495 lines
15 KiB
Markdown
495 lines
15 KiB
Markdown
# NATS - Go Client
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A [Go](http://golang.org) client for the [NATS messaging system](https://nats.io).
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[![License Apache 2][License-Image]][License-Url] [![Go Report Card][ReportCard-Image]][ReportCard-Url] [![Build Status][Build-Status-Image]][Build-Status-Url] [![GoDoc][GoDoc-Image]][GoDoc-Url] [![Coverage Status][Coverage-image]][Coverage-Url]
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[License-Url]: https://www.apache.org/licenses/LICENSE-2.0
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[License-Image]: https://img.shields.io/badge/License-Apache2-blue.svg
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[ReportCard-Url]: https://goreportcard.com/report/github.com/nats-io/nats.go
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[ReportCard-Image]: https://goreportcard.com/badge/github.com/nats-io/nats.go
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[Build-Status-Url]: https://travis-ci.com/github/nats-io/nats.go
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[Build-Status-Image]: https://travis-ci.com/nats-io/nats.go.svg?branch=main
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[GoDoc-Url]: https://pkg.go.dev/github.com/nats-io/nats.go
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[GoDoc-Image]: https://img.shields.io/badge/GoDoc-reference-007d9c
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[Coverage-Url]: https://coveralls.io/r/nats-io/nats.go?branch=main
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[Coverage-image]: https://coveralls.io/repos/github/nats-io/nats.go/badge.svg?branch=main
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**Check out [NATS by example](https://natsbyexample.com) - An evolving collection of runnable, cross-client reference examples for NATS.**
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## Installation
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```bash
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# Go client
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go get github.com/nats-io/nats.go/
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# Server
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go get github.com/nats-io/nats-server
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```
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When using or transitioning to Go modules support:
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```bash
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# Go client latest or explicit version
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go get github.com/nats-io/nats.go/@latest
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go get github.com/nats-io/nats.go/@v1.36.0
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# For latest NATS Server, add /v2 at the end
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go get github.com/nats-io/nats-server/v2
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# NATS Server v1 is installed otherwise
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# go get github.com/nats-io/nats-server
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```
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## Basic Usage
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```go
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import "github.com/nats-io/nats.go"
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// Connect to a server
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nc, _ := nats.Connect(nats.DefaultURL)
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// Simple Publisher
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nc.Publish("foo", []byte("Hello World"))
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// Simple Async Subscriber
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nc.Subscribe("foo", func(m *nats.Msg) {
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fmt.Printf("Received a message: %s\n", string(m.Data))
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})
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// Responding to a request message
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nc.Subscribe("request", func(m *nats.Msg) {
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m.Respond([]byte("answer is 42"))
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})
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// Simple Sync Subscriber
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sub, err := nc.SubscribeSync("foo")
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m, err := sub.NextMsg(timeout)
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// Channel Subscriber
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ch := make(chan *nats.Msg, 64)
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sub, err := nc.ChanSubscribe("foo", ch)
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msg := <- ch
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// Unsubscribe
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sub.Unsubscribe()
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// Drain
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sub.Drain()
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// Requests
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msg, err := nc.Request("help", []byte("help me"), 10*time.Millisecond)
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// Replies
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nc.Subscribe("help", func(m *nats.Msg) {
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nc.Publish(m.Reply, []byte("I can help!"))
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})
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// Drain connection (Preferred for responders)
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// Close() not needed if this is called.
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nc.Drain()
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// Close connection
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nc.Close()
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```
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## JetStream
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JetStream is the built-in NATS persistence system. `nats.go` provides a built-in
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API enabling both managing JetStream assets as well as publishing/consuming
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persistent messages.
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### Basic usage
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```go
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// connect to nats server
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nc, _ := nats.Connect(nats.DefaultURL)
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// create jetstream context from nats connection
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js, _ := jetstream.New(nc)
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ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
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defer cancel()
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// get existing stream handle
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stream, _ := js.Stream(ctx, "foo")
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// retrieve consumer handle from a stream
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cons, _ := stream.Consumer(ctx, "cons")
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// consume messages from the consumer in callback
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cc, _ := cons.Consume(func(msg jetstream.Msg) {
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fmt.Println("Received jetstream message: ", string(msg.Data()))
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msg.Ack()
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})
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defer cc.Stop()
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```
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To find more information on `nats.go` JetStream API, visit
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[`jetstream/README.md`](jetstream/README.md)
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> The current JetStream API replaces the [legacy JetStream API](legacy_jetstream.md)
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## Service API
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The service API (`micro`) allows you to [easily build NATS services](micro/README.md) The
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services API is currently in beta release.
