aboutsummaryrefslogtreecommitdiff
path: root/tools/plink/sshzlib.c
diff options
context:
space:
mode:
Diffstat (limited to 'tools/plink/sshzlib.c')
-rw-r--r--tools/plink/sshzlib.c2779
1 files changed, 1394 insertions, 1385 deletions
diff --git a/tools/plink/sshzlib.c b/tools/plink/sshzlib.c
index 9c780a41f..8a64e3563 100644
--- a/tools/plink/sshzlib.c
+++ b/tools/plink/sshzlib.c
@@ -1,1385 +1,1394 @@
-/*
- * Zlib (RFC1950 / RFC1951) compression for PuTTY.
- *
- * There will no doubt be criticism of my decision to reimplement
- * Zlib compression from scratch instead of using the existing zlib
- * code. People will cry `reinventing the wheel'; they'll claim
- * that the `fundamental basis of OSS' is code reuse; they'll want
- * to see a really good reason for me having chosen not to use the
- * existing code.
- *
- * Well, here are my reasons. Firstly, I don't want to link the
- * whole of zlib into the PuTTY binary; PuTTY is justifiably proud
- * of its small size and I think zlib contains a lot of unnecessary
- * baggage for the kind of compression that SSH requires.
- *
- * Secondly, I also don't like the alternative of using zlib.dll.
- * Another thing PuTTY is justifiably proud of is its ease of
- * installation, and the last thing I want to do is to start
- * mandating DLLs. Not only that, but there are two _kinds_ of
- * zlib.dll kicking around, one with C calling conventions on the
- * exported functions and another with WINAPI conventions, and
- * there would be a significant danger of getting the wrong one.
- *
- * Thirdly, there seems to be a difference of opinion on the IETF
- * secsh mailing list about the correct way to round off a
- * compressed packet and start the next. In particular, there's
- * some talk of switching to a mechanism zlib isn't currently
- * capable of supporting (see below for an explanation). Given that
- * sort of uncertainty, I thought it might be better to have code
- * that will support even the zlib-incompatible worst case.
- *
- * Fourthly, it's a _second implementation_. Second implementations
- * are fundamentally a Good Thing in standardisation efforts. The
- * difference of opinion mentioned above has arisen _precisely_
- * because there has been only one zlib implementation and
- * everybody has used it. I don't intend that this should happen
- * again.
- */
-
-#include <stdlib.h>
-#include <assert.h>
-
-#ifdef ZLIB_STANDALONE
-
-/*
- * This module also makes a handy zlib decoding tool for when
- * you're picking apart Zip files or PDFs or PNGs. If you compile
- * it with ZLIB_STANDALONE defined, it builds on its own and
- * becomes a command-line utility.
- *
- * Therefore, here I provide a self-contained implementation of the
- * macros required from the rest of the PuTTY sources.
- */
-#define snew(type) ( (type *) malloc(sizeof(type)) )
-#define snewn(n, type) ( (type *) malloc((n) * sizeof(type)) )
-#define sresize(x, n, type) ( (type *) realloc((x), (n) * sizeof(type)) )
-#define sfree(x) ( free((x)) )
-
-#else
-#include "ssh.h"
-#endif
-
-#ifndef FALSE
-#define FALSE 0
-#define TRUE (!FALSE)
-#endif
-
-/* ----------------------------------------------------------------------
- * Basic LZ77 code. This bit is designed modularly, so it could be
- * ripped out and used in a different LZ77 compressor. Go to it,
- * and good luck :-)
- */
-
-struct LZ77InternalContext;
-struct LZ77Context {
- struct LZ77InternalContext *ictx;
- void *userdata;
- void (*literal) (struct LZ77Context * ctx, unsigned char c);
- void (*match) (struct LZ77Context * ctx, int distance, int len);
-};
-
-/*
- * Initialise the private fields of an LZ77Context. It's up to the
- * user to initialise the public fields.
- */
-static int lz77_init(struct LZ77Context *ctx);
-
-/*
- * Supply data to be compressed. Will update the private fields of
- * the LZ77Context, and will call literal() and match() to output.
- * If `compress' is FALSE, it will never emit a match, but will
- * instead call literal() for everything.
- */
-static void lz77_compress(struct LZ77Context *ctx,
- unsigned char *data, int len, int compress);
-
-/*
- * Modifiable parameters.
- */
-#define WINSIZE 32768 /* window size. Must be power of 2! */
-#define HASHMAX 2039 /* one more than max hash value */
-#define MAXMATCH 32 /* how many matches we track */
-#define HASHCHARS 3 /* how many chars make a hash */
-
-/*
- * This compressor takes a less slapdash approach than the
- * gzip/zlib one. Rather than allowing our hash chains to fall into
- * disuse near the far end, we keep them doubly linked so we can
- * _find_ the far end, and then every time we add a new byte to the
- * window (thus rolling round by one and removing the previous
- * byte), we can carefully remove the hash chain entry.
- */
-
-#define INVALID -1 /* invalid hash _and_ invalid offset */
-struct WindowEntry {
- short next, prev; /* array indices within the window */
- short hashval;
-};
-
-struct HashEntry {
- short first; /* window index of first in chain */
-};
-
-struct Match {
- int distance, len;
-};
-
-struct LZ77InternalContext {
- struct WindowEntry win[WINSIZE];
- unsigned char data[WINSIZE];
- int winpos;
- struct HashEntry hashtab[HASHMAX];
- unsigned char pending[HASHCHARS];
- int npending;
-};
-
-static int lz77_hash(unsigned char *data)
-{
- return (257 * data[0] + 263 * data[1] + 269 * data[2]) % HASHMAX;
-}
-
-static int lz77_init(struct LZ77Context *ctx)
-{
- struct LZ77InternalContext *st;
- int i;
-
- st = snew(struct LZ77InternalContext);
- if (!st)
- return 0;
-
- ctx->ictx = st;
-
- for (i = 0; i < WINSIZE; i++)
- st->win[i].next = st->win[i].prev = st->win[i].hashval = INVALID;
- for (i = 0; i < HASHMAX; i++)
- st->hashtab[i].first = INVALID;
- st->winpos = 0;
-
- st->npending = 0;
-
- return 1;
-}
-
-static void lz77_advance(struct LZ77InternalContext *st,
- unsigned char c, int hash)
-{
- int off;
-
- /*
- * Remove the hash entry at winpos from the tail of its chain,
- * or empty the chain if it's the only thing on the chain.
- */
- if (st->win[st->winpos].prev != INVALID) {
- st->win[st->win[st->winpos].prev].next = INVALID;
- } else if (st->win[st->winpos].hashval != INVALID) {
- st->hashtab[st->win[st->winpos].hashval].first = INVALID;
- }
-
- /*
- * Create a new entry at winpos and add it to the head of its
- * hash chain.
- */
- st->win[st->winpos].hashval = hash;
- st->win[st->winpos].prev = INVALID;
- off = st->win[st->winpos].next = st->hashtab[hash].first;
- st->hashtab[hash].first = st->winpos;
- if (off != INVALID)
- st->win[off].prev = st->winpos;
- st->data[st->winpos] = c;
-
- /*
- * Advance the window pointer.
- */
- st->winpos = (st->winpos + 1) & (WINSIZE - 1);
-}
-
-#define CHARAT(k) ( (k)<0 ? st->data[(st->winpos+k)&(WINSIZE-1)] : data[k] )
-
-static void lz77_compress(struct LZ77Context *ctx,
- unsigned char *data, int len, int compress)
-{
- struct LZ77InternalContext *st = ctx->ictx;
- int i, hash, distance, off, nmatch, matchlen, advance;
- struct Match defermatch, matches[MAXMATCH];
- int deferchr;
-
- /*
- * Add any pending characters from last time to the window. (We
- * might not be able to.)
- */
- for (i = 0; i < st->npending; i++) {
- unsigned char foo[HASHCHARS];
- int j;
- if (len + st->npending - i < HASHCHARS) {
- /* Update the pending array. */
- for (j = i; j < st->npending; j++)
- st->pending[j - i] = st->pending[j];
- break;
- }
- for (j = 0; j < HASHCHARS; j++)
- foo[j] = (i + j < st->npending ? st->pending[i + j] :
- data[i + j - st->npending]);
- lz77_advance(st, foo[0], lz77_hash(foo));
- }
- st->npending -= i;
-
- defermatch.distance = 0; /* appease compiler */
- defermatch.len = 0;
- deferchr = '\0';
- while (len > 0) {
-
- /* Don't even look for a match, if we're not compressing. */
- if (compress && len >= HASHCHARS) {
- /*
- * Hash the next few characters.
- */
- hash = lz77_hash(data);
-
- /*
- * Look the hash up in the corresponding hash chain and see
- * what we can find.
- */
- nmatch = 0;
- for (off = st->hashtab[hash].first;
- off != INVALID; off = st->win[off].next) {
- /* distance = 1 if off == st->winpos-1 */
- /* distance = WINSIZE if off == st->winpos */
- distance =
- WINSIZE - (off + WINSIZE - st->winpos) % WINSIZE;
- for (i = 0; i < HASHCHARS; i++)
- if (CHARAT(i) != CHARAT(i - distance))
- break;
- if (i == HASHCHARS) {
- matches[nmatch].distance = distance;
- matches[nmatch].len = 3;
- if (++nmatch >= MAXMATCH)
- break;
- }
- }
- } else {
- nmatch = 0;
- hash = INVALID;
- }
-
- if (nmatch > 0) {
- /*
- * We've now filled up matches[] with nmatch potential
- * matches. Follow them down to find the longest. (We
- * assume here that it's always worth favouring a
- * longer match over a shorter one.)
- */
- matchlen = HASHCHARS;
- while (matchlen < len) {
- int j;
- for (i = j = 0; i < nmatch; i++) {
- if (CHARAT(matchlen) ==
- CHARAT(matchlen - matches[i].distance)) {
- matches[j++] = matches[i];
- }
- }
- if (j == 0)
- break;
- matchlen++;
- nmatch = j;
- }
-
- /*
- * We've now got all the longest matches. We favour the
- * shorter distances, which means we go with matches[0].
- * So see if we want to defer it or throw it away.
- */
- matches[0].len = matchlen;
- if (defermatch.len > 0) {
- if (matches[0].len > defermatch.len + 1) {
- /* We have a better match. Emit the deferred char,
- * and defer this match. */
- ctx->literal(ctx, (unsigned char) deferchr);
- defermatch = matches[0];
- deferchr = data[0];
- advance = 1;
- } else {
- /* We don't have a better match. Do the deferred one. */
- ctx->match(ctx, defermatch.distance, defermatch.len);
- advance = defermatch.len - 1;
- defermatch.len = 0;
- }
- } else {
- /* There was no deferred match. Defer this one. */
- defermatch = matches[0];
- deferchr = data[0];
- advance = 1;
- }
- } else {
- /*
- * We found no matches. Emit the deferred match, if
- * any; otherwise emit a literal.
- */
- if (defermatch.len > 0) {
- ctx->match(ctx, defermatch.distance, defermatch.len);
- advance = defermatch.len - 1;
- defermatch.len = 0;
- } else {
- ctx->literal(ctx, data[0]);
- advance = 1;
- }
- }
-
- /*
- * Now advance the position by `advance' characters,
- * keeping the window and hash chains consistent.
