NoSuchMethodError: Class '_Map<String, Object>' has no instance getter 'toJson'

[mrasityilmaz]

NoSuchMethodError: Class '_Map<String, Object>' has no instance getter 'toJson' in socket.io usage with EVENT type packets

Description

I am encountering a NoSuchMethodError with the following details:
This error occurs when I receive packets of type EVENT while using socket_io_client. To resolve this, I updated the package version from 3.0.0-beta.2 to 3.0.2 as I saw a similar issue addressed in socket_io_common. However, the issue persists in the latest version as well.

The problem seems to be related to a missing toJson method in the Map implementation. The issue likely stems from how packets are being handled or parsed within the socket library.

Steps to Reproduce

1. Use the socket_io_client package version 3.0.2.
2. Establish a socket connection to a server.
3. Receive a packet of type EVENT.
4. Observe the following error in the logs:

NoSuchMethodError: Class ‘_Map<String, Object>’ has no instance getter ‘toJson’.
Receiver: _Map
Tried calling: toJson
---
NoSuchMethodError (NoSuchMethodError: Class '_Map<String, Object>' has no instance getter 'toJson'.
Receiver: _Map len:4
Tried calling: toJson)
---
NoSuchMethodError (NoSuchMethodError: Class 'int' has no instance getter 'toJSON'.
Receiver: 2
Tried calling: toJSON)
---
NoSuchMethodError (NoSuchMethodError: Class 'String' has no instance getter 'toJSON'.
Receiver: "exitRoom"
Tried calling: toJSON)
---
NoSuchMethodError (NoSuchMethodError: Class 'List<dynamic>' has no instance getter 'toJSON'.
Receiver: Instance(length:2) of '_GrowableList'
Tried calling: toJSON)

Environment

• Package: socket_io_client 3.0.2
• Dart/Flutter version: 3.5.4 - Dart SDK / 3.24.4 - Flutter SDK
• Platform: IOS

Expected Behavior

The library should correctly handle or parse EVENT type packets without throwing a NoSuchMethodError. Ideally, any _Map object should be deserialized properly or handled internally.

Actual Behavior

The application throws a NoSuchMethodError when a toJson method is called on _Map<String, Object> during the handling of an EVENT type packet.

Attachments

• A screenshot of the error is attached.

Example Code Snippet

socket.emit('eventName','StringValue');

[mostafasany]

I am getting the same issue.

[mostafasany]

@mrasityilmaz were you able to find out any workaround?

[jumperchen]

It’s strange; this issue should not have occurred. According to the code, all exceptions should be caught by the try-catch statement. - https://github.com/rikulo/socket_io_common/blob/master/lib/src/parser/is_binary.dart#L67-L77

FYI, a few weeks ago, someone who encountered this issue cleared his environment and rebuilt his code, and everything went well.

[mostafasany]

This is how i call the emit method

_socket?.emitWithAck('sync-messages', { 'messages': [message] }, 
ack: (dynamic ackResponse) {
});

In this screenshot its shows that .toJSON not exists on obj (Map)

Also something doesn't look right in this function https://github.com/rikulo/socket_io_common/blob/master/lib/src/parser/is_binary.dart#L67-L77

Unnecessary Nesting of Try-Catch , the code in first Try and Catch is the same as in the second try and catch without adding any value.

Function? _getToJsonMethod(obj) {
  var toJsonMethod = null;
  try {
    // backwards compatibility for toJSON method
    var toJsonMethod = obj.toJSON;
    if (toJsonMethod is Function) {
      return toJsonMethod;
    }
  } catch (e) {
    try {
      // from dart-lang json.dart, the method is called toJson
      toJsonMethod = obj.toJson;
      if (toJsonMethod is Function) {
        return toJsonMethod;
      }
    } catch (e) {
      // Catch and ignore errors if the method is not present
    }
    // Catch and ignore errors if the method is not present
  }
  return null;
}

The old is_binary has this condition to guard .toJson again object without toJSON, and this condition not exists in latest version
if (obj['toJSON'] != null && obj['toJSON'] is Function && toJSON == false) {
return hasBinary(obj.toJSON(), true);
}

[mrasityilmaz]

@mrasityilmaz were you able to find out any workaround?

No, I couldn’t find it. There hasn’t been any progress either.
I think I’ll fork it myself and remove this function.

[mostafasany]

@mrasityilmaz Can you share your forked repo when you have it?

[jumperchen]

Maybe we can check the built in types first to see if that can help you.

For example,

Function? _getToJsonMethod(Object obj) {
  if (obj is Map || obj is List || obj is String || obj is num || obj is bool || obj == null) {
    return null; // Skip built-in types
  }

  try {
    // Dynamically check for `toJSON` method
    if ((obj as dynamic).toJSON != null && (obj as dynamic).toJSON is Function) {
      return (obj as dynamic).toJSON;
    }
  } catch (e) {
    // Ignore if `toJSON` is not found
  }

  try {
    // Dynamically check for `toJson` method
    if ((obj as dynamic).toJson != null && (obj as dynamic).toJson is Function) {
      return (obj as dynamic).toJson;
    }
  } catch (e) {
    // Ignore if `toJson` is not found
  }

  // If no suitable method is found, return null
  return null;
}