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## Encoded Connections
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```go
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nc, _ := nats.Connect(nats.DefaultURL)
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c, _ := nats.NewEncodedConn(nc, nats.JSON_ENCODER)
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defer c.Close()
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// Simple Publisher
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c.Publish("foo", "Hello World")
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// Simple Async Subscriber
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c.Subscribe("foo", func(s string) {
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fmt.Printf("Received a message: %s\n", s)
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})
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// EncodedConn can Publish any raw Go type using the registered Encoder
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type person struct {
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Name string
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Address string
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Age int
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}
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// Go type Subscriber
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c.Subscribe("hello", func(p *person) {
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fmt.Printf("Received a person: %+v\n", p)
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})
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me := &person{Name: "derek", Age: 22, Address: "140 New Montgomery Street, San Francisco, CA"}
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// Go type Publisher
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c.Publish("hello", me)
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// Unsubscribe
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sub, err := c.Subscribe("foo", nil)
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// ...
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sub.Unsubscribe()
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// Requests
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var response string
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err = c.Request("help", "help me", &response, 10*time.Millisecond)
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if err != nil {
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fmt.Printf("Request failed: %v\n", err)
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}
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// Replying
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c.Subscribe("help", func(subj, reply string, msg string) {
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c.Publish(reply, "I can help!")
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})
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// Close connection
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c.Close();
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```
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## New Authentication (Nkeys and User Credentials)
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This requires server with version >= 2.0.0
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NATS servers have a new security and authentication mechanism to authenticate with user credentials and Nkeys.
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The simplest form is to use the helper method UserCredentials(credsFilepath).
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```go
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nc, err := nats.Connect(url, nats.UserCredentials("user.creds"))
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```
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The helper methods creates two callback handlers to present the user JWT and sign the nonce challenge from the server.
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The core client library never has direct access to your private key and simply performs the callback for signing the server challenge.
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The helper will load and wipe and erase memory it uses for each connect or reconnect.
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The helper also can take two entries, one for the JWT and one for the NKey seed file.
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```go
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nc, err := nats.Connect(url, nats.UserCredentials("user.jwt", "user.nk"))
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```
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You can also set the callback handlers directly and manage challenge signing directly.
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```go
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nc, err := nats.Connect(url, nats.UserJWT(jwtCB, sigCB))
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```
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Bare Nkeys are also supported. The nkey seed should be in a read only file, e.g. seed.txt
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```bash
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> cat seed.txt
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# This is my seed nkey!
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SUAGMJH5XLGZKQQWAWKRZJIGMOU4HPFUYLXJMXOO5NLFEO2OOQJ5LPRDPM
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```
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This is a helper function which will load and decode and do the proper signing for the server nonce.
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It will clear memory in between invocations.
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You can choose to use the low level option and provide the public key and a signature callback on your own.
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```go
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opt, err := nats.NkeyOptionFromSeed("seed.txt")
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nc, err := nats.Connect(serverUrl, opt)
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// Direct
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nc, err := nats.Connect(serverUrl, nats.Nkey(pubNkey, sigCB))
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```
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## TLS
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```go
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// tls as a scheme will enable secure connections by default. This will also verify the server name.
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nc, err := nats.Connect("tls://nats.demo.io:4443")
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// If you are using a self-signed certificate, you need to have a tls.Config with RootCAs setup.
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// We provide a helper method to make this case easier.
