复制 package main
import (
"context"
"log"
"net"
"time"
"github.com/nats-io/nats.go"
)
type customDialer struct {
ctx context.Context
nc *nats.Conn
connectTimeout time.Duration
connectTimeWait time.Duration
}
func (cd *customDialer) Dial(network, address string) (net.Conn, error) {
ctx, cancel := context.WithTimeout(cd.ctx, cd.connectTimeout)
defer cancel()
for {
log.Println("Attempting to connect to", address)
if ctx.Err() != nil {
return nil, ctx.Err()
}
select {
case <-cd.ctx.Done():
return nil, cd.ctx.Err()
default:
d := &net.Dialer{}
if conn, err := d.DialContext(ctx, network, address); err == nil {
log.Println("Connected to NATS successfully")
return conn, nil
} else {
time.Sleep(cd.connectTimeWait)
}
}
}
}
With the dialer implementation above, the NATS client will retry a number of times to connect to the NATS server until the context is no longer valid:
复制 func main() {
// Parent context cancels connecting/reconnecting altogether.
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
var err error
var nc *nats.Conn
cd := &customDialer{
ctx: ctx,
connectTimeout: 10 * time.Second,
connectTimeWait: 1 * time.Second,
}
opts := []nats.Option{
nats.SetCustomDialer(cd),
nats.ReconnectWait(2 * time.Second),
nats.ReconnectHandler(func(c *nats.Conn) {
log.Println("Reconnected to", c.ConnectedUrl())
}),
nats.DisconnectHandler(func(c *nats.Conn) {
log.Println("Disconnected from NATS")
}),
nats.ClosedHandler(func(c *nats.Conn) {
log.Println("NATS connection is closed.")
}),
nats.NoReconnect(),
}
go func() {
nc, err = nats.Connect("127.0.0.1:4222", opts...)
}()
WaitForEstablishedConnection:
for {
if err != nil {
log.Fatal(err)
}
// Wait for context to be canceled either by timeout
// or because of establishing a connection...
select {
case <-ctx.Done():
break WaitForEstablishedConnection
default:
}
if nc == nil || !nc.IsConnected() {
log.Println("Connection not ready")
time.Sleep(200 * time.Millisecond)
continue
}
break WaitForEstablishedConnection
}
if ctx.Err() != nil {
log.Fatal(ctx.Err())
}
for {
if nc.IsClosed() {
break
}
if err := nc.Publish("hello", []byte("world")); err != nil {
log.Println(err)
time.Sleep(1 * time.Second)
continue
}
log.Println("Published message")
time.Sleep(1 * time.Second)
}
// Disconnect and flush pending messages
if err := nc.Drain(); err != nil {
log.Println(err)
}
log.Println("Disconnected")
}