[Dart] Add Uint8List support to Dart generator (#12161)

* Adds Uint8List as a valid return type for type: string format: binary definitions
* Adds support for using bodyBytes instead of body for deserializing response data

Author: 0xNF

modules/openapi-generator/src/main/resources/dart2/api.mustache

@@ -164,7 +164,7 @@ class {{{classname}}} {
   Future<{{#returnType}}{{{.}}}?{{/returnType}}{{^returnType}}void{{/returnType}}> {{{nickname}}}({{#allParams}}{{#required}}{{{dataType}}} {{{paramName}}},{{^-last}} {{/-last}}{{/required}}{{/allParams}}{{#hasOptionalParams}}{ {{#allParams}}{{^required}}{{{dataType}}}? {{{paramName}}},{{^-last}} {{/-last}}{{/required}}{{/allParams}} }{{/hasOptionalParams}}) async {
     final response = await {{{nickname}}}WithHttpInfo({{#allParams}}{{#required}}{{{paramName}}},{{^-last}} {{/-last}}{{/required}}{{/allParams}}{{#hasOptionalParams}} {{#allParams}}{{^required}}{{{paramName}}}: {{{paramName}}},{{^-last}} {{/-last}}{{/required}}{{/allParams}} {{/hasOptionalParams}});
     if (response.statusCode >= HttpStatus.badRequest) {
-      throw ApiException(response.statusCode, await _decodeBodyBytes(response));
+      throw ApiException(response.statusCode, decodeError(await response.bodyBytes));
     }
     {{#returnType}}
     // When a remote server returns no body with a status of 204, we shall not decode it.
@@ -173,17 +173,16 @@ class {{{classname}}} {
     if (response.body.isNotEmpty && response.statusCode != HttpStatus.noContent) {
     {{#native_serialization}}
     {{#isArray}}
-      final responseBody = await _decodeBodyBytes(response);
-      return (await apiClient.deserializeAsync(responseBody, '{{{returnType}}}') as List)
+      return (await apiClient.deserializeAsync(response.bodyBytes, '{{{returnType}}}') as List)
         .cast<{{{returnBaseType}}}>()
         .{{#uniqueItems}}toSet(){{/uniqueItems}}{{^uniqueItems}}toList(){{/uniqueItems}};
     {{/isArray}}
     {{^isArray}}
     {{#isMap}}
-      return {{{returnType}}}.from(await apiClient.deserializeAsync(await _decodeBodyBytes(response), '{{{returnType}}}'),);
+      return {{{returnType}}}.from(await apiClient.deserializeAsync(response.bodyBytes, '{{{returnType}}}'),);
     {{/isMap}}
     {{^isMap}}
-      return await apiClient.deserializeAsync(await _decodeBodyBytes(response), '{{{returnType}}}',) as {{{returnType}}};
+      return await apiClient.deserializeAsync(response.bodyBytes, '{{{returnType}}}',) as {{{returnType}}};
     {{/isMap}}{{/isArray}}{{/native_serialization}}
     }
     return null;

modules/openapi-generator/src/main/resources/dart2/api_client.mustache

@@ -134,19 +134,25 @@ class ApiClient {
   }
 {{#native_serialization}}
 
-  Future<dynamic> deserializeAsync(String json, String targetType, {bool growable = false,}) async =>
+  Future<dynamic> deserializeAsync(Uint8List responseBytes, String targetType, {bool growable = false,}) async =>
     // ignore: deprecated_member_use_from_same_package
-    deserialize(json, targetType, growable: growable);
+    deserialize(responseBytes, targetType, growable: growable);
 
   @Deprecated('Scheduled for removal in OpenAPI Generator 6.x. Use deserializeAsync() instead.')
-  dynamic deserialize(String json, String targetType, {bool growable = false,}) {
+  dynamic deserialize(Uint8List responseBytes, String targetType, {bool growable = false,}) {
     // Remove all spaces. Necessary for regular expressions as well.
     targetType = targetType.replaceAll(' ', ''); // ignore: parameter_assignments
 
+    // if the expected target type is a byte-array, then just return the response bytes as-is
+    if (targetType == 'Uint8List') {
+      return responseBytes;
+    }
+
+    final decodedString = const Utf8Decoder().convert(responseBytes);
     // If the expected target type is String, nothing to do...
     return targetType == 'String'
-      ? json
-      : _deserialize(jsonDecode(json), targetType, growable: growable);
+      ? decodedString
+      : _deserialize(jsonDecode(decodedString), targetType, growable: growable);
   }
 {{/native_serialization}}
 

modules/openapi-generator/src/main/resources/dart2/api_helper.mustache

@@ -57,13 +57,10 @@ String parameterToString(dynamic value) {
   return value.toString();
 }
 
-/// Returns the decoded body as UTF-8 if the given headers indicate an 'application/json'
-/// content type. Otherwise, returns the decoded body as decoded by dart:http package.
-Future<String> _decodeBodyBytes(Response response) async {
-  final contentType = response.headers['content-type'];
-  return contentType != null && contentType.toLowerCase().startsWith('application/json')
-    ? response.bodyBytes.isEmpty ? '' : utf8.decode(response.bodyBytes)
-    : response.body;
+/// Decodes the response body for error reporting purposes.
+/// Decodes as UTF-8 but allows for malformed bytes to avoid crashing.
+String decodeError(Uint8List responseBytes) {
+  return const Utf8Decoder(allowMalformed: true).convert(responseBytes);
 }
 
 /// Returns a valid [T] value found at the specified Map [key], null otherwise.

modules/openapi-generator/src/main/resources/dart2/apilib.mustache

@@ -4,6 +4,7 @@
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:http/http.dart';
 import 'package:intl/intl.dart';