Go的运行时库文档过时了吗？

So, I'm working on parsing a POST using GO. What I want is the body of the post, so I try the following (r is of type *http.Request in this context):

var body io.Reader
var d []byte
body = r.Body.Reader
body.Read( d)

However, this results in a compilation error:

Compile error: <file>:44: 
    r.Body.Reader undefined (type io.ReadCloser has no field or method Reader)

Odd. I could have sworn that it was defined in the docs... Ah! here it is.

Now, I'm fairly new to Go, but this smells a little odd -- what have I screwed up?

From your link, the doc for a ReadCloser is:

type ReadCloser interface {
    Reader
    Closer
}

What this is telling you, is that a ReadCloser interface is composed of a Reader and a Closer functionality. It IS both. That means the ReadCloser takes on those interface definitions. They are not actually members, the way you are accessing them.

A Reader is:

type Reader interface {
    Read(p []byte) (n int, err error)
}

So that means you should be accessing Read like this:

body = r.Body
body.Read(d)

The way interfaces are defined in Go documents, it looked like it was a "has-a" relationship. It's actually an "is-a" relationship, so the following code does what I want:

var d []byte
r.Body.Read(d)