~drizzle-trunk/drizzle/development

/*
  azio is a modified version of gzio. It  makes use of mysys and removes mallocs.
    -Brian Aker
*/

/* gzio.c -- IO on .gz files
 * Copyright (C) 1995-2005 Jean-loup Gailly.
 * For conditions of distribution and use, see copyright notice in zlib.h
 *
 */

/* @(#) $Id$ */

#include "config.h"

#include "azio.h"

#include <fcntl.h>
#include <unistd.h>

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cassert>

using namespace drizzled;

static int const az_magic[3] = {0xfe, 0x03, 0x01}; /* az magic header */

static unsigned int azwrite(azio_stream *s, void *buf, unsigned int len);
static int azrewind (azio_stream *s);
static unsigned int azio_enable_aio(azio_stream *s);
static int do_flush(azio_stream *file, int flush);
static int    get_byte(azio_stream *s);
static void   check_header(azio_stream *s);
static int write_header(azio_stream *s);
static int    destroy(azio_stream *s);
static void putLong(azio_stream *s, uLong x);
static uLong  getLong(azio_stream *s);
static void read_header(azio_stream *s, unsigned char *buffer);
static void get_block(azio_stream *s);
#ifdef AZIO_AIO
static void do_aio_cleanup(azio_stream *s);
#endif

extern "C" pthread_handler_t run_task(void *p);

extern "C" pthread_handler_t run_task(void *p)
{
  int fd;
  char *buffer;
  size_t offset;
  azio_stream *s= (azio_stream *)p;

  while (1)
  {
    pthread_mutex_lock(&s->container.thresh_mutex);
    while (s->container.ready == AZ_THREAD_FINISHED)
    {
      pthread_cond_wait(&s->container.threshhold, &s->container.thresh_mutex);
    }
    offset= s->container.offset;
    fd= s->container.fd;
    buffer= (char *)s->container.buffer;
    pthread_mutex_unlock(&s->container.thresh_mutex);

    if (s->container.ready == AZ_THREAD_DEAD)
      break;

    s->container.read_size= pread((int)fd, (void *)buffer,
                                  (size_t)AZ_BUFSIZE_READ, (off_t)offset);

    pthread_mutex_lock(&s->container.thresh_mutex);
    s->container.ready= AZ_THREAD_FINISHED;
    pthread_mutex_unlock(&s->container.thresh_mutex);
  }

  return 0;
}

static void azio_kill(azio_stream *s)
{
  pthread_mutex_lock(&s->container.thresh_mutex);
  s->container.ready= AZ_THREAD_DEAD;
  pthread_mutex_unlock(&s->container.thresh_mutex);

  pthread_cond_signal(&s->container.threshhold);
  pthread_join(s->container.mainthread, NULL);
}

static size_t azio_return(azio_stream *s)
{
  return s->container.read_size;
}

/*
  Worried about spin?
  Don't be. In tests it never has spun more then 1 times.
*/

static az_thread_type azio_ready(azio_stream *s)
{
  az_thread_type temp;

  while (1)
  {
    pthread_mutex_lock(&s->container.thresh_mutex);
    temp= s->container.ready;
    pthread_mutex_unlock(&s->container.thresh_mutex);

    if (temp == AZ_THREAD_FINISHED || temp == AZ_THREAD_DEAD)
      break;
  }

  return temp;
}

static int azio_start(azio_stream *s)
{
  int rc= 0;
  pthread_attr_t attr;          /* Thread attributes */

  pthread_attr_init(&attr);
  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

  s->container.ready= AZ_THREAD_FINISHED;

  /* If we don't create a thread, signal the caller */
  if (pthread_create(&s->container.mainthread, &attr, run_task,
                     (void *)s) != 0)
    rc= 1;

  pthread_attr_destroy(&attr);

  return rc;
}

static int azio_read(azio_stream *s)
{
  pthread_mutex_lock(&s->container.thresh_mutex);
  s->container.ready= AZ_THREAD_ACTIVE;
  pthread_mutex_unlock(&s->container.thresh_mutex);
  pthread_cond_broadcast(&s->container.threshhold);

