path: root/src/common/compat.c

/* Copyright (c) 2003-2004, Roger Dingledine
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2009, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file compat.c
 * \brief Wrappers to make calls more portable.  This code defines
 * functions such as tor_malloc, tor_snprintf, get/set various data types,
 * renaming, setting socket options, switching user IDs.  It is basically
 * where the non-portable items are conditionally included depending on
 * the platform.
 **/

/* This is required on rh7 to make strptime not complain.
 * We also need it to make memmem get defined (where available)
 */
#define _GNU_SOURCE

#include "compat.h"

#ifdef MS_WINDOWS
#include <process.h>
#include <windows.h>
#include <sys/locking.h>
#endif

#ifdef HAVE_UNAME
#include <sys/utsname.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_FCNTL_H
#include <sys/fcntl.h>
#endif
#ifdef HAVE_PWD_H
#include <pwd.h>
#endif
#ifdef HAVE_GRP_H
#include <grp.h>
#endif
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif

#ifndef HAVE_GETTIMEOFDAY
#ifdef HAVE_FTIME
#include <sys/timeb.h>
#endif
#endif

#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef HAVE_SYS_PARAM_H
#include <sys/param.h> /* FreeBSD needs this to know what version it is */
#endif
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#ifdef HAVE_SIGNAL_H
#include <signal.h>
#endif
#ifdef HAVE_UTIME_H
#include <utime.h>
#endif
#ifdef HAVE_SYS_UTIME_H
#include <sys/utime.h>
#endif
#ifdef HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif
#ifdef HAVE_SYS_SYSLIMITS_H
#include <sys/syslimits.h>
#endif
#ifdef HAVE_SYS_FILE_H
#include <sys/file.h>
#endif
#if defined(HAVE_SYS_PRCTL_H) && defined(__linux__)
/* Only use the linux prctl;  the IRIX prctl is totally different */
#include <sys/prctl.h>
#endif

#include "log.h"
#include "util.h"
#include "container.h"
#include "address.h"

/* Inline the strl functions if the platform doesn't have them. */
#ifndef HAVE_STRLCPY
#include "strlcpy.c"
#endif
#ifndef HAVE_STRLCAT
#include "strlcat.c"
#endif

#ifdef HAVE_SYS_MMAN_H
/** Try to create a memory mapping for <b>filename</b> and return it.  On
 * failure, return NULL.  Sets errno properly, using ERANGE to mean
 * "empty file". */
tor_mmap_t *
tor_mmap_file(const char *filename)
{
  int fd; /* router file */
  char *string;
  int page_size;
  tor_mmap_t *res;
  size_t size, filesize;

  tor_assert(filename);

  fd = open(filename, O_RDONLY, 0);
  if (fd<0) {
    int save_errno = errno;
    int severity = (errno == ENOENT) ? LOG_INFO : LOG_WARN;
    log_fn(severity, LD_FS,"Could not open \"%s\" for mmap(): %s",filename,
           strerror(errno));
    errno = save_errno;
    return NULL;
  }

  size = filesize = (size_t) lseek(fd, 0, SEEK_END);
  lseek(fd, 0, SEEK_SET);
  /* ensure page alignment */
  page_size = getpagesize();
  size += (size%page_size) ? page_size-(size%page_size) : 0;

  if (!size) {
    /* Zero-length file. If we call mmap on it, it will succeed but
     * return NULL, and bad things will happen. So just fail. */
    log_info(LD_FS,"File \"%s\" is empty. Ignoring.",filename);
    errno = ERANGE;
    close(fd);
    return NULL;
  }

  string = mmap(0, size, PROT_READ, MAP_PRIVATE, fd, 0);
  close(fd);
  if (string == MAP_FAILED) {
    int save_errno = errno;
    log_warn(LD_FS,"Could not mmap file \"%s\": %s", filename,
             strerror(errno));
    errno = save_errno;
    return NULL;
  }

  res = tor_malloc_zero(sizeof(tor_mmap_t));
  res->data = string;
  res->size = filesize;
  res->mapping_size = size;

  return res;
}
/** Release storage held for a memory mapping. */
void
tor_munmap_file(tor_mmap_t *handle)
{
  munmap((char*)handle->data, handle->mapping_size);
  tor_free(handle);
}
#elif defined(MS_WINDOWS)
tor_mmap_t *
tor_mmap_file(const char *filename)
{
  tor_mmap_t *res = tor_malloc_zero(sizeof(tor_mmap_t));
  int empty = 0;
  res->file_handle = INVALID_HANDLE_VALUE;
  res->mmap_handle = NULL;

  res->file_handle = CreateFile(filename,
                                GENERIC_READ, FILE_SHARE_READ,
                                NULL,
                                OPEN_EXISTING,
                                FILE_ATTRIBUTE_NORMAL,
                                0);

  if (res->file_handle == INVALID_HANDLE_VALUE)
    goto win_err;

  res->size = GetFileSize(res->file_handle, NULL);

  if (res->size == 0) {
    log_info(LD_FS,"File \"%s\" is empty. Ignoring.",filename);
    empty = 1;
    goto err;
  }

  res->mmap_handle = CreateFileMapping(res->file_handle,
                                       NULL,
                                       PAGE_READONLY,
#if SIZEOF_SIZE_T > 4
                                       (res->base.size >> 32),
#else
                                       0,
#endif
                                       (res->size & 0xfffffffful),
                                       NULL);
  if (res->mmap_handle == NULL)
    goto win_err;
  res->data = (char*) MapViewOfFile(res->mmap_handle,
                                    FILE_MAP_READ,
                                    0, 0, 0);
  if (!res->data)
    goto win_err;

  return res;
 win_err: {
    DWORD e = GetLastError();
    int severity = (e == ERROR_FILE_NOT_FOUND || e == ERROR_PATH_NOT_FOUND) ?
      LOG_INFO : LOG_WARN;
    char *msg = format_win32_error(e);
    log_fn(severity, LD_FS, "Couldn't mmap file \"%s\": %s", filename, msg);
    tor_free(msg);
    if (e == ERROR_FILE_NOT_FOUND || e == ERROR_PATH_NOT_FOUND)
      errno = ENOENT;
    else
      errno = EINVAL;
  }
 err:
  if (empty)
    errno = ERANGE;
  tor_munmap_file(res);
  return NULL;
}
void
tor_munmap_file(tor_mmap_t *handle)
{
  if (handle->data)
    /* This is an ugly cast, but without it, "data" in struct tor_mmap_t would
       have to be redefined as non-const. */
    UnmapViewOfFile( (LPVOID) handle->data);

  if (handle->mmap_handle != NULL)
    CloseHandle(handle->mmap_handle);
  if (handle->file_handle != INVALID_HANDLE_VALUE)
    CloseHandle(handle->file_handle);
  tor_free(handle);
}
#else
tor_mmap_t *
tor_mmap_file(const char *filename)
{
  struct stat st;
  char *res = read_file_to_str(filename, RFTS_BIN|RFTS_IGNORE_MISSING, &st);
  tor_mmap_t *handle;
  if (! res)
    return NULL;
  handle = tor_malloc_zero(sizeof(tor_mmap_t));
  handle->data = res;
  handle->size = st.st_size;
  return handle;
}
void
tor_munmap_file(tor_mmap_t *handle)
{
  char *d = (char*)handle->data;
  tor_free(d);
  memset(handle, 0, sizeof(tor_mmap_t));
  tor_free(handle);
}
#endif

/** Replacement for snprintf.  Differs from platform snprintf in two
 * ways: First, always NUL-terminates its output.  Second, always
 * returns -1 if the result is truncated.  (Note that this return
 * behavior does <i>not</i> conform to C99; it just happens to be
 * easier to emulate "return -1" with conformant implementations than
 * it is to emulate "return number that would be written" with
 * non-conformant implementations.) */
int
tor_snprintf(char *str, size_t size, const char *format, ...)
{
  va_list ap;
  int r;
  va_start(ap,format);
  r = tor_vsnprintf(str,size,format,ap);
  va_end(ap);
  return r;
}

/** Replacement for vsnprintf; behavior differs as tor_snprintf differs from
 * snprintf.
 */
int
tor_vsnprintf(char *str, size_t size, const char *format, va_list args)
{
  int r;
  if (size == 0)
    return -1; /* no place for the NUL */
  if (size > SSIZE_T_MAX-16)
    return -1;
#ifdef MS_WINDOWS
  r = _vsnprintf(str, size, format, args);
#else
  r = vsnprintf(str, size, format, args);
#endif
  str[size-1] = '\0';
  if (r < 0 || r >= (ssize_t)size)
    return -1;
  return r;
}

/** Given <b>hlen</b> bytes at <b>haystack</b> and <b>nlen</b> bytes at
 * <b>needle</b>, return a pointer to the first occurrence of the needle
 * within the haystack, or NULL if there is no such occurrence.
 *
 * Requires that nlen be greater than zero.
 */
const void *
tor_memmem(const void *_haystack, size_t hlen,
           const void *_needle, size_t nlen)
{
#if defined(HAVE_MEMMEM) && (!defined(__GNUC__) || __GNUC__ >= 2)
  tor_assert(nlen);
  return memmem(_haystack, hlen, _needle, nlen);
#else
  /* This isn't as fast as the GLIBC implementation, but it doesn't need to
   * be. */
  const char *p, *end;
  const char *haystack = (const char*)_haystack;
  const char *needle = (const char*)_needle;
  char first;
  tor_assert(nlen);

  p = haystack;
  end = haystack + hlen;
  first = *(const char*)needle;
  while ((p = memchr(p, first, end-p))) {
    if (p+nlen > end)
      return NULL;
    if (!memcmp(p, needle, nlen))
      return p;
    ++p;
  }
  return NULL;
#endif
}

