[pigeon] Channel name in flutter error. (flutter#5273)

Adds the channel name in the connection error message on all platforms host and flutter api methods.

Also fixes a bug with error handling for swift flutter api void methods.

Also adds method to all generators to help clean up duplicated code.

fixes flutter/flutter#136277

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,12 @@
+## 13.1.0
+
+* [swift] Fixes Flutter Api void return error handling.
+  * This shouldn't be breaking for anyone, but if you were incorrectly getting 
+    success responses, you may now be failing (correctly).
+* Adds method channel name to error response when channel fails to connect.
+* Reduces code generation duplication.
+* Changes some methods to only be generated if needed.
+
 ## 13.0.0
 
 * **Breaking Change** [objc] Eliminates boxing of non-nullable primitive types

packages/pigeon/example/app/android/app/src/main/java/io/flutter/plugins/Messages.java

@@ -55,6 +55,12 @@ protected static ArrayList<Object> wrapError(@NonNull Throwable exception) {
     return errorList;
   }
 
+  @NonNull
+  protected static FlutterError createConnectionError(@NonNull String channelName) {
+    return new FlutterError(
+        "channel-error", "Unable to establish connection on channel: " + channelName + ".", "");
+  }
+
   public enum Code {
     ONE(0),
     TWO(1);
@@ -341,11 +347,10 @@ public MessageFlutterApi(@NonNull BinaryMessenger argBinaryMessenger) {
     }
 
     public void flutterMethod(@Nullable String aStringArg, @NonNull Result<String> result) {
+      final String channelName =
+          "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod";
       BasicMessageChannel<Object> channel =
-          new BasicMessageChannel<>(
-              binaryMessenger,
-              "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod",
-              getCodec());
+          new BasicMessageChannel<>(binaryMessenger, channelName, getCodec());
       channel.send(
           new ArrayList<Object>(Collections.singletonList(aStringArg)),
           channelReply -> {
@@ -369,9 +374,7 @@ public void flutterMethod(@Nullable String aStringArg, @NonNull Result<String> r
                 result.success(output);
               }
             } else {
-              result.error(
-                  new FlutterError(
-                      "channel-error", "Unable to establish connection on channel.", ""));
+              result.error(createConnectionError(channelName));
             }
           });
     }

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/Messages.g.kt

@@ -33,6 +33,9 @@ private fun wrapError(exception: Throwable): List<Any?> {
   }
 }
 
+private fun createConnectionError(channelName: String): FlutterError {
+  return FlutterError("channel-error",  "Unable to establish connection on channel: '$channelName'.", "")}
+
 /**
  * Error class for passing custom error details to Flutter via a thrown PlatformException.
  * @property code The error code.
@@ -189,7 +192,8 @@ class MessageFlutterApi(private val binaryMessenger: BinaryMessenger) {
     }
   }
   fun flutterMethod(aStringArg: String?, callback: (Result<String>) -> Unit) {
-    val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod", codec)
+    val channelName = "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod"
+    val channel = BasicMessageChannel<Any?>(binaryMessenger, channelName, codec)
     channel.send(listOf(aStringArg)) {
       if (it is List<*>) {
         if (it.size > 1) {
@@ -201,7 +205,7 @@ class MessageFlutterApi(private val binaryMessenger: BinaryMessenger) {
           callback(Result.success(output));
         }
       } else {
-        callback(Result.failure(FlutterError("channel-error",  "Unable to establish connection on channel.", "")));
+        callback(Result.failure(createConnectionError(channelName)));
       } 
     }
   }

packages/pigeon/example/app/ios/Runner/Messages.g.swift

@@ -13,10 +13,6 @@ import FlutterMacOS
 #error("Unsupported platform.")
 #endif
 
-private func isNullish(_ value: Any?) -> Bool {
-  return value is NSNull || value == nil
-}
-
 private func wrapResult(_ result: Any?) -> [Any?] {
   return [result]
 }
@@ -36,6 +32,14 @@ private func wrapError(_ error: Any) -> [Any?] {
   ]
 }
 