  return 0;
}

/* ===========================================================================
  Opens a gzip (.gz) file for reading or writing. The mode parameter
  is as in fopen ("rb" or "wb"). The file is given either by file descriptor
  or path name (if fd == -1).
  az_open returns NULL if the file could not be opened or if there was
  insufficient memory to allocate the (de)compression state; errno
  can be checked to distinguish the two cases (if errno is zero, the
  zlib error is Z_MEM_ERROR).
*/
int azopen(azio_stream *s, const char *path, int Flags, az_method method)
{
  int err;
  int level = Z_DEFAULT_COMPRESSION ; /* compression level */
  int strategy = Z_DEFAULT_STRATEGY; /* compression strategy */
  int fd= -1;

  memset(s, 0, sizeof(azio_stream));

  s->stream.zalloc = (alloc_func)0;
  s->stream.zfree = (free_func)0;
  s->stream.opaque = (voidpf)0;


  s->container.offset= 0;
  s->container.buffer= (void *)s->buffer1;
  s->container.ready= AZ_THREAD_FINISHED;

  s->inbuf= s->buffer1;
  s->stream.next_in = s->inbuf;
  s->stream.next_out = s->outbuf;
  s->z_err = Z_OK;
  s->back = EOF;
  s->crc = crc32(0L, Z_NULL, 0);
  s->mode = 'r';
  s->version = (unsigned char)az_magic[1]; /* this needs to be a define to version */
  s->version = (unsigned char)az_magic[2]; /* minor version */
  s->method= method;

  /*
    We do our own version of append by nature.
    We must always have write access to take card of the header.
  */
  assert(Flags | O_APPEND);
  assert(Flags | O_WRONLY);

  if (Flags & O_RDWR)
    s->mode = 'w';

  if (s->mode == 'w')
  {
    err = deflateInit2(&(s->stream), level,
                       Z_DEFLATED, -MAX_WBITS, 8, strategy);
    /* windowBits is passed < 0 to suppress zlib header */

    s->stream.next_out = s->outbuf;
    if (err != Z_OK)
    {
      destroy(s);
      return Z_NULL;
    }
  } else {
    /* Threads are only used when we are running with azio */
    s->stream.next_in  = s->inbuf;

    err = inflateInit2(&(s->stream), -MAX_WBITS);
    /* windowBits is passed < 0 to tell that there is no zlib header.
     * Note that in this case inflate *requires* an extra "dummy" byte
     * after the compressed stream in order to complete decompression and
     * return Z_STREAM_END. Here the gzip CRC32 ensures that 4 bytes are
     * present after the compressed stream.
   */
    if (err != Z_OK)
    {
      destroy(s);
      return Z_NULL;
    }
  }
  s->stream.avail_out = AZ_BUFSIZE_WRITE;

  errno = 0;
  s->file = fd < 0 ? internal::my_open(path, Flags, MYF(0)) : fd;
#ifdef AZIO_AIO
  s->container.fd= s->file;
#endif

  if (s->file < 0 )
  {
    destroy(s);
    return Z_NULL;
  }

  if (Flags & O_CREAT || Flags & O_TRUNC)
  {
    s->rows= 0;
    s->forced_flushes= 0;
    s->shortest_row= 0;
    s->longest_row= 0;
    s->auto_increment= 0;
    s->check_point= 0;
    s->comment_start_pos= 0;
    s->comment_length= 0;
    s->frm_start_pos= 0;
    s->frm_length= 0;
    s->dirty= 1; /* We create the file dirty */
    s->start = AZHEADER_SIZE + AZMETA_BUFFER_SIZE;
    if(write_header(s))
      return Z_NULL;
    s->pos= (size_t)lseek(s->file, 0, SEEK_END);
  }
  else if (s->mode == 'w')
  {
    unsigned char buffer[AZHEADER_SIZE + AZMETA_BUFFER_SIZE];
    const ssize_t read_size= AZHEADER_SIZE + AZMETA_BUFFER_SIZE;
    if(pread(s->file, buffer, read_size, 0) < read_size)
      return Z_NULL;
    read_header(s, buffer);
    s->pos= (size_t)lseek(s->file, 0, SEEK_END);
  }
  else
  {
    check_header(s); /* skip the .az header */
  }

  switch (s->method)
  {
  case AZ_METHOD_AIO:
    azio_enable_aio(s);
    break;
  case AZ_METHOD_BLOCK:
  case AZ_METHOD_MAX:
    break;
  }

  return 1;
}


int write_header(azio_stream *s)
{
  char buffer[AZHEADER_SIZE + AZMETA_BUFFER_SIZE];
  char *ptr= buffer;

  s->block_size= AZ_BUFSIZE_WRITE;
  s->version = (unsigned char)az_magic[1];
  s->minor_version = (unsigned char)az_magic[2];