- */
- while (advance > 0) {
- if (len >= HASHCHARS) {
- lz77_advance(st, *data, lz77_hash(data));
- } else {
- st->pending[st->npending++] = *data;
- }
- data++;
- len--;
- advance--;
- }
- }
-}
-
-/* ----------------------------------------------------------------------
- * Zlib compression. We always use the static Huffman tree option.
- * Mostly this is because it's hard to scan a block in advance to
- * work out better trees; dynamic trees are great when you're
- * compressing a large file under no significant time constraint,
- * but when you're compressing little bits in real time, things get
- * hairier.
- *
- * I suppose it's possible that I could compute Huffman trees based
- * on the frequencies in the _previous_ block, as a sort of
- * heuristic, but I'm not confident that the gain would balance out
- * having to transmit the trees.
- */
-
-struct Outbuf {
- unsigned char *outbuf;
- int outlen, outsize;
- unsigned long outbits;
- int noutbits;
- int firstblock;
- int comp_disabled;
-};
-
-static void outbits(struct Outbuf *out, unsigned long bits, int nbits)
-{
- assert(out->noutbits + nbits <= 32);
- out->outbits |= bits << out->noutbits;
- out->noutbits += nbits;
- while (out->noutbits >= 8) {
- if (out->outlen >= out->outsize) {
- out->outsize = out->outlen + 64;
- out->outbuf = sresize(out->outbuf, out->outsize, unsigned char);
- }
- out->outbuf[out->outlen++] = (unsigned char) (out->outbits & 0xFF);
- out->outbits >>= 8;
- out->noutbits -= 8;
- }
-}
-
-static const unsigned char mirrorbytes[256] = {
- 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
- 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
- 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
- 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
- 0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
- 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
- 0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
- 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
- 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
- 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
- 0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
- 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
- 0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
- 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
- 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
- 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
- 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
- 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
- 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
- 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
- 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
- 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
- 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
- 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
- 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
- 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
- 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
- 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
- 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
- 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
- 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
- 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
-};
-
-typedef struct {
- short code, extrabits;
- int min, max;
-} coderecord;
-
-static const coderecord lencodes[] = {
- {257, 0, 3, 3},
- {258, 0, 4, 4},
- {259, 0, 5, 5},
- {260, 0, 6, 6},
- {261, 0, 7, 7},
- {262, 0, 8, 8},
- {263, 0, 9, 9},
- {264, 0, 10, 10},
- {265, 1, 11, 12},
- {266, 1, 13, 14},
- {267, 1, 15, 16},
- {268, 1, 17, 18},
- {269, 2, 19, 22},
- {270, 2, 23, 26},
- {271, 2, 27, 30},
- {272, 2, 31, 34},
- {273, 3, 35, 42},
- {274, 3, 43, 50},
- {275, 3, 51, 58},
- {276, 3, 59, 66},
- {277, 4, 67, 82},
- {278, 4, 83, 98},
- {279, 4, 99, 114},
- {280, 4, 115, 130},
- {281, 5, 131, 162},
- {282, 5, 163, 194},
- {283, 5, 195, 226},
- {284, 5, 227, 257},
- {285, 0, 258, 258},
-};
-
-static const coderecord distcodes[] = {
- {0, 0, 1, 1},
- {1, 0, 2, 2},
- {2, 0, 3, 3},
- {3, 0, 4, 4},
- {4, 1, 5, 6},
- {5, 1, 7, 8},
- {6, 2, 9, 12},
- {7, 2, 13, 16},
- {8, 3, 17, 24},
- {9, 3, 25, 32},
- {10, 4, 33, 48},
- {11, 4, 49, 64},
- {12, 5, 65, 96},
- {13, 5, 97, 128},
- {14, 6, 129, 192},
- {15, 6, 193, 256},
- {16, 7, 257, 384},
- {17, 7, 385, 512},
- {18, 8, 513, 768},
- {19, 8, 769, 1024},
- {20, 9, 1025, 1536},
- {21, 9, 1537, 2048},
- {22, 10, 2049, 3072},
- {23, 10, 3073, 4096},
- {24, 11, 4097, 6144},
- {25, 11, 6145, 8192},
- {26, 12, 8193, 12288},
- {27, 12, 12289, 16384},
- {28, 13, 16385, 24576},
- {29, 13, 24577, 32768},
-};
-
-static void zlib_literal(struct LZ77Context *ectx, unsigned char c)
-{
- struct Outbuf *out = (struct Outbuf *) ectx->userdata;
-
- if (out->comp_disabled) {
- /*
- * We're in an uncompressed block, so just output the byte.
- */
- outbits(out, c, 8);
- return;
- }
-
- if (c <= 143) {
- /* 0 through 143 are 8 bits long starting at 00110000. */
- outbits(out, mirrorbytes[0x30 + c], 8);
- } else {
- /* 144 through 255 are 9 bits long starting at 110010000. */
- outbits(out, 1 + 2 * mirrorbytes[0x90 - 144 + c], 9);
- }
-}
-
-static void zlib_match(struct LZ77Context *ectx, int distance, int len)
-{
- const coderecord *d, *l;
- int i, j, k;
- struct Outbuf *out = (struct Outbuf *) ectx->userdata;
-
- assert(!out->comp_disabled);
-
- while (len > 0) {
- int thislen;
-
- /*
- * We can transmit matches of lengths 3 through 258
- * inclusive. So if len exceeds 258, we must transmit in
- * several steps, with 258 or less in each step.
- *
- * Specifically: if len >= 261, we can transmit 258 and be
- * sure of having at least 3 left for the next step. And if
- * len <= 258, we can just transmit len. But if len == 259
- * or 260, we must transmit len-3.
- */
- thislen = (len > 260 ? 258 : len <= 258 ? len : len - 3);
- len -= thislen;
-
- /*
- * Binary-search to find which length code we're
- * transmitting.
- */
- i = -1;
- j = sizeof(lencodes) / sizeof(*lencodes);
- while (1) {
- assert(j - i >= 2);
- k = (j + i) / 2;
- if (thislen < lencodes[k].min)
- j = k;
- else if (thislen > lencodes[k].max)
- i = k;
- else {
- l = &lencodes[k];
- break; /* found it! */
- }
- }
-
- /*
- * Transmit the length code. 256-279 are seven bits
- * starting at 0000000; 280-287 are eight bits starting at
- * 11000000.
- */
- if (l->code <= 279) {
- outbits(out, mirrorbytes[(l->code - 256) * 2], 7);
- } else {
- outbits(out, mirrorbytes[0xc0 - 280 + l->code], 8);
- }
-
- /*
- * Transmit the extra bits.
- */
- if (l->extrabits)
- outbits(out, thislen - l->min, l->extrabits);
-
- /*
- * Binary-search to find which distance code we're
- * transmitting.
- */
- i = -1;
- j = sizeof(distcodes) / sizeof(*distcodes);
- while (1) {
- assert(j - i >= 2);
- k = (j + i) / 2;
- if (distance < distcodes[k].min)
- j = k;
- else if (distance > distcodes[k].max)
- i = k;
- else {
- d = &distcodes[k];
- break; /* found it! */
- }
- }
-
- /*
- * Transmit the distance code. Five bits starting at 00000.
- */
- outbits(out, mirrorbytes[d->code * 8], 5);
-
- /*
- * Transmit the extra bits.
- */
- if (d->extrabits)
- outbits(out, distance - d->min, d->extrabits);
- }
-}
-
-void *zlib_compress_init(void)
-{
- struct Outbuf *out;
- struct LZ77Context *ectx = snew(struct LZ77Context);
-
- lz77_init(ectx);
- ectx->literal = zlib_literal;
- ectx->match = zlib_match;
-
- out = snew(struct Outbuf);
- out->outbits = out->noutbits = 0;
- out->firstblock = 1;
- out->comp_disabled = FALSE;
- ectx->userdata = out;
-
- return ectx;
-}
-
-void zlib_compress_cleanup(void *handle)
-{
- struct LZ77Context *ectx = (struct LZ77Context *)handle;
- sfree(ectx->userdata);
- sfree(ectx->ictx);
- sfree(ectx);
-}
-
-/*
- * Turn off actual LZ77 analysis for one block, to facilitate
- * construction of a precise-length IGNORE packet. Returns the
- * length adjustment (which is only valid for packets < 65536
- * bytes, but that seems reasonable enough).
- */
-static int zlib_disable_compression(void *handle)
-{
- struct LZ77Context *ectx = (struct LZ77Context *)handle;
- struct Outbuf *out = (struct Outbuf *) ectx->userdata;
- int n;
-
- out->comp_disabled = TRUE;
-
- n = 0;
- /*
- * If this is the first block, we will start by outputting two
- * header bytes, and then three bits to begin an uncompressed
- * block. This will cost three bytes (because we will start on
- * a byte boundary, this is certain).
- */
- if (out->firstblock) {
- n = 3;
- } else {
- /*
- * Otherwise, we will output seven bits to close the
- * previous static block, and _then_ three bits to begin an
- * uncompressed block, and then flush the current byte.
- * This may cost two bytes or three, depending on noutbits.
- */
- n += (out->noutbits + 10) / 8;
- }
-
- /*
- * Now we output four bytes for the length / ~length pair in
- * the uncompressed block.
- */
- n += 4;
-
- return n;
-}
-
-int zlib_compress_block(void *handle, unsigned char *block, int len,
- unsigned char **outblock, int *outlen)
-{
- struct LZ77Context *ectx = (struct LZ77Context *)handle;
- struct Outbuf *out = (struct Outbuf *) ectx->userdata;
- int in_block;
-
- out->outbuf = NULL;
- out->outlen = out->outsize = 0;
-
- /*
- * If this is the first block, output the Zlib (RFC1950) header
- * bytes 78 9C. (Deflate compression, 32K window size, default
- * algorithm.)
- */
- if (out->firstblock) {
- outbits(out, 0x9C78, 16);
- out->firstblock = 0;
-
- in_block = FALSE;
- } else
- in_block = TRUE;
-
- if (out->comp_disabled) {
- if (in_block)
- outbits(out, 0, 7); /* close static block */
-
- while (len > 0) {
- int blen = (len < 65535 ? len : 65535);
-
- /*
- * Start a Deflate (RFC1951) uncompressed block. We
- * transmit a zero bit (BFINAL=0), followed by two more
- * zero bits (BTYPE=00). Of course these are in the
- * wrong order (00 0), not that it matters.
- */
- outbits(out, 0, 3);
-
- /*
- * Output zero bits to align to a byte boundary.
- */
- if (out->noutbits)
- outbits(out, 0, 8 - out->noutbits);
-
- /*
- * Output the block length, and then its one's
- * complement. They're little-endian, so all we need to
- * do is pass them straight to outbits() with bit count
- * 16.
- */
- outbits(out, blen, 16);
- outbits(out, blen ^ 0xFFFF, 16);
-
- /*
- * Do the `compression': we need to pass the data to
- * lz77_compress so that it will be taken into account
- * for subsequent (distance,length) pairs. But
- * lz77_compress is passed FALSE, which means it won't
- * actually find (or even look for) any matches; so
- * every character will be passed straight to
- * zlib_literal which will spot out->comp_disabled and
- * emit in the uncompressed format.