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nc, err = nats.Connect("tls://localhost:4443", nats.RootCAs("./configs/certs/ca.pem"))
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// If the server requires client certificate, there is an helper function for that too:
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cert := nats.ClientCert("./configs/certs/client-cert.pem", "./configs/certs/client-key.pem")
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nc, err = nats.Connect("tls://localhost:4443", cert)
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// You can also supply a complete tls.Config
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certFile := "./configs/certs/client-cert.pem"
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keyFile := "./configs/certs/client-key.pem"
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cert, err := tls.LoadX509KeyPair(certFile, keyFile)
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if err != nil {
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t.Fatalf("error parsing X509 certificate/key pair: %v", err)
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}
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config := &tls.Config{
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ServerName: opts.Host,
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Certificates: []tls.Certificate{cert},
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RootCAs: pool,
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MinVersion: tls.VersionTLS12,
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}
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nc, err = nats.Connect("nats://localhost:4443", nats.Secure(config))
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if err != nil {
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t.Fatalf("Got an error on Connect with Secure Options: %+v\n", err)
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}
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```
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## Using Go Channels (netchan)
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```go
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nc, _ := nats.Connect(nats.DefaultURL)
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ec, _ := nats.NewEncodedConn(nc, nats.JSON_ENCODER)
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defer ec.Close()
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type person struct {
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Name string
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Address string
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Age int
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}
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recvCh := make(chan *person)
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ec.BindRecvChan("hello", recvCh)
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sendCh := make(chan *person)
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ec.BindSendChan("hello", sendCh)
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me := &person{Name: "derek", Age: 22, Address: "140 New Montgomery Street"}
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// Send via Go channels
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sendCh <- me
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// Receive via Go channels
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who := <- recvCh
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```
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## Wildcard Subscriptions
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```go
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// "*" matches any token, at any level of the subject.
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nc.Subscribe("foo.*.baz", func(m *Msg) {
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fmt.Printf("Msg received on [%s] : %s\n", m.Subject, string(m.Data));
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})
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nc.Subscribe("foo.bar.*", func(m *Msg) {
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fmt.Printf("Msg received on [%s] : %s\n", m.Subject, string(m.Data));
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})
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// ">" matches any length of the tail of a subject, and can only be the last token
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// E.g. 'foo.>' will match 'foo.bar', 'foo.bar.baz', 'foo.foo.bar.bax.22'
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nc.Subscribe("foo.>", func(m *Msg) {
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fmt.Printf("Msg received on [%s] : %s\n", m.Subject, string(m.Data));
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})
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// Matches all of the above
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nc.Publish("foo.bar.baz", []byte("Hello World"))
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```
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## Queue Groups
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```go
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// All subscriptions with the same queue name will form a queue group.
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// Each message will be delivered to only one subscriber per queue group,
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// using queuing semantics. You can have as many queue groups as you wish.
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// Normal subscribers will continue to work as expected.
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nc.QueueSubscribe("foo", "job_workers", func(_ *Msg) {
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received += 1;
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})
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```
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## Advanced Usage
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```go
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// Normally, the library will return an error when trying to connect and
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// there is no server running. The RetryOnFailedConnect option will set
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// the connection in reconnecting state if it failed to connect right away.
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nc, err := nats.Connect(nats.DefaultURL,
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nats.RetryOnFailedConnect(true),
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nats.MaxReconnects(10),
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nats.ReconnectWait(time.Second),
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nats.ReconnectHandler(func(_ *nats.Conn) {
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// Note that this will be invoked for the first asynchronous connect.
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}))
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if err != nil {
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// Should not return an error even if it can't connect, but you still
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// need to check in case there are some configuration errors.
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}
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// Flush connection to server, returns when all messages have been processed.
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nc.Flush()
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fmt.Println("All clear!")
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// FlushTimeout specifies a timeout value as well.
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err := nc.FlushTimeout(1*time.Second)
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if err != nil {
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fmt.Println("All clear!")
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} else {
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fmt.Println("Flushed timed out!")
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}
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// Auto-unsubscribe after MAX_WANTED messages received
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const MAX_WANTED = 10
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sub, err := nc.Subscribe("foo")
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sub.AutoUnsubscribe(MAX_WANTED)
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// Multiple connections
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nc1 := nats.Connect("nats://host1:4222")
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nc2 := nats.Connect("nats://host2:4222")
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nc1.Subscribe("foo", func(m *Msg) {
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fmt.Printf("Received a message: %s\n", string(m.Data))
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})
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nc2.Publish("foo", []byte("Hello World!"));
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```
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## Clustered Usage
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```go
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var servers = "nats://localhost:1222, nats://localhost:1223, nats://localhost:1224"
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nc, err := nats.Connect(servers)
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// Optionally set ReconnectWait and MaxReconnect attempts.
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// This example means 10 seconds total per backend.
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nc, err = nats.Connect(servers, nats.MaxReconnects(5), nats.ReconnectWait(2 * time.Second))
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// You can also add some jitter for the reconnection.