  /* Write a very simple .az header: */
  memset(buffer, 0, AZHEADER_SIZE + AZMETA_BUFFER_SIZE);
  *(ptr + AZ_MAGIC_POS)= az_magic[0];
  *(ptr + AZ_VERSION_POS)= (unsigned char)s->version;
  *(ptr + AZ_MINOR_VERSION_POS)= (unsigned char)s->minor_version;
  *(ptr + AZ_BLOCK_POS)= (unsigned char)(s->block_size/1024); /* Reserved for block size */
  *(ptr + AZ_STRATEGY_POS)= (unsigned char)Z_DEFAULT_STRATEGY; /* Compression Type */

  int4store(ptr + AZ_FRM_POS, s->frm_start_pos); /* FRM Block */
  int4store(ptr + AZ_FRM_LENGTH_POS, s->frm_length); /* FRM Block */
  int4store(ptr + AZ_COMMENT_POS, s->comment_start_pos); /* COMMENT Block */
  int4store(ptr + AZ_COMMENT_LENGTH_POS, s->comment_length); /* COMMENT Block */
  int4store(ptr + AZ_META_POS, 0); /* Meta Block */
  int4store(ptr + AZ_META_LENGTH_POS, 0); /* Meta Block */
  int8store(ptr + AZ_START_POS, (uint64_t)s->start); /* Start of Data Block Index Block */
  int8store(ptr + AZ_ROW_POS, (uint64_t)s->rows); /* Start of Data Block Index Block */
  int8store(ptr + AZ_FLUSH_POS, (uint64_t)s->forced_flushes); /* Start of Data Block Index Block */
  int8store(ptr + AZ_CHECK_POS, (uint64_t)s->check_point); /* Start of Data Block Index Block */
  int8store(ptr + AZ_AUTOINCREMENT_POS, (uint64_t)s->auto_increment); /* Start of Data Block Index Block */
  int4store(ptr+ AZ_LONGEST_POS , s->longest_row); /* Longest row */
  int4store(ptr+ AZ_SHORTEST_POS, s->shortest_row); /* Shorest row */
  int4store(ptr+ AZ_FRM_POS,
            AZHEADER_SIZE + AZMETA_BUFFER_SIZE); /* FRM position */
  *(ptr + AZ_DIRTY_POS)= (unsigned char)s->dirty; /* Start of Data Block Index Block */

  /* Always begin at the begining, and end there as well */
  const ssize_t write_size= AZHEADER_SIZE + AZMETA_BUFFER_SIZE;
  if(pwrite(s->file, (unsigned char*) buffer, write_size, 0)!=write_size)
    return -1;

  return 0;
}

/* ===========================================================================
  Read a byte from a azio_stream; update next_in and avail_in. Return EOF
  for end of file.
  IN assertion: the stream s has been sucessfully opened for reading.
*/
int get_byte(azio_stream *s)
{
  if (s->z_eof) return EOF;
  if (s->stream.avail_in == 0)
  {
    errno = 0;
    if (s->stream.avail_in == 0)
    {
      s->z_eof = 1;
      return EOF;
    }
    else if (s->stream.avail_in == (uInt) -1)
    {
      s->z_eof= 1;
      s->z_err= Z_ERRNO;
      return EOF;
    }
    s->stream.next_in = s->inbuf;
  }
  s->stream.avail_in--;
  return *(s->stream.next_in)++;
}

/* ===========================================================================
  Check the gzip header of a azio_stream opened for reading.
  IN assertion: the stream s has already been created sucessfully;
  s->stream.avail_in is zero for the first time, but may be non-zero
  for concatenated .gz files.
*/
void check_header(azio_stream *s)
{
  uInt len;