/* Tables to implement ctypes-replacement TOR_IS*() functions.  Each table
 * has 256 bits to look up whether a character is in some set or not.  This
 * fails on non-ASCII platforms, but it is hard to find a platform whose
 * character set is not a superset of ASCII nowadays. */
const uint32_t TOR_ISALPHA_TABLE[8] =
  { 0, 0, 0x7fffffe, 0x7fffffe, 0, 0, 0, 0 };
const uint32_t TOR_ISALNUM_TABLE[8] =
  { 0, 0x3ff0000, 0x7fffffe, 0x7fffffe, 0, 0, 0, 0 };
const uint32_t TOR_ISSPACE_TABLE[8] = { 0x3e00, 0x1, 0, 0, 0, 0, 0, 0 };
const uint32_t TOR_ISXDIGIT_TABLE[8] =
  { 0, 0x3ff0000, 0x7e, 0x7e, 0, 0, 0, 0 };
const uint32_t TOR_ISDIGIT_TABLE[8] = { 0, 0x3ff0000, 0, 0, 0, 0, 0, 0 };
const uint32_t TOR_ISPRINT_TABLE[8] =
  { 0, 0xffffffff, 0xffffffff, 0x7fffffff, 0, 0, 0, 0x0 };
const uint32_t TOR_ISUPPER_TABLE[8] = { 0, 0, 0x7fffffe, 0, 0, 0, 0, 0 };
const uint32_t TOR_ISLOWER_TABLE[8] = { 0, 0, 0, 0x7fffffe, 0, 0, 0, 0 };
/* Upper-casing and lowercasing tables to map characters to upper/lowercase
 * equivalents. */
const char TOR_TOUPPER_TABLE[256] = {
  0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
  16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,
  32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,
  48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,
  64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,
  80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,
  96,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,
  80,81,82,83,84,85,86,87,88,89,90,123,124,125,126,127,
  128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,
  144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,
  160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,
  176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,
  192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,
  208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,
  224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,
  240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,
};
const char TOR_TOLOWER_TABLE[256] = {
  0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
  16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,
  32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,
  48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,
  64,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,
  112,113,114,115,116,117,118,119,120,121,122,91,92,93,94,95,
  96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,
  112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,
  128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,
  144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,
  160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,
  176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,
  192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,
  208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,
  224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,
  240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,
};

/** Implementation of strtok_r for platforms whose coders haven't figured out
 * how to write one.  Hey guys!  You can use this code here for free! */
char *
tor_strtok_r_impl(char *str, const char *sep, char **lasts)
{
  char *cp, *start;
  if (str)
    start = cp = *lasts = str;
  else if (!*lasts)
    return NULL;
  else
    start = cp = *lasts;

  tor_assert(*sep);
  if (sep[1]) {
    while (*cp && !strchr(sep, *cp))
      ++cp;
  } else {
    tor_assert(strlen(sep) == 1);
    cp = strchr(cp, *sep);
  }

  if (!cp || !*cp) {
    *lasts = NULL;
  } else {
    *cp++ = '\0';
    *lasts = cp;
  }
  return start;
}

#ifdef MS_WINDOWS
/** Take a filename and return a pointer to its final element.  This
 * function is called on __FILE__ to fix a MSVC nit where __FILE__
 * contains the full path to the file.  This is bad, because it
 * confuses users to find the home directory of the person who
 * compiled the binary in their warning messages.
 */
const char *
tor_fix_source_file(const char *fname)
{
  const char *cp1, *cp2, *r;
  cp1 = strrchr(fname, '/');
  cp2 = strrchr(fname, '\\');
  if (cp1 && cp2) {
    r = (cp1<cp2)?(cp2+1):(cp1+1);
  } else if (cp1) {
    r = cp1+1;
  } else if (cp2) {
    r = cp2+1;
  } else {
    r = fname;
  }
  return r;
}
#endif

/**
 * Read a 16-bit value beginning at <b>cp</b>.  Equivalent to
 * *(uint16_t*)(cp), but will not cause segfaults on platforms that forbid
 * unaligned memory access.
 */
uint16_t
get_uint16(const char *cp)
{
  uint16_t v;
  memcpy(&v,cp,2);
  return v;
}
/**
 * Read a 32-bit value beginning at <b>cp</b>.  Equivalent to
 * *(uint32_t*)(cp), but will not cause segfaults on platforms that forbid
 * unaligned memory access.
 */
uint32_t
get_uint32(const char *cp)
{
  uint32_t v;
  memcpy(&v,cp,4);
  return v;
}
/**
 * Read a 64-bit value beginning at <b>cp</b>.  Equivalent to
 * *(uint64_t*)(cp), but will not cause segfaults on platforms that forbid
 * unaligned memory access.
 */
uint64_t
get_uint64(const char *cp)
{
  uint64_t v;
  memcpy(&v,cp,8);
  return v;
}

/**
 * Set a 16-bit value beginning at <b>cp</b> to <b>v</b>. Equivalent to
 * *(uint16_t*)(cp) = v, but will not cause segfaults on platforms that forbid
 * unaligned memory access. */
void
set_uint16(char *cp, uint16_t v)
{
  memcpy(cp,&v,2);
}
/**
 * Set a 32-bit value beginning at <b>cp</b> to <b>v</b>. Equivalent to
 * *(uint32_t*)(cp) = v, but will not cause segfaults on platforms that forbid
 * unaligned memory access. */
void
set_uint32(char *cp, uint32_t v)
{
  memcpy(cp,&v,4);
}
/**
 * Set a 64-bit value beginning at <b>cp</b> to <b>v</b>. Equivalent to
 * *(uint64_t*)(cp) = v, but will not cause segfaults on platforms that forbid
 * unaligned memory access. */
void
set_uint64(char *cp, uint64_t v)
{
  memcpy(cp,&v,8);
}

/**
 * Rename the file <b>from</b> to the file <b>to</b>.  On Unix, this is
 * the same as rename(2).  On windows, this removes <b>to</b> first if
 * it already exists.
 * Returns 0 on success.  Returns -1 and sets errno on failure.
 */
int
replace_file(const char *from, const char *to)
{
#ifndef MS_WINDOWS
  return rename(from,to);
#else
  switch (file_status(to))
    {
    case FN_NOENT:
      break;
    case FN_FILE:
      if (unlink(to)) return -1;
      break;
    case FN_ERROR:
      return -1;
    case FN_DIR:
      errno = EISDIR;
      return -1;
    }
  return rename(from,to);
#endif
}

/** Change <b>fname</b>'s modification time to now. */
int
touch_file(const char *fname)
{
  if (utime(fname, NULL)!=0)
    return -1;
  return 0;
}

/** Represents a lockfile on which we hold the lock. */
struct tor_lockfile_t {
  char *filename;
  int fd;
};

/** Try to get a lock on the lockfile <b>filename</b>, creating it as
 * necessary.  If someone else has the lock and <b>blocking</b> is true,
 * wait until the lock is available.  Otherwise return immediately whether
 * we succeeded or not.
 *
 * Set *<b>locked_out</b> to true if somebody else had the lock, and to false
 * otherwise.
 *
 * Return a <b>tor_lockfile_t</b> on success, NULL on failure.
 *
 * (Implementation note: because we need to fall back to fcntl on some
 *  platforms, these locks are per-process, not per-thread.  If you want
 *  to do in-process locking, use tor_mutex_t like a normal person.)
 */
tor_lockfile_t *
tor_lockfile_lock(const char *filename, int blocking, int *locked_out)
{
  tor_lockfile_t *result;
  int fd;
  *locked_out = 0;

  log_info(LD_FS, "Locking \"%s\"", filename);
  fd = open(filename, O_RDWR|O_CREAT|O_TRUNC, 0600);
  if (fd < 0) {
    log_warn(LD_FS,"Couldn't open \"%s\" for locking: %s", filename,
             strerror(errno));
    return NULL;
  }

#ifdef WIN32
  _lseek(fd, 0, SEEK_SET);
  if (_locking(fd, blocking ? _LK_LOCK : _LK_NBLCK, 1) < 0) {
    if (errno != EDEADLOCK)
      log_warn(LD_FS,"Couldn't lock \"%s\": %s", filename, strerror(errno));
    else
      *locked_out = 1;
    close(fd);
    return NULL;
  }
#elif defined(HAVE_FLOCK)
  if (flock(fd, LOCK_EX|(blocking ? 0 : LOCK_NB)) < 0) {
    if (errno != EWOULDBLOCK)
      log_warn(LD_FS,"Couldn't lock \"%s\": %s", filename, strerror(errno));
    else
      *locked_out = 1;
    close(fd);
    return NULL;
  }
#else
  {
    struct flock lock;
    memset(&lock, 0, sizeof(lock));
    lock.l_type = F_WRLCK;
    lock.l_whence = SEEK_SET;
    if (fcntl(fd, blocking ? F_SETLKW : F_SETLK, &lock) < 0) {
      if (errno != EACCES && errno != EAGAIN)
        log_warn(LD_FS, "Couldn't lock \"%s\": %s", filename, strerror(errno));
      else
        *locked_out = 1;
      close(fd);
      return NULL;
    }
  }
#endif

  result = tor_malloc(sizeof(tor_lockfile_t));
  result->filename = tor_strdup(filename);
  result->fd = fd;
  return result;
}

