package main

import (
    "bytes"
    "fmt"
    "io"
    "net/http"
)

type SimpleBufWriter []byte

func (s *SimpleBufWriter) Write(w io.Writer) (int, error) {
    return w.Write([]byte(*s))
}

func main() {
    var (
        buf  = bytes.NewBuffer(nil)
        data = SimpleBufWriter([]byte{0, 1})
    )

    //Tmp buffer is created
    if _, err := data.Write(buf); err != nil {
        fmt.Println("data.Write:", err)
        return
    }

    /*
        Body can be only a io.ReadCloser It would be so much easier to just pass a writer here
        Or something like http.BodyWriter(w) with basicly returns errors for Read and Close but is forwarding Write just for the underlying writer
    */
    req, err := http.NewRequest("POST", "http://example.ex/post", buf)
    if err != nil {
        fmt.Println("NewRequest:", err)
        return
    }

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        fmt.Println("Do:", err)
        return
    }

    defer resp.Body.Close()
}