  /* Assure two bytes in the buffer so we can peek ahead -- handle case
    where first byte of header is at the end of the buffer after the last
    gzip segment */
  len = s->stream.avail_in;
  if (len < 2) {
    if (len) s->inbuf[0] = s->stream.next_in[0];
    errno = 0;
    len = (uInt)pread(s->file, (unsigned char *)s->inbuf + len, AZ_BUFSIZE_READ >> len, s->pos);
    s->pos+= len;
    if (len == (uInt)-1) s->z_err = Z_ERRNO;
    s->stream.avail_in += len;
    s->stream.next_in = s->inbuf;
  }

  /* Now we check the actual header */
  if ( s->stream.next_in[0] == az_magic[0]  && s->stream.next_in[1] == az_magic[1])
  {
    unsigned char buffer[AZHEADER_SIZE + AZMETA_BUFFER_SIZE];

    for (len = 0; len < (AZHEADER_SIZE + AZMETA_BUFFER_SIZE); len++)
      buffer[len]= get_byte(s);
    s->z_err = s->z_eof ? Z_DATA_ERROR : Z_OK;
    read_header(s, buffer);
    for (; len < s->start; len++)
      get_byte(s);
  }
  else
  {
    s->z_err = Z_OK;

    return;
  }
}

void read_header(azio_stream *s, unsigned char *buffer)
{
  if (buffer[0] == az_magic[0]  && buffer[1] == az_magic[1])
  {
    s->version= (unsigned int)buffer[AZ_VERSION_POS];
    s->minor_version= (unsigned int)buffer[AZ_MINOR_VERSION_POS];
    s->block_size= 1024 * buffer[AZ_BLOCK_POS];
    s->start= (size_t)uint8korr(buffer + AZ_START_POS);
    s->rows= (uint64_t)uint8korr(buffer + AZ_ROW_POS);
    s->check_point= (uint64_t)uint8korr(buffer + AZ_CHECK_POS);
    s->forced_flushes= (uint64_t)uint8korr(buffer + AZ_FLUSH_POS);
    s->auto_increment= (uint64_t)uint8korr(buffer + AZ_AUTOINCREMENT_POS);
    s->longest_row= (unsigned int)uint4korr(buffer + AZ_LONGEST_POS);
    s->shortest_row= (unsigned int)uint4korr(buffer + AZ_SHORTEST_POS);
    s->frm_start_pos= (unsigned int)uint4korr(buffer + AZ_FRM_POS);
    s->frm_length= (unsigned int)uint4korr(buffer + AZ_FRM_LENGTH_POS);
    s->comment_start_pos= (unsigned int)uint4korr(buffer + AZ_COMMENT_POS);
    s->comment_length= (unsigned int)uint4korr(buffer + AZ_COMMENT_LENGTH_POS);
    s->dirty= (unsigned int)buffer[AZ_DIRTY_POS];
  }
  else
  {
    s->z_err = Z_OK;
    return;
  }
}

/* ===========================================================================
 * Cleanup then free the given azio_stream. Return a zlib error code.
 Try freeing in the reverse order of allocations.
 */
int destroy (azio_stream *s)
{
  int err = Z_OK;

  if (s->stream.state != NULL)
  {
    if (s->mode == 'w')
    {
      err = deflateEnd(&(s->stream));
      internal::my_sync(s->file, MYF(0));
    }
    else if (s->mode == 'r')
      err = inflateEnd(&(s->stream));
  }

  do_aio_cleanup(s);

  if (s->file > 0 && internal::my_close(s->file, MYF(0)))
      err = Z_ERRNO;

  s->file= -1;

  if (s->z_err < 0) err = s->z_err;

  return err;
}

/* ===========================================================================
  Reads the given number of uncompressed bytes from the compressed file.
  azread returns the number of bytes actually read (0 for end of file).
*/
/*
   This function is legacy, do not use.

