/*
* 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);
+ unsigned char *data, int len, int compress);
/*
* Modifiable parameters.
#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) {
+ 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];
defermatch.len = 0;
while (len > 0) {
- if (len >= HASHCHARS) {
+ /* Don't even look for a match, if we're not compressing. */
+ if (compress && len >= HASHCHARS) {
/*
* Hash the next few characters.
*/
unsigned long outbits;
int noutbits;
int firstblock;
+ int comp_disabled;
};
static void outbits(struct Outbuf *out, unsigned long bits, int nbits) {
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);
const coderecord *d, *l;
int i, j, k;
struct Outbuf *out = (struct Outbuf *)ectx->userdata;
+
+ assert(!out->comp_disabled);
+
while (len > 0) {
int thislen;
out = smalloc(sizeof(struct Outbuf));
out->outbits = out->noutbits = 0;
out->firstblock = 1;
+ out->comp_disabled = FALSE;
ectx.userdata = out;
logevent("Initialised zlib (RFC1950) compression");
}
+/*
+ * 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).
+ */
+int zlib_disable_compression(void) {
+ struct Outbuf *out = (struct Outbuf *)ectx.userdata;
+ int n, startbits;
+
+ 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(unsigned char *block, int len,
unsigned char **outblock, int *outlen) {
struct Outbuf *out = (struct Outbuf *)ectx.userdata;
+ int in_block;
out->outbuf = NULL;
out->outlen = out->outsize = 0;
if (out->firstblock) {
outbits(out, 0x9C78, 16);
out->firstblock = 0;
- /*
- * 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);
+
+ in_block = FALSE;
}
- /*
- * Do the compression.
- */
- lz77_compress(&ectx, block, len);
- /*
- * 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 */
+ 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 a zero
+ * bit and a one bit (BTYPE=00). Of course these are in
+ * the wrong order (00 0).
+ */
+ 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;
zlib_compress_init,
zlib_compress_block,
zlib_decompress_init,
- zlib_decompress_block
+ zlib_decompress_block,
+ zlib_disable_compression
};
projects / u / mdw / putty / commitdiff