Headers (outbound and inbound) do not comply with KafkaJS type definitions

[apeloquin-agilysys]

The header implementation for both producers and consumers does not comply with the type definitions offered up in kafkajs.d.ts (which are unmodified from the KafkaJS originals).

Below is a comparison between KafkaJS and Confluent.

KafkaJS

import {Kafka} from "kafkajs";

const topic = "test-kafkajs-topic";
let receivedCount = 0;

const kafka = new Kafka({brokers: ["localhost:9092"]});

const consumer = kafka.consumer({groupId:`${topic}-group`});
await consumer.connect();
await consumer.subscribe({topic: TOPIC});
await consumer.run({
  eachMessage: async ({message}) => {
    log.info(JSON.stringify(message.headers, null, 2));
    receivedCount++;
  }
});

const producer = kafka.producer();
await producer.connect();
await producer.send({
  topic: TOPIC,
  messages: [{value: "one", headers: {header1: "alpha", header2: "beta"}}]
});

await until(async () => receivedCount == 1);

await producer.disconnect();
await consumer.disconnect();

{
  "header1": {
    "type": "Buffer",
    "data": [
      97,
      108,
      112,
      104,
      97
    ]
  },
  "header2": {
    "type": "Buffer",
    "data": [
      98,
      101,
      116,
      97
    ]
  }
}

Confluent

import {KafkaJS as Confluent} from "@confluentinc/kafka-javascript";

const topic = "test-confluent-topic";
let receivedCount = 0;

const kafka = new Confluent.Kafka({kafkaJS: {brokers: ["localhost:9092"]}});

const consumer = kafka.consumer({kafkaJS: {groupId: `${topic}-group`}});
await consumer.connect();
await consumer.subscribe({topic});
await consumer.run({
  eachMessage: async ({message}) => {
    log.info(JSON.stringify(message.headers, null, 2));
    receivedCount++;
  }
});

await until(async () => consumer.assignment().length > 0);

const producer = kafka.producer({"linger.ms": 0});
await producer.connect();
await producer.send({
  topic,
  messages: [{value: "one", headers: {header1: "alpha", header2: "beta"}}]
});

await until(async () => receivedCount == 1);

await producer.disconnect();
await consumer.disconnect();

{
  "0": {
    "key": {
      "type": "Buffer",
      "data": [
        104,
        101,
        97,
        100,
        101,
        114,
        49
      ]
    }
  },
  "1": {
    "key": {
      "type": "Buffer",
      "data": [
        104,
        101,
        97,
        100,
        101,
        114,
        50
      ]
    }
  }
}

Two (maybe three) notable issues:

1. The headers header1=alpha and header2=beta were sent to Kafka as key=header1 and key=header2
2. When that message was received, the headers object does not match the IHeaders type definition:

export interface IHeaders {
  [key: string]: Buffer | string | (Buffer | string)[] | undefined
}

3. if I had actually sent key=header1 and key=header2, KafkaJS compatibility would dictate a string key of "key" and a string[] value of ["header1","header2"]

[apeloquin-agilysys]

I can workaround this on the consumer side:

const result: IHeaders = {};
for (const header of Object.values(headers)) {
  for (const [key, value] of Object.entries(header as unknown as IHeaders)) {
    if (!value) continue;
    const existing = result[key];
    result[key] = existing ? isArray(existing) ? [...existing, value] : [existing, value] : value;
  }
}
return result;

However, I'm unable to determine a headers format for the producer side that results in correctly delivered headers.

[milindl]

Thanks for filing this. There were a bunch of issues with conversions for the headers within JS and within C++ also. I've fixed those on the development branch. These are OK to use immediately and will match the IHeaders interface.

Additionally, there is a PR #39 improving the typing support.

I've added it within the examples/typescript/kafkajs.ts too for reference.

headers: {
  'header1': 'value1', 
  'header2': [Buffer.from('value2'), 'value3']
}

[milindl]

Closing this as I released 0.1.15-devel with the fixes, given example works too