when using fmt.Printf() many blanks are displayed-CodePudding

I'm trying to complete an echo server using golang. server like this:

// use tcp to echo time
func main() {
    // listen tcp localhost:8000
    listener, err := net.Listen("tcp", "localhost:8000")
    if err != nil {
        fmt.Fprintf(os.Stderr, "listen error, %s", err)
        return
    }
    for {
        // accept
        connection, err := listener.Accept()
        if err != nil {
            fmt.Fprintf(os.Stderr, "listen error, %s\n", err)
        } else {
            handle(connection)
        }
    }
}

// handle the tcp connection
// return the time in one second gap
func handle(connection net.Conn) {
    defer connection.Close()
    for {
        // return written bytes, err
        if _, err := fmt.Fprintf(connection, time.Now().Format("15:04:05\n")); err != nil {
            // write error, probably the client close the connection
            fmt.Fprintf(os.Stderr, "%s close connection\n", connection.RemoteAddr())
            break
        }
        // wait one second
        time.Sleep(1 * time.Second)
    }
}

client like this

package main

const (
    proto = "tcp"
    addr  = "localhost:8000"
)

func main() {
    // client connect to tcp localhost:8000
    connection, err := net.Dial(proto, addr)
    if err != nil {
        fmt.Fprintf(os.Stderr, "connect to %s error, %s", addr, err)
    } else {
        buf := make([]byte, 1024)
        for {
            if _, err := connection.Read(buf); err != nil {
                fmt.Fprintf(os.Stderr, "read from %s error, %s\n", addr, err)
                break
            } else {
                fmt.Printf("data:%s ending\n", buf)
            }
        }
    }

}

when running , the result is : enter image description here

I have no idea why so many blanks are shown. I guess it's probably caused by the built-in function make, but why golang by defalut, displays so many blanks at the end of a string, unlike other high-level languages? Could explain this and fix it?

CodePudding user response：

Read returns n, the number of bytes read. Don't ignore it. Read into a buffer of length cap(buf): buf[:cap(buf)]. Then use n to update the buffer length: buf = buf[:n].

buf := make([]byte, 0, 1024)
for {
    n, err := connection.Read(buf[:cap(buf)])
    buf = buf[:n]
    if err != nil {
        fmt.Fprintf(os.Stderr, "read from %s error, %s\n", addr, err)
        break
    }
    fmt.Printf("data:%s ending\n", buf)
}

CodePudding user response：

You are right, built-in make declare a slice with length and capacity equals to 1024.The better way to deal with such info is to use a protocol which can first read the size of the body, and declare the fit size of the reponse body.

CodePudding user response：

you reserved capacity for byte array that why shown blank, by the way easy way to remove this blank space you can try to use like this

bufString := string(buf)
b := strings.Replace(bufString, "\n", "", 1)
fmt.Printf("data:%s ending\n", b)

please make sure you use "\n" for end of write only

edited (string.Replace() will be clear your blank value in your byte array and convert to string)