+private func createConnectionError(withChannelName channelName: String) -> FlutterError {
+  return FlutterError(code: "channel-error", message: "Unable to establish connection on channel: '\(channelName)'.", details: "")
+}
+
+private func isNullish(_ value: Any?) -> Bool {
+  return value is NSNull || value == nil
+}
+
 private func nilOrValue<T>(_ value: Any?) -> T? {
   if value is NSNull { return nil }
   return value as! T?
@@ -175,18 +179,19 @@ class ExampleHostApiSetup {
 }
 /// Generated protocol from Pigeon that represents Flutter messages that can be called from Swift.
 protocol MessageFlutterApiProtocol {
-  func flutterMethod(aString aStringArg: String?, completion: @escaping (Result<String, FlutterError>) -> Void) 
+  func flutterMethod(aString aStringArg: String?, completion: @escaping (Result<String, FlutterError>) -> Void)
 }
 class MessageFlutterApi: MessageFlutterApiProtocol {
   private let binaryMessenger: FlutterBinaryMessenger
   init(binaryMessenger: FlutterBinaryMessenger){
     self.binaryMessenger = binaryMessenger
   }
-  func flutterMethod(aString aStringArg: String?, completion: @escaping (Result<String, FlutterError>) -> Void)  {
-    let channel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod", binaryMessenger: binaryMessenger)
+  func flutterMethod(aString aStringArg: String?, completion: @escaping (Result<String, FlutterError>) -> Void) {
+    let channelName: String = "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod"
+    let channel = FlutterBasicMessageChannel(name: channelName, binaryMessenger: binaryMessenger)
     channel.sendMessage([aStringArg] as [Any?]) { response in
       guard let listResponse = response as? [Any?] else {
-        completion(.failure(FlutterError(code: "channel-error", message: "Unable to establish connection on channel.", details: "")))
+        completion(.failure(createConnectionError(withChannelName:channelName)))
         return
       }
       if (listResponse.count > 1) {

packages/pigeon/example/app/lib/src/messages.g.dart

@@ -11,6 +11,13 @@ import 'dart:typed_data' show Float64List, Int32List, Int64List, Uint8List;
 import 'package:flutter/foundation.dart' show ReadBuffer, WriteBuffer;
 import 'package:flutter/services.dart';
 
+PlatformException _createConnectionError(String channelName) {
+  return PlatformException(
+    code: 'channel-error',
+    message: 'Unable to establish connection on channel: "$channelName".',
+  );
+}
+
 List<Object?> wrapResponse(
     {Object? result, PlatformException? error, bool empty = false}) {
   if (empty) {
@@ -97,16 +104,16 @@ class ExampleHostApi {
   static const MessageCodec<Object?> codec = _ExampleHostApiCodec();
 
   Future<String> getHostLanguage() async {
+    const String channelName =
+        'dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.getHostLanguage';
     final BasicMessageChannel<Object?> channel = BasicMessageChannel<Object?>(
-        'dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.getHostLanguage',
-        codec,
-        binaryMessenger: _binaryMessenger);
+      channelName,
+      codec,
+      binaryMessenger: _binaryMessenger,
+    );
     final List<Object?>? replyList = await channel.send(null) as List<Object?>?;
     if (replyList == null) {
-      throw PlatformException(
-        code: 'channel-error',
-        message: 'Unable to establish connection on channel.',
-      );
+      throw _createConnectionError(channelName);
     } else if (replyList.length > 1) {
       throw PlatformException(
         code: replyList[0]! as String,
@@ -124,16 +131,17 @@ class ExampleHostApi {
   }
 
