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main.go
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main.go
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// Copyright 2016-2019 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"
"os"
"os/signal"
"time"
nats "github.com/nats-io/nats.go"
"github.com/nats-io/stan.go"
"github.com/nats-io/stan.go/pb"
)
var usageStr = `
Usage: stan-sub [options] <subject>
Options:
-s, --server <url> NATS Streaming server URL(s)
-c, --cluster <cluster name> NATS Streaming cluster name
-id, --clientid <client ID> NATS Streaming client ID
-cr, --creds <credentials> NATS 2.0 Credentials
Subscription Options:
--qgroup <name> Queue group
--all Deliver all available messages
--last Deliver starting with last published message
--since <time_ago> Deliver messages in last interval (e.g. 1s, 1hr)
--seq <seqno> Start at seqno
--new_only Only deliver new messages
--durable <name> Durable subscriber name
--unsub Unsubscribe the durable on exit
`
// NOTE: Use tls scheme for TLS, e.g. stan-sub -s tls://demo.nats.io:4443 foo
func usage() {
log.Fatalf(usageStr)
}
func printMsg(m *stan.Msg, i int) {
log.Printf("[#%d] Received: %s\n", i, m)
}
func main() {
var (
clusterID, clientID string
URL string
userCreds string
showTime bool
qgroup string
unsubscribe bool
startSeq uint64
startDelta string
deliverAll bool
newOnly bool
deliverLast bool
durable string
)
flag.StringVar(&URL, "s", stan.DefaultNatsURL, "The nats server URLs (separated by comma)")
flag.StringVar(&URL, "server", stan.DefaultNatsURL, "The nats server URLs (separated by comma)")
flag.StringVar(&clusterID, "c", "test-cluster", "The NATS Streaming cluster ID")
flag.StringVar(&clusterID, "cluster", "test-cluster", "The NATS Streaming cluster ID")
flag.StringVar(&clientID, "id", "stan-sub", "The NATS Streaming client ID to connect with")
flag.StringVar(&clientID, "clientid", "stan-sub", "The NATS Streaming client ID to connect with")
flag.BoolVar(&showTime, "t", false, "Display timestamps")
// Subscription options
flag.Uint64Var(&startSeq, "seq", 0, "Start at sequence no.")
flag.BoolVar(&deliverAll, "all", true, "Deliver all")
flag.BoolVar(&newOnly, "new_only", false, "Only new messages")
flag.BoolVar(&deliverLast, "last", false, "Start with last value")
flag.StringVar(&startDelta, "since", "", "Deliver messages since specified time offset")
flag.StringVar(&durable, "durable", "", "Durable subscriber name")
flag.StringVar(&qgroup, "qgroup", "", "Queue group name")
flag.BoolVar(&unsubscribe, "unsub", false, "Unsubscribe the durable on exit")
flag.BoolVar(&unsubscribe, "unsubscribe", false, "Unsubscribe the durable on exit")
flag.StringVar(&userCreds, "cr", "", "Credentials File")
flag.StringVar(&userCreds, "creds", "", "Credentials File")
log.SetFlags(0)
flag.Usage = usage
flag.Parse()
args := flag.Args()
if len(args) < 1 {
log.Printf("Error: A subject must be specified.")
usage()
}
// Connect Options.
opts := []nats.Option{nats.Name("NATS Streaming Example Subscriber")}
// Use UserCredentials
if userCreds != "" {
opts = append(opts, nats.UserCredentials(userCreds))
}
// Connect to NATS
nc, err := nats.Connect(URL, opts...)
if err != nil {
log.Fatal(err)
}
defer nc.Close()
sc, err := stan.Connect(clusterID, clientID, stan.NatsConn(nc),
stan.SetConnectionLostHandler(func(_ stan.Conn, reason error) {
log.Fatalf("Connection lost, reason: %v", reason)
}))
if err != nil {
log.Fatalf("Can't connect: %v.\nMake sure a NATS Streaming Server is running at: %s", err, URL)
}
log.Printf("Connected to %s clusterID: [%s] clientID: [%s]\n", URL, clusterID, clientID)
// Process Subscriber Options.
startOpt := stan.StartAt(pb.StartPosition_NewOnly)
if startSeq != 0 {
startOpt = stan.StartAtSequence(startSeq)
} else if deliverLast {
startOpt = stan.StartWithLastReceived()
} else if deliverAll && !newOnly {
startOpt = stan.DeliverAllAvailable()
} else if startDelta != "" {
ago, err := time.ParseDuration(startDelta)
if err != nil {
sc.Close()
log.Fatal(err)
}
startOpt = stan.StartAtTimeDelta(ago)
}
subj, i := args[0], 0
mcb := func(msg *stan.Msg) {
i++
printMsg(msg, i)
}
sub, err := sc.QueueSubscribe(subj, qgroup, mcb, startOpt, stan.DurableName(durable))
if err != nil {
sc.Close()
log.Fatal(err)
}
log.Printf("Listening on [%s], clientID=[%s], qgroup=[%s] durable=[%s]\n", subj, clientID, qgroup, durable)
if showTime {
log.SetFlags(log.LstdFlags)
}
// Wait for a SIGINT (perhaps triggered by user with CTRL-C)
// Run cleanup when signal is received
signalChan := make(chan os.Signal, 1)
cleanupDone := make(chan bool)
signal.Notify(signalChan, os.Interrupt)
go func() {
for range signalChan {
fmt.Printf("\nReceived an interrupt, unsubscribing and closing connection...\n\n")
// Do not unsubscribe a durable on exit, except if asked to.
if durable == "" || unsubscribe {
sub.Unsubscribe()
}
sc.Close()
cleanupDone <- true
}
}()
<-cleanupDone
}