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.
Avsc
![Coverage status](https://coveralls.io/repos/mtth/avsc/badge.svg?branch=master&service=github)
Pure JavaScript implementation of the Avro
specification.
Features
Installation
$ npm install avsc
avsc
is compatible with all versions of node.js since 0.11
.
Documentation
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',
name: 'Pet',
fields: [
{
name: 'kind',
type: {type: 'enum', name: 'PetKind', symbols: ['CAT', 'DOG']}
},
{name: 'name', type: 'string'}
]
});
const buf = type.toBuffer({kind: 'CAT', name: 'Albert'});
const val = type.fromBuffer(buf);
-
Infer a value's schema and encode similar values:
const type = avro.Type.forValue({
city: 'Cambridge',
zipCodes: ['02138', '02139'],
visits: 2
});
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');
const codecs = {
snappy: function (buf, cb) {
return snappy.uncompress(buf.slice(0, buf.length - 4), cb);
}
};
avro.createFileDecoder('./values.avro', {codecs})
.on('metadata', function (type) { })
.on('data', function (val) { });
-
Implement a TCP server for an IDL-defined protocol:
const protocol = avro.readProtocol(`
protocol LengthService {
/** Endpoint which returns the length of the input string. */
int stringLength(string str);
}
`);
const server = avro.Service.forProtocol(protocol)
.createServer()
.onStringLength(function (str, cb) { cb(null, str.length); });
require('net').createServer()
.on('connection', (con) => { server.createChannel(con); })
.listen(24950);