     Reads the given number of uncompressed bytes from the compressed file.
   If the input file was not in gzip format, gzread copies the given number
   of bytes into the buffer.
     gzread returns the number of uncompressed bytes actually read (0 for
   end of file, -1 for error).
*/
static unsigned int azread_internal( azio_stream *s, voidp buf, unsigned int len, int *error)
{
  Bytef *start = (Bytef*)buf; /* starting point for crc computation */
  Byte  *next_out; /* == stream.next_out but not forced far (for MSDOS) */
  *error= 0;

  if (s->mode != 'r')
  {
    *error= Z_STREAM_ERROR;
    return 0;
  }

  if (s->z_err == Z_DATA_ERROR || s->z_err == Z_ERRNO)
  {
    *error= s->z_err;
    return 0;
  }

  if (s->z_err == Z_STREAM_END)  /* EOF */
  {
    return 0;
  }

  next_out = (Byte*)buf;
  s->stream.next_out = (Bytef*)buf;
  s->stream.avail_out = len;

  if (s->stream.avail_out && s->back != EOF) {
    *next_out++ = s->back;
    s->stream.next_out++;
    s->stream.avail_out--;
    s->back = EOF;
    s->out++;
    start++;
    if (s->last) {
      s->z_err = Z_STREAM_END;
      {
        return 1;
      }
    }
  }

  while (s->stream.avail_out != 0) {

    if (s->stream.avail_in == 0 && !s->z_eof) {

      errno = 0;
      get_block(s);
      if (s->stream.avail_in == 0)
      {
        s->z_eof = 1;
      }
      s->stream.next_in = (Bytef *)s->inbuf;
    }
    s->in += s->stream.avail_in;
    s->out += s->stream.avail_out;
    s->z_err = inflate(&(s->stream), Z_NO_FLUSH);
    s->in -= s->stream.avail_in;
    s->out -= s->stream.avail_out;

    if (s->z_err == Z_STREAM_END) {
      /* Check CRC and original size */
      s->crc = crc32(s->crc, start, (uInt)(s->stream.next_out - start));
      start = s->stream.next_out;

      if (getLong(s) != s->crc) {
        s->z_err = Z_DATA_ERROR;
      } else {
        (void)getLong(s);
        /* The uncompressed length returned by above getlong() may be
         * different from s->out in case of concatenated .gz files.
         * Check for such files:
       */
        check_header(s);
        if (s->z_err == Z_OK)
        {
          inflateReset(&(s->stream));
          s->crc = crc32(0L, Z_NULL, 0);
        }
      }
    }
    if (s->z_err != Z_OK || s->z_eof) break;
  }
  s->crc = crc32(s->crc, start, (uInt)(s->stream.next_out - start));

  if (len == s->stream.avail_out &&
      (s->z_err == Z_DATA_ERROR || s->z_err == Z_ERRNO))
  {
    *error= s->z_err;

    return 0;
  }

  return (len - s->stream.avail_out);
}

/* ===========================================================================
  Experimental Interface. We abstract out a concecpt of rows
*/
size_t azwrite_row(azio_stream *s, void *buf, unsigned int len)
{
  size_t length;
  /* First we write length */
  length= azwrite(s, &len, sizeof(unsigned int));

  if (length != sizeof(unsigned int))
    return length;

  /* Now we write the actual data */
  length= (size_t)azwrite(s, buf, len);

  if (length > 0)
    s->rows++;

  if (len > s->longest_row)
    s->longest_row= len;

  if (len < s->shortest_row || !(s->shortest_row))
    s->shortest_row= len;

  return length;
}

size_t azread_row(azio_stream *s, int *error)
{
  unsigned int row_length; /* Currently we are limited to this size for rows */
  char buffer[sizeof(unsigned int)];
  char *new_ptr;
  size_t read;

  read= azread_internal(s, buffer, sizeof(unsigned int), error);

  /* On error the return value will be zero as well */
  if (read == 0)
    return read;
  memcpy(&row_length, buffer, sizeof(unsigned int));

  new_ptr= (char *)realloc(s->row_ptr, (sizeof(char) * row_length));

  if (!new_ptr)
    return SIZE_MAX;

  s->row_ptr= new_ptr;

  /* TODO We should now adjust the length... */
  read= azread_internal(s, (voidp)s->row_ptr, row_length, error);

  return read;
}


/* ===========================================================================
  Writes the given number of uncompressed bytes into the compressed file.
  azwrite returns the number of bytes actually written (0 in case of error).
*/
static unsigned int azwrite(azio_stream *s, void *buf, unsigned int len)
{
  s->stream.next_in = (Bytef*)buf;
  s->stream.avail_in = len;