- */
- lz77_compress(ectx, block, blen, FALSE);
-
- len -= blen;
- block += blen;
- }
- outbits(out, 2, 3); /* open new block */
- } else {
- if (!in_block) {
- /*
- * Start a Deflate (RFC1951) fixed-trees block. We
- * transmit a zero bit (BFINAL=0), followed by a zero
- * bit and a one bit (BTYPE=01). Of course these are in
- * the wrong order (01 0).
- */
- outbits(out, 2, 3);
- }
-
- /*
- * Do the compression.
- */
- lz77_compress(ectx, block, len, TRUE);
-
- /*
- * End the block (by transmitting code 256, which is
- * 0000000 in fixed-tree mode), and transmit some empty
- * blocks to ensure we have emitted the byte containing the
- * last piece of genuine data. There are three ways we can
- * do this:
- *
- * - Minimal flush. Output end-of-block and then open a
- * new static block. This takes 9 bits, which is
- * guaranteed to flush out the last genuine code in the
- * closed block; but allegedly zlib can't handle it.
- *
- * - Zlib partial flush. Output EOB, open and close an
- * empty static block, and _then_ open the new block.
- * This is the best zlib can handle.
- *
- * - Zlib sync flush. Output EOB, then an empty
- * _uncompressed_ block (000, then sync to byte
- * boundary, then send bytes 00 00 FF FF). Then open the
- * new block.
- *
- * For the moment, we will use Zlib partial flush.
- */
- outbits(out, 0, 7); /* close block */
- outbits(out, 2, 3 + 7); /* empty static block */
- outbits(out, 2, 3); /* open new block */
- }
-
- out->comp_disabled = FALSE;
-
- *outblock = out->outbuf;
- *outlen = out->outlen;
-
- return 1;
-}
-
-/* ----------------------------------------------------------------------
- * Zlib decompression. Of course, even though our compressor always
- * uses static trees, our _decompressor_ has to be capable of
- * handling dynamic trees if it sees them.
- */
-
-/*
- * The way we work the Huffman decode is to have a table lookup on
- * the first N bits of the input stream (in the order they arrive,
- * of course, i.e. the first bit of the Huffman code is in bit 0).
- * Each table entry lists the number of bits to consume, plus
- * either an output code or a pointer to a secondary table.
- */
-struct zlib_table;
-struct zlib_tableentry;
-
-struct zlib_tableentry {
- unsigned char nbits;
- short code;
- struct zlib_table *nexttable;
-};
-
-struct zlib_table {
- int mask; /* mask applied to input bit stream */
- struct zlib_tableentry *table;
-};
-
-#define MAXCODELEN 16
-#define MAXSYMS 288
-
-/*
- * Build a single-level decode table for elements
- * [minlength,maxlength) of the provided code/length tables, and
- * recurse to build subtables.
- */
-static struct zlib_table *zlib_mkonetab(int *codes, unsigned char *lengths,
- int nsyms,
- int pfx, int pfxbits, int bits)
-{
- struct zlib_table *tab = snew(struct zlib_table);
- int pfxmask = (1 << pfxbits) - 1;
- int nbits, i, j, code;
-
- tab->table = snewn(1 << bits, struct zlib_tableentry);
- tab->mask = (1 << bits) - 1;
-
- for (code = 0; code <= tab->mask; code++) {
- tab->table[code].code = -1;
- tab->table[code].nbits = 0;
- tab->table[code].nexttable = NULL;
- }
-
- for (i = 0; i < nsyms; i++) {
- if (lengths[i] <= pfxbits || (codes[i] & pfxmask) != pfx)
- continue;
- code = (codes[i] >> pfxbits) & tab->mask;
- for (j = code; j <= tab->mask; j += 1 << (lengths[i] - pfxbits)) {
- tab->table[j].code = i;
- nbits = lengths[i] - pfxbits;
- if (tab->table[j].nbits < nbits)
- tab->table[j].nbits = nbits;
- }
- }
- for (code = 0; code <= tab->mask; code++) {
- if (tab->table[code].nbits <= bits)
- continue;
- /* Generate a subtable. */
- tab->table[code].code = -1;
- nbits = tab->table[code].nbits - bits;
- if (nbits > 7)
- nbits = 7;
- tab->table[code].nbits = bits;
- tab->table[code].nexttable = zlib_mkonetab(codes, lengths, nsyms,
- pfx | (code << pfxbits),
- pfxbits + bits, nbits);
- }
-
- return tab;
-}
-
-/*
- * Build a decode table, given a set of Huffman tree lengths.
- */
-static struct zlib_table *zlib_mktable(unsigned char *lengths,
- int nlengths)
-{
- int count[MAXCODELEN], startcode[MAXCODELEN], codes[MAXSYMS];
- int code, maxlen;
- int i, j;
-
- /* Count the codes of each length. */
- maxlen = 0;
- for (i = 1; i < MAXCODELEN; i++)
- count[i] = 0;
- for (i = 0; i < nlengths; i++) {
- count[lengths[i]]++;
- if (maxlen < lengths[i])
- maxlen = lengths[i];
- }
- /* Determine the starting code for each length block. */
- code = 0;
- for (i = 1; i < MAXCODELEN; i++) {
- startcode[i] = code;
- code += count[i];
- code <<= 1;
- }
- /* Determine the code for each symbol. Mirrored, of course. */
- for (i = 0; i < nlengths; i++) {
- code = startcode[lengths[i]]++;
- codes[i] = 0;
- for (j = 0; j < lengths[i]; j++) {
- codes[i] = (codes[i] << 1) | (code & 1);
- code >>= 1;
- }
- }
-
- /*
- * Now we have the complete list of Huffman codes. Build a
- * table.
- */
- return zlib_mkonetab(codes, lengths, nlengths, 0, 0,
- maxlen < 9 ? maxlen : 9);
-}
-
-static int zlib_freetable(struct zlib_table **ztab)
-{
- struct zlib_table *tab;
- int code;
-
- if (ztab == NULL)
- return -1;
-
- if (*ztab == NULL)
- return 0;
-
- tab = *ztab;
-
- for (code = 0; code <= tab->mask; code++)
- if (tab->table[code].nexttable != NULL)
- zlib_freetable(&tab->table[code].nexttable);
-
- sfree(tab->table);
- tab->table = NULL;
-
- sfree(tab);
- *ztab = NULL;
-
- return (0);
-}
-
-struct zlib_decompress_ctx {
- struct zlib_table *staticlentable, *staticdisttable;
- struct zlib_table *currlentable, *currdisttable, *lenlentable;
- enum {
- START, OUTSIDEBLK,
- TREES_HDR, TREES_LENLEN, TREES_LEN, TREES_LENREP,
- INBLK, GOTLENSYM, GOTLEN, GOTDISTSYM,
- UNCOMP_LEN, UNCOMP_NLEN, UNCOMP_DATA
- } state;
- int sym, hlit, hdist, hclen, lenptr, lenextrabits, lenaddon, len,
- lenrep;
- int uncomplen;
- unsigned char lenlen[19];
- unsigned char lengths[286 + 32];
- unsigned long bits;
- int nbits;
- unsigned char window[WINSIZE];
- int winpos;
- unsigned char *outblk;
- int outlen, outsize;
-};
-
-void *zlib_decompress_init(void)
-{
- struct zlib_decompress_ctx *dctx = snew(struct zlib_decompress_ctx);
- unsigned char lengths[288];
-
- memset(lengths, 8, 144);
- memset(lengths + 144, 9, 256 - 144);
- memset(lengths + 256, 7, 280 - 256);
- memset(lengths + 280, 8, 288 - 280);
- dctx->staticlentable = zlib_mktable(lengths, 288);
- memset(lengths, 5, 32);
- dctx->staticdisttable = zlib_mktable(lengths, 32);
- dctx->state = START; /* even before header */
- dctx->currlentable = dctx->currdisttable = dctx->lenlentable = NULL;
- dctx->bits = 0;
- dctx->nbits = 0;
- dctx->winpos = 0;
-
- return dctx;
-}
-
-void zlib_decompress_cleanup(void *handle)
-{
- struct zlib_decompress_ctx *dctx = (struct zlib_decompress_ctx *)handle;
-
- if (dctx->currlentable && dctx->currlentable != dctx->staticlentable)
- zlib_freetable(&dctx->currlentable);
- if (dctx->currdisttable && dctx->currdisttable != dctx->staticdisttable)
- zlib_freetable(&dctx->currdisttable);
- if (dctx->lenlentable)
- zlib_freetable(&dctx->lenlentable);
- zlib_freetable(&dctx->staticlentable);
- zlib_freetable(&dctx->staticdisttable);
- sfree(dctx);
-}
-
-static int zlib_huflookup(unsigned long *bitsp, int *nbitsp,
- struct zlib_table *tab)
-{
- unsigned long bits = *bitsp;
- int nbits = *nbitsp;
- while (1) {
- struct zlib_tableentry *ent;
- ent = &tab->table[bits & tab->mask];
- if (ent->nbits > nbits)
- return -1; /* not enough data */
- bits >>= ent->nbits;
- nbits -= ent->nbits;
- if (ent->code == -1)
- tab = ent->nexttable;
- else {
- *bitsp = bits;
- *nbitsp = nbits;
- return ent->code;
- }
-
- if (!tab) {
- /*
- * There was a missing entry in the table, presumably
- * due to an invalid Huffman table description, and the
- * subsequent data has attempted to use the missing
- * entry. Return a decoding failure.
- */
- return -2;
- }
- }
-}
-
-static void zlib_emit_char(struct zlib_decompress_ctx *dctx, int c)
-{
- dctx->window[dctx->winpos] = c;
- dctx->winpos = (dctx->winpos + 1) & (WINSIZE - 1);
- if (dctx->outlen >= dctx->outsize) {
- dctx->outsize = dctx->outlen + 512;
- dctx->outblk = sresize(dctx->outblk, dctx->outsize, unsigned char);
- }
- dctx->outblk[dctx->outlen++] = c;
-}
-
-#define EATBITS(n) ( dctx->nbits -= (n), dctx->bits >>= (n) )
-
-int zlib_decompress_block(void *handle, unsigned char *block, int len,
- unsigned char **outblock, int *outlen)
-{
- struct zlib_decompress_ctx *dctx = (struct zlib_decompress_ctx *)handle;
- const coderecord *rec;
- int code, blktype, rep, dist, nlen, header;
- static const unsigned char lenlenmap[] = {
- 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
- };
-
- dctx->outblk = snewn(256, unsigned char);
- dctx->outsize = 256;
- dctx->outlen = 0;
-
- while (len > 0 || dctx->nbits > 0) {
- while (dctx->nbits < 24 && len > 0) {
- dctx->bits |= (*block++) << dctx->nbits;
- dctx->nbits += 8;
- len--;
- }
- switch (dctx->state) {
- case START:
- /* Expect 16-bit zlib header. */
- if (dctx->nbits < 16)
- goto finished; /* done all we can */
-
- /*
- * The header is stored as a big-endian 16-bit integer,
- * in contrast to the general little-endian policy in
- * the rest of the format :-(
- */
- header = (((dctx->bits & 0xFF00) >> 8) |
- ((dctx->bits & 0x00FF) << 8));
- EATBITS(16);
-
- /*
- * Check the header:
- *
- * - bits 8-11 should be 1000 (Deflate/RFC1951)
- * - bits 12-15 should be at most 0111 (window size)
- * - bit 5 should be zero (no dictionary present)
- * - we don't care about bits 6-7 (compression rate)
- * - bits 0-4 should be set up to make the whole thing
- * a multiple of 31 (checksum).
