Lesson 13 · Read the body with Content-Length

Read the body with Content-Length

A request that carries data announces its size in the Content-Length header. Today you read exactly that many body bytes, connecting the header map to the read-exactly primitive you built earlier.

The goal

Use the Content-Length header to read exactly that many bytes of body, and read no body when the header is absent.

Start here - the target

TO DO

Scenario: Reading a Content-Length body

Givenheaders with "Content-Length: 5" and the stream positioned at "hello!"

Whenthe body is read

Thenthe body is "hello" (5 bytes) and "!" remains unread

Andwith no Content-Length header the body is empty

Background

Now the header map and the read-exactly primitive combine. A body’s length is not in the byte stream — it is announced by the Content-Length header. Parse that number, then read precisely that many bytes off the reader that is still parked at the start of the body.

When there is no Content-Length, treat the body as empty: a plain GET sends no body and no length header, and reading zero bytes is the correct behavior. Do not read past what the header promised, or you will swallow the start of the next request on a reused connection.

Make it work

n := 0
if cl := headers.Get("Content-Length"); cl != "" {
    n, _ = strconv.Atoi(cl)
}
body := readBody(r, n) // read-exactly, from chapter 1

CheckpointDONE

Bodies are read to the length Content-Length announces. Commit.