  while (s->stream.avail_in != 0)
  {
    if (s->stream.avail_out == 0)
    {

      s->stream.next_out = s->outbuf;
      if (pwrite(s->file, (unsigned char *)s->outbuf, AZ_BUFSIZE_WRITE, s->pos) != AZ_BUFSIZE_WRITE)
      {
        s->z_err = Z_ERRNO;
        break;
      }
      s->pos+= AZ_BUFSIZE_WRITE;
      s->stream.avail_out = AZ_BUFSIZE_WRITE;
    }
    s->in += s->stream.avail_in;
    s->out += s->stream.avail_out;
    s->z_err = deflate(&(s->stream), Z_NO_FLUSH);
    s->in -= s->stream.avail_in;
    s->out -= s->stream.avail_out;
    if (s->z_err != Z_OK) break;
  }
  s->crc = crc32(s->crc, (const Bytef *)buf, len);

  return (unsigned int)(len - s->stream.avail_in);
}


/* ===========================================================================
  Flushes all pending output into the compressed file. The parameter
  flush is as in the deflate() function.
*/
int do_flush (azio_stream *s, int flush)
{
  uInt len;
  int done = 0;
  size_t afterwrite_pos;

  if (s == NULL || s->mode != 'w') return Z_STREAM_ERROR;

  s->stream.avail_in = 0; /* should be zero already anyway */

  for (;;)
  {
    len = AZ_BUFSIZE_WRITE - s->stream.avail_out;

    if (len != 0)
    {
      if ((uInt)pwrite(s->file, (unsigned char *)s->outbuf, len, s->pos) != len)
      {
        s->z_err = Z_ERRNO;
        assert(0);
        return Z_ERRNO;
      }
      s->pos+= len;
      s->check_point= s->pos;
      s->stream.next_out = s->outbuf;
      s->stream.avail_out = AZ_BUFSIZE_WRITE;
    }
    if (done) break;
    s->out += s->stream.avail_out;
    s->z_err = deflate(&(s->stream), flush);
    s->out -= s->stream.avail_out;

    /* Ignore the second of two consecutive flushes: */
    if (len == 0 && s->z_err == Z_BUF_ERROR) s->z_err = Z_OK;

    /* deflate has finished flushing only when it hasn't used up
     * all the available space in the output buffer:
   */
    done = (s->stream.avail_out != 0 || s->z_err == Z_STREAM_END);

    if (s->z_err != Z_OK && s->z_err != Z_STREAM_END) break;
  }

  if (flush == Z_FINISH)
    s->dirty= AZ_STATE_CLEAN; /* Mark it clean, we should be good now */
  else
    s->dirty= AZ_STATE_SAVED; /* Mark it clean, we should be good now */

  afterwrite_pos= (size_t)lseek(s->file, 0, SEEK_CUR);
  if(write_header(s))
    return Z_ERRNO;

  return  s->z_err == Z_STREAM_END ? Z_OK : s->z_err;
}

static unsigned int azio_enable_aio(azio_stream *s)
{
  pthread_cond_init(&s->container.threshhold, NULL);
  pthread_mutex_init(&s->container.thresh_mutex, NULL);
  azio_start(s);

  return 0;
}

static void azio_disable_aio(azio_stream *s)
{
  azio_kill(s);

  pthread_mutex_destroy(&s->container.thresh_mutex);
  pthread_cond_destroy(&s->container.threshhold);

  s->method= AZ_METHOD_BLOCK;
}

int ZEXPORT azflush (azio_stream *s,int flush)
{
  int err;

  if (s->mode == 'r')
  {
    unsigned char buffer[AZHEADER_SIZE + AZMETA_BUFFER_SIZE];
    const ssize_t read_size= AZHEADER_SIZE + AZMETA_BUFFER_SIZE;
    if(pread(s->file, (unsigned char*) buffer, read_size, 0)!=read_size)
      return Z_ERRNO;
    read_header(s, buffer); /* skip the .az header */
    azrewind(s);

    return Z_OK;
  }
  else
  {
    s->forced_flushes++;
    err= do_flush(s, flush);

    if (err) return err;
    internal::my_sync(s->file, MYF(0));
    return  s->z_err == Z_STREAM_END ? Z_OK : s->z_err;
  }
}

/* ===========================================================================
  Initiazliaze for reading
*/
int azread_init(azio_stream *s)
{
  int returnable;

  /* This will reset any aio reads */
  returnable= azrewind(s);

  if (returnable == -1)
    return returnable;