/** Release the lock held as <b>lockfile</b>. */
void
tor_lockfile_unlock(tor_lockfile_t *lockfile)
{
  tor_assert(lockfile);

  log_info(LD_FS, "Unlocking \"%s\"", lockfile->filename);
#ifdef WIN32
  _lseek(lockfile->fd, 0, SEEK_SET);
  if (_locking(lockfile->fd, _LK_UNLCK, 1) < 0) {
    log_warn(LD_FS,"Error unlocking \"%s\": %s", lockfile->filename,
             strerror(errno));
  }
#elif defined(HAVE_FLOCK)
  if (flock(lockfile->fd, LOCK_UN) < 0) {
    log_warn(LD_FS, "Error unlocking \"%s\": %s", lockfile->filename,
             strerror(errno));
  }
#else
  /* Closing the lockfile is sufficient. */
#endif

  close(lockfile->fd);
  lockfile->fd = -1;
  tor_free(lockfile->filename);
  tor_free(lockfile);
}

/* Some old versions of Unix didn't define constants for these values,
 * and instead expect you to say 0, 1, or 2. */
#ifndef SEEK_CUR
#define SEEK_CUR 1
#endif
#ifndef SEEK_END
#define SEEK_END 2
#endif

/** Return the position of <b>fd</b> with respect to the start of the file. */
off_t
tor_fd_getpos(int fd)
{
#ifdef WIN32
  return (off_t) _lseek(fd, 0, SEEK_CUR);
#else
  return (off_t) lseek(fd, 0, SEEK_CUR);
#endif
}

/** Move <b>fd</b> to the end of the file. Return -1 on error, 0 on success. */
int
tor_fd_seekend(int fd)
{
#ifdef WIN32
  return _lseek(fd, 0, SEEK_END) < 0 ? -1 : 0;
#else
  return lseek(fd, 0, SEEK_END) < 0 ? -1 : 0;
#endif
}

#undef DEBUG_SOCKET_COUNTING
#ifdef DEBUG_SOCKET_COUNTING
/** A bitarray of all fds that should be passed to tor_socket_close(). Only
 * used if DEBUG_SOCKET_COUNTING is defined. */
static bitarray_t *open_sockets = NULL;
/** The size of <b>open_sockets</b>, in bits. */
static int max_socket = -1;
#endif

/** Count of number of sockets currently open.  (Undercounts sockets opened by
 * eventdns and libevent.) */
static int n_sockets_open = 0;

/** Mutex to protect open_sockets, max_socket, and n_sockets_open. */
static tor_mutex_t *socket_accounting_mutex = NULL;

static INLINE void
socket_accounting_lock(void)
{
  if (PREDICT_UNLIKELY(!socket_accounting_mutex))
    socket_accounting_mutex = tor_mutex_new();
  tor_mutex_acquire(socket_accounting_mutex);
}

static INLINE void
socket_accounting_unlock(void)
{
  tor_mutex_release(socket_accounting_mutex);
}

/** As close(), but guaranteed to work for sockets across platforms (including
 * Windows, where close()ing a socket doesn't work.  Returns 0 on success, -1
 * on failure. */
int
tor_close_socket(int s)
{
  int r = 0;

  /* On Windows, you have to call close() on fds returned by open(),
   * and closesocket() on fds returned by socket().  On Unix, everything
   * gets close()'d.  We abstract this difference by always using
   * tor_close_socket to close sockets, and always using close() on
   * files.
   */
#if defined(MS_WINDOWS)
  r = closesocket(s);
#else
  r = close(s);
#endif

  socket_accounting_lock();
#ifdef DEBUG_SOCKET_COUNTING
  if (s > max_socket || ! bitarray_is_set(open_sockets, s)) {
    log_warn(LD_BUG, "Closing a socket (%d) that wasn't returned by tor_open_"
             "socket(), or that was already closed or something.", s);
  } else {
    tor_assert(open_sockets && s <= max_socket);
    bitarray_clear(open_sockets, s);
  }
#endif
  if (r == 0) {
    --n_sockets_open;
  } else {
    int err = tor_socket_errno(-1);
    log_info(LD_NET, "Close returned an error: %s", tor_socket_strerror(err));
#ifdef WIN32
    if (err != WSAENOTSOCK)
      --n_sockets_open;
#else
    if (err != EBADF)
      --n_sockets_open;
#endif
    r = -1;
  }

  if (n_sockets_open < 0)
    log_warn(LD_BUG, "Our socket count is below zero: %d. Please submit a "
             "bug report.", n_sockets_open);
  socket_accounting_unlock();
  return r;
}

#ifdef DEBUG_SOCKET_COUNTING
/** Helper: if DEBUG_SOCKET_COUNTING is enabled, remember that <b>s</b> is
 * now an open socket. */
static INLINE void
mark_socket_open(int s)
{
  if (s > max_socket) {
    if (max_socket == -1) {
      open_sockets = bitarray_init_zero(s+128);
      max_socket = s+128;
    } else {
      open_sockets = bitarray_expand(open_sockets, max_socket, s+128);
      max_socket = s+128;
    }
  }
  if (bitarray_is_set(open_sockets, s)) {
    log_warn(LD_BUG, "I thought that %d was already open, but socket() just "
             "gave it to me!", s);
  }
  bitarray_set(open_sockets, s);
}
#else
#define mark_socket_open(s) STMT_NIL
#endif

/** As socket(), but counts the number of open sockets. */
int
tor_open_socket(int domain, int type, int protocol)
{
  int s = socket(domain, type, protocol);
  if (s >= 0) {
    socket_accounting_lock();
    ++n_sockets_open;
    mark_socket_open(s);
    socket_accounting_unlock();
  }
  return s;
}

/** As socket(), but counts the number of open sockets. */
int
tor_accept_socket(int sockfd, struct sockaddr *addr, socklen_t *len)
{
  int s = accept(sockfd, addr, len);
  if (s >= 0) {
    socket_accounting_lock();
    ++n_sockets_open;
    mark_socket_open(s);
    socket_accounting_unlock();
  }
  return s;
}

/** Return the number of sockets we currently have opened. */
int
get_n_open_sockets(void)
{
  int n;
  socket_accounting_lock();
  n = n_sockets_open;
  socket_accounting_unlock();
  return n;
}

/** Turn <b>socket</b> into a nonblocking socket.
 */
void
set_socket_nonblocking(int socket)
{
#if defined(MS_WINDOWS)
  unsigned long nonblocking = 1;
  ioctlsocket(socket, FIONBIO, (unsigned long*) &nonblocking);
#else
  fcntl(socket, F_SETFL, O_NONBLOCK);
#endif
}

/**
 * Allocate a pair of connected sockets.  (Like socketpair(family,
 * type,protocol,fd), but works on systems that don't have
 * socketpair.)
 *
 * Currently, only (AF_UNIX, SOCK_STREAM, 0) sockets are supported.
 *
 * Note that on systems without socketpair, this call will fail if
 * localhost is inaccessible (for example, if the networking
 * stack is down). And even if it succeeds, the socket pair will not
 * be able to read while localhost is down later (the socket pair may
 * even close, depending on OS-specific timeouts).
 *
 * Returns 0 on success and -errno on failure; do not rely on the value
 * of errno or WSAGetLastError().
 **/
/* It would be nicer just to set errno, but that won't work for windows. */
int
tor_socketpair(int family, int type, int protocol, int fd[2])
{
//don't use win32 socketpairs (they are always bad)
#if defined(HAVE_SOCKETPAIR) && !defined(MS_WINDOWS)
  int r;
  r = socketpair(family, type, protocol, fd);
  if (r == 0) {
    socket_accounting_lock();
    if (fd[0] >= 0) {
      ++n_sockets_open;
      mark_socket_open(fd[0]);
    }
    if (fd[1] >= 0) {
      ++n_sockets_open;
      mark_socket_open(fd[1]);
    }
    socket_accounting_unlock();
  }
  return r < 0 ? -errno : r;
#else
    /* This socketpair does not work when localhost is down. So
     * it's really not the same thing at all. But it's close enough
     * for now, and really, when localhost is down sometimes, we
     * have other problems too.
     */
    int listener = -1;
    int connector = -1;
    int acceptor = -1;
    struct sockaddr_in listen_addr;
    struct sockaddr_in connect_addr;
    int size;
    int saved_errno = -1;

    if (protocol
#ifdef AF_UNIX
        || family != AF_UNIX
#endif
        ) {
#ifdef MS_WINDOWS
      return -WSAEAFNOSUPPORT;
#else
      return -EAFNOSUPPORT;
#endif
    }
    if (!fd) {
      return -EINVAL;
    }

    listener = tor_open_socket(AF_INET, type, 0);
    if (listener < 0)
      return -tor_socket_errno(-1);
    memset(&listen_addr, 0, sizeof(listen_addr));
    listen_addr.sin_family = AF_INET;
    listen_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    listen_addr.sin_port = 0;   /* kernel chooses port.  */
    if (bind(listener, (struct sockaddr *) &listen_addr, sizeof (listen_addr))
        == -1)
      goto tidy_up_and_fail;
    if (listen(listener, 1) == -1)
      goto tidy_up_and_fail;

    connector = tor_open_socket(AF_INET, type, 0);
    if (connector < 0)
      goto tidy_up_and_fail;
    /* We want to find out the port number to connect to.  */
    size = sizeof(connect_addr);
    if (getsockname(listener, (struct sockaddr *) &connect_addr, &size) == -1)
      goto tidy_up_and_fail;
    if (size != sizeof (connect_addr))
      goto abort_tidy_up_and_fail;
    if (connect(connector, (struct sockaddr *) &connect_addr,
                sizeof(connect_addr)) == -1)
      goto tidy_up_and_fail;

    size = sizeof(listen_addr);
    acceptor = tor_accept_socket(listener,
                                 (struct sockaddr *) &listen_addr, &size);
    if (acceptor < 0)
      goto tidy_up_and_fail;
    if (size != sizeof(listen_addr))
      goto abort_tidy_up_and_fail;
    tor_close_socket(listener);
    /* Now check we are talking to ourself by matching port and host on the
       two sockets.  */
    if (getsockname(connector, (struct sockaddr *) &connect_addr, &size) == -1)
      goto tidy_up_and_fail;
    if (size != sizeof (connect_addr)
        || listen_addr.sin_family != connect_addr.sin_family
        || listen_addr.sin_addr.s_addr != connect_addr.sin_addr.s_addr
        || listen_addr.sin_port != connect_addr.sin_port) {
      goto abort_tidy_up_and_fail;
    }
    fd[0] = connector;
    fd[1] = acceptor;

    return 0;

  abort_tidy_up_and_fail:
#ifdef MS_WINDOWS
    saved_errno = WSAECONNABORTED;
#else
    saved_errno = ECONNABORTED; /* I hope this is portable and appropriate.  */
#endif
  tidy_up_and_fail:
    if (saved_errno < 0)
      saved_errno = errno;
    if (listener != -1)
      tor_close_socket(listener);
    if (connector != -1)
      tor_close_socket(connector);
    if (acceptor != -1)
      tor_close_socket(acceptor);
    return -saved_errno;
#endif
}

