/usr.bin/gzip/unpack.c

  1/*-
  2 * Copyright (c) 2009 Xin LI <delphij@FreeBSD.org>
  3 * All rights reserved.
  4 *
  5 * Redistribution and use in source and binary forms, with or without
  6 * modification, are permitted provided that the following conditions
  7 * are met:
  8 * 1. Redistributions of source code must retain the above copyright
  9 *    notice, this list of conditions and the following disclaimer.
 10 * 2. Redistributions in binary form must reproduce the above copyright
 11 *    notice, this list of conditions and the following disclaimer in the
 12 *    documentation and/or other materials provided with the distribution.
 13 *
 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 24 * SUCH DAMAGE.
 25 *
 26 * $FreeBSD$
 27 */
 28
 29/* This file is #included by gzip.c */
 30
 31/*
 32 * pack(1) file format:
 33 *
 34 * The first 7 bytes is the header:
 35 *	00, 01 - Signature (US, RS), we already validated it earlier.
 36 *	02..05 - Uncompressed size
 37 *	    06 - Level for the huffman tree (<=24)
 38 *
 39 * pack(1) will then store symbols (leaf) nodes count in each huffman
 40 * tree levels, each level would consume 1 byte (See [1]).
 41 *
 42 * After the symbol count table, there is the symbol table, storing
 43 * symbols represented by corresponding leaf node.  EOB is not being
 44 * explicitly transmitted (not necessary anyway) in the symbol table.
 45 *
 46 * Compressed data goes after the symbol table.
 47 *
 48 * NOTES
 49 *
 50 * [1] If we count EOB into the symbols, that would mean that we will
 51 * have at most 256 symbols in the huffman tree.  pack(1) rejects empty
 52 * file and files that just repeats one character, which means that we
 53 * will have at least 2 symbols.  Therefore, pack(1) would reduce the
 54 * last level symbol count by 2 which makes it a number in
 55 * range [0..254], so all levels' symbol count would fit into 1 byte.
 56 */
 57
 58#define	PACK_HEADER_LENGTH	7
 59#define	HTREE_MAXLEVEL		24
 60
 61/*
 62 * unpack descriptor
 63 *
 64 * Represent the huffman tree in a similar way that pack(1) would
 65 * store in a packed file.  We store all symbols in a linear table,
 66 * and store pointers to each level's first symbol.  In addition to
 67 * that, maintain two counts for each level: inner nodes count and
 68 * leaf nodes count.
 69 */
 70typedef struct {
 71	int		symbol_size;	/* Size of the symbol table */
 72	int		treelevels;	/* Levels for the huffman tree */
 73
 74	int		*symbolsin;	/* Table of leaf symbols count in
 75					   each level */
 76	int		*inodesin;	/* Table of internal nodes count in
 77					   each level */
 78
 79	char		*symbol;	/* The symbol table */
 80	char		*symbol_eob;	/* Pointer to the EOB symbol */
 81	char		**tree;		/* Decoding huffman tree (pointers to
 82					   first symbol of each tree level */
 83
 84	off_t		uncompressed_size; /* Uncompressed size */
 85	FILE		*fpIn;		/* Input stream */
 86	FILE		*fpOut;		/* Output stream */
 87} unpack_descriptor_t;
 88
 89/*
 90 * Release resource allocated to an unpack descriptor.
 91 *
 92 * Caller is responsible to make sure that all of these pointers are
 93 * initialized (in our case, they all point to valid memory block).
 94 * We don't zero out pointers here because nobody else would ever
 95 * reference the memory block without scrubbing them.
 96 */
 97static void
 98unpack_descriptor_fini(unpack_descriptor_t *unpackd)
 99{
100
101	free(unpackd->symbolsin);
102	free(unpackd->inodesin);
103	free(unpackd->symbol);
104	free(unpackd->tree);
105
106	fclose(unpackd->fpIn);
107	fclose(unpackd->fpOut);
108}
109
110/*
111 * Recursively fill the internal node count table
112 */
113static void
114unpackd_fill_inodesin(const unpack_descriptor_t *unpackd, int level)
115{
116
117	/*
118	 * The internal nodes would be 1/2 of total internal nodes and
119	 * leaf nodes in the next level.  For the last level there
120	 * would be no internal node by definition.