- */
- if ((header & 0x0F00) != 0x0800 ||
- (header & 0xF000) > 0x7000 ||
- (header & 0x0020) != 0x0000 ||
- (header % 31) != 0)
- goto decode_error;
-
- dctx->state = OUTSIDEBLK;
- break;
- case OUTSIDEBLK:
- /* Expect 3-bit block header. */
- if (dctx->nbits < 3)
- goto finished; /* done all we can */
- EATBITS(1);
- blktype = dctx->bits & 3;
- EATBITS(2);
- if (blktype == 0) {
- int to_eat = dctx->nbits & 7;
- dctx->state = UNCOMP_LEN;
- EATBITS(to_eat); /* align to byte boundary */
- } else if (blktype == 1) {
- dctx->currlentable = dctx->staticlentable;
- dctx->currdisttable = dctx->staticdisttable;
- dctx->state = INBLK;
- } else if (blktype == 2) {
- dctx->state = TREES_HDR;
- }
- break;
- case TREES_HDR:
- /*
- * Dynamic block header. Five bits of HLIT, five of
- * HDIST, four of HCLEN.
- */
- if (dctx->nbits < 5 + 5 + 4)
- goto finished; /* done all we can */
- dctx->hlit = 257 + (dctx->bits & 31);
- EATBITS(5);
- dctx->hdist = 1 + (dctx->bits & 31);
- EATBITS(5);
- dctx->hclen = 4 + (dctx->bits & 15);
- EATBITS(4);
- dctx->lenptr = 0;
- dctx->state = TREES_LENLEN;
- memset(dctx->lenlen, 0, sizeof(dctx->lenlen));
- break;
- case TREES_LENLEN:
- if (dctx->nbits < 3)
- goto finished;
- while (dctx->lenptr < dctx->hclen && dctx->nbits >= 3) {
- dctx->lenlen[lenlenmap[dctx->lenptr++]] =
- (unsigned char) (dctx->bits & 7);
- EATBITS(3);
- }
- if (dctx->lenptr == dctx->hclen) {
- dctx->lenlentable = zlib_mktable(dctx->lenlen, 19);
- dctx->state = TREES_LEN;
- dctx->lenptr = 0;
- }
- break;
- case TREES_LEN:
- if (dctx->lenptr >= dctx->hlit + dctx->hdist) {
- dctx->currlentable = zlib_mktable(dctx->lengths, dctx->hlit);
- dctx->currdisttable = zlib_mktable(dctx->lengths + dctx->hlit,
- dctx->hdist);
- zlib_freetable(&dctx->lenlentable);
- dctx->lenlentable = NULL;
- dctx->state = INBLK;
- break;
- }
- code =
- zlib_huflookup(&dctx->bits, &dctx->nbits, dctx->lenlentable);
- if (code == -1)
- goto finished;
- if (code == -2)
- goto decode_error;
- if (code < 16)
- dctx->lengths[dctx->lenptr++] = code;
- else {
- dctx->lenextrabits = (code == 16 ? 2 : code == 17 ? 3 : 7);
- dctx->lenaddon = (code == 18 ? 11 : 3);
- dctx->lenrep = (code == 16 && dctx->lenptr > 0 ?
- dctx->lengths[dctx->lenptr - 1] : 0);
- dctx->state = TREES_LENREP;
- }
- break;
- case TREES_LENREP:
- if (dctx->nbits < dctx->lenextrabits)
- goto finished;
- rep =
- dctx->lenaddon +
- (dctx->bits & ((1 << dctx->lenextrabits) - 1));
- EATBITS(dctx->lenextrabits);
- while (rep > 0 && dctx->lenptr < dctx->hlit + dctx->hdist) {
- dctx->lengths[dctx->lenptr] = dctx->lenrep;
- dctx->lenptr++;
- rep--;
- }
- dctx->state = TREES_LEN;
- break;
- case INBLK:
- code =
- zlib_huflookup(&dctx->bits, &dctx->nbits, dctx->currlentable);
- if (code == -1)
- goto finished;
- if (code == -2)
- goto decode_error;
- if (code < 256)
- zlib_emit_char(dctx, code);
- else if (code == 256) {
- dctx->state = OUTSIDEBLK;
- if (dctx->currlentable != dctx->staticlentable) {
- zlib_freetable(&dctx->currlentable);
- dctx->currlentable = NULL;
- }
- if (dctx->currdisttable != dctx->staticdisttable) {
- zlib_freetable(&dctx->currdisttable);
- dctx->currdisttable = NULL;
- }
- } else if (code < 286) { /* static tree can give >285; ignore */
- dctx->state = GOTLENSYM;
- dctx->sym = code;
- }
- break;
- case GOTLENSYM:
- rec = &lencodes[dctx->sym - 257];
- if (dctx->nbits < rec->extrabits)
- goto finished;
- dctx->len =
- rec->min + (dctx->bits & ((1 << rec->extrabits) - 1));
- EATBITS(rec->extrabits);
- dctx->state = GOTLEN;
- break;
- case GOTLEN:
- code =
- zlib_huflookup(&dctx->bits, &dctx->nbits,
- dctx->currdisttable);
- if (code == -1)
- goto finished;
- if (code == -2)
- goto decode_error;
- dctx->state = GOTDISTSYM;
- dctx->sym = code;
- break;
- case GOTDISTSYM:
- rec = &distcodes[dctx->sym];
- if (dctx->nbits < rec->extrabits)
- goto finished;
- dist = rec->min + (dctx->bits & ((1 << rec->extrabits) - 1));
- EATBITS(rec->extrabits);
- dctx->state = INBLK;
- while (dctx->len--)
- zlib_emit_char(dctx, dctx->window[(dctx->winpos - dist) &
- (WINSIZE - 1)]);
- break;
- case UNCOMP_LEN:
- /*
- * Uncompressed block. We expect to see a 16-bit LEN.
- */
- if (dctx->nbits < 16)
- goto finished;
- dctx->uncomplen = dctx->bits & 0xFFFF;
- EATBITS(16);
- dctx->state = UNCOMP_NLEN;
- break;
- case UNCOMP_NLEN:
- /*
- * Uncompressed block. We expect to see a 16-bit NLEN,
- * which should be the one's complement of the previous
- * LEN.
- */
- if (dctx->nbits < 16)
- goto finished;
- nlen = dctx->bits & 0xFFFF;
- EATBITS(16);
- if (dctx->uncomplen != (nlen ^ 0xFFFF))
- goto decode_error;
- if (dctx->uncomplen == 0)
- dctx->state = OUTSIDEBLK; /* block is empty */
- else
- dctx->state = UNCOMP_DATA;
- break;
- case UNCOMP_DATA:
- if (dctx->nbits < 8)
- goto finished;
- zlib_emit_char(dctx, dctx->bits & 0xFF);
- EATBITS(8);
- if (--dctx->uncomplen == 0)
- dctx->state = OUTSIDEBLK; /* end of uncompressed block */
- break;
- }
- }
-
- finished:
- *outblock = dctx->outblk;
- *outlen = dctx->outlen;
- return 1;
-
- decode_error:
- sfree(dctx->outblk);
- *outblock = dctx->outblk = NULL;
- *outlen = 0;
- return 0;
-}
-
-#ifdef ZLIB_STANDALONE
-
-#include <stdio.h>
-#include <string.h>
-
-int main(int argc, char **argv)
-{
- unsigned char buf[16], *outbuf;
- int ret, outlen;
- void *handle;
- int noheader = FALSE, opts = TRUE;
- char *filename = NULL;
- FILE *fp;
-
- while (--argc) {
- char *p = *++argv;
-
- if (p[0] == '-' && opts) {
- if (!strcmp(p, "-d"))
- noheader = TRUE;
- else if (!strcmp(p, "--"))
- opts = FALSE; /* next thing is filename */
- else {
- fprintf(stderr, "unknown command line option '%s'\n", p);
- return 1;
- }
- } else if (!filename) {
- filename = p;
- } else {
- fprintf(stderr, "can only handle one filename\n");
- return 1;
- }
- }
-
- handle = zlib_decompress_init();
-
- if (noheader) {
- /*
- * Provide missing zlib header if -d was specified.
- */
- zlib_decompress_block(handle, "\x78\x9C", 2, &outbuf, &outlen);
- assert(outlen == 0);
- }
-
- if (filename)
- fp = fopen(filename, "rb");
- else
- fp = stdin;
-
- if (!fp) {
- assert(filename);
- fprintf(stderr, "unable to open '%s'\n", filename);
- return 1;
- }
-
- while (1) {
- ret = fread(buf, 1, sizeof(buf), fp);
- if (ret <= 0)
- break;
- zlib_decompress_block(handle, buf, ret, &outbuf, &outlen);
- if (outbuf) {
- if (outlen)
- fwrite(outbuf, 1, outlen, stdout);
- sfree(outbuf);
- } else {
- fprintf(stderr, "decoding error\n");
- return 1;
- }
- }
-
- zlib_decompress_cleanup(handle);
-
- if (filename)
- fclose(fp);
-
- return 0;
-}
-
-#else
-
-const struct ssh_compress ssh_zlib = {
- "zlib",
- "zlib@openssh.com", /* delayed version */
- zlib_compress_init,
- zlib_compress_cleanup,
- zlib_compress_block,
- zlib_decompress_init,
- zlib_decompress_cleanup,
- zlib_decompress_block,
- zlib_disable_compression,
- "zlib (RFC1950)"
-};
-
-#endif
+/*
+ * Zlib (RFC1950 / RFC1951) compression for PuTTY.
+ *
+ * There will no doubt be criticism of my decision to reimplement
+ * Zlib compression from scratch instead of using the existing zlib
+ * code. People will cry `reinventing the wheel'; they'll claim
+ * that the `fundamental basis of OSS' is code reuse; they'll want
+ * to see a really good reason for me having chosen not to use the
+ * existing code.
+ *
+ * Well, here are my reasons. Firstly, I don't want to link the
+ * whole of zlib into the PuTTY binary; PuTTY is justifiably proud
+ * of its small size and I think zlib contains a lot of unnecessary
+ * baggage for the kind of compression that SSH requires.
+ *
+ * Secondly, I also don't like the alternative of using zlib.dll.
+ * Another thing PuTTY is justifiably proud of is its ease of
+ * installation, and the last thing I want to do is to start
+ * mandating DLLs. Not only that, but there are two _kinds_ of
+ * zlib.dll kicking around, one with C calling conventions on the
+ * exported functions and another with WINAPI conventions, and
+ * there would be a significant danger of getting the wrong one.
