Lesson 04 · Read the header block - Build an HTTP Server

Read the header block

A request's head is a run of lines that ends at the first blank line. Today you read that whole block, so you have the request line and all its headers in hand before parsing any of them.

The goal

Read lines until a blank line and return every non-empty line that came before it.

Start here - the target

TO DO

Scenario: Reading the head of a request

Givena stream holding "GET / HTTP/1.1\r\nHost: example.com\r\nAccept: */*\r\n\r\nBODY" (some body bytes follow the blank line)

Whenyou read the head

Thenyou get the lines ["GET / HTTP/1.1", "Host: example.com", "Accept: */*"]

Andreading stops at the blank line, so a following read still yields "BODY"

Background

Every HTTP request begins with a head: the request line followed by zero or more header lines. The head is terminated by a single empty line — the \r\n\r\n sequence you have surely seen at the end of raw requests. Reading the head means looping readLine until you hit that empty line.

Stopping exactly at the blank line matters: whatever comes after it is the message body, which is not line-based and must not be read as lines. Break the moment you see an empty line and leave the reader parked at the start of the body for a later lesson.

Make it work

var lines []string
for {
    line, _ := readLine(r) // from the previous lesson
    if line == "" {        // the blank line ends the head
        break
    }
    lines = append(lines, line)
}

CheckpointDONE

Your reader pulls a request's whole head off the wire and stops at the blank line. Commit.