#define ULIMIT_BUFFER 32 /* keep 32 extra fd's beyond _ConnLimit */

/** Learn the maximum allowed number of file descriptors. (Some systems
 * have a low soft limit.
 *
 * We compute this by finding the largest number that we can use.
 * If we can't find a number greater than or equal to <b>limit</b>,
 * then we fail: return -1.
 *
 * Otherwise, return 0 and store the maximum we found inside <b>max_out</b>.*/
int
set_max_file_descriptors(rlim_t limit, int *max_out)
{
  /* Define some maximum connections values for systems where we cannot
   * automatically determine a limit. Re Cygwin, see
   * http://archives.seul.org/or/talk/Aug-2006/msg00210.html
   * For an iPhone, 9999 should work. For Windows and all other unknown
   * systems we use 15000 as the default. */
#ifndef HAVE_GETRLIMIT
#if defined(CYGWIN) || defined(__CYGWIN__)
  const char *platform = "Cygwin";
  const unsigned long MAX_CONNECTIONS = 3200;
#elif defined(IPHONE)
  const char *platform = "iPhone";
  const unsigned long MAX_CONNECTIONS = 9999;
#elif defined(MS_WINDOWS)
  const char *platform = "Windows";
  const unsigned long MAX_CONNECTIONS = 15000;
#else
  const char *platform = "unknown platforms with no getrlimit()";
  const unsigned long MAX_CONNECTIONS = 15000;
#endif
  log_fn(LOG_INFO, LD_NET,
         "This platform is missing getrlimit(). Proceeding.");
  if (limit > MAX_CONNECTIONS) {
    log_warn(LD_CONFIG,
             "We do not support more than %lu file descriptors "
             "on %s. Tried to raise to %lu.",
             (unsigned long)MAX_CONNECTIONS, platform, (unsigned long)limit);
    return -1;
  }
  limit = MAX_CONNECTIONS;
#else /* HAVE_GETRLIMIT */
  struct rlimit rlim;
  tor_assert(limit > 0);

  if (getrlimit(RLIMIT_NOFILE, &rlim) != 0) {
    log_warn(LD_NET, "Could not get maximum number of file descriptors: %s",
             strerror(errno));
    return -1;
  }

  if (rlim.rlim_max < limit) {
    log_warn(LD_CONFIG,"We need %lu file descriptors available, and we're "
             "limited to %lu. Please change your ulimit -n.",
             (unsigned long)limit, (unsigned long)rlim.rlim_max);
    return -1;
  }

  if (rlim.rlim_max > rlim.rlim_cur) {
    log_info(LD_NET,"Raising max file descriptors from %lu to %lu.",
             (unsigned long)rlim.rlim_cur, (unsigned long)rlim.rlim_max);
  }
  rlim.rlim_cur = rlim.rlim_max;

  if (setrlimit(RLIMIT_NOFILE, &rlim) != 0) {
    int bad = 1;
#ifdef OPEN_MAX
    if (errno == EINVAL && OPEN_MAX < rlim.rlim_cur) {
      /* On some platforms, OPEN_MAX is the real limit, and getrlimit() is
       * full of nasty lies.  I'm looking at you, OSX 10.5.... */
      rlim.rlim_cur = OPEN_MAX;
      if (setrlimit(RLIMIT_NOFILE, &rlim) == 0) {
        if (rlim.rlim_cur < (rlim_t)limit) {
          log_warn(LD_CONFIG, "We are limited to %lu file descriptors by "
                 "OPEN_MAX, and ConnLimit is %lu.  Changing ConnLimit; sorry.",
                   (unsigned long)OPEN_MAX, (unsigned long)limit);
        } else {
          log_info(LD_CONFIG, "Dropped connection limit to OPEN_MAX (%lu); "
                   "Apparently, %lu was too high and rlimit lied to us.",
                   (unsigned long)OPEN_MAX, (unsigned long)rlim.rlim_max);
        }
        bad = 0;
      }
    }
#endif /* OPEN_MAX */
    if (bad) {
      log_warn(LD_CONFIG,"Couldn't set maximum number of file descriptors: %s",
               strerror(errno));
      return -1;
    }
  }
  /* leave some overhead for logs, etc, */
  limit = rlim.rlim_cur;
#endif /* HAVE_GETRLIMIT */

  if (limit < ULIMIT_BUFFER) {
    log_warn(LD_CONFIG,
             "ConnLimit must be at least %d. Failing.", ULIMIT_BUFFER);
    return -1;
  }
  if (limit > INT_MAX)
    limit = INT_MAX;
  tor_assert(max_out);
  *max_out = (int)limit - ULIMIT_BUFFER;
  return 0;
}

#ifndef MS_WINDOWS
/** Log details of current user and group credentials. Return 0 on
 * success. Logs and return -1 on failure.
 */
static int
log_credential_status(void)
{
#define CREDENTIAL_LOG_LEVEL LOG_INFO
  /* Real, effective and saved UIDs */
  uid_t ruid, euid, suid;
  /* Read, effective and saved GIDs */
  gid_t rgid, egid, sgid;
  /* Supplementary groups */
  gid_t sup_gids[NGROUPS_MAX + 1];
  /* Number of supplementary groups */
  int ngids;

  /* log UIDs */
#ifdef HAVE_GETRESUID
  if (getresuid(&ruid, &euid, &suid) != 0 ) {
    log_warn(LD_GENERAL, "Error getting changed UIDs: %s", strerror(errno));
    return -1;
  } else {
    log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
           "UID is %u (real), %u (effective), %u (saved)",
           (unsigned)ruid, (unsigned)euid, (unsigned)suid);
  }
#else
  /* getresuid is not present on MacOS X, so we can't get the saved (E)UID */
  ruid = getuid();
  euid = geteuid();
  (void)suid;

  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
         "UID is %u (real), %u (effective), unknown (saved)",
         (unsigned)ruid, (unsigned)euid);
#endif

  /* log GIDs */
#ifdef HAVE_GETRESGID
  if (getresgid(&rgid, &egid, &sgid) != 0 ) {
    log_warn(LD_GENERAL, "Error getting changed GIDs: %s", strerror(errno));
    return -1;
  } else {
    log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
           "GID is %u (real), %u (effective), %u (saved)",
           (unsigned)rgid, (unsigned)egid, (unsigned)sgid);
  }
#else
  /* getresgid is not present on MacOS X, so we can't get the saved (E)GID */
  rgid = getgid();
  egid = getegid();
  (void)sgid;
  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
         "GID is %u (real), %u (effective), unknown (saved)",
         (unsigned)rgid, (unsigned)egid);
#endif

  /* log supplementary groups */
  if ((ngids = getgroups(NGROUPS_MAX + 1, sup_gids)) < 0) {
    log_warn(LD_GENERAL, "Error getting supplementary GIDs: %s",
             strerror(errno));
    return -1;
  } else {
    int i, retval = 0;
    char *strgid;
    char *s = NULL;
    smartlist_t *elts = smartlist_create();

    for (i = 0; i<ngids; i++) {
      strgid = tor_malloc(11);
      if (tor_snprintf(strgid, 11, "%u", (unsigned)sup_gids[i]) < 0) {
        log_warn(LD_GENERAL, "Error printing supplementary GIDs");
        tor_free(strgid);
        retval = -1;
        goto error;
      }
      smartlist_add(elts, strgid);
    }

    s = smartlist_join_strings(elts, " ", 0, NULL);

    log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL, "Supplementary groups are: %s",s);

   error:
    tor_free(s);
    SMARTLIST_FOREACH(elts, char *, cp,
    {
      tor_free(cp);
    });
    smartlist_free(elts);

    return retval;
  }

  return 0;
}
#endif

/** Call setuid and setgid to run as <b>user</b> and switch to their
 * primary group.  Return 0 on success.  On failure, log and return -1.
 */
int
switch_id(const char *user)
{
#ifndef MS_WINDOWS
  struct passwd *pw = NULL;
  uid_t old_uid;
  gid_t old_gid;
  static int have_already_switched_id = 0;

  tor_assert(user);

  if (have_already_switched_id)
    return 0;

  /* Log the initial credential state */
  if (log_credential_status())
    return -1;

  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL, "Changing user and groups");

  /* Get old UID/GID to check if we changed correctly */
  old_uid = getuid();
  old_gid = getgid();

  /* Lookup the user and group information, if we have a problem, bail out. */
  pw = getpwnam(user);
  if (pw == NULL) {
    log_warn(LD_CONFIG, "Error setting configured user: %s not found", user);
    return -1;
  }

