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// Copyright 2012-2022 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package main
import (
"flag"
"log"
"os"
"runtime"
"time"
"github.com/nats-io/nats.go"
)
// NOTE: Can test with demo servers.
// nats-sub -s demo.nats.io <subject>
func usage() {
log.Printf("Usage: nats-sub [-s server] [-creds file] [-nkey file] [-tlscert file] [-tlskey file] [-tlscacert file] [-t] <subject>\n")
flag.PrintDefaults()
}
func showUsageAndExit(exitcode int) {
usage()
os.Exit(exitcode)
}
func printMsg(m *nats.Msg, i int) {
log.Printf("[#%d] Received on [%s]: '%s'", i, m.Subject, string(m.Data))
}
func main() {
var urls = flag.String("s", nats.DefaultURL, "The nats server URLs (separated by comma)")
var userCreds = flag.String("creds", "", "User Credentials File")
var nkeyFile = flag.String("nkey", "", "NKey Seed File")
var tlsClientCert = flag.String("tlscert", "", "TLS client certificate file")
var tlsClientKey = flag.String("tlskey", "", "Private key file for client certificate")
var tlsCACert = flag.String("tlscacert", "", "CA certificate to verify peer against")
var showTime = flag.Bool("t", false, "Display timestamps")
var showHelp = flag.Bool("h", false, "Show help message")
log.SetFlags(0)
flag.Usage = usage
flag.Parse()
if *showHelp {
showUsageAndExit(0)
}
args := flag.Args()
if len(args) != 1 {
showUsageAndExit(1)
}
// Connect Options.
opts := []nats.Option{nats.Name("NATS Sample Subscriber")}
opts = setupConnOptions(opts)
if *userCreds != "" && *nkeyFile != "" {
log.Fatal("specify -seed or -creds")
}
// Use UserCredentials
if *userCreds != "" {
opts = append(opts, nats.UserCredentials(*userCreds))
}
// Use TLS client authentication
if *tlsClientCert != "" && *tlsClientKey != "" {
opts = append(opts, nats.ClientCert(*tlsClientCert, *tlsClientKey))
}
// Use specific CA certificate
if *tlsCACert != "" {
opts = append(opts, nats.RootCAs(*tlsCACert))
}
// Use Nkey authentication.
if *nkeyFile != "" {
opt, err := nats.NkeyOptionFromSeed(*nkeyFile)
if err != nil {
log.Fatal(err)
}
opts = append(opts, opt)
}
// Connect to NATS
nc, err := nats.Connect(*urls, opts...)
if err != nil {
log.Fatal(err)
}
subj, i := args[0], 0
nc.Subscribe(subj, func(msg *nats.Msg) {
i += 1
printMsg(msg, i)
})
nc.Flush()
if err := nc.LastError(); err != nil {
log.Fatal(err)
}
log.Printf("Listening on [%s]", subj)
if *showTime {
log.SetFlags(log.LstdFlags)
}
runtime.Goexit()
}
func setupConnOptions(opts []nats.Option) []nats.Option {
totalWait := 10 * time.Minute
reconnectDelay := time.Second
opts = append(opts, nats.ReconnectWait(reconnectDelay))
opts = append(opts, nats.MaxReconnects(int(totalWait/reconnectDelay)))
opts = append(opts, nats.DisconnectErrHandler(func(nc *nats.Conn, err error) {
log.Printf("Disconnected due to:%s, will attempt reconnects for %.0fm", err, totalWait.Minutes())
}))
opts = append(opts, nats.ReconnectHandler(func(nc *nats.Conn) {
log.Printf("Reconnected [%s]", nc.ConnectedUrl())
}))
opts = append(opts, nats.ClosedHandler(func(nc *nats.Conn) {
log.Fatalf("Exiting: %v", nc.LastError())
}))
return opts
}
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