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: head/usr.bin/gzip/unpack.c 194579 2009-06-21 09:39:43Z delphij $
  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 coresponding 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 similiar 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  */
  70 typedef 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 scrubing them.
  96  */
  97 static void
  98 unpack_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  */
 113 static void
 114 unpackd_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 defination.
 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  */
 133 static void
 134 accepted_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 rountine.
 144  *
 145  * Return value is uncompressed size.
 146  */
 147 static void
 148 unpack_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 caculate 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          * Caculate 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  */
 248 static void
 249 unpack_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
 304 finished:
 305         if (bytes_out != unpackd->uncompressed_size)
 306                 maybe_errx("Premature EOF");
 307 }
 308
 309 /* Handler for pack(1)'ed file */
 310 static off_t
 311 unpack(int in, int out, char *pre, size_t prelen, off_t *bytes_in)
 312 {
 313         unpack_descriptor_t     unpackd;
 314
 315         unpack_parse_header(dup(in), dup(out), pre, prelen, bytes_in, &unpackd);
 316         unpack_decode(&unpackd, bytes_in);
 317         unpack_descriptor_fini(&unpackd);
 318
 319         /* If we reached here, the unpack was successful */
 320         return (unpackd.uncompressed_size);
 321 }