How to get the size of an io.reader object

Question

I would like to get the size of an io.reader to return the length of a picture for a bse64 concerns.

The main problem is to get the size of dec to return a content-length header

Here is my code :

package main

import (
    "fmt"
    "net/http"
    "time"
    "strconv"
    "io"
        base64 "encoding/base64"
    "bytes"

)

func pix(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "Hi there, I love %s!", r.URL.Path[1:])
    cookie, _ := r.Cookie("csrftoken")
    fmt.Printf(cookie.Value)
}



func img(w http.ResponseWriter, r *http.Request) {
    expiration := time.Now().Add(365 * 24 * time.Hour)
    cookie    :=    http.Cookie{Name: "csrftoken",Value:"abcd",Expires:expiration,HttpOnly: false}
    http.SetCookie(w, &cookie)
    img := bytes.NewBufferString("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")
    dec := base64.NewDecoder(base64.StdEncoding, img)
    w.Header().Set("Content-Type", "image/jpeg")

// the problem is here i would like to get the size to return the length of the picture  (lend(dec))

    w.Header().Set("Content-Length", strconv.Itoa(len(dec)))

    io.Copy(w, dec)

}


func main() {
    http.HandleFunc("/pix/", pix)
    http.HandleFunc("/img/", img)
    http.HandleFunc("/red/", img)
    http.HandleFunc("/", img)
    http.ListenAndServe(":8080", nil)

}

regards and thanks

Answer 1

func getSize(stream io.Reader) int {
    buf := new(bytes.Buffer)
    buf.ReadFrom(stream)
    return buf.Len()
}