf_t a, byte * buf, unsigned buflen)
{
  int n = 0;

  if (a->filter_eof)
    return -1;

  if (!(a->d.start < a->d.len))
    {
      if (underflow (a) == -1)
        return -1;
      /* And unget this character. */
      assert (a->d.start == 1);
      a->d.start = 0;
    }

  for (n = 0; n < buflen && (a->d.start + n) < a->d.len; n++, buf++)
    *buf = a->d.buf[n];
  return n;
}




int
iobuf_writebyte (iobuf_t a, unsigned int c)
{
  int rc;

  if (a->directfp)
    BUG ();

  if (a->d.len == a->d.size)
    if ((rc=iobuf_flush (a)))
      return rc;

  assert (a->d.len < a->d.size);
  a->d.buf[a->d.len++] = c;
  return 0;
}


int
iobuf_write (iobuf_t a, const void *buffer, unsigned int buflen)
{
  const unsigned char *buf = (const unsigned char *)buffer;
  int rc;

  if (a->directfp)
    BUG ();

  do
    {
      if (buflen && a->d.len < a->d.size)
        {
          unsigned size = a->d.size - a->d.len;
          if (size > buflen)
            size = buflen;
          memcpy (a->d.buf + a->d.len, buf, size);
          buflen -= size;
          buf += size;
          a->d.len += size;
        }
      if (buflen)
        {
          rc = iobuf_flush (a);
          if (rc)
            return rc;
        }
    }
  while (buflen);
  return 0;
}


int
iobuf_writestr (iobuf_t a, const char *buf)
{
  int rc;

  for (; *buf; buf++)
    if ((rc=iobuf_writebyte (a, *buf)))
      return rc;
  return 0;
}



/****************
 * copy the contents of TEMP to A.
 */
int
iobuf_write_temp (iobuf_t a, iobuf_t temp)
{
  while (temp->chain)
    pop_filter (temp, temp->filter, NULL);
  return iobuf_write (a, temp->d.buf, temp->d.len);
}

/****************
 * copy the contents of the temp io stream to BUFFER.
 */
size_t
iobuf_temp_to_buffer (iobuf_t a, byte * buffer, size_t buflen)
{
  size_t n = a->d.len;

  if (n > buflen)
    n = buflen;
  memcpy (buffer, a->d.buf, n);
  return n;
}


/****************
 * Call this function to terminate processing of the temp stream
 * without closing it.  This removes all filters from the stream
 * makes sure that iobuf_get_temp_{buffer,length}() returns correct
 * values.
 */
void
iobuf_flush_temp (iobuf_t temp)
{
  while (temp->chain)
    pop_filter (temp, temp->filter, NULL);
}


/****************
 * Set a limit on how many bytes may be read from the input stream A.
 * Setting the limit to 0 disables this feature.
 */
void
iobuf_set_limit (iobuf_t a, off_t nlimit)
{
  if (nlimit)
    a->nofast |= 1;
  else
    a->nofast &= ~1;
  a->nlimit = nlimit;
  a->ntotal += a->nbytes;
  a->nbytes = 0;
}



/* Return the length of an open file A.  IF OVERFLOW is not NULL it
   will be set to true if the file is larger than what off_t can cope
   with.  The function return 0 on error or on overflow condition.  */
off_t
iobuf_get_filelength (iobuf_t a, int *overflow)
{
  struct stat st;

  if (overflow)
    *overflow = 0;
  
  if ( a->directfp )  
    {
      FILE *fp = a->directfp;
      
      if ( !fstat(fileno(fp), &st) )
        return st.st_size;
      log_error("fstat() failed: %s\n", strerror(errno) );
      return 0;
    }
  
  /* Hmmm: file_filter may have already been removed */
  for ( ; a; a = a->chain )
    if ( !a->chain && a->filter == file_filter )
      {
        file_filter_ctx_t *b = a->filter_ov;
        fp_or_fd_t fp = b->fp;
        
#if defined(HAVE_W32_SYSTEM) && !defined(FILE_FILTER_USES_STDIO)
        ulong size;
        static int (* __stdcall get_file_size_ex) (void *handle,
                                                   LARGE_INTEGER *r_size);
        static int get_file_size_ex_initialized;

        if (!get_file_size_ex_initialized)
          {
            void *handle;
            
            handle = dlopen ("kernel32.dll", RTLD_LAZY);
            if (handle)
              {
                get_file_size_ex = dlsym (handle, "GetFileSizeEx");
                if (!get_file_size_ex)
                  dlclose (handle);
              }
            get_file_size_ex_initialized = 1;
          }
        
        if (get_file_size_ex)
          {
            /* This is a newer system with GetFileSizeEx; we use this
               then because it seem that GetFileSize won't return a
               proper error in case a file is larger than 4GB. */
            LARGE_INTEGER exsize;
            
