tighten code according to tag invariant

skeletons/asn_codecs_prim.c

@@ -143,20 +143,26 @@ struct xdp_arg_s {
 	int want_more;
 };
 
-
+/*
+ * Since some kinds of primitive values can be encoded using value-specific
+ * tags (<MINUS-INFINITY>, <enum-element>, etc), the primitive decoder must
+ * be supplied with such tags to parse them as needed.
+ */
 static int
 xer_decode__unexpected_tag(void *key, const void *chunk_buf, size_t chunk_size) {
 	struct xdp_arg_s *arg = (struct xdp_arg_s *)key;
 	enum xer_pbd_rval bret;
 
-	if(arg->decoded_something) {
-		if(xer_is_whitespace(chunk_buf, chunk_size))
-			return 0;	/* Skip it. */
-		/*
-		 * Decoding was done once already. Prohibit doing it again.
-		 */
+	/*
+	 * The chunk_buf is guaranteed to start at '<'.
+	 */
+	assert(chunk_size && ((const char *)chunk_buf)[0] == 0x3c);
+
+	/*
+	 * Decoding was performed once already. Prohibit doing it again.
+	 */
+	if(arg->decoded_something)
 		return -1;
-	}
 
 	bret = arg->prim_body_decoder(arg->type_descriptor,
 		arg->struct_key, chunk_buf, chunk_size);
@@ -177,13 +183,19 @@ xer_decode__unexpected_tag(void *key, const void *chunk_buf, size_t chunk_size)
 }
 
 static ssize_t
-xer_decode__body(void *key, const void *chunk_buf, size_t chunk_size, int have_more) {
+xer_decode__primitive_body(void *key, const void *chunk_buf, size_t chunk_size, int have_more) {
 	struct xdp_arg_s *arg = (struct xdp_arg_s *)key;
 	enum xer_pbd_rval bret;
 
 	if(arg->decoded_something) {
-		if(xer_is_whitespace(chunk_buf, chunk_size))
+		if(xer_is_whitespace(chunk_buf, chunk_size)) {
+			/*
+			 * Example:
+			 * "<INTEGER>123<!--/--> </INTEGER>"
+			 *                      ^- chunk_buf position.
+			 */
 			return chunk_size;
+		}
 		/*
 		 * Decoding was done once already. Prohibit doing it again.
 		 */
@@ -253,7 +265,7 @@ xer_decode_primitive(asn_codec_ctx_t *opt_codec_ctx,
 
 	rc = xer_decode_general(opt_codec_ctx, &s_ctx, &s_arg,
 		xml_tag, buf_ptr, size,
-		xer_decode__unexpected_tag, xer_decode__body);
+		xer_decode__unexpected_tag, xer_decode__primitive_body);
 	switch(rc.code) {
 	case RC_OK:
 		if(!s_arg.decoded_something) {