+ *
+ * Thirdly, there seems to be a difference of opinion on the IETF
+ * secsh mailing list about the correct way to round off a
+ * compressed packet and start the next. In particular, there's
+ * some talk of switching to a mechanism zlib isn't currently
+ * capable of supporting (see below for an explanation). Given that
+ * sort of uncertainty, I thought it might be better to have code
+ * that will support even the zlib-incompatible worst case.
+ *
+ * Fourthly, it's a _second implementation_. Second implementations
+ * are fundamentally a Good Thing in standardisation efforts. The
+ * difference of opinion mentioned above has arisen _precisely_
+ * because there has been only one zlib implementation and
+ * everybody has used it. I don't intend that this should happen
+ * again.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#ifdef ZLIB_STANDALONE
+
+/*
+ * This module also makes a handy zlib decoding tool for when
+ * you're picking apart Zip files or PDFs or PNGs. If you compile
+ * it with ZLIB_STANDALONE defined, it builds on its own and
+ * becomes a command-line utility.
+ *
+ * Therefore, here I provide a self-contained implementation of the
+ * macros required from the rest of the PuTTY sources.
+ */
+#define snew(type) ( (type *) malloc(sizeof(type)) )
+#define snewn(n, type) ( (type *) malloc((n) * sizeof(type)) )
+#define sresize(x, n, type) ( (type *) realloc((x), (n) * sizeof(type)) )
+#define sfree(x) ( free((x)) )
+
+#else
+#include "ssh.h"
+#endif
+
+#ifndef FALSE
+#define FALSE 0
+#define TRUE (!FALSE)
+#endif
+
+/* ----------------------------------------------------------------------
+ * Basic LZ77 code. This bit is designed modularly, so it could be
+ * ripped out and used in a different LZ77 compressor. Go to it,
+ * and good luck :-)
+ */
+
+struct LZ77InternalContext;
+struct LZ77Context {
+ struct LZ77InternalContext *ictx;
+ void *userdata;
+ void (*literal) (struct LZ77Context * ctx, unsigned char c);
+ void (*match) (struct LZ77Context * ctx, int distance, int len);
+};
+
+/*
+ * Initialise the private fields of an LZ77Context. It's up to the
+ * user to initialise the public fields.
+ */
+static int lz77_init(struct LZ77Context *ctx);
+
+/*
+ * Supply data to be compressed. Will update the private fields of
+ * the LZ77Context, and will call literal() and match() to output.
+ * If `compress' is FALSE, it will never emit a match, but will
+ * instead call literal() for everything.
+ */
+static void lz77_compress(struct LZ77Context *ctx,
+ unsigned char *data, int len, int compress);
+
+/*
+ * Modifiable parameters.
+ */
+#define WINSIZE 32768 /* window size. Must be power of 2! */
+#define HASHMAX 2039 /* one more than max hash value */
+#define MAXMATCH 32 /* how many matches we track */
+#define HASHCHARS 3 /* how many chars make a hash */
+
+/*
+ * This compressor takes a less slapdash approach than the
+ * gzip/zlib one. Rather than allowing our hash chains to fall into
+ * disuse near the far end, we keep them doubly linked so we can
+ * _find_ the far end, and then every time we add a new byte to the
+ * window (thus rolling round by one and removing the previous
+ * byte), we can carefully remove the hash chain entry.
+ */
+
+#define INVALID -1 /* invalid hash _and_ invalid offset */
+struct WindowEntry {
+ short next, prev; /* array indices within the window */
+ short hashval;
+};
+
+struct HashEntry {
+ short first; /* window index of first in chain */
+};
+
+struct Match {
+ int distance, len;
+};
+
+struct LZ77InternalContext {
+ struct WindowEntry win[WINSIZE];
+ unsigned char data[WINSIZE];
+ int winpos;
+ struct HashEntry hashtab[HASHMAX];
+ unsigned char pending[HASHCHARS];
+ int npending;
+};
+
+static int lz77_hash(unsigned char *data)
+{
+ return (257 * data[0] + 263 * data[1] + 269 * data[2]) % HASHMAX;
+}
+
+static int lz77_init(struct LZ77Context *ctx)
+{
+ struct LZ77InternalContext *st;
+ int i;
+
+ st = snew(struct LZ77InternalContext);
+ if (!st)
+ return 0;
+
+ ctx->ictx = st;
+
+ for (i = 0; i < WINSIZE; i++)
+ st->win[i].next = st->win[i].prev = st->win[i].hashval = INVALID;
+ for (i = 0; i < HASHMAX; i++)
+ st->hashtab[i].first = INVALID;
+ st->winpos = 0;
+
+ st->npending = 0;
+
+ return 1;
+}
+
+static void lz77_advance(struct LZ77InternalContext *st,
+ unsigned char c, int hash)
+{
+ int off;
+
+ /*
+ * Remove the hash entry at winpos from the tail of its chain,
+ * or empty the chain if it's the only thing on the chain.
+ */
+ if (st->win[st->winpos].prev != INVALID) {
+ st->win[st->win[st->winpos].prev].next = INVALID;
+ } else if (st->win[st->winpos].hashval != INVALID) {
+ st->hashtab[st->win[st->winpos].hashval].first = INVALID;
+ }
+
+ /*
+ * Create a new entry at winpos and add it to the head of its
+ * hash chain.
+ */
+ st->win[st->winpos].hashval = hash;
+ st->win[st->winpos].prev = INVALID;
+ off = st->win[st->winpos].next = st->hashtab[hash].first;
+ st->hashtab[hash].first = st->winpos;
+ if (off != INVALID)
+ st->win[off].prev = st->winpos;
+ st->data[st->winpos] = c;
+
+ /*
+ * Advance the window pointer.
+ */
+ st->winpos = (st->winpos + 1) & (WINSIZE - 1);
+}
+
+#define CHARAT(k) ( (k)<0 ? st->data[(st->winpos+k)&(WINSIZE-1)] : data[k] )
+
+static void lz77_compress(struct LZ77Context *ctx,
+ unsigned char *data, int len, int compress)
+{
+ struct LZ77InternalContext *st = ctx->ictx;
+ int i, hash, distance, off, nmatch, matchlen, advance;
+ struct Match defermatch, matches[MAXMATCH];
+ int deferchr;
+
+ assert(st->npending <= HASHCHARS);
+
+ /*
+ * Add any pending characters from last time to the window. (We
+ * might not be able to.)
+ *
+ * This leaves st->pending empty in the usual case (when len >=
+ * HASHCHARS); otherwise it leaves st->pending empty enough that
+ * adding all the remaining 'len' characters will not push it past
+ * HASHCHARS in size.
+ */
+ for (i = 0; i < st->npending; i++) {
+ unsigned char foo[HASHCHARS];
+ int j;
+ if (len + st->npending - i < HASHCHARS) {
+ /* Update the pending array. */
+ for (j = i; j < st->npending; j++)
+ st->pending[j - i] = st->pending[j];
+ break;
+ }
+ for (j = 0; j < HASHCHARS; j++)
+ foo[j] = (i + j < st->npending ? st->pending[i + j] :
+ data[i + j - st->npending]);
+ lz77_advance(st, foo[0], lz77_hash(foo));
+ }
+ st->npending -= i;
+
+ defermatch.distance = 0; /* appease compiler */
+ defermatch.len = 0;
+ deferchr = '\0';
+ while (len > 0) {
+
+ /* Don't even look for a match, if we're not compressing. */
+ if (compress && len >= HASHCHARS) {
+ /*
+ * Hash the next few characters.
+ */
+ hash = lz77_hash(data);
+
+ /*
+ * Look the hash up in the corresponding hash chain and see
+ * what we can find.
+ */
+ nmatch = 0;
+ for (off = st->hashtab[hash].first;
+ off != INVALID; off = st->win[off].next) {
+ /* distance = 1 if off == st->winpos-1 */
+ /* distance = WINSIZE if off == st->winpos */
+ distance =
+ WINSIZE - (off + WINSIZE - st->winpos) % WINSIZE;
+ for (i = 0; i < HASHCHARS; i++)
+ if (CHARAT(i) != CHARAT(i - distance))
+ break;
+ if (i == HASHCHARS) {
+ matches[nmatch].distance = distance;
+ matches[nmatch].len = 3;
+ if (++nmatch >= MAXMATCH)
+ break;
+ }
+ }
+ } else {
+ nmatch = 0;
+ hash = INVALID;
+ }
+
+ if (nmatch > 0) {
+ /*
+ * We've now filled up matches[] with nmatch potential
+ * matches. Follow them down to find the longest. (We
+ * assume here that it's always worth favouring a
+ * longer match over a shorter one.)
+ */
+ matchlen = HASHCHARS;
+ while (matchlen < len) {
+ int j;
+ for (i = j = 0; i < nmatch; i++) {
+ if (CHARAT(matchlen) ==
+ CHARAT(matchlen - matches[i].distance)) {
+ matches[j++] = matches[i];
+ }
+ }
+ if (j == 0)
+ break;
+ matchlen++;
+ nmatch = j;
+ }
+
+ /*
+ * We've now got all the longest matches. We favour the
+ * shorter distances, which means we go with matches[0].
+ * So see if we want to defer it or throw it away.
+ */
+ matches[0].len = matchlen;
+ if (defermatch.len > 0) {
+ if (matches[0].len > defermatch.len + 1) {
+ /* We have a better match. Emit the deferred char,
+ * and defer this match. */
+ ctx->literal(ctx, (unsigned char) deferchr);
+ defermatch = matches[0];
+ deferchr = data[0];
+ advance = 1;
+ } else {
+ /* We don't have a better match. Do the deferred one. */
+ ctx->match(ctx, defermatch.distance, defermatch.len);
+ advance = defermatch.len - 1;
+ defermatch.len = 0;
+ }
+ } else {
+ /* There was no deferred match. Defer this one. */
+ defermatch = matches[0];
+ deferchr = data[0];
+ advance = 1;
+ }
+ } else {
+ /*
+ * We found no matches. Emit the deferred match, if
+ * any; otherwise emit a literal.
+ */
+ if (defermatch.len > 0) {
+ ctx->match(ctx, defermatch.distance, defermatch.len);
+ advance = defermatch.len - 1;
+ defermatch.len = 0;
+ } else {
+ ctx->literal(ctx, data[0]);
+ advance = 1;
+ }
+ }
+
+ /*
+ * Now advance the position by `advance' characters,
+ * keeping the window and hash chains consistent.
+ */
+ while (advance > 0) {
+ if (len >= HASHCHARS) {
+ lz77_advance(st, *data, lz77_hash(data));
+ } else {
+ assert(st->npending < HASHCHARS);
+ st->pending[st->npending++] = *data;
+ }
+ data++;
+ len--;
+ advance--;
+ }
+ }
+}
+
+/* ----------------------------------------------------------------------
+ * Zlib compression. We always use the static Huffman tree option.
+ * Mostly this is because it's hard to scan a block in advance to
+ * work out better trees; dynamic trees are great when you're
+ * compressing a large file under no significant time constraint,
+ * but when you're compressing little bits in real time, things get
+ * hairier.
+ *
+ * I suppose it's possible that I could compute Huffman trees based
+ * on the frequencies in the _previous_ block, as a sort of
+ * heuristic, but I'm not confident that the gain would balance out
+ * having to transmit the trees.
