mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2024-11-20 13:23:43 +00:00
51 lines
1.1 KiB
Go
51 lines
1.1 KiB
Go
|
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
|
||
|
|
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
|
||
|
|
|
||
|
|
// See page 130.
|
||
|
|
|
||
|
|
// The wait program waits for an HTTP server to start responding.
|
||
|
|
package main
|
||
|
|
|
||
|
|
import (
|
||
|
|
"fmt"
|
||
|
|
"log"
|
||
|
|
"net/http"
|
||
|
|
"os"
|
||
|
|
"time"
|
||
|
|
)
|
||
|
|
|
||
|
|
//!+
|
||
|
|
// WaitForServer attempts to contact the server of a URL.
|
||
|
|
// It tries for one minute using exponential back-off.
|
||
|
|
// It reports an error if all attempts fail.
|
||
|
|
func WaitForServer(url string) error {
|
||
|
|
const timeout = 1 * time.Minute
|
||
|
|
deadline := time.Now().Add(timeout)
|
||
|
|
for tries := 0; time.Now().Before(deadline); tries++ {
|
||
|
|
_, err := http.Head(url)
|
||
|
|
if err == nil {
|
||
|
|
return nil // success
|
||
|
|
}
|
||
|
|
log.Printf("server not responding (%s); retrying...", err)
|
||
|
|
time.Sleep(time.Second << uint(tries)) // exponential back-off
|
||
|
|
}
|
||
|
|
return fmt.Errorf("server %s failed to respond after %s", url, timeout)
|
||
|
|
}
|
||
|
|
|
||
|
|
//!-
|
||
|
|
|
||
|
|
func main() {
|
||
|
|
if len(os.Args) != 2 {
|
||
|
|
fmt.Fprintf(os.Stderr, "usage: wait url\n")
|
||
|
|
os.Exit(1)
|
||
|
|
}
|
||
|
|
url := os.Args[1]
|
||
|
|
//!+main
|
||
|
|
// (In function main.)
|
||
|
|
if err := WaitForServer(url); err != nil {
|
||
|
|
fmt.Fprintf(os.Stderr, "Site is down: %v\n", err)
|
||
|
|
os.Exit(1)
|
||
|
|
}
|
||
|
|
//!-main
|
||
|
|
}
|