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// This call will add up to 500 milliseconds for non TLS connections and 2 seconds for TLS connections.
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// If not specified, the library defaults to 100 milliseconds and 1 second, respectively.
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nc, err = nats.Connect(servers, nats.ReconnectJitter(500*time.Millisecond, 2*time.Second))
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// You can also specify a custom reconnect delay handler. If set, the library will invoke it when it has tried
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// all URLs in its list. The value returned will be used as the total sleep time, so add your own jitter.
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// The library will pass the number of times it went through the whole list.
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nc, err = nats.Connect(servers, nats.CustomReconnectDelay(func(attempts int) time.Duration {
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return someBackoffFunction(attempts)
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}))
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// Optionally disable randomization of the server pool
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nc, err = nats.Connect(servers, nats.DontRandomize())
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// Setup callbacks to be notified on disconnects, reconnects and connection closed.
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nc, err = nats.Connect(servers,
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nats.DisconnectErrHandler(func(nc *nats.Conn, err error) {
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fmt.Printf("Got disconnected! Reason: %q\n", err)
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}),
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nats.ReconnectHandler(func(nc *nats.Conn) {
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fmt.Printf("Got reconnected to %v!\n", nc.ConnectedUrl())
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}),
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nats.ClosedHandler(func(nc *nats.Conn) {
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fmt.Printf("Connection closed. Reason: %q\n", nc.LastError())
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})
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)
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// When connecting to a mesh of servers with auto-discovery capabilities,
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// you may need to provide a username/password or token in order to connect
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// to any server in that mesh when authentication is required.
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// Instead of providing the credentials in the initial URL, you will use
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// new option setters:
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nc, err = nats.Connect("nats://localhost:4222", nats.UserInfo("foo", "bar"))
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// For token based authentication:
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nc, err = nats.Connect("nats://localhost:4222", nats.Token("S3cretT0ken"))
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// You can even pass the two at the same time in case one of the server
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// in the mesh requires token instead of user name and password.
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nc, err = nats.Connect("nats://localhost:4222",
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nats.UserInfo("foo", "bar"),
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nats.Token("S3cretT0ken"))
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// Note that if credentials are specified in the initial URLs, they take
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// precedence on the credentials specified through the options.
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// For instance, in the connect call below, the client library will use
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// the user "my" and password "pwd" to connect to localhost:4222, however,
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// it will use username "foo" and password "bar" when (re)connecting to
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// a different server URL that it got as part of the auto-discovery.
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nc, err = nats.Connect("nats://my:pwd@localhost:4222", nats.UserInfo("foo", "bar"))
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```
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## Context support (+Go 1.7)
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```go
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ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
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defer cancel()
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nc, err := nats.Connect(nats.DefaultURL)
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// Request with context
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msg, err := nc.RequestWithContext(ctx, "foo", []byte("bar"))
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// Synchronous subscriber with context
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sub, err := nc.SubscribeSync("foo")
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msg, err := sub.NextMsgWithContext(ctx)
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// Encoded Request with context
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c, err := nats.NewEncodedConn(nc, nats.JSON_ENCODER)
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type request struct {
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Message string `json:"message"`
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}
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type response struct {
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Code int `json:"code"`
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}
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req := &request{Message: "Hello"}
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resp := &response{}
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err := c.RequestWithContext(ctx, "foo", req, resp)
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```
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## Backwards compatibility
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In the development of nats.go, we are committed to maintaining backward compatibility and ensuring a stable and reliable experience for all users. In general, we follow the standard go compatibility guidelines.
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However, it's important to clarify our stance on certain types of changes:
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- **Expanding structures:**
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Adding new fields to structs is not considered a breaking change.
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- **Adding methods to exported interfaces:**
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Extending public interfaces with new methods is also not viewed as a breaking change within the context of this project. It is important to note that no unexported methods will be added to interfaces allowing users to implement them.
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Additionally, this library always supports at least 2 latest minor Go versions. For example, if the latest Go version is 1.22, the library will support Go 1.21 and 1.22.
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## License
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Unless otherwise noted, the NATS source files are distributed
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under the Apache Version 2.0 license found in the LICENSE file.
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[](https://app.fossa.io/projects/git%2Bgithub.com%2Fnats-io%2Fgo-nats?ref=badge_large)
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