  /* Properly switch egid,gid,euid,uid here or bail out */
  if (setgroups(1, &pw->pw_gid)) {
    log_warn(LD_GENERAL, "Error setting groups to gid %d: \"%s\".",
             (int)pw->pw_gid, strerror(errno));
    if (old_uid == pw->pw_uid) {
      log_warn(LD_GENERAL, "Tor is already running as %s.  You do not need "
               "the \"User\" option if you are already running as the user "
               "you want to be.  (If you did not set the User option in your "
               "torrc, check whether it was specified on the command line "
               "by a startup script.)", user);
    } else {
      log_warn(LD_GENERAL, "If you set the \"User\" option, you must start Tor"
               " as root.");
    }
    return -1;
  }

  if (setegid(pw->pw_gid)) {
    log_warn(LD_GENERAL, "Error setting egid to %d: %s",
             (int)pw->pw_gid, strerror(errno));
    return -1;
  }

  if (setgid(pw->pw_gid)) {
    log_warn(LD_GENERAL, "Error setting gid to %d: %s",
             (int)pw->pw_gid, strerror(errno));
    return -1;
  }

  if (setuid(pw->pw_uid)) {
    log_warn(LD_GENERAL, "Error setting configured uid to %s (%d): %s",
             user, (int)pw->pw_uid, strerror(errno));
    return -1;
  }

  if (seteuid(pw->pw_uid)) {
    log_warn(LD_GENERAL, "Error setting configured euid to %s (%d): %s",
             user, (int)pw->pw_uid, strerror(errno));
    return -1;
  }

  /* This is how OpenBSD rolls:
  if (setgroups(1, &pw->pw_gid) || setegid(pw->pw_gid) ||
      setgid(pw->pw_gid) || setuid(pw->pw_uid) || seteuid(pw->pw_uid)) {
      setgid(pw->pw_gid) || seteuid(pw->pw_uid) || setuid(pw->pw_uid)) {
    log_warn(LD_GENERAL, "Error setting configured UID/GID: %s",
    strerror(errno));
    return -1;
  }
  */

  /* We've properly switched egid, gid, euid, uid, and supplementary groups if
   * we're here. */

#if !defined(CYGWIN) && !defined(__CYGWIN__)
  /* If we tried to drop privilege to a group/user other than root, attempt to
   * restore root (E)(U|G)ID, and abort if the operation succeeds */

  /* Only check for privilege dropping if we were asked to be non-root */
  if (pw->pw_uid) {
    /* Try changing GID/EGID */
    if (pw->pw_gid != old_gid &&
        (setgid(old_gid) != -1 || setegid(old_gid) != -1)) {
      log_warn(LD_GENERAL, "Was able to restore group credentials even after "
               "switching GID: this means that the setgid code didn't work.");
      return -1;
    }

    /* Try changing UID/EUID */
    if (pw->pw_uid != old_uid &&
        (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) {
      log_warn(LD_GENERAL, "Was able to restore user credentials even after "
               "switching UID: this means that the setuid code didn't work.");
      return -1;
    }
  }
#endif

  /* Check what really happened */
  if (log_credential_status()) {
    return -1;
  }

  have_already_switched_id = 1; /* mark success so we never try again */

#if defined(__linux__) && defined(HAVE_SYS_PRCTL_H) && defined(HAVE_PRCTL)
#ifdef PR_SET_DUMPABLE
  if (pw->pw_uid) {
    /* Re-enable core dumps if we're not running as root. */
    log_info(LD_CONFIG, "Re-enabling coredumps");
    if (prctl(PR_SET_DUMPABLE, 1)) {
      log_warn(LD_CONFIG, "Unable to re-enable coredumps: %s",strerror(errno));
    }
  }
#endif
#endif
  return 0;

#else
  (void)user;

  log_warn(LD_CONFIG,
           "User specified but switching users is unsupported on your OS.");
  return -1;
#endif
}

#ifdef HAVE_PWD_H
/** Allocate and return a string containing the home directory for the
 * user <b>username</b>. Only works on posix-like systems. */
char *
get_user_homedir(const char *username)
{
  struct passwd *pw;
  tor_assert(username);

  if (!(pw = getpwnam(username))) {
    log_err(LD_CONFIG,"User \"%s\" not found.", username);
    return NULL;
  }
  return tor_strdup(pw->pw_dir);
}
#endif

/** Set *addr to the IP address (in dotted-quad notation) stored in c.
 * Return 1 on success, 0 if c is badly formatted.  (Like inet_aton(c,addr),
 * but works on Windows and Solaris.)
 */
int
tor_inet_aton(const char *str, struct in_addr* addr)
{
  unsigned a,b,c,d;
  char more;
  if (tor_sscanf(str, "%3u.%3u.%3u.%3u%c", &a,&b,&c,&d,&more) != 4)
    return 0;
  if (a > 255) return 0;
  if (b > 255) return 0;
  if (c > 255) return 0;
  if (d > 255) return 0;
  addr->s_addr = htonl((a<<24) | (b<<16) | (c<<8) | d);
  return 1;
}

/** Given <b>af</b>==AF_INET and <b>src</b> a struct in_addr, or
 * <b>af</b>==AF_INET6 and <b>src</b> a struct in6_addr, try to format the
 * address and store it in the <b>len</b>-byte buffer <b>dst</b>.  Returns
 * <b>dst</b> on success, NULL on failure.
 *
 * (Like inet_ntop(af,src,dst,len), but works on platforms that don't have it:
 * Tor sometimes needs to format ipv6 addresses even on platforms without ipv6
 * support.) */
const char *
tor_inet_ntop(int af, const void *src, char *dst, size_t len)
{
  if (af == AF_INET) {
    if (tor_inet_ntoa(src, dst, len) < 0)
      return NULL;
    else
      return dst;
  } else if (af == AF_INET6) {
    const struct in6_addr *addr = src;
    char buf[64], *cp;
    int longestGapLen = 0, longestGapPos = -1, i,
      curGapPos = -1, curGapLen = 0;
    uint16_t words[8];
    for (i = 0; i < 8; ++i) {
      words[i] = (((uint16_t)addr->s6_addr[2*i])<<8) + addr->s6_addr[2*i+1];
    }
    if (words[0] == 0 && words[1] == 0 && words[2] == 0 && words[3] == 0 &&
        words[4] == 0 && ((words[5] == 0 && words[6] && words[7]) ||
                          (words[5] == 0xffff))) {
      /* This is an IPv4 address. */
      if (words[5] == 0) {
        tor_snprintf(buf, sizeof(buf), "::%d.%d.%d.%d",
                     addr->s6_addr[12], addr->s6_addr[13],
                     addr->s6_addr[14], addr->s6_addr[15]);
      } else {
        tor_snprintf(buf, sizeof(buf), "::%x:%d.%d.%d.%d", words[5],
                     addr->s6_addr[12], addr->s6_addr[13],
                     addr->s6_addr[14], addr->s6_addr[15]);
      }
      if (strlen(buf) > len)
        return NULL;
      strlcpy(dst, buf, len);
      return dst;
    }
    i = 0;
    while (i < 8) {
      if (words[i] == 0) {
        curGapPos = i++;
        curGapLen = 1;
        while (i<8 && words[i] == 0) {
          ++i; ++curGapLen;
        }
        if (curGapLen > longestGapLen) {
          longestGapPos = curGapPos;
          longestGapLen = curGapLen;
        }
      } else {
        ++i;
      }
    }
    if (longestGapLen<=1)
      longestGapPos = -1;

    cp = buf;
    for (i = 0; i < 8; ++i) {
      if (words[i] == 0 && longestGapPos == i) {
        if (i == 0)
          *cp++ = ':';
        *cp++ = ':';
        while (i < 8 && words[i] == 0)
          ++i;
        --i; /* to compensate for loop increment. */
      } else {
        tor_snprintf(cp, sizeof(buf)-(cp-buf), "%x", (unsigned)words[i]);
        cp += strlen(cp);
        if (i != 7)
          *cp++ = ':';
      }
    }
    *cp = '\0';
    if (strlen(buf) > len)
      return NULL;
    strlcpy(dst, buf, len);
    return dst;
  } else {
    return NULL;
  }
}

/** Given <b>af</b>==AF_INET or <b>af</b>==AF_INET6, and a string <b>src</b>
 * encoding an IPv4 address or IPv6 address correspondingly, try to parse the
 * address and store the result in <b>dst</b> (which must have space for a
 * struct in_addr or a struct in6_addr, as appropriate).  Return 1 on success,
 * 0 on a bad parse, and -1 on a bad <b>af</b>.
 *
 * (Like inet_pton(af,src,dst) but works on platforms that don't have it: Tor
 * sometimes needs to format ipv6 addresses even on platforms without ipv6
 * support.) */
int
tor_inet_pton(int af, const char *src, void *dst)
{
  if (af == AF_INET) {
    return tor_inet_aton(src, dst);
  } else if (af == AF_INET6) {
    struct in6_addr *out = dst;
    uint16_t words[8];
    int gapPos = -1, i, setWords=0;
    const char *dot = strchr(src, '.');
    const char *eow; /* end of words. */
    if (dot == src)
      return 0;
    else if (!dot)
      eow = src+strlen(src);
    else {
      unsigned byte1,byte2,byte3,byte4;
      char more;
      for (eow = dot-1; eow >= src && TOR_ISDIGIT(*eow); --eow)
        ;
      ++eow;

