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Diffstat (limited to 'file_cmds/gzip/unpack.c')
| -rw-r--r-- | file_cmds/gzip/unpack.c | 329 |
1 files changed, 329 insertions, 0 deletions
diff --git a/file_cmds/gzip/unpack.c b/file_cmds/gzip/unpack.c new file mode 100644 index 0000000..dbad588 --- /dev/null +++ b/file_cmds/gzip/unpack.c @@ -0,0 +1,329 @@ +/*- + * Copyright (c) 2009 Xin LI <delphij@FreeBSD.org> + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + * + * $FreeBSD: src/usr.bin/gzip/unpack.c,v 1.3 2010/10/16 15:24:04 bcr Exp $ + */ + +/* This file is #included by gzip.c */ + +/* + * pack(1) file format: + * + * The first 7 bytes is the header: + * 00, 01 - Signature (US, RS), we already validated it earlier. + * 02..05 - Uncompressed size + * 06 - Level for the huffman tree (<=24) + * + * pack(1) will then store symbols (leaf) nodes count in each huffman + * tree levels, each level would consume 1 byte (See [1]). + * + * After the symbol count table, there is the symbol table, storing + * symbols represented by corresponding leaf node. EOB is not being + * explicitly transmitted (not necessary anyway) in the symbol table. + * + * Compressed data goes after the symbol table. + * + * NOTES + * + * [1] If we count EOB into the symbols, that would mean that we will + * have at most 256 symbols in the huffman tree. pack(1) rejects empty + * file and files that just repeats one character, which means that we + * will have at least 2 symbols. Therefore, pack(1) would reduce the + * last level symbol count by 2 which makes it a number in + * range [0..254], so all levels' symbol count would fit into 1 byte. + */ + +#define PACK_HEADER_LENGTH 7 +#define HTREE_MAXLEVEL 24 + +/* + * unpack descriptor + * + * Represent the huffman tree in a similar way that pack(1) would + * store in a packed file. We store all symbols in a linear table, + * and store pointers to each level's first symbol. In addition to + * that, maintain two counts for each level: inner nodes count and + * leaf nodes count. + */ +typedef struct { + int symbol_size; /* Size of the symbol table */ + int treelevels; /* Levels for the huffman tree */ + + int *symbolsin; /* Table of leaf symbols count in + each level */ + int *inodesin; /* Table of internal nodes count in + each level */ + + char *symbol; /* The symbol table */ + char *symbol_eob; /* Pointer to the EOB symbol */ + char **tree; /* Decoding huffman tree (pointers to + first symbol of each tree level */ + + off_t uncompressed_size; /* Uncompressed size */ + FILE *fpIn; /* Input stream */ + FILE *fpOut; /* Output stream */ +} unpack_descriptor_t; + +/* + * Release resource allocated to an unpack descriptor. + * + * Caller is responsible to make sure that all of these pointers are + * initialized (in our case, they all point to valid memory block). + * We don't zero out pointers here because nobody else would ever + * reference the memory block without scrubbing them. + */ +static void +unpack_descriptor_fini(unpack_descriptor_t *unpackd) +{ + + free(unpackd->symbolsin); + free(unpackd->inodesin); + free(unpackd->symbol); + free(unpackd->tree); + + fclose(unpackd->fpIn); + fclose(unpackd->fpOut); +} + +/* + * Recursively fill the internal node count table + */ +static void +unpackd_fill_inodesin(const unpack_descriptor_t *unpackd, int level) +{ + + /* + * The internal nodes would be 1/2 of total internal nodes and + * leaf nodes in the next level. For the last level there + * would be no internal node by definition. + */ + if (level < unpackd->treelevels) { + unpackd_fill_inodesin(unpackd, level + 1); + unpackd->inodesin[level] = (unpackd->inodesin[level + 1] + + unpackd->symbolsin[level + 1]) / 2; + } else + unpackd->inodesin[level] = 0; +} + +/* + * Update counter for accepted bytes + */ +static void +accepted_bytes(off_t *bytes_in, off_t newbytes) +{ + + if (bytes_in != NULL) + (*bytes_in) += newbytes; +} + +/* + * Read file header and construct the tree. Also, prepare the buffered I/O + * for decode routine. + * + * Return value is uncompressed size. + */ +static void +unpack_parse_header(int in, int out, char *pre, size_t prelen, off_t *bytes_in, + unpack_descriptor_t *unpackd) +{ + unsigned char hdr[PACK_HEADER_LENGTH]; /* buffer for header */ + ssize_t bytesread; /* Bytes read from the file */ + int i, j, thisbyte; + + /* Prepend the header buffer if we already read some data */ + if (prelen != 0) + memcpy(hdr, pre, prelen); + + /* Read in and fill the rest bytes of header */ + bytesread = read(in, hdr + prelen, PACK_HEADER_LENGTH - prelen); + if (bytesread < 0) + maybe_err("Error reading pack header"); + + accepted_bytes(bytes_in, PACK_HEADER_LENGTH); + + /* Obtain uncompressed length (bytes 2,3,4,5)*/ + unpackd->uncompressed_size = 0; + for (i = 2; i <= 5; i++) { + unpackd->uncompressed_size <<= 