chunked-encoding: stop hiding the CURLE_BAD_CONTENT_ENCODING error

Unknown content-encoding would get returned as CURLE_WRITE_ERROR if the
response is chunked-encoded.

Reported-by: Ilya Kosarev
Fixes #4310
Closes #4449

lib/http_chunks.h

@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -21,6 +21,9 @@
  * KIND, either express or implied.
  *
  ***************************************************************************/
+
+struct connectdata;
+
 /*
  * The longest possible hexadecimal number we support in a chunked transfer.
  * Weird enough, RFC2616 doesn't set a maximum size! Since we use strtoul()
@@ -71,9 +74,9 @@ typedef enum {
   CHUNKE_TOO_LONG_HEX = 1,
   CHUNKE_ILLEGAL_HEX,
   CHUNKE_BAD_CHUNK,
-  CHUNKE_WRITE_ERROR,
   CHUNKE_BAD_ENCODING,
   CHUNKE_OUT_OF_MEMORY,
+  CHUNKE_PASSTHRU_ERROR, /* Curl_httpchunk_read() returns a CURLcode to use */
   CHUNKE_LAST
 } CHUNKcode;
 
@@ -87,4 +90,10 @@ struct Curl_chunker {
   size_t dataleft; /* untouched data amount at the end of the last buffer */
 };
 
+/* The following functions are defined in http_chunks.c */
+void Curl_httpchunk_init(struct connectdata *conn);
+CHUNKcode Curl_httpchunk_read(struct connectdata *conn, char *datap,
+                              ssize_t length, ssize_t *wrote,
+                              CURLcode *passthru);
+
 #endif /* HEADER_CURL_HTTP_CHUNKS_H */