/* 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 "main.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 = (struct bufline_s *) safemalloc (sizeof (struct bufline_s));
        if (!newline)
                return NULL;

        newline->string = (unsigned char *) 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;

        buffptr = (struct buffer_s *) safemalloc (sizeof (struct buffer_s));
        if (!buffptr)
                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 = (unsigned char *) 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,
                                     "read_buffer: read() failed on fd %d: %s",
                                     fd, strerror(errno));
                        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;
                }
        }
}