            if (get_file_size_ex (fp, &exsize))
              {
                if (!exsize.u.HighPart)
                  return exsize.u.LowPart;
                if (overflow)
                  *overflow = 1;
                return 0; 
              }
          }
        else
          {
            if ((size=GetFileSize (fp, NULL)) != 0xffffffff)
              return size;
          }
        log_error ("GetFileSize for handle %p failed: %s\n",
                   fp, w32_strerror (0));
#else
        if ( !fstat(my_fileno(fp), &st) )
          return st.st_size;
        log_error("fstat() failed: %s\n", strerror(errno) );
#endif
        break/*the for loop*/;
      }
  
    return 0;
}


/* Return the file descriptor of the underlying file or -1 if it is
   not available.  */
int 
iobuf_get_fd (iobuf_t a)
{
  if (a->directfp)
    return fileno ( (FILE*)a->directfp );

  for ( ; a; a = a->chain )
    if (!a->chain && a->filter == file_filter)
      {
        file_filter_ctx_t *b = a->filter_ov;
        fp_or_fd_t fp = b->fp;

        return my_fileno (fp);
      }

  return -1;
}



/****************
 * Tell the file position, where the next read will take place
 */
off_t
iobuf_tell (iobuf_t a)
{
  return a->ntotal + a->nbytes;
}


#if !defined(HAVE_FSEEKO) && !defined(fseeko)

#ifdef HAVE_LIMITS_H
# include <limits.h>
#endif
#ifndef LONG_MAX
# define LONG_MAX ((long) ((unsigned long) -1 >> 1))
#endif
#ifndef LONG_MIN
# define LONG_MIN (-1 - LONG_MAX)
#endif

/****************
 * A substitute for fseeko, for hosts that don't have it.
 */
static int
fseeko (FILE * stream, off_t newpos, int whence)
{
  while (newpos != (long) newpos)
    {
      long pos = newpos < 0 ? LONG_MIN : LONG_MAX;
      if (fseek (stream, pos, whence) != 0)
        return -1;
      newpos -= pos;
      whence = SEEK_CUR;
    }
  return fseek (stream, (long) newpos, whence);
}
#endif

/****************
 * This is a very limited implementation. It simply discards all internal
 * buffering and removes all filters but the first one.
 */
int
iobuf_seek (iobuf_t a, off_t newpos)
{
  file_filter_ctx_t *b = NULL;

  if (a->directfp)
    {
      FILE *fp = a->directfp;
      if (fseeko (fp, newpos, SEEK_SET))
        {
          log_error ("can't seek: %s\n", strerror (errno));
          return -1;
        }
      clearerr (fp);
    }
  else
    {
      for (; a; a = a->chain)
        {
          if (!a->chain && a->filter == file_filter)
            {
              b = a->filter_ov;
              break;
            }
        }
      if (!a)
        return -1;
#ifdef FILE_FILTER_USES_STDIO
      if (fseeko (b->fp, newpos, SEEK_SET))
        {
          log_error ("can't fseek: %s\n", strerror (errno));
          return -1;
        }
#else
#ifdef HAVE_W32_SYSTEM
      if (SetFilePointer (b->fp, newpos, NULL, FILE_BEGIN) == 0xffffffff)
        {
          log_error ("SetFilePointer failed on handle %p: ec=%d\n",
                     b->fp, (int) GetLastError ());
          return -1;
        }
#else
      if (lseek (b->fp, newpos, SEEK_SET) == (off_t) - 1)
        {
          log_error ("can't lseek: %s\n", strerror (errno));
          return -1;
        }
#endif
#endif
    }
  a->d.len = 0;                 /* discard buffer */
  a->d.start = 0;
  a->nbytes = 0;
  a->nlimit = 0;
  a->nofast &= ~1;
  a->ntotal = newpos;
  a->error = 0;
  /* remove filters, but the last */
  if (a->chain)
    log_debug ("pop_filter called in iobuf_seek - please report\n");
  while (a->chain)
    pop_filter (a, a->filter, NULL);

  return 0;
}






/****************
 * Retrieve the real filename
 */
const char *
iobuf_get_real_fname (iobuf_t a)
{
  if (a->real_fname)
    return a->real_fname;

  /* the old solution */
  for (; a; a = a->chain)
    if (!a->chain && a->filter == file_filter)
      {
        file_filter_ctx_t *b = a->filter_ov;
        return b->print_only_name ? NULL : b->fname;
      }

  return NULL;
}


/****************
 * Retrieve the filename
 */
const char *
iobuf_get_fname (iobuf_t a)
{
  for (; a; a = a->chain)
    if (!a->chain && a->filter == file_filter)
      {
        file_filter_ctx_t *b = a->filter_ov;
        return b->fname;
      }
  return NULL;
}


