package mainimport (    "net/http")func main() {    http.Handle("/", http.FileServer(http.Dir("./www/")))    http.ListenAndServe(":8123", nil)}

package mainimport (    "bytes"    "expvar"    "flag"    "fmt"    "io"    "log"    "net/http"    "os"    "os/exec"    "strconv"    "sync")// hello world, the web servervar helloRequests = expvar.NewInt("hello-requests")func HelloServer(w http.ResponseWriter, req *http.Request) {    helloRequests.Add(1)    io.WriteString(w, "hello, world!\n")}// Simple counter server. POSTing to it will set the value.type Counter struct {    mu sync.Mutex // protects n    n  int}// This makes Counter satisfy the expvar.Var interface, so we can export// it directly.func (ctr *Counter) String() string {    ctr.mu.Lock()    defer ctr.mu.Unlock()    return fmt.Sprintf("%d", ctr.n)}func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {    ctr.mu.Lock()    defer ctr.mu.Unlock()    switch req.Method {    case "GET":        ctr.n++    case "POST":        buf := new(bytes.Buffer)        io.Copy(buf, req.Body)        body := buf.String()        if n, err := strconv.Atoi(body); err != nil {            fmt.Fprintf(w, "bad POST: %v\nbody: [%v]\n", err, body)        } else {            ctr.n = n            fmt.Fprint(w, "counter reset\n")        }    }    fmt.Fprintf(w, "counter = %d\n", ctr.n)}// simple flag servervar booleanflag = flag.Bool("boolean", true, "another flag for testing")func FlagServer(w http.ResponseWriter, req *http.Request) {    w.Header().Set("Content-Type", "text/plain; charset=utf-8")    fmt.Fprint(w, "Flags:\n")    flag.VisitAll(func(f *flag.Flag) {        if f.Value.String() != f.DefValue {            fmt.Fprintf(w, "%s = %s [default = %s]\n", f.Name, f.Value.String(), f.DefValue)        } else {            fmt.Fprintf(w, "%s = %s\n", f.Name, f.Value.String())        }    })}// simple argument serverfunc ArgServer(w http.ResponseWriter, req *http.Request) {    for _, s := range os.Args {        fmt.Fprint(w, s, " ")    }}// a channel (just for the fun of it)type Chan chan intfunc ChanCreate() Chan {    c := make(Chan)    go func(c Chan) {        for x := 0; ; x++ {            c <- x        }    }(c)    return c}func (ch Chan) ServeHTTP(w http.ResponseWriter, req *http.Request) {    io.WriteString(w, fmt.Sprintf("channel send #%d\n", <-ch))}// exec a program, redirecting outputfunc DateServer(rw http.ResponseWriter, req *http.Request) {    rw.Header().Set("Content-Type", "text/plain; charset=utf-8")    date, err := exec.Command("/bin/date").Output()    if err != nil {        http.Error(rw, err.Error(), 500)        return    }    rw.Write(date)}func Logger(w http.ResponseWriter, req *http.Request) {    log.Print(req.URL)    http.Error(w, "oops", 404)}var webroot = flag.String("root", os.Getenv("HOME"), "web root directory")func main() {    flag.Parse()    // The counter is published as a variable directly.    ctr := new(Counter)    expvar.Publish("counter", ctr)    http.Handle("/counter", ctr)    http.Handle("/", http.HandlerFunc(Logger))    http.Handle("/go/", http.StripPrefix("/go/", http.FileServer(http.Dir(*webroot))))    http.Handle("/chan", ChanCreate())    http.HandleFunc("/flags", FlagServer)    http.HandleFunc("/args", ArgServer)    http.HandleFunc("/go/hello", HelloServer)    http.HandleFunc("/date", DateServer)    err := http.ListenAndServe(":12345", nil)    if err != nil {        log.Panicln("ListenAndServe:", err)    }}