io.copyn

package main

import (
    "io"
    "net/http"
    "os"
)

func main() {
    resp, err := http.Get("http://example.com")
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()

    file, err := os.Create("output.txt")
    if err != nil {
        panic(err)
    }
    defer file.Close()

    buf := make([]byte, 1)
    for {
        n, err := resp.Body.Read(buf)
        if n > 0 {
            _, err = file.Write(buf[:n])
            if err != nil {
                panic(err)
            }
        }
        if err == io.EOF {
            break
        }
        if err != nil {
            panic(err)
        }
    }
}