84 lines
2.1 KiB
Go
84 lines
2.1 KiB
Go
//
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// Binary Star client proof-of-concept implementation. This client does no
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// real work; it just demonstrates the Binary Star failover model.
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package main
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import (
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zmq "github.com/pebbe/zmq4"
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"fmt"
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"strconv"
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"time"
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)
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const (
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REQUEST_TIMEOUT = 1000 * time.Millisecond // msecs
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SETTLE_DELAY = 2000 * time.Millisecond // Before failing over
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)
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func main() {
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server := []string{"tcp://localhost:5001", "tcp://localhost:5002"}
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server_nbr := 0
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fmt.Printf("I: connecting to server at %s...\n", server[server_nbr])
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client, _ := zmq.NewSocket(zmq.REQ)
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client.Connect(server[server_nbr])
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poller := zmq.NewPoller()
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poller.Add(client, zmq.POLLIN)
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sequence := 0
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LOOP:
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for {
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// We send a request, then we work to get a reply
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sequence++
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client.SendMessage(sequence)
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for expect_reply := true; expect_reply; {
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// Poll socket for a reply, with timeout
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polled, err := poller.Poll(REQUEST_TIMEOUT)
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if err != nil {
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break LOOP // Interrupted
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}
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// We use a Lazy Pirate strategy in the client. If there's no
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// reply within our timeout, we close the socket and try again.
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// In Binary Star, it's the client vote which decides which
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// server is primary; the client must therefore try to connect
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// to each server in turn:
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if len(polled) == 1 {
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// We got a reply from the server, must match sequence
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reply, _ := client.RecvMessage(0)
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seq, _ := strconv.Atoi(reply[0])
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if seq == sequence {
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fmt.Printf("I: server replied OK (%s)\n", reply[0])
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expect_reply = false
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time.Sleep(time.Second) // One request per second
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} else {
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fmt.Printf("E: bad reply from server: %q\n", reply)
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}
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} else {
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fmt.Println("W: no response from server, failing over")
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// Old socket is confused; close it and open a new one
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client.Close()
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server_nbr = 1 - server_nbr
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time.Sleep(SETTLE_DELAY)
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fmt.Printf("I: connecting to server at %s...\n", server[server_nbr])
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client, _ = zmq.NewSocket(zmq.REQ)
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client.Connect(server[server_nbr])
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poller = zmq.NewPoller()
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poller.Add(client, zmq.POLLIN)
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// Send request again, on new socket
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client.SendMessage(sequence)
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}
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}
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}
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}
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