/* tinyproxy - A fast light-weight HTTP proxy
 * Copyright (C) 1999, 2001 Robert James Kaes <rjkaes@users.sourceforge.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

/* The buffer used in each connection is a linked list of lines. As the lines
 * are read in and written out the buffer expands and contracts. Basically,
 * by using this method we can increase the buffer size dynamically. However,
 * we have a hard limit of 64 KB for the size of the buffer. The buffer can be
 * thought of as a queue were we act on both the head and tail. The various
 * functions act on each end (the names are taken from what Perl uses to act on
 * the ends of an array. :)
 */

#include "tinyproxy.h"

#include "buffer.h"
#include "heap.h"
#include "log.h"

#define BUFFER_HEAD(x) (x)->head
#define BUFFER_TAIL(x) (x)->tail

struct bufline_s
{
  unsigned char *string;        /* the actual string of data */
  struct bufline_s *next;       /* pointer to next in linked list */
  size_t length;                /* length of the string of data */
  size_t pos;                   /* start sending from this offset */
};

/*
 * The buffer structure points to the beginning and end of the buffer list
 * (and includes the total size)
 */
struct buffer_s
{
  struct bufline_s *head;       /* top of the buffer */
  struct bufline_s *tail;       /* bottom of the buffer */
  size_t size;                  /* total size of the buffer */
};

/*
 * Take a string of data and a length and make a new line which can be added
 * to the buffer. The data IS copied, so make sure if you allocated your
 * data buffer on the heap, delete it because you now have TWO copies.
 */
static struct bufline_s *
makenewline (unsigned char *data, size_t length)
{
  struct bufline_s *newline;

  assert (data != NULL);
  assert (length > 0);

  newline = safemalloc (sizeof (struct bufline_s));
  if (!newline)
    return NULL;

  newline->string = safemalloc (length);
  if (!newline->string)
    {
      safefree (newline);
      return NULL;
    }

  memcpy (newline->string, data, length);

  newline->next = NULL;
  newline->length = length;

  /* Position our "read" pointer at the beginning of the data */
  newline->pos = 0;

  return newline;
}

/*
 * Free the allocated buffer line
 */
static void
free_line (struct bufline_s *line)
{
  assert (line != NULL);

  if (!line)
    return;

  if (line->string)
    safefree (line->string);

  safefree (line);
}

/*
 * Create a new buffer
 */
struct buffer_s *
new_buffer (void)
{
  struct buffer_s *buffptr;

  if (!(buffptr = safemalloc (sizeof (struct buffer_s))))
    return NULL;

  /*
   * Since the buffer is initially empty, set the HEAD and TAIL
   * pointers to NULL since they can't possibly point anywhere at the
   * moment.
   */
  BUFFER_HEAD (buffptr) = BUFFER_TAIL (buffptr) = NULL;
  buffptr->size = 0;

  return buffptr;
}

/*
 * Delete all the lines in the buffer and the buffer itself
 */
void
delete_buffer (struct buffer_s *buffptr)
{
  struct bufline_s *next;

  assert (buffptr != NULL);

  while (BUFFER_HEAD (buffptr))
    {
      next = BUFFER_HEAD (buffptr)->next;
      free_line (BUFFER_HEAD (buffptr));
      BUFFER_HEAD (buffptr) = next;
    }

  safefree (buffptr);
}

/*
 * Return the current size of the buffer.
 */
size_t
buffer_size (struct buffer_s *buffptr)
{
  return buffptr->size;
}

/*
 * Push a new line on to the end of the buffer.
 */
int
add_to_buffer (struct buffer_s *buffptr, unsigned char *data, size_t length)
{
  struct bufline_s *newline;

  assert (buffptr != NULL);
  assert (data != NULL);
  assert (length > 0);

  /*
   * Sanity check here. A buffer with a non-NULL head pointer must
   * have a size greater than zero, and vice-versa.
   */
  if (BUFFER_HEAD (buffptr) == NULL)
    assert (buffptr->size == 0);
  else
    assert (buffptr->size > 0);