   Future<int> add(int arg_a, int arg_b) async {
+    const String channelName =
+        'dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.add';
     final BasicMessageChannel<Object?> channel = BasicMessageChannel<Object?>(
-        'dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.add', codec,
-        binaryMessenger: _binaryMessenger);
+      channelName,
+      codec,
+      binaryMessenger: _binaryMessenger,
+    );
     final List<Object?>? replyList =
         await channel.send(<Object?>[arg_a, arg_b]) as List<Object?>?;
     if (replyList == null) {
-      throw PlatformException(
-        code: 'channel-error',
-        message: 'Unable to establish connection on channel.',
-      );
+      throw _createConnectionError(channelName);
     } else if (replyList.length > 1) {
       throw PlatformException(
         code: replyList[0]! as String,
@@ -151,17 +159,17 @@ class ExampleHostApi {
   }
 
   Future<bool> sendMessage(MessageData arg_message) async {
+    const String channelName =
+        'dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.sendMessage';
     final BasicMessageChannel<Object?> channel = BasicMessageChannel<Object?>(
-        'dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.sendMessage',
-        codec,
-        binaryMessenger: _binaryMessenger);
+      channelName,
+      codec,
+      binaryMessenger: _binaryMessenger,
+    );
     final List<Object?>? replyList =
         await channel.send(<Object?>[arg_message]) as List<Object?>?;
     if (replyList == null) {
-      throw PlatformException(
-        code: 'channel-error',
-        message: 'Unable to establish connection on channel.',
-      );
+      throw _createConnectionError(channelName);
     } else if (replyList.length > 1) {
       throw PlatformException(
         code: replyList[0]! as String,

packages/pigeon/example/app/macos/Runner/messages.g.m

@@ -16,16 +16,6 @@
 #error File requires ARC to be enabled.
 #endif
 
-@implementation PGNCodeBox
-- (instancetype)initWithValue:(PGNCode)value {
-  self = [super init];
-  if (self) {
-    _value = value;
-  }
-  return self;
-}
-@end
-
 static NSArray *wrapResult(id result, FlutterError *error) {
   if (error) {
     return @[
@@ -34,11 +24,31 @@ - (instancetype)initWithValue:(PGNCode)value {
   }
   return @[ result ?: [NSNull null] ];
 }
+
+static FlutterError *createConnectionError(NSString *channelName) {
+  return [FlutterError
+      errorWithCode:@"channel-error"
+            message:[NSString stringWithFormat:@"%@/%@/%@",
+                                               @"Unable to establish connection on channel: '",
+                                               channelName, @"'."]
+            details:@""];
+}
+
 static id GetNullableObjectAtIndex(NSArray *array, NSInteger key) {
   id result = array[key];
   return (result == [NSNull null]) ? nil : result;
 }
 
+@implementation PGNCodeBox
+- (instancetype)initWithValue:(PGNCode)value {
+  self = [super init];
+  if (self) {
+    _value = value;
+  }
+  return self;
+}
+@end
+
 @interface PGNMessageData ()
 + (PGNMessageData *)fromList:(NSArray *)list;
 + (nullable PGNMessageData *)nullableFromList:(NSArray *)list;
@@ -213,11 +223,12 @@ - (instancetype)initWithBinaryMessenger:(NSObject<FlutterBinaryMessenger> *)bina
 }
 - (void)flutterMethodAString:(nullable NSString *)arg_aString
                   completion:(void (^)(NSString *_Nullable, FlutterError *_Nullable))completion {
-  FlutterBasicMessageChannel *channel = [FlutterBasicMessageChannel
-      messageChannelWithName:
-          @"dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod"
-             binaryMessenger:self.binaryMessenger
-                       codec:PGNMessageFlutterApiGetCodec()];
+  NSString *channelName =
+      @"dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod";
+  FlutterBasicMessageChannel *channel =
+      [FlutterBasicMessageChannel messageChannelWithName:channelName
+                                         binaryMessenger:self.binaryMessenger
+                                                   codec:PGNMessageFlutterApiGetCodec()];
   [channel sendMessage:@[ arg_aString ?: [NSNull null] ]
                  reply:^(NSArray<id> *reply) {
                    if (reply != nil) {
@@ -230,10 +241,7 @@ - (void)flutterMethodAString:(nullable NSString *)arg_aString
                        completion(output, nil);
                      }
                    } else {
-                     completion(nil, [FlutterError
-                                         errorWithCode:@"channel-error"
-                                               message:@"Unable to establish connection on channel."
-                                               details:@""]);
+                     completion(nil, createConnectionError(channelName));
                    }
                  }];
 }