8; + unpackd->uncompressed_size |= hdr[i]; + } + + /* Get the levels of the tree */ + unpackd->treelevels = hdr[6]; + if (unpackd->treelevels > HTREE_MAXLEVEL || unpackd->treelevels < 1) + maybe_errx("Huffman tree has insane levels"); + + /* Let libc take care for buffering from now on */ + if ((unpackd->fpIn = fdopen(in, "r")) == NULL) + maybe_err("Can not fdopen() input stream"); + if ((unpackd->fpOut = fdopen(out, "w")) == NULL) + maybe_err("Can not fdopen() output stream"); + + /* Allocate for the tables of bounds and the tree itself */ + unpackd->inodesin = + calloc(unpackd->treelevels, sizeof(*(unpackd->inodesin))); + unpackd->symbolsin = + calloc(unpackd->treelevels, sizeof(*(unpackd->symbolsin))); + unpackd->tree = + calloc(unpackd->treelevels, (sizeof (*(unpackd->tree)))); + if (unpackd->inodesin == NULL || unpackd->symbolsin == NULL || + unpackd->tree == NULL) + maybe_err("calloc"); + + /* We count from 0 so adjust to match array upper bound */ + unpackd->treelevels--; + + /* Read the levels symbol count table and calculate total */ + unpackd->symbol_size = 1; /* EOB */ + for (i = 0; i <= unpackd->treelevels; i++) { + if ((thisbyte = fgetc(unpackd->fpIn)) == EOF) + maybe_err("File appears to be truncated"); + unpackd->symbolsin[i] = (unsigned char)thisbyte; + unpackd->symbol_size += unpackd->symbolsin[i]; + } + accepted_bytes(bytes_in, unpackd->treelevels); + if (unpackd->symbol_size > 256) + maybe_errx("Bad symbol table"); + + /* Allocate for the symbol table, point symbol_eob at the beginning */ + unpackd->symbol_eob = unpackd->symbol = calloc(1, unpackd->symbol_size); + if (unpackd->symbol == NULL) + maybe_err("calloc"); + + /* + * Read in the symbol table, which contain [2, 256] symbols. + * In order to fit the count in one byte, pack(1) would offset + * it by reducing 2 from the actual number from the last level. + * + * We adjust the last level's symbol count by 1 here, because + * the EOB symbol is not being transmitted explicitly. Another + * adjustment would be done later afterward. + */ + unpackd->symbolsin[unpackd->treelevels]++; + for (i = 0; i <= unpackd->treelevels; i++) { + unpackd->tree[i] = unpackd->symbol_eob; + for (j = 0; j < unpackd->symbolsin[i]; j++) { + if ((thisbyte = fgetc(unpackd->fpIn)) == EOF) + maybe_errx("Symbol table truncated"); + *unpackd->symbol_eob++ = (char)thisbyte; + } + accepted_bytes(bytes_in, unpackd->symbolsin[i]); + } + + /* Now, take account for the EOB symbol as well */ + unpackd->symbolsin[unpackd->treelevels]++; + + /* + * The symbolsin table has been constructed now. + * Calculate the internal nodes count table based on it. + */ + unpackd_fill_inodesin(unpackd, 0); +} + +/* + * Decode huffman stream, based on the huffman tree. + */ +static void +unpack_decode(const unpack_descriptor_t *unpackd, off_t *bytes_in) +{ + int thislevel, thiscode, thisbyte, inlevelindex; + int i; + off_t bytes_out = 0; + const char *thissymbol; /* The symbol pointer decoded from stream */ + + /* + * Decode huffman. Fetch every bytes from the file, get it + * into 'thiscode' bit-by-bit, then output the symbol we got + * when one has been found. + * + * Assumption: sizeof(int) > ((max tree levels + 1) / 8). + * bad things could happen if not. + */ + thislevel = 0; + thiscode = thisbyte = 0; + + while ((thisbyte = fgetc(unpackd->fpIn)) != EOF) { + accepted_bytes(bytes_in, 1); + + /* + * Split one bit from thisbyte, from highest to lowest, + * feed the bit into thiscode, until we got a symbol from + * the tree. + */ + for (i = 7; i >= 0; i--) { + thiscode = (thiscode << 1) | ((thisbyte >> i) & 1); + + /* Did we got a symbol? (referencing leaf node) */ + if (thiscode >= unpackd->inodesin[thislevel]) { + inlevelindex = + thiscode - unpackd->inodesin[thislevel]; + if (inlevelindex > unpackd->symbolsin[thislevel]) + maybe_errx("File corrupt"); + + thissymbol = + &(unpackd->tree[thislevel][inlevelindex]); + if ((thissymbol == unpackd->symbol_eob) && + (bytes_out == unpackd->uncompressed_size)) + goto finished; + + fputc((*thissymbol), unpackd->fpOut); + bytes_out++; + + /* Prepare for next input */ + thislevel = 0; thiscode = 0; + } else { + thislevel++; + if (thislevel > unpackd->treelevels) + maybe_errx("File corrupt"); + } + } + } + +finished: + if (bytes_out != unpackd->uncompressed_size) + maybe_errx("Premature EOF"); +} + +/* Handler for pack(1)'ed file */ +static off_t +unpack(int in, int out, char *pre, size_t prelen, off_t *bytes_in) +{ + unpack_descriptor_t unpackd; + + in = dup(in); + if (in == -1) + maybe_err("dup"); + out = dup(out); + if (out == -1) + maybe_err("dup"); + + unpack_parse_header(in, out, pre, prelen, bytes_in, &unpackd); + unpack_decode(&unpackd, bytes_in); + unpack_descriptor_fini(&unpackd); + + /* If we reached here, the unpack was successful */ + return (unpackd.uncompressed_size); +} + |