avro-schema-registry/README.md

Confluent Schema Registry implementation in javascript to easily serialize and deserialize kafka messages

# avro-schema-registry

Confluent Schema Registry implementation to easily serialize and deserialize kafka messages with only one peer depencency.

# Quickstart

```
const registry = require('avro-schema-registry')('https://host.com:8081');

const schema = {type: 'string'};
const message = 'test message';

registry.encodeMessage('topic', schema, message)
  .then((msg) => {
    console.log(msg);   // <Buffer 00 00 00 00 01 18 74 65 73 74 20 6d 65 73 73 61 67 65>

    return registry.decode(msg);
  })
  .then((msg) => {
    console.log(msg);  // test message
  });

registry.encodeById(1, message)
  .then((msg) => {
    console.log(msg);   // <Buffer 00 00 00 00 01 18 74 65 73 74 20 6d 65 73 73 61 67 65>

    return registry.decode(msg);
  })

```

# Install

```
npm install avsc // if not already installed
npm install avro-schema-registry
```

# Doc

The module exports one function only, which expects a `url` parameter, which is a Confluent Schema Registry endpoint and an optional auth object. The function returns an object .

Every method returns a Promise.
Every method uses an internal cache to store already retrieved schemas and if the same id or schema is used again it won't perform another network call. Schemas are cached with their parsing options.

## Authentication with the Schema Registry

You can set username and password in the url object:
```
require('avro-schema-registry')('https://username:password@host.com:8081');
```

You can pass in an optional second parameter for the registry, with the username and password:
```
require('avro-schema-registry')('https://host.com:8081', {username: 'username', password: 'password'});
```

If both the url contains the authencation information and there's an authentication object parameter then the object takes precedence.

## decode
Parameters:
- msg: object to decode
- parseOptions: parsiong options to pass to `avsc.parse`, default: `null`

Decodes an avro encoded buffer into a javascript object.

## decodeMessage
Same as **decode**, only exists for backward compatibility reason.

## encodeKey
Parameters:
- topic: the topic to register the schema, if it doesn't exist already in the registry. The schema will be put under the subject `${topic}-key`
- schema: object representing an avro schema
- msg: message object to be encoded
- parseOptions: parsiong options to pass to `avsc.parse`, default: `null`

Encodes an object into an avro encoded buffer.

## encodeMessage
Parameters:
- topic: the topic to register the schema, if it doesn't exist already in the registry. The schema will be put under the subject `${topic}-value`
- schema: object representing an avro schema
- msg: message object to be encoded
- parseOptions: parsiong options to pass to `avsc.parse`, default: `null`

Encodes a message object into an avro encoded buffer.

## encodeById
Parameters:
- id: schema id in the registry
- msg: message object to be encoded
- parseOptions: parsiong options to pass to `avsc.parse`, default: `null`

Encodes a message object into an avro encoded buffer by fetching the schema from the registry.

## encodeMessageByTopicName

Try to get already existing schema from the schema registry and encode message with obtained schema. Please note, that the latest schema will be obtained.

This may be useful when topic consumer is on duty of providing the schema for the topic's messages.

Parameters:

- topic: topic name to fetch schema for
- msg: message object to be encoded
- parseOptions: parsiong options to pass to `avsc.parse`, default: `null`

## getSchemaByTopicName

This method tries to get already existing schema from the schema registry. Please note, that the latest schema will be obtained.

Parameters:

- topic: topic name to fetch schema for
- parseOptions: parsiong options to pass to `avsc.parse`, default: `null`

# Peer dependency

The module has no dependency, only one peer dependency: [avsc](https://github.com/mtth/avsc)