f9d452ad2c
This is an example of a race-free long-poll server and client. It uses a redirection method to signal that the "Watch" is running. Other race-free methods exist.
57 lines
1.9 KiB
Go
57 lines
1.9 KiB
Go
// This is an example longpoll server. On client connection it starts a "Watch",
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// and notifies the client with a redirect when that watch is ready. This is
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// important to avoid a possible race between when the client believes the watch
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// is actually ready, and when the server actually is watching.
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package main
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import (
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"fmt"
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"io"
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"log"
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"math/rand"
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"net/http"
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"time"
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)
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// you can use `wget http://127.0.0.1:12345/hello -O /dev/null`
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// or `go run client.go`
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const (
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addr = ":12345"
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)
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// WatchStart kicks off the initial watch and then redirects the client to
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// notify them that we're ready. The watch operation here is simulated.
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func WatchStart(w http.ResponseWriter, req *http.Request) {
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log.Printf("Start received...")
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time.Sleep(time.Duration(5) * time.Second) // 5 seconds to get ready and start *our* watch ;)
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//started := time.Now().UnixNano() // time since watch is "started"
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log.Printf("URL: %+v", req.URL)
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token := fmt.Sprintf("%d", rand.Intn(2^32-1))
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http.Redirect(w, req, fmt.Sprintf("/ready?token=%s", token), http.StatusSeeOther) // TODO: which code should we use ?
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log.Printf("Redirect sent!")
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}
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// WatchReady receives the client connection when it has been notified that the
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// watch has started, and it returns to signal that an event on the watch
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// occurred. The event operation here is simulated.
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func WatchReady(w http.ResponseWriter, req *http.Request) {
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log.Printf("Ready received")
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log.Printf("URL: %+v", req.URL)
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//time.Sleep(time.Duration(10) * time.Second)
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time.Sleep(time.Duration(rand.Intn(10)) * time.Second) // wait until an "event" happens
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io.WriteString(w, "Event happened!\n")
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log.Printf("Event sent")
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}
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func main() {
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log.Printf("Starting...")
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//rand.Seed(time.Now().UTC().UnixNano())
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http.HandleFunc("/watch", WatchStart)
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http.HandleFunc("/ready", WatchReady)
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log.Printf("Listening on %s", addr)
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log.Fatal(http.ListenAndServe(addr, nil))
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}
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