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main.go
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main.go
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// Copyright 2019 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"
"fmt"
"log"
"sync"
"github.com/nats-io/nats.go"
"github.com/nats-io/not.go"
"github.com/opentracing/opentracing-go"
"github.com/opentracing/opentracing-go/ext"
)
func usage() {
log.Fatalf("Usage: reply [-s server] [-creds file] [-t] <subject> <response>")
}
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 showTime = flag.Bool("t", false, "Display timestamps")
var numMsgs = flag.Int("n", 1, "Exit after N msgs processed.")
log.SetFlags(0)
flag.Usage = usage
flag.Parse()
args := flag.Args()
if len(args) < 2 {
usage()
}
tracer, closer := not.InitTracing("NATS Responder")
opentracing.SetGlobalTracer(tracer)
defer closer.Close()
// Connect Options.
opts := []nats.Option{nats.Name("NATS Sample Responder")}
opts = not.SetupConnOptions(tracer, opts)
// Use UserCredentials
if *userCreds != "" {
opts = append(opts, nats.UserCredentials(*userCreds))
}
// Connect to NATS
nc, err := nats.Connect(*urls, opts...)
if err != nil {
log.Fatal(err)
}
wg := sync.WaitGroup{}
wg.Add(*numMsgs)
subj, reply := args[0], []byte(args[1])
nc.Subscribe(subj, func(msg *nats.Msg) {
defer wg.Done()
// Create new TraceMsg from the NATS message.
t := not.NewTraceMsg(msg)
// Extract the span context from the request message.
sc, err := tracer.Extract(opentracing.Binary, t)
if err != nil {
log.Printf("Extract error: %v", err)
}
// Setup a span referring to the span context of the incoming NATS message.
replySpan := tracer.StartSpan("Service Responder", ext.SpanKindRPCServer, ext.RPCServerOption(sc))
ext.MessageBusDestination.Set(replySpan, msg.Subject)
defer replySpan.Finish()
log.Printf("Received request: %s", t)
if err := nc.Publish(msg.Reply, reply); err != nil {
replySpan.LogEvent(fmt.Sprintf("error: %v", err))
}
replySpan.LogEvent(fmt.Sprintf("Response msg: %s", reply))
})
if err := nc.LastError(); err != nil {
log.Fatal(err)
}
log.Printf("Listening on [%s]", subj)
if *showTime {
log.SetFlags(log.LstdFlags)
}
wg.Wait()
}