How to read multiple times from same io.Reader

I want to use request.Body(type io.ReadCloser) which is containing a image.

I dont want to use ioutil.ReadAll() as i want to write this body directly to the file as well as want to decode it, so i only want to use the reference to the content to pass to further function calls,

I tried creating multiple instances of reader for example shown below

package main

import (
    "io/ioutil"
    "log"
    "strings"
)

func main() {
    r := strings.NewReader("some io.Reader stream to be read\n")
    a := &r
    b := &r
    log.Println(ioutil.ReadAll(*a))
    log.Println(ioutil.ReadAll(*b))

}

but in second call it always results into nil.

Please help me how can i pass multiple separate reference for the same reader?

io.Reader is treated like a stream. Because of this you cannot read it twice. Imagine an incoming TCP connection - you cannot rewind what's coming in.

But you can use the io.TeeReader to duplicate the stream:
package main

import (
"bytes"
"io"
"io/ioutil"
"log"
"strings"
)

func main() {
r := strings.NewReader("some io.Reader stream to be read\n")
var buf bytes.Buffer
tee := io.TeeReader(r, &buf)

log.Println(ioutil.ReadAll(tee))
log.Println(ioutil.ReadAll(&buf))
}


Example on Go Playground

Edit: As @mrclx pointed out: You need to read from the TeeReader first, otherwise the buffer will be empty.

Stack Overflow Q#39791021, score: 151