      /* We use "scanf" because some platform inet_aton()s are too lax
       * about IPv4 addresses of the form "1.2.3" */
      if (tor_sscanf(eow, "%3u.%3u.%3u.%3u%c",
                     &byte1,&byte2,&byte3,&byte4,&more) != 4)
        return 0;

      if (byte1 > 255 || byte2 > 255 || byte3 > 255 || byte4 > 255)
        return 0;

      words[6] = (byte1<<8) | byte2;
      words[7] = (byte3<<8) | byte4;
      setWords += 2;
    }

    i = 0;
    while (src < eow) {
      if (i > 7)
        return 0;
      if (TOR_ISXDIGIT(*src)) {
        char *next;
        long r = strtol(src, &next, 16);
        if (next > 4+src)
          return 0;
        if (next == src)
          return 0;
        if (r<0 || r>65536)
          return 0;

        words[i++] = (uint16_t)r;
        setWords++;
        src = next;
        if (*src != ':' && src != eow)
          return 0;
        ++src;
      } else if (*src == ':' && i > 0 && gapPos==-1) {
        gapPos = i;
        ++src;
      } else if (*src == ':' && i == 0 && src[1] == ':' && gapPos==-1) {
        gapPos = i;
        src += 2;
      } else {
        return 0;
      }
    }

    if (setWords > 8 ||
        (setWords == 8 && gapPos != -1) ||
        (setWords < 8 && gapPos == -1))
      return 0;

    if (gapPos >= 0) {
      int nToMove = setWords - (dot ? 2 : 0) - gapPos;
      int gapLen = 8 - setWords;
      tor_assert(nToMove >= 0);
      memmove(&words[gapPos+gapLen], &words[gapPos],
              sizeof(uint16_t)*nToMove);
      memset(&words[gapPos], 0, sizeof(uint16_t)*gapLen);
    }
    for (i = 0; i < 8; ++i) {
      out->s6_addr[2*i  ] = words[i] >> 8;
      out->s6_addr[2*i+1] = words[i] & 0xff;
    }

    return 1;
  } else {
    return -1;
  }
}

/** Similar behavior to Unix gethostbyname: resolve <b>name</b>, and set
 * *<b>addr</b> to the proper IP address, in host byte order.  Returns 0
 * on success, -1 on failure; 1 on transient failure.
 *
 * (This function exists because standard windows gethostbyname
 * doesn't treat raw IP addresses properly.)
 */
int
tor_lookup_hostname(const char *name, uint32_t *addr)
{
  tor_addr_t myaddr;
  int ret;

  if ((ret = tor_addr_lookup(name, AF_INET, &myaddr)))
    return ret;

  if (tor_addr_family(&myaddr) == AF_INET) {
    *addr = tor_addr_to_ipv4h(&myaddr);
    return ret;
  }

  return -1;
}

/** Hold the result of our call to <b>uname</b>. */
static char uname_result[256];
/** True iff uname_result is set. */
static int uname_result_is_set = 0;

/** Return a pointer to a description of our platform.
 */
const char *
get_uname(void)
{
#ifdef HAVE_UNAME
  struct utsname u;
#endif
  if (!uname_result_is_set) {
#ifdef HAVE_UNAME
    if (uname(&u) != -1) {
      /* (Linux says 0 is success, Solaris says 1 is success) */
      tor_snprintf(uname_result, sizeof(uname_result), "%s %s",
               u.sysname, u.machine);
    } else
#endif
      {
#ifdef MS_WINDOWS
        OSVERSIONINFOEX info;
        int i;
        unsigned int leftover_mask;
        const char *plat = NULL;
        const char *extra = NULL;
        static struct {
          unsigned major; unsigned minor; const char *version;
        } win_version_table[] = {
          { 6, 0, "Windows \"Longhorn\"" },
          { 5, 2, "Windows Server 2003" },
          { 5, 1, "Windows XP" },
          { 5, 0, "Windows 2000" },
          /* { 4, 0, "Windows NT 4.0" }, */
          { 4, 90, "Windows Me" },
          { 4, 10, "Windows 98" },
          /* { 4, 0, "Windows 95" } */
          { 3, 51, "Windows NT 3.51" },
          { 0, 0, NULL }
        };
#ifdef VER_SUITE_BACKOFFICE
        static struct {
          unsigned int mask; const char *str;
        } win_mask_table[] = {
          { VER_SUITE_BACKOFFICE,         " {backoffice}" },
          { VER_SUITE_BLADE,              " {\"blade\" (2003, web edition)}" },
          { VER_SUITE_DATACENTER,         " {datacenter}" },
          { VER_SUITE_ENTERPRISE,         " {enterprise}" },
          { VER_SUITE_EMBEDDEDNT,         " {embedded}" },
          { VER_SUITE_PERSONAL,           " {personal}" },
          { VER_SUITE_SINGLEUSERTS,
            " {terminal services, single user}" },
          { VER_SUITE_SMALLBUSINESS,      " {small business}" },
          { VER_SUITE_SMALLBUSINESS_RESTRICTED,
            " {small business, restricted}" },
          { VER_SUITE_TERMINAL,           " {terminal services}" },
          { 0, NULL },
        };
#endif
        memset(&info, 0, sizeof(info));
        info.dwOSVersionInfoSize = sizeof(info);
        if (! GetVersionEx((LPOSVERSIONINFO)&info)) {
          strlcpy(uname_result, "Bizarre version of Windows where GetVersionEx"
                  " doesn't work.", sizeof(uname_result));
          uname_result_is_set = 1;
          return uname_result;
        }
        if (info.dwMajorVersion == 4 && info.dwMinorVersion == 0) {
          if (info.dwPlatformId == VER_PLATFORM_WIN32_NT)
            plat = "Windows NT 4.0";
          else
            plat = "Windows 95";
          if (info.szCSDVersion[1] == 'B')
            extra = "OSR2 (B)";
          else if (info.szCSDVersion[1] == 'C')
            extra = "OSR2 (C)";
        } else {
          for (i=0; win_version_table[i].major>0; ++i) {
            if (win_version_table[i].major == info.dwMajorVersion &&
                win_version_table[i].minor == info.dwMinorVersion) {
              plat = win_version_table[i].version;
              break;
            }
          }
        }
        if (plat && !strcmp(plat, "Windows 98")) {
          if (info.szCSDVersion[1] == 'A')
            extra = "SE (A)";
          else if (info.szCSDVersion[1] == 'B')
            extra = "SE (B)";
        }
        if (plat) {
          if (!extra)
            extra = info.szCSDVersion;
          tor_snprintf(uname_result, sizeof(uname_result), "%s %s",
                       plat, extra);
        } else {
          if (info.dwMajorVersion > 6 ||
              (info.dwMajorVersion==6 && info.dwMinorVersion>0))
            tor_snprintf(uname_result, sizeof(uname_result),
                      "Very recent version of Windows [major=%d,minor=%d] %s",
                      (int)info.dwMajorVersion,(int)info.dwMinorVersion,
                      info.szCSDVersion);
          else
            tor_snprintf(uname_result, sizeof(uname_result),
                      "Unrecognized version of Windows [major=%d,minor=%d] %s",
                      (int)info.dwMajorVersion,(int)info.dwMinorVersion,
                      info.szCSDVersion);
        }
#ifdef VER_SUITE_BACKOFFICE
        if (info.wProductType == VER_NT_DOMAIN_CONTROLLER) {
          strlcat(uname_result, " [domain controller]", sizeof(uname_result));
        } else if (info.wProductType == VER_NT_SERVER) {
          strlcat(uname_result, " [server]", sizeof(uname_result));
        } else if (info.wProductType == VER_NT_WORKSTATION) {
          strlcat(uname_result, " [workstation]", sizeof(uname_result));
        }
        leftover_mask = info.wSuiteMask;
        for (i = 0; win_mask_table[i].mask; ++i) {
          if (info.wSuiteMask & win_mask_table[i].mask) {
            strlcat(uname_result, win_mask_table[i].str, sizeof(uname_result));
            leftover_mask &= ~win_mask_table[i].mask;
          }
        }
        if (leftover_mask) {
          size_t len = strlen(uname_result);
          tor_snprintf(uname_result+len, sizeof(uname_result)-len,
                       " {0x%x}", info.wSuiteMask);
        }
#endif
#else
        strlcpy(uname_result, "Unknown platform", sizeof(uname_result));
#endif
      }
    uname_result_is_set = 1;
  }
  return uname_result;
}

/*
 *   Process control
 */

#if defined(USE_PTHREADS)
/** Wraps a void (*)(void*) function and its argument so we can
 * invoke them in a way pthreads would expect.
 */
typedef struct tor_pthread_data_t {
  void (*func)(void *);
  void *data;
} tor_pthread_data_t;
/** Given a tor_pthread_data_t <b>_data</b>, call _data-&gt;func(d-&gt;data)
 * and free _data.  Used to make sure we can call functions the way pthread
 * expects. */
static void *
tor_pthread_helper_fn(void *_data)
{
  tor_pthread_data_t *data = _data;
  void (*func)(void*);
  void *arg;
  /* mask signals to worker threads to avoid SIGPIPE, etc */
  sigset_t sigs;
  /* We're in a subthread; don't handle any signals here. */
  sigfillset(&sigs);
  pthread_sigmask(SIG_SETMASK, &sigs, NULL);

  func = data->func;
  arg = data->data;
  tor_free(_data);
  func(arg);
  return NULL;
}
#endif

/** Minimalist interface to run a void function in the background.  On
 * Unix calls fork, on win32 calls beginthread.  Returns -1 on failure.
 * func should not return, but rather should call spawn_exit.
 *
 * NOTE: if <b>data</b> is used, it should not be allocated on the stack,
 * since in a multithreaded environment, there is no way to be sure that
 * the caller's stack will still be around when the called function is
 * running.
 */
int
spawn_func(void (*func)(void *), void *data)
{
#if defined(USE_WIN32_THREADS)
  int rv;
  rv = (int)_beginthread(func, 0, data);
  if (rv == (int)-1)
    return -1;
  return 0;
#elif defined(USE_PTHREADS)
  pthread_t thread;
  tor_pthread_data_t *d;
  d = tor_malloc(sizeof(tor_pthread_data_t));
  d->data = data;
  d->func = func;
  if (pthread_create(&thread,NULL,tor_pthread_helper_fn,d))
    return -1;
  if (pthread_detach(thread))
    return -1;
  return 0;
#else
  pid_t pid;
  pid = fork();
  if (pid<0)
    return -1;
  if (pid==0) {
    /* Child */
    func(data);
    tor_assert(0); /* Should never reach here. */
    return 0; /* suppress "control-reaches-end-of-non-void" warning. */
  } else {
    /* Parent */
    return 0;
  }
#endif
}