packages/pigeon/example/app/windows/runner/messages.g.cpp

@@ -24,6 +24,13 @@ using flutter::EncodableList;
 using flutter::EncodableMap;
 using flutter::EncodableValue;
 
+FlutterError CreateConnectionError(const std::string channel_name) {
+  return FlutterError(
+      "channel-error",
+      "Unable to establish connection on channel: '" + channel_name + "'.",
+      EncodableValue(""));
+}
+
 // MessageData
 
 MessageData::MessageData(const Code& code, const EncodableMap& data)
@@ -263,39 +270,38 @@ void MessageFlutterApi::FlutterMethod(
     const std::string* a_string_arg,
     std::function<void(const std::string&)>&& on_success,
     std::function<void(const FlutterError&)>&& on_error) {
-  auto channel = std::make_unique<BasicMessageChannel<>>(
-      binary_messenger_,
+  const std::string channel_name =
       "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi."
-      "flutterMethod",
-      &GetCodec());
+      "flutterMethod";
+  auto channel = std::make_unique<BasicMessageChannel<>>(
+      binary_messenger_, channel_name, &GetCodec());
   EncodableValue encoded_api_arguments = EncodableValue(EncodableList{
       a_string_arg ? EncodableValue(*a_string_arg) : EncodableValue(),
   });
-  channel->Send(encoded_api_arguments, [on_success = std::move(on_success),
-                                        on_error = std::move(on_error)](
-                                           const uint8_t* reply,
-                                           size_t reply_size) {
-    std::unique_ptr<EncodableValue> response =
-        GetCodec().DecodeMessage(reply, reply_size);
-    const auto& encodable_return_value = *response;
-    const auto* list_return_value =
-        std::get_if<EncodableList>(&encodable_return_value);
-    if (list_return_value) {
-      if (list_return_value->size() > 1) {
-        on_error(FlutterError(std::get<std::string>(list_return_value->at(0)),
-                              std::get<std::string>(list_return_value->at(1)),
-                              list_return_value->at(2)));
-      } else {
-        const auto& return_value =
-            std::get<std::string>(list_return_value->at(0));
-        on_success(return_value);
-      }
-    } else {
-      on_error(FlutterError("channel-error",
-                            "Unable to establish connection on channel.",
-                            EncodableValue("")));
-    }
-  });
+  channel->Send(
+      encoded_api_arguments, [channel_name, on_success = std::move(on_success),
+                              on_error = std::move(on_error)](
+                                 const uint8_t* reply, size_t reply_size) {
+        std::unique_ptr<EncodableValue> response =
+            GetCodec().DecodeMessage(reply, reply_size);
+        const auto& encodable_return_value = *response;
+        const auto* list_return_value =
+            std::get_if<EncodableList>(&encodable_return_value);
+        if (list_return_value) {
+          if (list_return_value->size() > 1) {
+            on_error(
+                FlutterError(std::get<std::string>(list_return_value->at(0)),
+                             std::get<std::string>(list_return_value->at(1)),
+                             list_return_value->at(2)));
+          } else {
+            const auto& return_value =
+                std::get<std::string>(list_return_value->at(0));
+            on_success(return_value);
+          }
+        } else {
+          on_error(CreateConnectionError(channel_name));
+        }
+      });
 }
 
 }  // namespace pigeon_example