Tour of Go 2.0

Readers

The io package defines io.Reader — one of the most important interfaces in Go’s standard library.

func (T) Read(b []byte) (n int, err error)

Read fills a byte slice with data and returns how many bytes it wrote, plus any error. When the stream is done, it returns io.EOF.

This one interface powers files, network connections, HTTP bodies, compressors, ciphers, and more. Anything that streams data implements it.

Try it: this example reads a string 8 bytes at a time. Watch the output to see how Read works through the data chunk by chunk until it hits io.EOF.

main.go ▶ Run in Playground 
package main

import (
	"fmt"
	"io"
	"strings"
)

func main() {
	r := strings.NewReader("Hello, Reader!")

	b := make([]byte, 8)
	for {
		n, err := r.Read(b)
		fmt.Printf("n = %v err = %v b = %v\n", n, err, b)
		fmt.Printf("b[:n] = %q\n", b[:n])
		if err == io.EOF {
			break
		}
	}
}