  /* Put one in the chamber */
  if (s->method != AZ_METHOD_BLOCK)
  {
    do_aio_cleanup(s);
    s->container.offset= s->pos;
    s->container.buffer= (unsigned char *)s->buffer1;
    azio_read(s);
    s->aio_inited= 1;
  }


  return returnable;
}

/* ===========================================================================
  Rewinds input file.
*/
int azrewind (azio_stream *s)
{
  if (s == NULL || s->mode != 'r') return -1;

#ifdef AZIO_AIO
  do_aio_cleanup(s);
#endif
  s->z_err = Z_OK;
  s->z_eof = 0;
  s->back = EOF;
  s->stream.avail_in = 0;
  s->stream.next_in = (Bytef *)s->inbuf;
  s->crc = crc32(0L, Z_NULL, 0);
  (void)inflateReset(&s->stream);
  s->in = 0;
  s->out = 0;
  s->aio_inited= 0; /* Reset the AIO reader */
  s->pos= s->start;
  return 0;
}

/* ===========================================================================
  Sets the starting position for the next azread or azwrite on the given
  compressed file. The offset represents a number of bytes in the
  azseek returns the resulting offset location as measured in bytes from
  the beginning of the uncompressed stream, or -1 in case of error.
  SEEK_END is not implemented, returns error.
  In this version of the library, azseek can be extremely slow.
*/
size_t azseek (azio_stream *s, size_t offset, int whence)
{

  if (s == NULL || whence == SEEK_END ||
      s->z_err == Z_ERRNO || s->z_err == Z_DATA_ERROR) {
    return SIZE_MAX;
  }

  if (s->mode == 'w')
  {
    if (whence == SEEK_SET)
      offset -= s->in;

    /* At this point, offset is the number of zero bytes to write. */
    /* There was a zmemzero here if inbuf was null -Brian */
    while (offset > 0)
    {
      uInt size = AZ_BUFSIZE_READ;
      if (offset < AZ_BUFSIZE_READ) size = (uInt)offset;

      size = azwrite(s, s->inbuf, size);
      if (size == 0)
        return SIZE_MAX;

      offset -= size;
    }
    return s->in;
  }
  /* Rest of function is for reading only */

  /* compute absolute position */
  if (whence == SEEK_CUR) {
    offset += s->out;
  }

  /* For a negative seek, rewind and use positive seek */
  if (offset >= s->out) {
    offset -= s->out;
  } else if (azrewind(s)) {
    return SIZE_MAX;
  }
  /* offset is now the number of bytes to skip. */

  if (offset && s->back != EOF) {
    s->back = EOF;
    s->out++;
    offset--;
    if (s->last) s->z_err = Z_STREAM_END;
  }
  while (offset > 0)  {
    int error;
    unsigned int size = AZ_BUFSIZE_WRITE;
    if (offset < AZ_BUFSIZE_WRITE) size = (int)offset;

    size = azread_internal(s, s->outbuf, size, &error);
    if (error < 0) return SIZE_MAX;
    offset -= size;
  }
  return s->out;
}

/* ===========================================================================
  Returns the starting position for the next azread or azwrite on the
  given compressed file. This position represents a number of bytes in the
  uncompressed data stream.
*/
size_t ZEXPORT aztell (azio_stream *file)
{
  return azseek(file, 0L, SEEK_CUR);
}


/* ===========================================================================
  Outputs a long in LSB order to the given file
*/
void putLong (azio_stream *s, uLong x)
{
  int n;
  unsigned char buffer[1];

  for (n = 0; n < 4; n++)
  {
    buffer[0]= (int)(x & 0xff);
    size_t ret= pwrite(s->file, buffer, 1, s->pos);
    assert(ret == 1);
    s->pos++;
    x >>= 8;
  }
}

/* ===========================================================================
  Reads a long in LSB order from the given azio_stream. Sets z_err in case
  of error.
*/
uLong getLong (azio_stream *s)
{
  uLong x = (uLong)get_byte(s);
  int c;

  x += ((uLong)get_byte(s))<<8;
  x += ((uLong)get_byte(s))<<16;
  c = get_byte(s);
  if (c == EOF) s->z_err = Z_DATA_ERROR;
  x += ((uLong)c)<<24;
  return x;
}

