ContextReadCloser issue

gistfile1.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
)

var next = 0

type ContextReadCloser interface {
	io.ReadCloser
	Context() map[interface{}]interface{}
}

type FooReadCloser interface {
	io.ReadCloser
	Foo() int
}

type X struct {
	Body io.ReadCloser
}

type contextReadCloser struct {
	io.ReadCloser
	context map[interface{}]interface{}
}

func (crc *contextReadCloser) Context() map[interface{}]interface{} {
	return crc.context
}

type fooReadCloser struct {
	io.ReadCloser
	foo int
}

func (frc *fooReadCloser) Foo() int {
	return frc.foo
}

func getContextReadCloser(req *X) ContextReadCloser {
	crc, ok := req.Body.(ContextReadCloser)
	if !ok {
		crc = &contextReadCloser{
			ReadCloser: req.Body,
			context:    make(map[interface{}]interface{}),
		}
		req.Body = crc
	}
	return crc
}

func getFooReadCloser(req *X) FooReadCloser {
	frc, ok := req.Body.(FooReadCloser)
	if !ok {
		next = next + 1
		frc = &fooReadCloser{
			ReadCloser: req.Body,
			foo:        next,
		}
		req.Body = frc
	}
	return frc
}

func main() {
	var req X
	var b bytes.Buffer

	req.Body = ioutil.NopCloser(&b)

	crc := getContextReadCloser(&req)
	crc.Context()["foo"] = "bar"

	crc = getContextReadCloser(&req)
	fmt.Printf("%#v\n", crc.Context()["foo"])

	frc := getFooReadCloser(&req)
	fmt.Printf("%#v\n", frc.Foo())

	crc = getContextReadCloser(&req)
	fmt.Printf("%#v\n", crc.Context()["foo"])

	frc = getFooReadCloser(&req)
	fmt.Printf("%#v\n", frc.Foo())
}