extmod/moduzlib: DecompIO: Add support for gzip-formatted streams.

This uses extension introduced in CPython 3.5: if wbits (dictionary size
code) has value 16 + 8..15, it means that gzip-formatted stream expected.

extmod/moduzlib.c

@@ -81,10 +81,18 @@ STATIC mp_obj_t decompio_make_new(const mp_obj_type_t *type, size_t n_args, size
     if (n_args > 1) {
         dict_opt = mp_obj_get_int(args[1]);
     }
-    if (dict_opt >= 0) {
+
+    if (dict_opt >= 16) {
+        int st = uzlib_gzip_parse_header(&o->decomp);
+        if (st != TINF_OK) {
+            goto header_error;
+        }
+        dict_sz = 1 << (dict_opt - 16);
+    } else if (dict_opt >= 0) {
         dict_opt = uzlib_zlib_parse_header(&o->decomp);
         if (dict_opt < 0) {
-            nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "zlib header"));
+header_error:
+            nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "compression header"));
         }
         dict_sz = 1 << dict_opt;
     } else {
@@ -212,6 +220,7 @@ const mp_obj_module_t mp_module_uzlib = {
 
 #include "uzlib/tinflate.c"
 #include "uzlib/tinfzlib.c"
+#include "uzlib/tinfgzip.c"
 #include "uzlib/adler32.c"
 #include "uzlib/crc32.c"