/****************
 * enable partial block mode as described in the OpenPGP draft.
 * LEN is the first length byte on read, but ignored on writes.
 */
void
iobuf_set_partial_block_mode (iobuf_t a, size_t len)
{
  block_filter_ctx_t *ctx = xcalloc (1, sizeof *ctx);

  assert (a->use == 1 || a->use == 2);
  ctx->use = a->use;
  if (!len)
    {
      if (a->use == 1)
        log_debug ("pop_filter called in set_partial_block_mode"
                   " - please report\n");
      pop_filter (a, block_filter, NULL);
    }
  else
    {
      ctx->partial = 1;
      ctx->size = 0;
      ctx->first_c = len;
      iobuf_push_filter (a, block_filter, ctx);
    }
}



/****************
 * Same as fgets() but if the buffer is too short a larger one will
 * be allocated up to some limit *max_length.
 * A line is considered a byte stream ending in a LF.
 * Returns the length of the line. EOF is indicated by a line of
 * length zero. The last LF may be missing due to an EOF.
 * is max_length is zero on return, the line has been truncated.
 *
 * Note: The buffer is allocated with enough space to append a CR,LF,EOL
 */
unsigned int
iobuf_read_line (iobuf_t a, byte ** addr_of_buffer,
                 unsigned *length_of_buffer, unsigned *max_length)
{
  int c;
  char *buffer = (char *)*addr_of_buffer;
  unsigned length = *length_of_buffer;
  unsigned nbytes = 0;
  unsigned maxlen = *max_length;
  char *p;

  if (!buffer)
    {                           /* must allocate a new buffer */
      length = 256;
      buffer = xmalloc (length);
      *addr_of_buffer = (unsigned char *)buffer;
      *length_of_buffer = length;
    }

  length -= 3;                  /* reserve 3 bytes (cr,lf,eol) */
  p = buffer;
  while ((c = iobuf_get (a)) != -1)
    {
      if (nbytes == length)
        {                       /* increase the buffer */
          if (length > maxlen)
            {                   /* this is out limit */
              /* skip the rest of the line */
              while (c != '\n' && (c = iobuf_get (a)) != -1)
                ;
              *p++ = '\n';      /* always append a LF (we have reserved space) */
              nbytes++;
              *max_length = 0;  /* indicate truncation */
              break;
            }
          length += 3;          /* correct for the reserved byte */
          length += length < 1024 ? 256 : 1024;
          buffer = xrealloc (buffer, length);
          *addr_of_buffer = (unsigned char *)buffer;
          *length_of_buffer = length;
          length -= 3;          /* and reserve again */
          p = buffer + nbytes;
        }
      *p++ = c;
      nbytes++;
      if (c == '\n')
        break;
    }
  *p = 0;                       /* make sure the line is a string */

  return nbytes;
}

static int
translate_file_handle (int fd, int for_write)
{
#ifdef HAVE_W32_SYSTEM
# ifdef FILE_FILTER_USES_STDIO
  fd = translate_sys2libc_fd (fd, for_write);
# else
  {
    int x;
    
    (void)for_write;

    if (fd == 0)
      x = (int) GetStdHandle (STD_INPUT_HANDLE);
    else if (fd == 1)
      x = (int) GetStdHandle (STD_OUTPUT_HANDLE);
    else if (fd == 2)
      x = (int) GetStdHandle (STD_ERROR_HANDLE);
    else
      x = fd;

    if (x == -1)
      log_debug ("GetStdHandle(%d) failed: ec=%d\n",
                 fd, (int) GetLastError ());

    fd = x;
  }
# endif
#else
  (void)for_write;
#endif
  return fd;
}


void
iobuf_skip_rest (iobuf_t a, unsigned long n, int partial)
{
  if ( partial )
    {
      for (;;)
        {
          if (a->nofast || a->d.start >= a->d.len) 
            {
              if (iobuf_readbyte (a) == -1)
                {
                  break;
                }
            } 
          else
            {
              unsigned long count = a->d.len - a->d.start;
              a->nbytes += count;
              a->d.start = a->d.len;
            }
        }
    } 
  else
    {
      unsigned long remaining = n;
      while (remaining > 0) 
        {
          if (a->nofast || a->d.start >= a->d.len)
            {
              if (iobuf_readbyte (a) == -1)
                {
                  break;
                }
              --remaining;
            } 
          else 
            {
              unsigned long count = a->d.len - a->d.start;
              if (count > remaining) 
                {
                  count = remaining;
                }
              a->nbytes += count;
              a->d.start += count;
              remaining -= count;
            }
        }
    }
}