121	 */
122	if (level < unpackd->treelevels) {
123		unpackd_fill_inodesin(unpackd, level + 1);
124		unpackd->inodesin[level] = (unpackd->inodesin[level + 1] +
125					  unpackd->symbolsin[level + 1]) / 2;
126	} else
127		unpackd->inodesin[level] = 0;
128}
129
130/*
131 * Update counter for accepted bytes
132 */
133static void
134accepted_bytes(off_t *bytes_in, off_t newbytes)
135{
136
137	if (bytes_in != NULL)
138		(*bytes_in) += newbytes;
139}
140
141/*
142 * Read file header and construct the tree.  Also, prepare the buffered I/O
143 * for decode routine.
144 *
145 * Return value is uncompressed size.
146 */
147static void
148unpack_parse_header(int in, int out, char *pre, size_t prelen, off_t *bytes_in,
149    unpack_descriptor_t *unpackd)
150{
151	unsigned char hdr[PACK_HEADER_LENGTH];	/* buffer for header */
152	ssize_t bytesread;		/* Bytes read from the file */
153	int i, j, thisbyte;
154
155	/* Prepend the header buffer if we already read some data */
156	if (prelen != 0)
157		memcpy(hdr, pre, prelen);
158
159	/* Read in and fill the rest bytes of header */
160	bytesread = read(in, hdr + prelen, PACK_HEADER_LENGTH - prelen);
161	if (bytesread < 0)
162		maybe_err("Error reading pack header");
163
164	accepted_bytes(bytes_in, PACK_HEADER_LENGTH);
165
166	/* Obtain uncompressed length (bytes 2,3,4,5)*/
167	unpackd->uncompressed_size = 0;
168	for (i = 2; i <= 5; i++) {
169		unpackd->uncompressed_size <<= 8;
170		unpackd->uncompressed_size |= hdr[i];
171	}
172
173	/* Get the levels of the tree */
174	unpackd->treelevels = hdr[6];
175	if (unpackd->treelevels > HTREE_MAXLEVEL || unpackd->treelevels < 1)
176		maybe_errx("Huffman tree has insane levels");
177
178	/* Let libc take care for buffering from now on */
179	if ((unpackd->fpIn = fdopen(in, "r")) == NULL)
180		maybe_err("Can not fdopen() input stream");
181	if ((unpackd->fpOut = fdopen(out, "w")) == NULL)
182		maybe_err("Can not fdopen() output stream");
183
184	/* Allocate for the tables of bounds and the tree itself */
185	unpackd->inodesin =
186	    calloc(unpackd->treelevels, sizeof(*(unpackd->inodesin)));
187	unpackd->symbolsin =
188	    calloc(unpackd->treelevels, sizeof(*(unpackd->symbolsin)));
189	unpackd->tree =
190	    calloc(unpackd->treelevels, (sizeof (*(unpackd->tree))));
191	if (unpackd->inodesin == NULL || unpackd->symbolsin == NULL ||
192	    unpackd->tree == NULL)
193		maybe_err("calloc");
194
195	/* We count from 0 so adjust to match array upper bound */
196	unpackd->treelevels--;
197
198	/* Read the levels symbol count table and calculate total */
199	unpackd->symbol_size = 1;		/* EOB */
200	for (i = 0; i <= unpackd->treelevels; i++) {
201		if ((thisbyte = fgetc(unpackd->fpIn)) == EOF)
202			maybe_err("File appears to be truncated");
203		unpackd->symbolsin[i] = (unsigned char)thisbyte;
204		unpackd->symbol_size += unpackd->symbolsin[i];
205	}
206	accepted_bytes(bytes_in, unpackd->treelevels);
207	if (unpackd->symbol_size > 256)
208		maybe_errx("Bad symbol table");
209
210	/* Allocate for the symbol table, point symbol_eob at the beginning */
211	unpackd->symbol_eob = unpackd->symbol = calloc(1, unpackd->symbol_size);
212	if (unpackd->symbol == NULL)
213		maybe_err("calloc");
214
215	/*
216	 * Read in the symbol table, which contain [2, 256] symbols.