+ */
+
+struct Outbuf {
+ unsigned char *outbuf;
+ int outlen, outsize;
+ unsigned long outbits;
+ int noutbits;
+ int firstblock;
+ int comp_disabled;
+};
+
+static void outbits(struct Outbuf *out, unsigned long bits, int nbits)
+{
+ assert(out->noutbits + nbits <= 32);
+ out->outbits |= bits << out->noutbits;
+ out->noutbits += nbits;
+ while (out->noutbits >= 8) {
+ if (out->outlen >= out->outsize) {
+ out->outsize = out->outlen + 64;
+ out->outbuf = sresize(out->outbuf, out->outsize, unsigned char);
+ }
+ out->outbuf[out->outlen++] = (unsigned char) (out->outbits & 0xFF);
+ out->outbits >>= 8;
+ out->noutbits -= 8;
+ }
+}
+
+static const unsigned char mirrorbytes[256] = {
+ 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
+ 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
+ 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
+ 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
+ 0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
+ 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
+ 0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
+ 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
+ 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
+ 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
+ 0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
+ 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
+ 0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
+ 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
+ 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
+ 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
+ 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
+ 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
+ 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
+ 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
+ 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
+ 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
+ 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
+ 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
+ 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
+ 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
+ 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
+ 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
+ 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
+ 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
+ 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
+ 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
+};
+
+typedef struct {
+ short code, extrabits;
+ int min, max;
+} coderecord;
+
+static const coderecord lencodes[] = {
+ {257, 0, 3, 3},
+ {258, 0, 4, 4},
+ {259, 0, 5, 5},
+ {260, 0, 6, 6},
+ {261, 0, 7, 7},
+ {262, 0, 8, 8},
+ {263, 0, 9, 9},
+ {264, 0, 10, 10},
+ {265, 1, 11, 12},
+ {266, 1, 13, 14},
+ {267, 1, 15, 16},
+ {268, 1, 17, 18},
+ {269, 2, 19, 22},
+ {270, 2, 23, 26},
+ {271, 2, 27, 30},
+ {272, 2, 31, 34},
+ {273, 3, 35, 42},
+ {274, 3, 43, 50},
+ {275, 3, 51, 58},
+ {276, 3, 59, 66},
+ {277, 4, 67, 82},
+ {278, 4, 83, 98},
+ {279, 4, 99, 114},
+ {280, 4, 115, 130},
+ {281, 5, 131, 162},
+ {282, 5, 163, 194},
+ {283, 5, 195, 226},
+ {284, 5, 227, 257},
+ {285, 0, 258, 258},
+};
+
+static const coderecord distcodes[] = {
+ {0, 0, 1, 1},
+ {1, 0, 2, 2},
+ {2, 0, 3, 3},
+ {3, 0, 4, 4},
+ {4, 1, 5, 6},
+ {5, 1, 7, 8},
+ {6, 2, 9, 12},
+ {7, 2, 13, 16},
+ {8, 3, 17, 24},
+ {9, 3, 25, 32},
+ {10, 4, 33, 48},
+ {11, 4, 49, 64},
+ {12, 5, 65, 96},
+ {13, 5, 97, 128},
+ {14, 6, 129, 192},
+ {15, 6, 193, 256},
+ {16, 7, 257, 384},
+ {17, 7, 385, 512},
+ {18, 8, 513, 768},
+ {19, 8, 769, 1024},
+ {20, 9, 1025, 1536},
+ {21, 9, 1537, 2048},
+ {22, 10, 2049, 3072},
+ {23, 10, 3073, 4096},
+ {24, 11, 4097, 6144},
+ {25, 11, 6145, 8192},
+ {26, 12, 8193, 12288},
+ {27, 12, 12289, 16384},
+ {28, 13, 16385, 24576},
+ {29, 13, 24577, 32768},
+};
+
+static void zlib_literal(struct LZ77Context *ectx, unsigned char c)
+{
+ struct Outbuf *out = (struct Outbuf *) ectx->userdata;
+
+ if (out->comp_disabled) {
+ /*
+ * We're in an uncompressed block, so just output the byte.
+ */
+ outbits(out, c, 8);
+ return;
+ }
+
+ if (c <= 143) {
+ /* 0 through 143 are 8 bits long starting at 00110000. */
+ outbits(out, mirrorbytes[0x30 + c], 8);
+ } else {
+ /* 144 through 255 are 9 bits long starting at 110010000. */
+ outbits(out, 1 + 2 * mirrorbytes[0x90 - 144 + c], 9);
+ }
+}
+
+static void zlib_match(struct LZ77Context *ectx, int distance, int len)
+{
+ const coderecord *d, *l;
+ int i, j, k;
+ struct Outbuf *out = (struct Outbuf *) ectx->userdata;
+
+ assert(!out->comp_disabled);
+
+ while (len > 0) {
+ int thislen;
+
+ /*
+ * We can transmit matches of lengths 3 through 258
+ * inclusive. So if len exceeds 258, we must transmit in
+ * several steps, with 258 or less in each step.
+ *
+ * Specifically: if len >= 261, we can transmit 258 and be
+ * sure of having at least 3 left for the next step. And if
+ * len <= 258, we can just transmit len. But if len == 259
+ * or 260, we must transmit len-3.
+ */
+ thislen = (len > 260 ? 258 : len <= 258 ? len : len - 3);
+ len -= thislen;
+
+ /*
+ * Binary-search to find which length code we're
+ * transmitting.
+ */
+ i = -1;
+ j = sizeof(lencodes) / sizeof(*lencodes);
+ while (1) {
+ assert(j - i >= 2);
+ k = (j + i) / 2;
+ if (thislen < lencodes[k].min)
+ j = k;
+ else if (thislen > lencodes[k].max)
+ i = k;
+ else {
+ l = &lencodes[k];
+ break; /* found it! */
+ }
+ }
+
+ /*
+ * Transmit the length code. 256-279 are seven bits
+ * starting at 0000000; 280-287 are eight bits starting at
+ * 11000000.
+ */
+ if (l->code <= 279) {
+ outbits(out, mirrorbytes[(l->code - 256) * 2], 7);
+ } else {
+ outbits(out, mirrorbytes[0xc0 - 280 + l->code], 8);
+ }
+
+ /*
+ * Transmit the extra bits.
+ */
+ if (l->extrabits)
+ outbits(out, thislen - l->min, l->extrabits);
+
+ /*
+ * Binary-search to find which distance code we're
+ * transmitting.
+ */
+ i = -1;
+ j = sizeof(distcodes) / sizeof(*distcodes);
+ while (1) {
+ assert(j - i >= 2);
+ k = (j + i) / 2;
+ if (distance < distcodes[k].min)
+ j = k;
+ else if (distance > distcodes[k].max)
+ i = k;
+ else {
+ d = &distcodes[k];
+ break; /* found it! */
+ }
+ }
+
+ /*
+ * Transmit the distance code. Five bits starting at 00000.
+ */
+ outbits(out, mirrorbytes[d->code * 8], 5);
+
+ /*
+ * Transmit the extra bits.
+ */
+ if (d->extrabits)
+ outbits(out, distance - d->min, d->extrabits);
+ }
+}
+
+void *zlib_compress_init(void)
+{
+ struct Outbuf *out;
+ struct LZ77Context *ectx = snew(struct LZ77Context);
+
+ lz77_init(ectx);
+ ectx->literal = zlib_literal;
+ ectx->match = zlib_match;
+
+ out = snew(struct Outbuf);
+ out->outbits = out->noutbits = 0;
+ out->firstblock = 1;
+ out->comp_disabled = FALSE;
+ ectx->userdata = out;
+
+ return ectx;
+}
+
+void zlib_compress_cleanup(void *handle)
+{
+ struct LZ77Context *ectx = (struct LZ77Context *)handle;
+ sfree(ectx->userdata);
+ sfree(ectx->ictx);
+ sfree(ectx);
+}
+
+/*
+ * Turn off actual LZ77 analysis for one block, to facilitate
+ * construction of a precise-length IGNORE packet. Returns the
+ * length adjustment (which is only valid for packets < 65536
+ * bytes, but that seems reasonable enough).
+ */
+static int zlib_disable_compression(void *handle)
+{
+ struct LZ77Context *ectx = (struct LZ77Context *)handle;
+ struct Outbuf *out = (struct Outbuf *) ectx->userdata;
+ int n;
+
+ out->comp_disabled = TRUE;
+
+ n = 0;
+ /*
+ * If this is the first block, we will start by outputting two
+ * header bytes, and then three bits to begin an uncompressed
+ * block. This will cost three bytes (because we will start on
+ * a byte boundary, this is certain).
+ */
+ if (out->firstblock) {
+ n = 3;
+ } else {
+ /*
+ * Otherwise, we will output seven bits to close the
+ * previous static block, and _then_ three bits to begin an
+ * uncompressed block, and then flush the current byte.
+ * This may cost two bytes or three, depending on noutbits.
+ */
+ n += (out->noutbits + 10) / 8;
+ }
+
+ /*
+ * Now we output four bytes for the length / ~length pair in
+ * the uncompressed block.
+ */
+ n += 4;
+
+ return n;
+}
+
+int zlib_compress_block(void *handle, unsigned char *block, int len,
+ unsigned char **outblock, int *outlen)
+{
+ struct LZ77Context *ectx = (struct LZ77Context *)handle;
+ struct Outbuf *out = (struct Outbuf *) ectx->userdata;
+ int in_block;
+
+ out->outbuf = NULL;
+ out->outlen = out->outsize = 0;
+
+ /*
+ * If this is the first block, output the Zlib (RFC1950) header
+ * bytes 78 9C. (Deflate compression, 32K window size, default
+ * algorithm.)
+ */
+ if (out->firstblock) {
+ outbits(out, 0x9C78, 16);
+ out->firstblock = 0;
+
+ in_block = FALSE;
+ } else
+ in_block = TRUE;
+
+ if (out->comp_disabled) {
+ if (in_block)
+ outbits(out, 0, 7); /* close static block */
+
+ while (len > 0) {
+ int blen = (len < 65535 ? len : 65535);
+
+ /*
+ * Start a Deflate (RFC1951) uncompressed block. We
+ * transmit a zero bit (BFINAL=0), followed by two more
+ * zero bits (BTYPE=00). Of course these are in the
+ * wrong order (00 0), not that it matters.
+ */
+ outbits(out, 0, 3);
+
+ /*
+ * Output zero bits to align to a byte boundary.
+ */
+ if (out->noutbits)
+ outbits(out, 0, 8 - out->noutbits);
+
+ /*
+ * Output the block length, and then its one's
+ * complement. They're little-endian, so all we need to
+ * do is pass them straight to outbits() with bit count
+ * 16.
+ */
+ outbits(out, blen, 16);
+ outbits(out, blen ^ 0xFFFF, 16);
+
+ /*
+ * Do the `compression': we need to pass the data to
+ * lz77_compress so that it will be taken into account
+ * for subsequent (distance,length) pairs. But
+ * lz77_compress is passed FALSE, which means it won't
+ * actually find (or even look for) any matches; so
+ * every character will be passed straight to
+ * zlib_literal which will spot out->comp_disabled and
+ * emit in the uncompressed format.
