quickest rsync server response

quickest.go

package main

import (
        "bufio"
        "fmt"
        "io"
        "log"
        "os"
        "os/exec"
        "sort"
        "strings"
        "sync"
        "time"
)

func main() {
        log.SetOutput(os.Stderr)
        fh, err := os.Open(os.Args[1])
        if err != nil {
                log.Fatal(err)
        }
        defer fh.Close()

        results := []Result{}
        buf := bufio.NewReader(fh)
        var wg sync.WaitGroup
        for {
                line, err := buf.ReadString('\n')
                if err == io.EOF {
                        break
                }
                if err != nil {
                        log.Fatal(err)
                }
                if strings.HasPrefix(line, "#") {
                        // ignore comments
                        continue
                }
                line = strings.TrimSpace(line)
                if line == "" {
                        continue
                }
                if strings.HasSuffix(line, "/") {
                        // don't get a directory listing of the remote, just a path validation
                        line = line[0 : len(line)-1]
                }

                wg.Add(1)
                go func() {
                        defer wg.Done()
                        cmd := exec.Command("rsync", "--no-motd", line)
                        start := time.Now()
                        out, err := cmd.CombinedOutput()
                        if err != nil {
                                log.Printf("%s failed with: %s", line, out)
                                return
                        }
                        elapsed := time.Since(start)
                        results = append(results, Result{T: elapsed, URL: line})
                }()
        }
        wg.Wait()

        for _, r := range results {
                log.Printf("time %s (%s)", r.T, r.URL)
        }
        sort.Sort(ByTime(results))
        fmt.Println(results[0].URL)
}

type Result struct {
        URL string
        T   time.Duration
}

type ByTime []Result

func (r ByTime) Len() int           { return len(r) }
func (r ByTime) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }
func (r ByTime) Less(i, j int) bool { return r[i].T < r[j].T }

rsync-mirrors.list

# list of mirrors to checkfor fastest
# find more "rsync://" at https://mirrors.slackware.com/mirrorlist/
rsync://mirrors.kernel.org/slackware/slackware64-current
rsync://slackware.osuosl.org/slackware/slackware64-current
rsync://mirror.cs.princeton.edu/slackware/slackware64-current
rsync://mirror.cs.princeton.edu/slackware/slackware64-current/

usage.txt

vbatts@poly:~$ /usr/bin/go version
go version go1.12.2 gccgo (GCC) 9.2.0 linux/amd64
vbatts@poly:~$ /usr/bin/go build slackware/quickest.go
vbatts@poly:~$ ls -lsh quickest 
76K -rwxr-xr-x 1 vbatts users 76K Nov 14 14:10 quickest*
vbatts@poly:~$ ldd quickest 
        linux-vdso.so.1 (0x00007ffc64cc6000)
        libgo.so.14 => /usr/lib64/libgo.so.14 (0x00007f7c02860000)
        libm.so.6 => /lib64/libm.so.6 (0x00007f7c02713000)
        libgcc_s.so.1 => /usr/lib64/libgcc_s.so.1 (0x00007f7c026f9000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f7c02514000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f7c03fe0000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f7c024f2000)
vbatts@poly:~$ ./quickest slackware/rsync-mirrors.list
2019/11/14 14:10:25 time 432.591008ms (rsync://mirror.cs.princeton.edu/slackware/slackware64-current)
2019/11/14 14:10:25 time 751.698997ms (rsync://slackware.osuosl.org/slackware/slackware64-current)
2019/11/14 14:10:25 time 885.012469ms (rsync://mirrors.kernel.org/slackware/slackware64-current)
2019/11/14 14:10:25 time 1.382961223s (rsync://mirror.cs.princeton.edu/slackware/slackware64-current)
rsync://mirror.cs.princeton.edu/slackware/slackware64-current
vbatts@poly:~$ ./quickest slackware/rsync-mirrors.list 2>/dev/null
rsync://mirror.cs.princeton.edu/slackware/slackware64-current