Lesson 05 · Read exactly N body bytes

Read exactly N body bytes

A message body is not line-based - it is a fixed number of raw bytes. Today you read exactly that many, the counterpart to line reading that the header block deliberately left alone.

The goal

Read exactly n bytes from a stream, no more and no fewer.

Start here - the target

TO DO

Scenario: Reading a length-delimited body

Givena stream positioned at "hello!" and n = 5

Whenyou read the body

Thenyou get exactly "hello" (5 bytes)

Andgiven n = 0, you get an empty body and read nothing

Background

Unlike the head, a body has no delimiter to scan for — its length is stated elsewhere (you will get it from a header next chapter). So reading a body means “give me exactly this many bytes.” A single Read can return fewer bytes than you asked for, so you must keep reading until the count is satisfied.

Read-exactly is the right primitive here: it loops internally until your buffer is full or the stream ends early. Handle n = 0 cleanly — a body of zero bytes is completely normal (every GET has one) and should read nothing and return empty.

Make it work

body := make([]byte, n)
_, err := io.ReadFull(r, body) // reads until the slice is full, or errors
// n == 0 is fine: ReadFull returns immediately with an empty body

CheckpointDONE

You can read exactly N body bytes, zero included. Commit.