+ */
+ lz77_compress(ectx, block, blen, FALSE);
+
+ len -= blen;
+ block += blen;
+ }
+ outbits(out, 2, 3); /* open new block */
+ } else {
+ if (!in_block) {
+ /*
+ * Start a Deflate (RFC1951) fixed-trees block. We
+ * transmit a zero bit (BFINAL=0), followed by a zero
+ * bit and a one bit (BTYPE=01). Of course these are in
+ * the wrong order (01 0).
+ */
+ outbits(out, 2, 3);
+ }
+
+ /*
+ * Do the compression.
+ */
+ lz77_compress(ectx, block, len, TRUE);
+
+ /*
+ * End the block (by transmitting code 256, which is
+ * 0000000 in fixed-tree mode), and transmit some empty
+ * blocks to ensure we have emitted the byte containing the
+ * last piece of genuine data. There are three ways we can
+ * do this:
+ *
+ * - Minimal flush. Output end-of-block and then open a
+ * new static block. This takes 9 bits, which is
+ * guaranteed to flush out the last genuine code in the
+ * closed block; but allegedly zlib can't handle it.
+ *
+ * - Zlib partial flush. Output EOB, open and close an
+ * empty static block, and _then_ open the new block.
+ * This is the best zlib can handle.
+ *
+ * - Zlib sync flush. Output EOB, then an empty
+ * _uncompressed_ block (000, then sync to byte
+ * boundary, then send bytes 00 00 FF FF). Then open the
+ * new block.
+ *
+ * For the moment, we will use Zlib partial flush.
+ */
+ outbits(out, 0, 7); /* close block */
+ outbits(out, 2, 3 + 7); /* empty static block */
+ outbits(out, 2, 3); /* open new block */
+ }
+
+ out->comp_disabled = FALSE;
+
+ *outblock = out->outbuf;
+ *outlen = out->outlen;
+
+ return 1;
+}
+
+/* ----------------------------------------------------------------------
+ * Zlib decompression. Of course, even though our compressor always
+ * uses static trees, our _decompressor_ has to be capable of
+ * handling dynamic trees if it sees them.
+ */
+
+/*
+ * The way we work the Huffman decode is to have a table lookup on
+ * the first N bits of the input stream (in the order they arrive,
+ * of course, i.e. the first bit of the Huffman code is in bit 0).
+ * Each table entry lists the number of bits to consume, plus
+ * either an output code or a pointer to a secondary table.
+ */
+struct zlib_table;
+struct zlib_tableentry;
+
+struct zlib_tableentry {
+ unsigned char nbits;
+ short code;
+ struct zlib_table *nexttable;
+};
+
+struct zlib_table {
+ int mask; /* mask applied to input bit stream */
+ struct zlib_tableentry *table;
+};
+
+#define MAXCODELEN 16
+#define MAXSYMS 288
+
+/*
+ * Build a single-level decode table for elements
+ * [minlength,maxlength) of the provided code/length tables, and
+ * recurse to build subtables.
+ */
+static struct zlib_table *zlib_mkonetab(int *codes, unsigned char *lengths,
+ int nsyms,
+ int pfx, int pfxbits, int bits)
+{
+ struct zlib_table *tab = snew(struct zlib_table);
+ int pfxmask = (1 << pfxbits) - 1;
+ int nbits, i, j, code;
+
+ tab->table = snewn(1 << bits, struct zlib_tableentry);
+ tab->mask = (1 << bits) - 1;
+
+ for (code = 0; code <= tab->mask; code++) {
+ tab->table[code].code = -1;
+ tab->table[code].nbits = 0;
+ tab->table[code].nexttable = NULL;
+ }
+
+ for (i = 0; i < nsyms; i++) {
+ if (lengths[i] <= pfxbits || (codes[i] & pfxmask) != pfx)
+ continue;
+ code = (codes[i] >> pfxbits) & tab->mask;
+ for (j = code; j <= tab->mask; j += 1 << (lengths[i] - pfxbits)) {
+ tab->table[j].code = i;
+ nbits = lengths[i] - pfxbits;
+ if (tab->table[j].nbits < nbits)
+ tab->table[j].nbits = nbits;
+ }
+ }
+ for (code = 0; code <= tab->mask; code++) {
+ if (tab->table[code].nbits <= bits)
+ continue;
+ /* Generate a subtable. */
+ tab->table[code].code = -1;
+ nbits = tab->table[code].nbits - bits;
+ if (nbits > 7)
+ nbits = 7;
+ tab->table[code].nbits = bits;
+ tab->table[code].nexttable = zlib_mkonetab(codes, lengths, nsyms,
+ pfx | (code << pfxbits),
+ pfxbits + bits, nbits);
+ }
+
+ return tab;
+}
+
+/*
+ * Build a decode table, given a set of Huffman tree lengths.
+ */
+static struct zlib_table *zlib_mktable(unsigned char *lengths,
+ int nlengths)
+{
+ int count[MAXCODELEN], startcode[MAXCODELEN], codes[MAXSYMS];
+ int code, maxlen;
+ int i, j;
+
+ /* Count the codes of each length. */
+ maxlen = 0;
+ for (i = 1; i < MAXCODELEN; i++)
+ count[i] = 0;
+ for (i = 0; i < nlengths; i++) {
+ count[lengths[i]]++;
+ if (maxlen < lengths[i])
+ maxlen = lengths[i];
+ }
+ /* Determine the starting code for each length block. */
+ code = 0;
+ for (i = 1; i < MAXCODELEN; i++) {
+ startcode[i] = code;
+ code += count[i];
+ code <<= 1;
+ }
+ /* Determine the code for each symbol. Mirrored, of course. */
+ for (i = 0; i < nlengths; i++) {
+ code = startcode[lengths[i]]++;
+ codes[i] = 0;
+ for (j = 0; j < lengths[i]; j++) {
+ codes[i] = (codes[i] << 1) | (code & 1);
+ code >>= 1;
+ }
+ }
+
+ /*
+ * Now we have the complete list of Huffman codes. Build a
+ * table.
+ */
+ return zlib_mkonetab(codes, lengths, nlengths, 0, 0,
+ maxlen < 9 ? maxlen : 9);
+}
+
+static int zlib_freetable(struct zlib_table **ztab)
+{
+ struct zlib_table *tab;
+ int code;
+
+ if (ztab == NULL)
+ return -1;
+
+ if (*ztab == NULL)
+ return 0;
+
+ tab = *ztab;
+
+ for (code = 0; code <= tab->mask; code++)
+ if (tab->table[code].nexttable != NULL)
+ zlib_freetable(&tab->table[code].nexttable);
+
+ sfree(tab->table);
+ tab->table = NULL;
+
+ sfree(tab);
+ *ztab = NULL;
+
+ return (0);
+}
+
+struct zlib_decompress_ctx {
+ struct zlib_table *staticlentable, *staticdisttable;
+ struct zlib_table *currlentable, *currdisttable, *lenlentable;
+ enum {
+ START, OUTSIDEBLK,
+ TREES_HDR, TREES_LENLEN, TREES_LEN, TREES_LENREP,
+ INBLK, GOTLENSYM, GOTLEN, GOTDISTSYM,
+ UNCOMP_LEN, UNCOMP_NLEN, UNCOMP_DATA
+ } state;
+ int sym, hlit, hdist, hclen, lenptr, lenextrabits, lenaddon, len,
+ lenrep;
+ int uncomplen;
+ unsigned char lenlen[19];
+ unsigned char lengths[286 + 32];
+ unsigned long bits;
+ int nbits;
+ unsigned char window[WINSIZE];
+ int winpos;
+ unsigned char *outblk;
+ int outlen, outsize;
+};
+
+void *zlib_decompress_init(void)
+{
+ struct zlib_decompress_ctx *dctx = snew(struct zlib_decompress_ctx);
+ unsigned char lengths[288];
+
+ memset(lengths, 8, 144);
+ memset(lengths + 144, 9, 256 - 144);
+ memset(lengths + 256, 7, 280 - 256);
+ memset(lengths + 280, 8, 288 - 280);
+ dctx->staticlentable = zlib_mktable(lengths, 288);
+ memset(lengths, 5, 32);
+ dctx->staticdisttable = zlib_mktable(lengths, 32);
+ dctx->state = START; /* even before header */
+ dctx->currlentable = dctx->currdisttable = dctx->lenlentable = NULL;
+ dctx->bits = 0;
+ dctx->nbits = 0;
+ dctx->winpos = 0;
+
+ return dctx;
+}
+
+void zlib_decompress_cleanup(void *handle)
+{
+ struct zlib_decompress_ctx *dctx = (struct zlib_decompress_ctx *)handle;
+
+ if (dctx->currlentable && dctx->currlentable != dctx->staticlentable)
+ zlib_freetable(&dctx->currlentable);
+ if (dctx->currdisttable && dctx->currdisttable != dctx->staticdisttable)
+ zlib_freetable(&dctx->currdisttable);
+ if (dctx->lenlentable)
+ zlib_freetable(&dctx->lenlentable);
+ zlib_freetable(&dctx->staticlentable);
+ zlib_freetable(&dctx->staticdisttable);
+ sfree(dctx);
+}
+
+static int zlib_huflookup(unsigned long *bitsp, int *nbitsp,
+ struct zlib_table *tab)
+{
+ unsigned long bits = *bitsp;
+ int nbits = *nbitsp;
+ while (1) {
+ struct zlib_tableentry *ent;
+ ent = &tab->table[bits & tab->mask];
+ if (ent->nbits > nbits)
+ return -1; /* not enough data */
+ bits >>= ent->nbits;
+ nbits -= ent->nbits;
+ if (ent->code == -1)
+ tab = ent->nexttable;
+ else {
+ *bitsp = bits;
+ *nbitsp = nbits;
+ return ent->code;
+ }
+
+ if (!tab) {
+ /*
+ * There was a missing entry in the table, presumably
+ * due to an invalid Huffman table description, and the
+ * subsequent data has attempted to use the missing
+ * entry. Return a decoding failure.
+ */
+ return -2;
+ }
+ }
+}
+
+static void zlib_emit_char(struct zlib_decompress_ctx *dctx, int c)
+{
+ dctx->window[dctx->winpos] = c;
+ dctx->winpos = (dctx->winpos + 1) & (WINSIZE - 1);
+ if (dctx->outlen >= dctx->outsize) {
+ dctx->outsize = dctx->outlen + 512;
+ dctx->outblk = sresize(dctx->outblk, dctx->outsize, unsigned char);
+ }
+ dctx->outblk[dctx->outlen++] = c;
+}
+
+#define EATBITS(n) ( dctx->nbits -= (n), dctx->bits >>= (n) )
+
+int zlib_decompress_block(void *handle, unsigned char *block, int len,
+ unsigned char **outblock, int *outlen)
+{
+ struct zlib_decompress_ctx *dctx = (struct zlib_decompress_ctx *)handle;
+ const coderecord *rec;
+ int code, blktype, rep, dist, nlen, header;
+ static const unsigned char lenlenmap[] = {
+ 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
+ };
+
+ dctx->outblk = snewn(256, unsigned char);
+ dctx->outsize = 256;
+ dctx->outlen = 0;
+
+ while (len > 0 || dctx->nbits > 0) {
+ while (dctx->nbits < 24 && len > 0) {
+ dctx->bits |= (*block++) << dctx->nbits;
+ dctx->nbits += 8;
+ len--;
+ }
+ switch (dctx->state) {
+ case START:
+ /* Expect 16-bit zlib header. */
+ if (dctx->nbits < 16)
+ goto finished; /* done all we can */
+
+ /*
+ * The header is stored as a big-endian 16-bit integer,
+ * in contrast to the general little-endian policy in
+ * the rest of the format :-(
+ */
+ header = (((dctx->bits & 0xFF00) >> 8) |
+ ((dctx->bits & 0x00FF) << 8));
+ EATBITS(16);
+
+ /*
+ * Check the header:
+ *
+ * - bits 8-11 should be 1000 (Deflate/RFC1951)
+ * - bits 12-15 should be at most 0111 (window size)
+ * - bit 5 should be zero (no dictionary present)
+ * - we don't care about bits 6-7 (compression rate)
+ * - bits 0-4 should be set up to make the whole thing
+ * a multiple of 31 (checksum).