/** End the current thread/process.
 */
void
spawn_exit(void)
{
#if defined(USE_WIN32_THREADS)
  _endthread();
  //we should never get here. my compiler thinks that _endthread returns, this
  //is an attempt to fool it.
  tor_assert(0);
  _exit(0);
#elif defined(USE_PTHREADS)
  pthread_exit(NULL);
#else
  /* http://www.erlenstar.demon.co.uk/unix/faq_2.html says we should
   * call _exit, not exit, from child processes. */
  _exit(0);
#endif

}

/** Set *timeval to the current time of day.  On error, log and terminate.
 * (Same as gettimeofday(timeval,NULL), but never returns -1.)
 */
void
tor_gettimeofday(struct timeval *timeval)
{
#ifdef MS_WINDOWS
  /* Epoch bias copied from perl: number of units between windows epoch and
   * Unix epoch. */
#define EPOCH_BIAS U64_LITERAL(116444736000000000)
#define UNITS_PER_SEC U64_LITERAL(10000000)
#define USEC_PER_SEC U64_LITERAL(1000000)
#define UNITS_PER_USEC U64_LITERAL(10)
  union {
    uint64_t ft_64;
    FILETIME ft_ft;
  } ft;
  /* number of 100-nsec units since Jan 1, 1601 */
  GetSystemTimeAsFileTime(&ft.ft_ft);
  if (ft.ft_64 < EPOCH_BIAS) {
    log_err(LD_GENERAL,"System time is before 1970; failing.");
    exit(1);
  }
  ft.ft_64 -= EPOCH_BIAS;
  timeval->tv_sec = (unsigned) (ft.ft_64 / UNITS_PER_SEC);
  timeval->tv_usec = (unsigned) ((ft.ft_64 / UNITS_PER_USEC) % USEC_PER_SEC);
#elif defined(HAVE_GETTIMEOFDAY)
  if (gettimeofday(timeval, NULL)) {
    log_err(LD_GENERAL,"gettimeofday failed.");
    /* If gettimeofday dies, we have either given a bad timezone (we didn't),
       or segfaulted.*/
    exit(1);
  }
#elif defined(HAVE_FTIME)
  struct timeb tb;
  ftime(&tb);
  timeval->tv_sec = tb.time;
  timeval->tv_usec = tb.millitm * 1000;
#else
#error "No way to get time."
#endif
  return;
}

#if defined(TOR_IS_MULTITHREADED) && !defined(MS_WINDOWS)
/** Defined iff we need to add locks when defining fake versions of reentrant
 * versions of time-related functions. */
#define TIME_FNS_NEED_LOCKS
#endif

#ifndef HAVE_LOCALTIME_R
#ifdef TIME_FNS_NEED_LOCKS
struct tm *
tor_localtime_r(const time_t *timep, struct tm *result)
{
  struct tm *r;
  static tor_mutex_t *m=NULL;
  if (!m) { m=tor_mutex_new(); }
  tor_assert(result);
  tor_mutex_acquire(m);
  r = localtime(timep);
  memcpy(result, r, sizeof(struct tm));
  tor_mutex_release(m);
  return result;
}
#else
struct tm *
tor_localtime_r(const time_t *timep, struct tm *result)
{
  struct tm *r;
  tor_assert(result);
  r = localtime(timep);
  memcpy(result, r, sizeof(struct tm));
  return result;
}
#endif
#endif

#ifndef HAVE_GMTIME_R
#ifdef TIME_FNS_NEED_LOCKS
struct tm *
tor_gmtime_r(const time_t *timep, struct tm *result)
{
  struct tm *r;
  static tor_mutex_t *m=NULL;
  if (!m) { m=tor_mutex_new(); }
  tor_assert(result);
  tor_mutex_acquire(m);
  r = gmtime(timep);
  memcpy(result, r, sizeof(struct tm));
  tor_mutex_release(m);
  return result;
}
#else
struct tm *
tor_gmtime_r(const time_t *timep, struct tm *result)
{
  struct tm *r;
  tor_assert(result);
  r = gmtime(timep);
  memcpy(result, r, sizeof(struct tm));
  return result;
}
#endif
#endif

#if defined(USE_WIN32_THREADS)
void
tor_mutex_init(tor_mutex_t *m)
{
  InitializeCriticalSection(&m->mutex);
}
void
tor_mutex_uninit(tor_mutex_t *m)
{
  DeleteCriticalSection(&m->mutex);
}
void
tor_mutex_acquire(tor_mutex_t *m)
{
  tor_assert(m);
  EnterCriticalSection(&m->mutex);
}
void
tor_mutex_release(tor_mutex_t *m)
{
  LeaveCriticalSection(&m->mutex);
}
unsigned long
tor_get_thread_id(void)
{
  return (unsigned long)GetCurrentThreadId();
}
#elif defined(USE_PTHREADS)
/** A mutex attribute that we're going to use to tell pthreads that we want
 * "reentrant" mutexes (i.e., once we can re-lock if we're already holding
 * them.) */
static pthread_mutexattr_t attr_reentrant;
/** True iff we've called tor_threads_init() */
static int threads_initialized = 0;
/** Initialize <b>mutex</b> so it can be locked.  Every mutex must be set
 * up with tor_mutex_init() or tor_mutex_new(); not both. */
void
tor_mutex_init(tor_mutex_t *mutex)
{
  int err;
  if (PREDICT_UNLIKELY(!threads_initialized))
    tor_threads_init();
  err = pthread_mutex_init(&mutex->mutex, &attr_reentrant);
  if (PREDICT_UNLIKELY(err)) {
    log_err(LD_GENERAL, "Error %d creating a mutex.", err);
    tor_fragile_assert();
  }
}
/** Wait until <b>m</b> is free, then acquire it. */
void
tor_mutex_acquire(tor_mutex_t *m)
{
  int err;
  tor_assert(m);
  err = pthread_mutex_lock(&m->mutex);
  if (PREDICT_UNLIKELY(err)) {
    log_err(LD_GENERAL, "Error %d locking a mutex.", err);
    tor_fragile_assert();
  }
}
/** Release the lock <b>m</b> so another thread can have it. */
void
tor_mutex_release(tor_mutex_t *m)
{
  int err;
  tor_assert(m);
  err = pthread_mutex_unlock(&m->mutex);
  if (PREDICT_UNLIKELY(err)) {
    log_err(LD_GENERAL, "Error %d unlocking a mutex.", err);
    tor_fragile_assert();
  }
}
/** Clean up the mutex <b>m</b> so that it no longer uses any system
 * resources.  Does not free <b>m</b>.  This function must only be called on
 * mutexes from tor_mutex_init(). */
void
tor_mutex_uninit(tor_mutex_t *m)
{
  int err;
  tor_assert(m);
  err = pthread_mutex_destroy(&m->mutex);
  if (PREDICT_UNLIKELY(err)) {
    log_err(LD_GENERAL, "Error %d destroying a mutex.", err);
    tor_fragile_assert();
  }
}
/** Return an integer representing this thread. */
unsigned long
tor_get_thread_id(void)
{
  union {
    pthread_t thr;
    unsigned long id;
  } r;
  r.thr = pthread_self();
  return r.id;
}
#endif

#ifdef TOR_IS_MULTITHREADED
/** Return a newly allocated, ready-for-use mutex. */
tor_mutex_t *
tor_mutex_new(void)
{
  tor_mutex_t *m = tor_malloc_zero(sizeof(tor_mutex_t));
  tor_mutex_init(m);
  return m;
}
/** Release all storage and system resources held by <b>m</b>. */
void
tor_mutex_free(tor_mutex_t *m)
{
  tor_mutex_uninit(m);
  tor_free(m);
}
#endif

/* Conditions. */
#ifdef USE_PTHREADS
#if 0
/** Cross-platform condition implementation. */
struct tor_cond_t {
  pthread_cond_t cond;
};
/** Return a newly allocated condition, with nobody waiting on it. */
tor_cond_t *
tor_cond_new(void)
{
  tor_cond_t *cond = tor_malloc_zero(sizeof(tor_cond_t));
  if (pthread_cond_init(&cond->cond, NULL)) {
    tor_free(cond);
    return NULL;
  }
  return cond;
}
/** Release all resources held by <b>cond</b>. */
void
tor_cond_free(tor_cond_t *cond)
{
  tor_assert(cond);
  if (pthread_cond_destroy(&cond->cond)) {
    log_warn(LD_GENERAL,"Error freeing condition: %s", strerror(errno));
    return;
  }
  tor_free(cond);
}
/** Wait until one of the tor_cond_signal functions is called on <b>cond</b>.
 * All waiters on the condition must wait holding the same <b>mutex</b>.
 * Returns 0 on success, negative on failure. */
int
tor_cond_wait(tor_cond_t *cond, tor_mutex_t *mutex)
{
  return pthread_cond_wait(&cond->cond, &mutex->mutex) ? -1 : 0;
}
/** Wake up one of the waiters on <b>cond</b>. */
void
tor_cond_signal_one(tor_cond_t *cond)
{
  pthread_cond_signal(&cond->cond);
}
/** Wake up all of the waiters on <b>cond</b>. */
void
tor_cond_signal_all(tor_cond_t *cond)
{
  pthread_cond_broadcast(&cond->cond);
}
#endif
/** Set up common structures for use by threading. */
void
tor_threads_init(void)
{
  if (!threads_initialized) {
    pthread_mutexattr_init(&attr_reentrant);
    pthread_mutexattr_settype(&attr_reentrant, PTHREAD_MUTEX_RECURSIVE);
    threads_initialized = 1;
    set_main_thread();
  }
}
#elif defined(USE_WIN32_THREADS)
#if 0
static DWORD cond_event_tls_index;
struct tor_cond_t {
  CRITICAL_SECTION mutex;
  smartlist_t *events;
};
tor_cond_t *
tor_cond_new(void)
{
  tor_cond_t *cond = tor_malloc_zero(sizeof(tor_cond_t));
  InitializeCriticalSection(&cond->mutex);
  cond->events = smartlist_create();
  return cond;
}
void
tor_cond_free(tor_cond_t *cond)
{
  tor_assert(cond);
  DeleteCriticalSection(&cond->mutex);
  /* XXXX notify? */
  smartlist_free(cond->events);
  tor_free(cond);
}
int
tor_cond_wait(tor_cond_t *cond, tor_mutex_t *mutex)
{
  HANDLE event;
  int r;
  tor_assert(cond);
  tor_assert(mutex);
  event = TlsGetValue(cond_event_tls_index);
  if (!event) {
    event = CreateEvent(0, FALSE, FALSE, NULL);
    TlsSetValue(cond_event_tls_index, event);
  }
  EnterCriticalSection(&cond->mutex);

