main.go 源码
// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
// For more tutorials : https://learngoprogramming.com
// In-person training : https://www.linkedin.com/in/inancgumus/
// Follow me on twitter: https://twitter.com/inancgumus
package main
import (
"bytes"
"fmt"
"io"
"net/http"
"os"
)
func main() {
// initiate the transmission channel (http connection) to the webserver.
resp, err := http.Get("https://inancgumus.github.com/x/rosie.unknown")
if err != nil {
fmt.Fprintln(os.Stderr, err)
return
}
// close it so the http package can reuse the connection.
defer resp.Body.Close()
// resp.Body here is an io.ReadCloser: Read() + Close() methods.
// but in the transfer function it's an io.Reader: Only the Read() method.
n, err := transfer(resp.Body)
if err != nil {
fmt.Fprintln(os.Stderr, err)
return
}
fmt.Printf("%d bytes transferred.\n", n)
// resp.Body.Close() runs here (because of the defer above)
}
func transfer(r io.Reader) (n int64, err error) {
const pngSign = "\x89PNG\r\n\x1a\n"
const pngSignLen = 8
// create an in-memory buffer (bytes.Buffer is an io.Reader and an io.Writer).
var memory bytes.Buffer
// stream from the standard input to the in-memory buffer in 32KB data chunks.
// r.Read(...) -> memory.Write(...)
if n, err = io.Copy(&memory, r); err != nil {
return n, err
}
// check the png signature.
buf := memory.Bytes()
fmt.Printf("% x\n", buf[:pngSignLen])
fmt.Printf("% x\n", pngSign)
return n, err
}
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