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main.go
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main.go
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// Copyright 2018-2019 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 (
"encoding/json"
"flag"
"fmt"
"io/ioutil"
"log"
"net/http"
"os"
"os/signal"
"runtime"
"syscall"
"time"
"github.com/nats-io/nats.go"
)
// NOTE: Can test with demo servers.
// nats-echo -s demo.nats.io <subject>
// nats-echo -s demo.nats.io:4443 <subject> (TLS version)
func usage() {
log.Printf("Usage: nats-echo [-s server] [-creds file] [-t] <subject>\n")
flag.PrintDefaults()
}
func showUsageAndExit(exitcode int) {
usage()
os.Exit(exitcode)
}
func printMsg(m *nats.Msg, i int) {
log.Printf("[#%d] Echoing to [%s]: %q", i, m.Reply, 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 showTime = flag.Bool("t", false, "Display timestamps")
var showHelp = flag.Bool("h", false, "Show help message")
var geoloc = flag.Bool("geo", false, "Display geo location of echo service")
var geo string
log.SetFlags(0)
flag.Usage = usage
flag.Parse()
if *showHelp {
showUsageAndExit(0)
}
args := flag.Args()
if len(args) != 1 {
showUsageAndExit(1)
}
// Lookup geo if requested
if *geoloc {
geo = lookupGeo()
}
// Connect Options.
opts := []nats.Option{nats.Name("NATS Echo Service")}
opts = setupConnOptions(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)
}
subj, i := args[0], 0
nc.QueueSubscribe(subj, "echo", func(msg *nats.Msg) {
i++
if msg.Reply != "" {
printMsg(msg, i)
// Just echo back what they sent us.
if geo != "" {
m := fmt.Sprintf("[%s]: %q", geo, msg.Data)
nc.Publish(msg.Reply, []byte(m))
} else {
nc.Publish(msg.Reply, msg.Data)
}
}
})
nc.Flush()
if err := nc.LastError(); err != nil {
log.Fatal(err)
}
log.Printf("Echo Service listening on [%s]\n", subj)
// Now handle signal to terminate so we cam drain on exit.
c := make(chan os.Signal, 1)
signal.Notify(c, syscall.SIGINT)
go func() {
// Wait for signal
<-c
log.Printf("<caught signal - draining>")
nc.Drain()
}()
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) {
if !nc.IsClosed() {
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) {
if !nc.IsClosed() {
log.Fatal("Exiting: no servers available")
} else {
log.Fatal("Exiting")
}
}))
return opts
}
// We only want region, country
type geo struct {
// There are others..
Region string
Country string
}
// lookup our current region and country..
func lookupGeo() string {
c := &http.Client{Timeout: 2 * time.Second}
resp, err := c.Get("https://ipapi.co/json")
if err != nil || resp == nil {
log.Fatalf("Could not retrive geo location data: %v", err)
}
defer resp.Body.Close()
body, _ := ioutil.ReadAll(resp.Body)
g := geo{}
if err := json.Unmarshal(body, &g); err != nil {
log.Fatalf("Error unmarshalling geo: %v", err)
}
return g.Region + ", " + g.Country
}