  tor_assert(WaitForSingleObject(event, 0) == WAIT_TIMEOUT);
  tor_assert(!smartlist_isin(cond->events, event));
  smartlist_add(cond->events, event);

  LeaveCriticalSection(&cond->mutex);

  tor_mutex_release(mutex);
  r = WaitForSingleObject(event, INFINITE);
  tor_mutex_acquire(mutex);

  switch (r) {
    case WAIT_OBJECT_0: /* we got the mutex normally. */
      break;
    case WAIT_ABANDONED: /* holding thread exited. */
    case WAIT_TIMEOUT: /* Should never happen. */
      tor_assert(0);
      break;
    case WAIT_FAILED:
      log_warn(LD_GENERAL, "Failed to acquire mutex: %d",(int) GetLastError());
  }
  return 0;
}
void
tor_cond_signal_one(tor_cond_t *cond)
{
  HANDLE event;
  tor_assert(cond);

  EnterCriticalSection(&cond->mutex);

  if ((event = smartlist_pop_last(cond->events)))
    SetEvent(event);

  LeaveCriticalSection(&cond->mutex);
}
void
tor_cond_signal_all(tor_cond_t *cond)
{
  tor_assert(cond);

  EnterCriticalSection(&cond->mutex);
  SMARTLIST_FOREACH(cond->events, HANDLE, event, SetEvent(event));
  smartlist_clear(cond->events);
  LeaveCriticalSection(&cond->mutex);
}
#endif
void
tor_threads_init(void)
{
#if 0
  cond_event_tls_index = TlsAlloc();
#endif
  set_main_thread();
}
#endif

/** Identity of the "main" thread */
static unsigned long main_thread_id = -1;

/** Start considering the current thread to be the 'main thread'.  This has
 * no effect on anything besides in_main_thread(). */
void
set_main_thread(void)
{
  main_thread_id = tor_get_thread_id();
}
/** Return true iff called from the main thread. */
int
in_main_thread(void)
{
  return main_thread_id == tor_get_thread_id();
}

/**
 * On Windows, WSAEWOULDBLOCK is not always correct: when you see it,
 * you need to ask the socket for its actual errno.  Also, you need to
 * get your errors from WSAGetLastError, not errno.  (If you supply a
 * socket of -1, we check WSAGetLastError, but don't correct
 * WSAEWOULDBLOCKs.)
 *
 * The upshot of all of this is that when a socket call fails, you
 * should call tor_socket_errno <em>at most once</em> on the failing
 * socket to get the error.
 */
#if defined(MS_WINDOWS)
int
tor_socket_errno(int sock)
{
  int optval, optvallen=sizeof(optval);
  int err = WSAGetLastError();
  if (err == WSAEWOULDBLOCK && sock >= 0) {
    if (getsockopt(sock, SOL_SOCKET, SO_ERROR, (void*)&optval, &optvallen))
      return err;
    if (optval)
      return optval;
  }
  return err;
}
#endif

#if defined(MS_WINDOWS)
#define E(code, s) { code, (s " [" #code " ]") }
struct { int code; const char *msg; } windows_socket_errors[] = {
  E(WSAEINTR, "Interrupted function call"),
  E(WSAEACCES, "Permission denied"),
  E(WSAEFAULT, "Bad address"),
  E(WSAEINVAL, "Invalid argument"),
  E(WSAEMFILE, "Too many open files"),
  E(WSAEWOULDBLOCK,  "Resource temporarily unavailable"),
  E(WSAEINPROGRESS, "Operation now in progress"),
  E(WSAEALREADY, "Operation already in progress"),
  E(WSAENOTSOCK, "Socket operation on nonsocket"),
  E(WSAEDESTADDRREQ, "Destination address required"),
  E(WSAEMSGSIZE, "Message too long"),
  E(WSAEPROTOTYPE, "Protocol wrong for socket"),
  E(WSAENOPROTOOPT, "Bad protocol option"),
  E(WSAEPROTONOSUPPORT, "Protocol not supported"),
  E(WSAESOCKTNOSUPPORT, "Socket type not supported"),
  /* What's the difference between NOTSUPP and NOSUPPORT? :) */
  E(WSAEOPNOTSUPP, "Operation not supported"),
  E(WSAEPFNOSUPPORT,  "Protocol family not supported"),
  E(WSAEAFNOSUPPORT, "Address family not supported by protocol family"),
  E(WSAEADDRINUSE, "Address already in use"),
  E(WSAEADDRNOTAVAIL, "Cannot assign requested address"),
  E(WSAENETDOWN, "Network is down"),
  E(WSAENETUNREACH, "Network is unreachable"),
  E(WSAENETRESET, "Network dropped connection on reset"),
  E(WSAECONNABORTED, "Software caused connection abort"),
  E(WSAECONNRESET, "Connection reset by peer"),
  E(WSAENOBUFS, "No buffer space available"),
  E(WSAEISCONN, "Socket is already connected"),
  E(WSAENOTCONN, "Socket is not connected"),
  E(WSAESHUTDOWN, "Cannot send after socket shutdown"),
  E(WSAETIMEDOUT, "Connection timed out"),
  E(WSAECONNREFUSED, "Connection refused"),
  E(WSAEHOSTDOWN, "Host is down"),
  E(WSAEHOSTUNREACH, "No route to host"),
  E(WSAEPROCLIM, "Too many processes"),
  /* Yes, some of these start with WSA, not WSAE. No, I don't know why. */
  E(WSASYSNOTREADY, "Network subsystem is unavailable"),
  E(WSAVERNOTSUPPORTED, "Winsock.dll out of range"),
  E(WSANOTINITIALISED, "Successful WSAStartup not yet performed"),
  E(WSAEDISCON, "Graceful shutdown now in progress"),
#ifdef WSATYPE_NOT_FOUND
  E(WSATYPE_NOT_FOUND, "Class type not found"),
#endif
  E(WSAHOST_NOT_FOUND, "Host not found"),
  E(WSATRY_AGAIN, "Nonauthoritative host not found"),
  E(WSANO_RECOVERY, "This is a nonrecoverable error"),
  E(WSANO_DATA, "Valid name, no data record of requested type)"),

  /* There are some more error codes whose numeric values are marked
   * <b>OS dependent</b>. They start with WSA_, apparently for the same
   * reason that practitioners of some craft traditions deliberately
   * introduce imperfections into their baskets and rugs "to allow the
   * evil spirits to escape."  If we catch them, then our binaries
   * might not report consistent results across versions of Windows.
   * Thus, I'm going to let them all fall through.
   */
  { -1, NULL },
};
/** There does not seem to be a strerror equivalent for Winsock errors.
 * Naturally, we have to roll our own.
 */
const char *
tor_socket_strerror(int e)
{
  int i;
  for (i=0; windows_socket_errors[i].code >= 0; ++i) {
    if (e == windows_socket_errors[i].code)
      return windows_socket_errors[i].msg;
  }
  return strerror(e);
}
#endif

/** Called before we make any calls to network-related functions.
 * (Some operating systems require their network libraries to be
 * initialized.) */
int
network_init(void)
{
#ifdef MS_WINDOWS
  /* This silly exercise is necessary before windows will allow
   * gethostbyname to work. */
  WSADATA WSAData;
  int r;
  r = WSAStartup(0x101,&WSAData);
  if (r) {
    log_warn(LD_NET,"Error initializing windows network layer: code was %d",r);
    return -1;
  }
  /* WSAData.iMaxSockets might show the max sockets we're allowed to use.
   * We might use it to complain if we're trying to be a server but have
   * too few sockets available. */
#endif
  return 0;
}

#ifdef MS_WINDOWS
/** Return a newly allocated string describing the windows system error code
 * <b>err</b>.  Note that error codes are different from errno.  Error codes
 * come from GetLastError() when a winapi call fails.  errno is set only when
 * ANSI functions fail.  Whee. */
char *
format_win32_error(DWORD err)
{
  LPVOID str = NULL;
  char *result;

  /* Somebody once decided that this interface was better than strerror(). */
  FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                 FORMAT_MESSAGE_FROM_SYSTEM |
                 FORMAT_MESSAGE_IGNORE_INSERTS,
                 NULL, err,
                 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                 (LPTSTR) &str,
                 0, NULL);

  if (str) {
    result = tor_strdup((char*)str);
    LocalFree(str); /* LocalFree != free() */
  } else {
    result = tor_strdup("<unformattable error>");
  }
  return result;
}
#endif