+ PB_RETURN_ERROR(stream, "invalid field type");
+ }
+}
+
+/* Default handler for extension fields. Expects a pb_field_t structure
+ * in extension->type->arg. */
+static bool checkreturn default_extension_decoder(pb_istream_t *stream,
+ pb_extension_t *extension, uint32_t tag, pb_wire_type_t wire_type)
+{
+ const pb_field_t *field = (const pb_field_t*)extension->type->arg;
+ pb_field_iterator_t iter;
+ bool dummy;
+
+ if (field->tag != tag)
+ return true;
+
+ iter.start = field;
+ iter.pos = field;
+ iter.field_index = 0;
+ iter.required_field_index = 0;
+ iter.dest_struct = extension->dest;
+ iter.pData = extension->dest;
+ iter.pSize = &dummy;
+
+ return decode_field(stream, wire_type, &iter);
+}
+
+/* Try to decode an unknown field as an extension field. Tries each extension
+ * decoder in turn, until one of them handles the field or loop ends. */
+static bool checkreturn decode_extension(pb_istream_t *stream,
+ uint32_t tag, pb_wire_type_t wire_type, pb_field_iterator_t *iter)
+{
+ pb_extension_t *extension = *(pb_extension_t* const *)iter->pData;
+ size_t pos = stream->bytes_left;
+
+ while (extension && pos == stream->bytes_left)
+ {
+ bool status;
+ if (extension->type->decode)
+ status = extension->type->decode(stream, extension, tag, wire_type);
+ else
+ status = default_extension_decoder(stream, extension, tag, wire_type);
+
+ if (!status)