Created
December 3, 2018 17:51
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Subscriber who only wants N responses
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// Copyright 2012-2018 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" | |
"runtime" | |
"time" | |
"github.com/nats-io/go-nats" | |
) | |
// NOTE: Can test with demo servers. | |
// nats-wantn -s demo.nats.io -n N | |
// nats-wantn -s demo.nats.io:4443 -n N (TLS version) | |
func usage() { | |
log.Fatalf("Usage: nats-wantn [-s server] [-t] [-n N]") | |
} | |
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 nkeyFile = flag.String("nkey", "", "Use the nkey seed file for authentication") | |
var showTime = flag.Bool("t", false, "Display timestamps") | |
var wantsN = flag.Int("n", 1, "Number of messages to receive") | |
log.SetFlags(0) | |
flag.Usage = usage | |
flag.Parse() | |
// Connect Options. | |
opts := []nats.Option{nats.Name("NATS Sample N Responses Subscriber")} | |
opts = setupConnOptions(opts) | |
// 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) | |
} | |
i := 0 | |
inbox := nc.NewRespInbox() | |
sub, _ := nc.Subscribe(inbox, func(msg *nats.Msg) { | |
i += 1 | |
printMsg(msg, i) | |
if i == *wantsN { | |
log.Fatalf("Reached max responses of %d, exiting", *wantsN) | |
} | |
}) | |
sub.AutoUnsubscribe(*wantsN) | |
nc.Flush() | |
if err := nc.LastError(); err != nil { | |
log.Fatal(err) | |
} | |
log.Printf("Listening on [%s]", inbox) | |
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.DisconnectHandler(func(nc *nats.Conn) { | |
log.Printf("Disconnected") | |
log.Printf("Reconnecting for next %.0fm", 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.Fatal("Exiting, no servers available") | |
})) | |
return opts | |
} |
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