/* ===========================================================================
  Flushes all pending output if necessary, closes the compressed file
  and deallocates all the (de)compression state.
*/
int azclose (azio_stream *s)
{
  int returnable;

  if (s == NULL) return Z_STREAM_ERROR;

  if (s->file < 1) return Z_OK;

  if (s->mode == 'w')
  {
    if (do_flush(s, Z_FINISH) != Z_OK)
      return destroy(s);

    putLong(s, s->crc);
    putLong(s, (uLong)(s->in & 0xffffffff));
    s->dirty= AZ_STATE_CLEAN;
    write_header(s);
  }

  returnable= destroy(s);

  switch (s->method)
  {
  case AZ_METHOD_AIO:
    azio_disable_aio(s);
    break;
  case AZ_METHOD_BLOCK:
  case AZ_METHOD_MAX:
    break;
  }

  /* If we allocated memory for row reading, now free it */
  if (s->row_ptr)
    free(s->row_ptr);

  return returnable;
}

/*
  Though this was added to support MySQL's FRM file, anything can be
  stored in this location.
*/
int azwrite_frm(azio_stream *s, const char *blob, unsigned int length)
{
  if (s->mode == 'r')
    return 1;

  if (s->rows > 0)
    return 1;

  s->frm_start_pos= (uint) s->start;
  s->frm_length= length;
  s->start+= length;

  if (pwrite(s->file, (unsigned char*) blob, s->frm_length, s->frm_start_pos) != (ssize_t)s->frm_length)
    return 1;

  write_header(s);
  s->pos= (size_t)lseek(s->file, 0, SEEK_END);

  return 0;
}

int azread_frm(azio_stream *s, char *blob)
{
  ssize_t r= pread(s->file, (unsigned char*) blob,
                   s->frm_length, s->frm_start_pos);
  if (r != (ssize_t)s->frm_length)
    return r;

  return 0;
}


/*
  Simple comment field
*/
int azwrite_comment(azio_stream *s, const char *blob, unsigned int length)
{
  if (s->mode == 'r')
    return -1;

  if (s->rows > 0)
    return -1;

  s->comment_start_pos= (uint) s->start;
  s->comment_length= length;
  s->start+= length;

  ssize_t r= pwrite(s->file, (unsigned char*) blob,
                    s->comment_length, s->comment_start_pos);
  if (r != (ssize_t)s->comment_length)
    return -1;

  write_header(s);
  s->pos= (size_t)lseek(s->file, 0, SEEK_END);

  return 0;
}

int azread_comment(azio_stream *s, char *blob)
{
  ssize_t r= pread(s->file, (unsigned char*) blob,
                   s->comment_length, s->comment_start_pos);
  if (r != (ssize_t)s->comment_length)
    return r;

  return 0;
}

#ifdef AZIO_AIO
static void do_aio_cleanup(azio_stream *s)
{
  if (s->method == AZ_METHOD_BLOCK)
    return;

  azio_ready(s);

}
#endif

/*
  Normally all IO goes through azio_read(), but in case of error or non-support
  we make use of pread().
*/
static void get_block(azio_stream *s)
{
#ifdef AZIO_AIO
  if (s->method == AZ_METHOD_AIO && s->mode == 'r'
      && s->pos < s->check_point
      && s->aio_inited)
  {
    azio_ready(s);
    s->stream.avail_in= (unsigned int)azio_return(s);
    if ((int)(s->stream.avail_in) == -1)
      goto use_pread;
    else if ((int)(s->stream.avail_in) == 0)
    {
      s->aio_inited= 0;
      return;
    }
    s->pos+= s->stream.avail_in;
    s->inbuf= (Byte *)s->container.buffer;
    /* We only azio_read when we know there is more data to be read */
    if (s->pos >= s->check_point)
    {
      s->aio_inited= 0;
      return;
    }
    s->container.buffer= (s->container.buffer == s->buffer2) ? s->buffer1 : s->buffer2;
    s->container.offset= s->pos;
    azio_read(s);
  }
  else
#endif
  {
#ifdef AZIO_AIO
use_pread:
#endif
    s->stream.avail_in = (uInt)pread(s->file, (unsigned char *)s->inbuf,
                                     AZ_BUFSIZE_READ, s->pos);
    s->pos+= s->stream.avail_in;
  }
}