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xianfeng |
/*
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* Copyright 2007 David Gibson, IBM Corporation.
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* Based on earlier work, Copyright (C) Paul Mackerras 1997.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <stddef.h>
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#include "string.h"
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#include "stdio.h"
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#include "ops.h"
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#include "gunzip_util.h"
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#define HEAD_CRC 2
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#define EXTRA_FIELD 4
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#define ORIG_NAME 8
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#define COMMENT 0x10
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#define RESERVED 0xe0
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/**
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* gunzip_start - prepare to decompress gzip data
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* @state: decompressor state structure to be initialized
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* @src: buffer containing gzip compressed or uncompressed data
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* @srclen: size in bytes of the buffer at src
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*
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* If the buffer at @src contains a gzip header, this function
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* initializes zlib to decompress the data, storing the decompression
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* state in @state. The other functions in this file can then be used
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* to decompress data from the gzipped stream.
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*
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* If the buffer at @src does not contain a gzip header, it is assumed
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* to contain uncompressed data. The buffer information is recorded
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* in @state and the other functions in this file will simply copy
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* data from the uncompressed data stream at @src.
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*
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* Any errors, such as bad compressed data, cause an error to be
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* printed an the platform's exit() function to be called.
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*/
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void gunzip_start(struct gunzip_state *state, void *src, int srclen)
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{
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char *hdr = src;
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int hdrlen = 0;
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memset(state, 0, sizeof(*state));
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/* Check for gzip magic number */
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if ((hdr[0] == 0x1f) && (hdr[1] == 0x8b)) {
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/* gzip data, initialize zlib parameters */
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int r, flags;
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state->s.workspace = state->scratch;
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if (zlib_inflate_workspacesize() > sizeof(state->scratch))
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fatal("insufficient scratch space for gunzip\n\r");
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/* skip header */
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hdrlen = 10;
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flags = hdr[3];
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if (hdr[2] != Z_DEFLATED || (flags & RESERVED) != 0)
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fatal("bad gzipped data\n\r");
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if ((flags & EXTRA_FIELD) != 0)
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hdrlen = 12 + hdr[10] + (hdr[11] << 8);
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if ((flags & ORIG_NAME) != 0)
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while (hdr[hdrlen++] != 0)
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;
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if ((flags & COMMENT) != 0)
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while (hdr[hdrlen++] != 0)
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;
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if ((flags & HEAD_CRC) != 0)
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hdrlen += 2;
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if (hdrlen >= srclen)
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fatal("gunzip_start: ran out of data in header\n\r");
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r = zlib_inflateInit2(&state->s, -MAX_WBITS);
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if (r != Z_OK)
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fatal("inflateInit2 returned %d\n\r", r);
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}
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state->s.total_in = hdrlen;
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state->s.next_in = src + hdrlen;
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state->s.avail_in = srclen - hdrlen;
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}
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/**
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* gunzip_partial - extract bytes from a gzip data stream
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* @state: gzip state structure previously initialized by gunzip_start()
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* @dst: buffer to store extracted data
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* @dstlen: maximum number of bytes to extract
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*
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* This function extracts at most @dstlen bytes from the data stream
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* previously associated with @state by gunzip_start(), decompressing
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* if necessary. Exactly @dstlen bytes are extracted unless the data
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* stream doesn't contain enough bytes, in which case the entire
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* remainder of the stream is decompressed.
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*
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* Returns the actual number of bytes extracted. If any errors occur,
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* such as a corrupted compressed stream, an error is printed an the
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* platform's exit() function is called.
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*/
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int gunzip_partial(struct gunzip_state *state, void *dst, int dstlen)
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{
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int len;
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if (state->s.workspace) {
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/* gunzipping */
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int r;
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state->s.next_out = dst;
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state->s.avail_out = dstlen;
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r = zlib_inflate(&state->s, Z_FULL_FLUSH);
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if (r != Z_OK && r != Z_STREAM_END)
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fatal("inflate returned %d msg: %s\n\r", r, state->s.msg);
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len = state->s.next_out - (unsigned char *)dst;
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} else {
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/* uncompressed image */
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len = min(state->s.avail_in, (unsigned)dstlen);
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memcpy(dst, state->s.next_in, len);
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state->s.next_in += len;
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state->s.avail_in -= len;
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}
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return len;
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}
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/**
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* gunzip_exactly - extract a fixed number of bytes from a gzip data stream
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* @state: gzip state structure previously initialized by gunzip_start()
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* @dst: buffer to store extracted data
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* @dstlen: number of bytes to extract
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*
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* This function extracts exactly @dstlen bytes from the data stream
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* previously associated with @state by gunzip_start(), decompressing
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* if necessary.
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*
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* If there are less @dstlen bytes available in the data stream, or if
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* any other errors occur, such as a corrupted compressed stream, an
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* error is printed an the platform's exit() function is called.
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*/
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void gunzip_exactly(struct gunzip_state *state, void *dst, int dstlen)
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{
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int len;
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len = gunzip_partial(state, dst, dstlen);
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if (len < dstlen)
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fatal("\n\rgunzip_exactly: ran out of data!"
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" Wanted %d, got %d.\n\r", dstlen, len);
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}
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/**
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* gunzip_discard - discard bytes from a gzip data stream
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* @state: gzip state structure previously initialized by gunzip_start()
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* @len: number of bytes to discard
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*
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* This function extracts, then discards exactly @len bytes from the
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* data stream previously associated with @state by gunzip_start().
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* Subsequent gunzip_partial(), gunzip_exactly() or gunzip_finish()
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* calls will extract the data following the discarded bytes in the
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* data stream.
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*
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* If there are less @len bytes available in the data stream, or if
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* any other errors occur, such as a corrupted compressed stream, an
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* error is printed an the platform's exit() function is called.
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*/
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void gunzip_discard(struct gunzip_state *state, int len)
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{
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static char discard_buf[128];
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while (len > sizeof(discard_buf)) {
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gunzip_exactly(state, discard_buf, sizeof(discard_buf));
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len -= sizeof(discard_buf);
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}
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if (len > 0)
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gunzip_exactly(state, discard_buf, len);
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}
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/**
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* gunzip_finish - extract all remaining bytes from a gzip data stream
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* @state: gzip state structure previously initialized by gunzip_start()
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* @dst: buffer to store extracted data
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* @dstlen: maximum number of bytes to extract
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*
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* This function extracts all remaining data, or at most @dstlen
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* bytes, from the stream previously associated with @state by
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* gunzip_start(). zlib is then shut down, so it is an error to use
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* any of the functions in this file on @state until it is
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* re-initialized with another call to gunzip_start().
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*
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* If any errors occur, such as a corrupted compressed stream, an
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* error is printed an the platform's exit() function is called.
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*/
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int gunzip_finish(struct gunzip_state *state, void *dst, int dstlen)
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{
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int len;
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len = gunzip_partial(state, dst, dstlen);
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if (state->s.workspace) {
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zlib_inflateEnd(&state->s);
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}
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return len;
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}
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