/*
 * Copyright 2007 David Gibson, IBM Corporation.
 * Based on earlier work, Copyright (C) Paul Mackerras 1997.
 *
 * 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.
 */

#include <stddef.h>
#include "string.h"
#include "stdio.h"
#include "ops.h"
#include "gunzip_util.h"

#define HEAD_CRC        2
#define EXTRA_FIELD     4
#define ORIG_NAME       8
#define COMMENT         0x10
#define RESERVED        0xe0

/**
 * gunzip_start - prepare to decompress gzip data
 * @state:     decompressor state structure to be initialized
 * @src:       buffer containing gzip compressed or uncompressed data
 * @srclen:    size in bytes of the buffer at src
 *
 * If the buffer at @src contains a gzip header, this function
 * initializes zlib to decompress the data, storing the decompression
 * state in @state.  The other functions in this file can then be used
 * to decompress data from the gzipped stream.
 *
 * If the buffer at @src does not contain a gzip header, it is assumed
 * to contain uncompressed data.  The buffer information is recorded
 * in @state and the other functions in this file will simply copy
 * data from the uncompressed data stream at @src.
 *
 * Any errors, such as bad compressed data, cause an error to be
 * printed an the platform's exit() function to be called.
 */
void gunzip_start(struct gunzip_state *state, void *src, int srclen)
{
        char *hdr = src;
        int hdrlen = 0;

        memset(state, 0, sizeof(*state));

        /* Check for gzip magic number */
        if ((hdr[0] == 0x1f) && (hdr[1] == 0x8b)) {
                /* gzip data, initialize zlib parameters */
                int r, flags;

                state->s.workspace = state->scratch;
                if (zlib_inflate_workspacesize() > sizeof(state->scratch))
                        fatal("insufficient scratch space for gunzip\n\r");

                /* skip header */
                hdrlen = 10;
                flags = hdr[3];
                if (hdr[2] != Z_DEFLATED || (flags & RESERVED) != 0)
                        fatal("bad gzipped data\n\r");
                if ((flags & EXTRA_FIELD) != 0)
                        hdrlen = 12 + hdr[10] + (hdr[11] << 8);
                if ((flags & ORIG_NAME) != 0)
                        while (hdr[hdrlen++] != 0)
                                ;
                if ((flags & COMMENT) != 0)
                        while (hdr[hdrlen++] != 0)
                                ;
                if ((flags & HEAD_CRC) != 0)
                        hdrlen += 2;
                if (hdrlen >= srclen)
                        fatal("gunzip_start: ran out of data in header\n\r");

                r = zlib_inflateInit2(&state->s, -MAX_WBITS);
                if (r != Z_OK)
                        fatal("inflateInit2 returned %d\n\r", r);
        }

        state->s.total_in = hdrlen;
        state->s.next_in = src + hdrlen;
        state->s.avail_in = srclen - hdrlen;
}

/**
 * gunzip_partial - extract bytes from a gzip data stream
 * @state:     gzip state structure previously initialized by gunzip_start()
 * @dst:       buffer to store extracted data
 * @dstlen:    maximum number of bytes to extract
 *
 * This function extracts at most @dstlen bytes from the data stream
 * previously associated with @state by gunzip_start(), decompressing
 * if necessary.  Exactly @dstlen bytes are extracted unless the data
 * stream doesn't contain enough bytes, in which case the entire
 * remainder of the stream is decompressed.
 *
 * Returns the actual number of bytes extracted.  If any errors occur,
 * such as a corrupted compressed stream, an error is printed an the
 * platform's exit() function is called.
 */
int gunzip_partial(struct gunzip_state *state, void *dst, int dstlen)
{
        int len;

        if (state->s.workspace) {
                /* gunzipping */
                int r;

                state->s.next_out = dst;
                state->s.avail_out = dstlen;
                r = zlib_inflate(&state->s, Z_FULL_FLUSH);
                if (r != Z_OK && r != Z_STREAM_END)
                        fatal("inflate returned %d msg: %s\n\r", r, state->s.msg);
                len = state->s.next_out - (unsigned char *)dst;
        } else {
                /* uncompressed image */
                len = min(state->s.avail_in, (unsigned)dstlen);
                memcpy(dst, state->s.next_in, len);
                state->s.next_in += len;
                state->s.avail_in -= len;
        }
        return len;
}

/**
 * gunzip_exactly - extract a fixed number of bytes from a gzip data stream
 * @state:     gzip state structure previously initialized by gunzip_start()
 * @dst:       buffer to store extracted data
 * @dstlen:    number of bytes to extract
 *
 * This function extracts exactly @dstlen bytes from the data stream
 * previously associated with @state by gunzip_start(), decompressing
 * if necessary.
 *
 * If there are less @dstlen bytes available in the data stream, or if
 * any other errors occur, such as a corrupted compressed stream, an
 * error is printed an the platform's exit() function is called.
 */
void gunzip_exactly(struct gunzip_state *state, void *dst, int dstlen)
{
        int len;

        len  = gunzip_partial(state, dst, dstlen);
        if (len < dstlen)
                fatal("\n\rgunzip_exactly: ran out of data!"
                                " Wanted %d, got %d.\n\r", dstlen, len);
}

/**
 * gunzip_discard - discard bytes from a gzip data stream
 * @state:     gzip state structure previously initialized by gunzip_start()
 * @len:       number of bytes to discard
 *
 * This function extracts, then discards exactly @len bytes from the
 * data stream previously associated with @state by gunzip_start().
 * Subsequent gunzip_partial(), gunzip_exactly() or gunzip_finish()
 * calls will extract the data following the discarded bytes in the
 * data stream.
 *
 * If there are less @len bytes available in the data stream, or if
 * any other errors occur, such as a corrupted compressed stream, an
 * error is printed an the platform's exit() function is called.
 */
void gunzip_discard(struct gunzip_state *state, int len)
{
        static char discard_buf[128];

        while (len > sizeof(discard_buf)) {
                gunzip_exactly(state, discard_buf, sizeof(discard_buf));
                len -= sizeof(discard_buf);
        }

        if (len > 0)
                gunzip_exactly(state, discard_buf, len);
}

/**
 * gunzip_finish - extract all remaining bytes from a gzip data stream
 * @state:     gzip state structure previously initialized by gunzip_start()
 * @dst:       buffer to store extracted data
 * @dstlen:    maximum number of bytes to extract
 *
 * This function extracts all remaining data, or at most @dstlen
 * bytes, from the stream previously associated with @state by
 * gunzip_start().  zlib is then shut down, so it is an error to use
 * any of the functions in this file on @state until it is
 * re-initialized with another call to gunzip_start().
 *
 * If any errors occur, such as a corrupted compressed stream, an
 * error is printed an the platform's exit() function is called.
 */
int gunzip_finish(struct gunzip_state *state, void *dst, int dstlen)
{
        int len;

        len = gunzip_partial(state, dst, dstlen);

        if (state->s.workspace) {
                zlib_inflateEnd(&state->s);
        }

        return len;
}