extmod/uzlib: Add tinfgzip.c (gzip header parsing) from upstream.

extmod/uzlib/tinfgzip.c

+/*
+ * tinfgzip  -  tiny gzip decompressor
+ *
+ * Copyright (c) 2003 by Joergen Ibsen / Jibz
+ * All Rights Reserved
+ *
+ * http://www.ibsensoftware.com/
+ *
+ * Copyright (c) 2014-2016 by Paul Sokolovsky
+ *
+ * This software is provided 'as-is', without any express
+ * or implied warranty.  In no event will the authors be
+ * held liable for any damages arising from the use of
+ * this software.
+ *
+ * Permission is granted to anyone to use this software
+ * for any purpose, including commercial applications,
+ * and to alter it and redistribute it freely, subject to
+ * the following restrictions:
+ *
+ * 1. The origin of this software must not be
+ *    misrepresented; you must not claim that you
+ *    wrote the original software. If you use this
+ *    software in a product, an acknowledgment in
+ *    the product documentation would be appreciated
+ *    but is not required.
+ *
+ * 2. Altered source versions must be plainly marked
+ *    as such, and must not be misrepresented as
+ *    being the original software.
+ *
+ * 3. This notice may not be removed or altered from
+ *    any source distribution.
+ */
+
+#include "tinf.h"
+
+#define FTEXT    1
+#define FHCRC    2
+#define FEXTRA   4
+#define FNAME    8
+#define FCOMMENT 16
+
+void tinf_skip_bytes(TINF_DATA *d, int num)
+{
+    while (num--) uzlib_get_byte(d);
+}
+
+uint16_t tinf_get_uint16(TINF_DATA *d)
+{
+    unsigned int v = uzlib_get_byte(d);
+    v = (uzlib_get_byte(d) << 8) | v;
+    return v;
+}
+
+int uzlib_gzip_parse_header(TINF_DATA *d)
+{
+    unsigned char flg;
+
+    /* -- check format -- */
+
+    /* check id bytes */
+    if (uzlib_get_byte(d) != 0x1f || uzlib_get_byte(d) != 0x8b) return TINF_DATA_ERROR;
+
+    /* check method is deflate */
+    if (uzlib_get_byte(d) != 8) return TINF_DATA_ERROR;
+
+    /* get flag byte */
+    flg = uzlib_get_byte(d);
+
+    /* check that reserved bits are zero */
+    if (flg & 0xe0) return TINF_DATA_ERROR;
+
+    /* -- find start of compressed data -- */
+
+    /* skip rest of base header of 10 bytes */
+    tinf_skip_bytes(d, 6);
+
+    /* skip extra data if present */
+    if (flg & FEXTRA)
+    {
+       unsigned int xlen = tinf_get_uint16(d);
+       tinf_skip_bytes(d, xlen);
+    }
+
+    /* skip file name if present */
+    if (flg & FNAME) { while (uzlib_get_byte(d)); }
+
+    /* skip file comment if present */
+    if (flg & FCOMMENT) { while (uzlib_get_byte(d)); }
+
+    /* check header crc if present */
+    if (flg & FHCRC)
+    {
+       /*unsigned int hcrc =*/ tinf_get_uint16(d);
+
+        // TODO: Check!
+//       if (hcrc != (tinf_crc32(src, start - src) & 0x0000ffff))
+//          return TINF_DATA_ERROR;
+    }
+
+    /* initialize for crc32 checksum */
+    d->checksum_type = TINF_CHKSUM_CRC;
+    d->checksum = ~0;
+
+    return TINF_OK;
+}