avsc

What is avsc?

The avsc npm package is a library for encoding and decoding data in the Avro serialization format. It provides tools for working with Avro schemas, serializing and deserializing data, and performing schema evolution.

What are avsc's main functionalities?

Schema Definition

This feature allows you to define Avro schemas using JSON. The code sample demonstrates how to define a simple Avro schema for a record with 'name' and 'age' fields.

const avro = require('avsc');
const type = avro.Type.forSchema({
  type: 'record',
  fields: [
    {name: 'name', type: 'string'},
    {name: 'age', type: 'int'}
  ]
});

Serialization

This feature allows you to serialize JavaScript objects into Avro binary format. The code sample shows how to serialize an object with 'name' and 'age' fields into a buffer.

const avro = require('avsc');
const type = avro.Type.forSchema({
  type: 'record',
  fields: [
    {name: 'name', type: 'string'},
    {name: 'age', type: 'int'}
  ]
});
const buf = type.toBuffer({name: 'John Doe', age: 30});

Deserialization

This feature allows you to deserialize Avro binary data back into JavaScript objects. The code sample demonstrates how to deserialize a buffer back into an object.

const avro = require('avsc');
const type = avro.Type.forSchema({
  type: 'record',
  fields: [
    {name: 'name', type: 'string'},
    {name: 'age', type: 'int'}
  ]
});
const buf = type.toBuffer({name: 'John Doe', age: 30});
const obj = type.fromBuffer(buf);

Schema Evolution

This feature supports schema evolution, allowing you to read data written with an older schema using a newer schema. The code sample shows how to evolve a schema by adding a new field with a default value.

const avro = require('avsc');
const oldType = avro.Type.forSchema({
  type: 'record',
  fields: [
    {name: 'name', type: 'string'}
  ]
});
const newType = avro.Type.forSchema({
  type: 'record',
  fields: [
    {name: 'name', type: 'string'},
    {name: 'age', type: 'int', 'default': 0}
  ]
});
const buf = oldType.toBuffer({name: 'John Doe'});
const obj = newType.fromBuffer(buf);

Other packages similar to avsc

avro-js

avro-js is another library for working with Avro data in JavaScript. It provides similar functionality for schema definition, serialization, and deserialization. However, avro-js is generally considered to be less performant compared to avsc.

node-avro-io

node-avro-io is a library for Avro serialization and deserialization in Node.js. It offers similar features to avsc but is less actively maintained and has fewer features related to schema evolution.

README

Avsc

Pure JavaScript implementation of the Avro specification.

Features

• Blazingly fast and compact serialization! Typically faster than JSON with much smaller encodings.
• All the Avro goodness and more: type inference, schema evolution, and remote procedure calls.
• Support for serializing arbitrary JavaScript objects.
• Unopinionated 64-bit integer compatibility.

Installation

$ npm install avsc

avsc is compatible with all versions of node.js since 0.11 and major browsers via browserify. For convenience, you can also find compiled distributions with the releases (but please host your own copy).

Documentation

• Home
• API
• Quickstart
• Advanced usage
• Benchmarks

Examples

Inside a node.js module, or using browserify:

const avro = require('avsc');

• Encode and decode values from a known schema:

  const type = avro.Type.forSchema({
    type: 'record',
    fields: [
      {name: 'kind', type: {type: 'enum', symbols: ['CAT', 'DOG']}},
      {name: 'name', type: 'string'}
    ]
  });
  
  const buf = type.toBuffer({kind: 'CAT', name: 'Albert'}); // Encoded buffer.
  const val = type.fromBuffer(buf); // = {kind: 'CAT', name: 'Albert'}
  

• Infer a value's schema and encode similar values:

  const type = avro.Type.forValue({
    city: 'Cambridge',
    zipCodes: ['02138', '02139'],
    visits: 2
  });
  
  // We can use `type` to encode any values with the same structure:
  const bufs = [
    type.toBuffer({city: 'Seattle', zipCodes: ['98101'], visits: 3}),
    type.toBuffer({city: 'NYC', zipCodes: [], visits: 0})
  ];
  

• Get a readable stream of decoded values from an Avro container file compressed using Snappy (see the BlockDecoder API for an example including checksum validation):

  const snappy = require('snappy'); // Or your favorite Snappy library.
  const codecs = {
    snappy: function (buf, cb) {
      // Avro appends checksums to compressed blocks, which we skip here.
      return snappy.uncompress(buf.slice(0, buf.length - 4), cb);
    }
  };
  
  avro.createFileDecoder('./values.avro', {codecs})
    .on('metadata', function (type) { /* `type` is the writer's type. */ })
    .on('data', function (val) { /* Do something with the decoded value. */ });
  

• Implement a TCP server for an IDL-defined protocol:

  // We first generate a protocol from its IDL specification.
  const protocol = avro.readProtocol(`
    protocol LengthService {
      /** Endpoint which returns the length of the input string. */
      int stringLength(string str);
    }
  `);
  
  // We then create a corresponding server, implementing our endpoint.
  const server = avro.Service.forProtocol(protocol)
    .createServer()
    .onStringLength(function (str, cb) { cb(null, str.length); });
  
  // Finally, we use our server to respond to incoming TCP connections!
  require('net').createServer()
    .on('connection', (con) => { server.createChannel(con); })
    .listen(24950);