  /*
   * Make a new line so we can add it to the buffer.
   */
  if (!(newline = makenewline (data, length)))
    return -1;

  if (buffptr->size == 0)
    BUFFER_HEAD (buffptr) = BUFFER_TAIL (buffptr) = newline;
  else
    {
      BUFFER_TAIL (buffptr)->next = newline;
      BUFFER_TAIL (buffptr) = newline;
    }

  buffptr->size += length;

  return 0;
}

/*
 * Remove the first line from the top of the buffer
 */
static struct bufline_s *
remove_from_buffer (struct buffer_s *buffptr)
{
  struct bufline_s *line;

  assert (buffptr != NULL);
  assert (BUFFER_HEAD (buffptr) != NULL);

  line = BUFFER_HEAD (buffptr);
  BUFFER_HEAD (buffptr) = line->next;

  buffptr->size -= line->length;

  return line;
}

/*
 * Reads the bytes from the socket, and adds them to the buffer.
 * Takes a connection and returns the number of bytes read.
 */
#define READ_BUFFER_SIZE (1024 * 2)
ssize_t
read_buffer (int fd, struct buffer_s * buffptr)
{
  ssize_t bytesin;
  unsigned char *buffer;

  assert (fd >= 0);
  assert (buffptr != NULL);

  /*
   * Don't allow the buffer to grow larger than MAXBUFFSIZE
   */
  if (buffptr->size >= MAXBUFFSIZE)
    return 0;

  buffer = safemalloc (READ_BUFFER_SIZE);
  if (!buffer)
    {
      return -ENOMEM;
    }

  bytesin = read (fd, buffer, READ_BUFFER_SIZE);

  if (bytesin > 0)
    {
      if (add_to_buffer (buffptr, buffer, bytesin) < 0)
        {
          log_message (LOG_ERR, "readbuff: add_to_buffer() error.");
          bytesin = -1;
        }
    }
  else
    {
      if (bytesin == 0)
        {
          /* connection was closed by client */
          bytesin = -1;
        }
      else
        {
          switch (errno)
            {
#ifdef EWOULDBLOCK
            case EWOULDBLOCK:
#else
#  ifdef EAGAIN
            case EAGAIN:
#  endif
#endif
            case EINTR:
              bytesin = 0;
              break;
            default:
              log_message (LOG_ERR,
                           "readbuff: recv() error \"%s\" on file descriptor %d",
                           strerror (errno), fd);
              bytesin = -1;
              break;
            }
        }
    }

  safefree (buffer);
  return bytesin;
}

/*
 * Write the bytes in the buffer to the socket.
 * Takes a connection and returns the number of bytes written.
 */
ssize_t
write_buffer (int fd, struct buffer_s * buffptr)
{
  ssize_t bytessent;
  struct bufline_s *line;

  assert (fd >= 0);
  assert (buffptr != NULL);

  if (buffptr->size == 0)
    return 0;

  /* Sanity check. It would be bad to be using a NULL pointer! */
  assert (BUFFER_HEAD (buffptr) != NULL);
  line = BUFFER_HEAD (buffptr);

  bytessent =
    send (fd, line->string + line->pos, line->length - line->pos,
          MSG_NOSIGNAL);

  if (bytessent >= 0)
    {
      /* bytes sent, adjust buffer */
      line->pos += bytessent;
      if (line->pos == line->length)
        free_line (remove_from_buffer (buffptr));
      return bytessent;
    }
  else
    {
      switch (errno)
        {
#ifdef EWOULDBLOCK
        case EWOULDBLOCK:
#else
#  ifdef EAGAIN
        case EAGAIN:
#  endif
#endif
        case EINTR:
          return 0;
        case ENOBUFS:
        case ENOMEM:
          log_message (LOG_ERR,
                       "writebuff: write() error [NOBUFS/NOMEM] \"%s\" on "
                       "file descriptor %d", strerror (errno), fd);
          return 0;
        default:
          log_message (LOG_ERR,
                       "writebuff: write() error \"%s\" on file descriptor %d",
                       strerror (errno), fd);
          return -1;
        }
    }
}