+ */
+ if ((header & 0x0F00) != 0x0800 ||
+ (header & 0xF000) > 0x7000 ||
+ (header & 0x0020) != 0x0000 ||
+ (header % 31) != 0)
+ goto decode_error;
+
+ dctx->state = OUTSIDEBLK;
+ break;
+ case OUTSIDEBLK:
+ /* Expect 3-bit block header. */
+ if (dctx->nbits < 3)
+ goto finished; /* done all we can */
+ EATBITS(1);
+ blktype = dctx->bits & 3;
+ EATBITS(2);
+ if (blktype == 0) {
+ int to_eat = dctx->nbits & 7;
+ dctx->state = UNCOMP_LEN;
+ EATBITS(to_eat); /* align to byte boundary */
+ } else if (blktype == 1) {
+ dctx->currlentable = dctx->staticlentable;
+ dctx->currdisttable = dctx->staticdisttable;
+ dctx->state = INBLK;
+ } else if (blktype == 2) {
+ dctx->state = TREES_HDR;
+ }
+ break;
+ case TREES_HDR:
+ /*
+ * Dynamic block header. Five bits of HLIT, five of
+ * HDIST, four of HCLEN.
+ */
+ if (dctx->nbits < 5 + 5 + 4)
+ goto finished; /* done all we can */
+ dctx->hlit = 257 + (dctx->bits & 31);
+ EATBITS(5);
+ dctx->hdist = 1 + (dctx->bits & 31);
+ EATBITS(5);
+ dctx->hclen = 4 + (dctx->bits & 15);
+ EATBITS(4);
+ dctx->lenptr = 0;
+ dctx->state = TREES_LENLEN;
+ memset(dctx->lenlen, 0, sizeof(dctx->lenlen));
+ break;
+ case TREES_LENLEN:
+ if (dctx->nbits < 3)
+ goto finished;
+ while (dctx->lenptr < dctx->hclen && dctx->nbits >= 3) {
+ dctx->lenlen[lenlenmap[dctx->lenptr++]] =
+ (unsigned char) (dctx->bits & 7);
+ EATBITS(3);
+ }
+ if (dctx->lenptr == dctx->hclen) {
+ dctx->lenlentable = zlib_mktable(dctx->lenlen, 19);
+ dctx->state = TREES_LEN;
+ dctx->lenptr = 0;
+ }
+ break;
+ case TREES_LEN:
+ if (dctx->lenptr >= dctx->hlit + dctx->hdist) {
+ dctx->currlentable = zlib_mktable(dctx->lengths, dctx->hlit);
+ dctx->currdisttable = zlib_mktable(dctx->lengths + dctx->hlit,
+ dctx->hdist);
+ zlib_freetable(&dctx->lenlentable);
+ dctx->lenlentable = NULL;
+ dctx->state = INBLK;
+ break;
+ }
+ code =
+ zlib_huflookup(&dctx->bits, &dctx->nbits, dctx->lenlentable);
+ if (code == -1)
+ goto finished;
+ if (code == -2)
+ goto decode_error;
+ if (code < 16)
+ dctx->lengths[dctx->lenptr++] = code;
+ else {
+ dctx->lenextrabits = (code == 16 ? 2 : code == 17 ? 3 : 7);
+ dctx->lenaddon = (code == 18 ? 11 : 3);
+ dctx->lenrep = (code == 16 && dctx->lenptr > 0 ?
+ dctx->lengths[dctx->lenptr - 1] : 0);
+ dctx->state = TREES_LENREP;
+ }
+ break;
+ case TREES_LENREP:
+ if (dctx->nbits < dctx->lenextrabits)
+ goto finished;
+ rep =
+ dctx->lenaddon +
+ (dctx->bits & ((1 << dctx->lenextrabits) - 1));
+ EATBITS(dctx->lenextrabits);
+ while (rep > 0 && dctx->lenptr < dctx->hlit + dctx->hdist) {
+ dctx->lengths[dctx->lenptr] = dctx->lenrep;
+ dctx->lenptr++;
+ rep--;
+ }
+ dctx->state = TREES_LEN;
+ break;
+ case INBLK:
+ code =
+ zlib_huflookup(&dctx->bits, &dctx->nbits, dctx->currlentable);
+ if (code == -1)
+ goto finished;
+ if (code == -2)
+ goto decode_error;
+ if (code < 256)
+ zlib_emit_char(dctx, code);
+ else if (code == 256) {
+ dctx->state = OUTSIDEBLK;
+ if (dctx->currlentable != dctx->staticlentable) {
+ zlib_freetable(&dctx->currlentable);
+ dctx->currlentable = NULL;
+ }
+ if (dctx->currdisttable != dctx->staticdisttable) {
+ zlib_freetable(&dctx->currdisttable);
+ dctx->currdisttable = NULL;
+ }
+ } else if (code < 286) { /* static tree can give >285; ignore */
+ dctx->state = GOTLENSYM;
+ dctx->sym = code;
+ }
+ break;
+ case GOTLENSYM:
+ rec = &lencodes[dctx->sym - 257];
+ if (dctx->nbits < rec->extrabits)
+ goto finished;
+ dctx->len =
+ rec->min + (dctx->bits & ((1 << rec->extrabits) - 1));
+ EATBITS(rec->extrabits);
+ dctx->state = GOTLEN;
+ break;
+ case GOTLEN:
+ code =
+ zlib_huflookup(&dctx->bits, &dctx->nbits,
+ dctx->currdisttable);
+ if (code == -1)
+ goto finished;
+ if (code == -2)
+ goto decode_error;
+ dctx->state = GOTDISTSYM;
+ dctx->sym = code;
+ break;
+ case GOTDISTSYM:
+ rec = &distcodes[dctx->sym];
+ if (dctx->nbits < rec->extrabits)
+ goto finished;
+ dist = rec->min + (dctx->bits & ((1 << rec->extrabits) - 1));
+ EATBITS(rec->extrabits);
+ dctx->state = INBLK;
+ while (dctx->len--)
+ zlib_emit_char(dctx, dctx->window[(dctx->winpos - dist) &
+ (WINSIZE - 1)]);
+ break;
+ case UNCOMP_LEN:
+ /*
+ * Uncompressed block. We expect to see a 16-bit LEN.
+ */
+ if (dctx->nbits < 16)
+ goto finished;
+ dctx->uncomplen = dctx->bits & 0xFFFF;
+ EATBITS(16);
+ dctx->state = UNCOMP_NLEN;
+ break;
+ case UNCOMP_NLEN:
+ /*
+ * Uncompressed block. We expect to see a 16-bit NLEN,
+ * which should be the one's complement of the previous
+ * LEN.
+ */
+ if (dctx->nbits < 16)
+ goto finished;
+ nlen = dctx->bits & 0xFFFF;
+ EATBITS(16);
+ if (dctx->uncomplen != (nlen ^ 0xFFFF))
+ goto decode_error;
+ if (dctx->uncomplen == 0)
+ dctx->state = OUTSIDEBLK; /* block is empty */
+ else
+ dctx->state = UNCOMP_DATA;
+ break;
+ case UNCOMP_DATA:
+ if (dctx->nbits < 8)
+ goto finished;
+ zlib_emit_char(dctx, dctx->bits & 0xFF);
+ EATBITS(8);
+ if (--dctx->uncomplen == 0)
+ dctx->state = OUTSIDEBLK; /* end of uncompressed block */
+ break;
+ }
+ }
+
+ finished:
+ *outblock = dctx->outblk;
+ *outlen = dctx->outlen;
+ return 1;
+
+ decode_error:
+ sfree(dctx->outblk);
+ *outblock = dctx->outblk = NULL;
+ *outlen = 0;
+ return 0;
+}
+
+#ifdef ZLIB_STANDALONE
+
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char **argv)
+{
+ unsigned char buf[16], *outbuf;
+ int ret, outlen;
+ void *handle;
+ int noheader = FALSE, opts = TRUE;
+ char *filename = NULL;
+ FILE *fp;
+
+ while (--argc) {
+ char *p = *++argv;
+
+ if (p[0] == '-' && opts) {
+ if (!strcmp(p, "-d"))
+ noheader = TRUE;
+ else if (!strcmp(p, "--"))
+ opts = FALSE; /* next thing is filename */
+ else {
+ fprintf(stderr, "unknown command line option '%s'\n", p);
+ return 1;
+ }
+ } else if (!filename) {
+ filename = p;
+ } else {
+ fprintf(stderr, "can only handle one filename\n");
+ return 1;
+ }
+ }
+
+ handle = zlib_decompress_init();
+
+ if (noheader) {
+ /*
+ * Provide missing zlib header if -d was specified.
+ */
+ zlib_decompress_block(handle, "\x78\x9C", 2, &outbuf, &outlen);
+ assert(outlen == 0);
+ }
+
+ if (filename)
+ fp = fopen(filename, "rb");
+ else
+ fp = stdin;
+
+ if (!fp) {
+ assert(filename);
+ fprintf(stderr, "unable to open '%s'\n", filename);
+ return 1;
+ }
+
+ while (1) {
+ ret = fread(buf, 1, sizeof(buf), fp);
+ if (ret <= 0)
+ break;
+ zlib_decompress_block(handle, buf, ret, &outbuf, &outlen);
+ if (outbuf) {
+ if (outlen)
+ fwrite(outbuf, 1, outlen, stdout);
+ sfree(outbuf);
+ } else {
+ fprintf(stderr, "decoding error\n");
+ return 1;
+ }
+ }
+
+ zlib_decompress_cleanup(handle);
+
+ if (filename)
+ fclose(fp);
+
+ return 0;
+}
+
+#else
+
+const struct ssh_compress ssh_zlib = {
+ "zlib",
+ "zlib@openssh.com", /* delayed version */
+ zlib_compress_init,
+ zlib_compress_cleanup,
+ zlib_compress_block,
+ zlib_decompress_init,
+ zlib_decompress_cleanup,
+ zlib_decompress_block,
+ zlib_disable_compression,
+ "zlib (RFC1950)"
+};
+
+#endif
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-22 20:00:35 +0000