217	 * In order to fit the count in one byte, pack(1) would offset
218	 * it by reducing 2 from the actual number from the last level.
219	 *
220	 * We adjust the last level's symbol count by 1 here, because
221	 * the EOB symbol is not being transmitted explicitly.  Another
222	 * adjustment would be done later afterward.
223	 */
224	unpackd->symbolsin[unpackd->treelevels]++;
225	for (i = 0; i <= unpackd->treelevels; i++) {
226		unpackd->tree[i] = unpackd->symbol_eob;
227		for (j = 0; j < unpackd->symbolsin[i]; j++) {
228			if ((thisbyte = fgetc(unpackd->fpIn)) == EOF)
229				maybe_errx("Symbol table truncated");
230			*unpackd->symbol_eob++ = (char)thisbyte;
231		}
232		accepted_bytes(bytes_in, unpackd->symbolsin[i]);
233	}
234
235	/* Now, take account for the EOB symbol as well */
236	unpackd->symbolsin[unpackd->treelevels]++;
237
238	/*
239	 * The symbolsin table has been constructed now.
240	 * Calculate the internal nodes count table based on it.
241	 */
242	unpackd_fill_inodesin(unpackd, 0);
243}
244
245/*
246 * Decode huffman stream, based on the huffman tree.
247 */
248static void
249unpack_decode(const unpack_descriptor_t *unpackd, off_t *bytes_in)
250{
251	int thislevel, thiscode, thisbyte, inlevelindex;
252	int i;
253	off_t bytes_out = 0;
254	const char *thissymbol;	/* The symbol pointer decoded from stream */
255
256	/*
257	 * Decode huffman.  Fetch every bytes from the file, get it
258	 * into 'thiscode' bit-by-bit, then output the symbol we got
259	 * when one has been found.
260	 *
261	 * Assumption: sizeof(int) > ((max tree levels + 1) / 8).
262	 * bad things could happen if not.
263	 */
264	thislevel = 0;
265	thiscode = thisbyte = 0;
266
267	while ((thisbyte = fgetc(unpackd->fpIn)) != EOF) {
268		accepted_bytes(bytes_in, 1);
269
270		/*
271		 * Split one bit from thisbyte, from highest to lowest,
272		 * feed the bit into thiscode, until we got a symbol from
273		 * the tree.
274		 */
275		for (i = 7; i >= 0; i--) {
276			thiscode = (thiscode << 1) | ((thisbyte >> i) & 1);
277
278			/* Did we got a symbol? (referencing leaf node) */
279			if (thiscode >= unpackd->inodesin[thislevel]) {
280				inlevelindex =
281				    thiscode - unpackd->inodesin[thislevel];
282				if (inlevelindex > unpackd->symbolsin[thislevel])
283					maybe_errx("File corrupt");
284
285				thissymbol =
286				    &(unpackd->tree[thislevel][inlevelindex]);
287				if ((thissymbol == unpackd->symbol_eob) &&
288				    (bytes_out == unpackd->uncompressed_size))
289					goto finished;
290
291				fputc((*thissymbol), unpackd->fpOut);
292				bytes_out++;
293
294				/* Prepare for next input */
295				thislevel = 0; thiscode = 0;
296			} else {
297				thislevel++;
298				if (thislevel > unpackd->treelevels)
299					maybe_errx("File corrupt");
300			}
301		}
302	}
303
304finished:
305	if (bytes_out != unpackd->uncompressed_size)
306		maybe_errx("Premature EOF");
307}
308
309/* Handler for pack(1)'ed file */
310static off_t
311unpack(int in, int out, char *pre, size_t prelen, off_t *bytes_in)
312{
313	unpack_descriptor_t	unpackd;
314
315	in = dup(in);
316	if (in == -1)
317		maybe_err("dup");
318	out = dup(out);
319	if (out == -1)
320		maybe_err("dup");
321
322	unpack_parse_header(in, out, pre, prelen, bytes_in, &unpackd);
323	unpack_decode(&unpackd, bytes_in);
324	unpack_descriptor_fini(&unpackd);
325
326	/* If we reached here, the unpack was successful */
327	return (unpackd.uncompressed_size);
328}
329