Lesson 09 · Collect headers into a map

Collect headers into a map

A request usually carries several headers, so today you parse each line of the header block and gather them into a lookup by name, the structure handlers will read from.

The goal

Parse every header line in the head into a map from name to value.

Start here - the target

TO DO

Scenario: Building the header map

Giventhe header lines "Host: example.com" and "Accept: */*"

Whenthey are collected and looked up by name

Thenlooking up "Host" gives "example.com" and "Accept" gives "*/*"

Andlooking up a name that was not sent gives the empty string

Background

With one header line parsed, the whole block is a loop: run every line after the request line through parseHeader and store the results in a Headers map with a Get accessor. That Get is how the rest of the server asks questions like “what is the Content-Length?” or “which Host was requested?” — and an absent header simply reads back as empty.

Keep the request line out of this — it was already parsed separately. You are folding just the header lines from the head into a name-to-value map, one entry per field.

Make it work

type Headers map[string]string
func (h Headers) Get(name string) string { return h[name] } // exact match, for now
// build it by running each header line through parseHeader and storing the result

CheckpointDONE

A request's headers collect into a lookup, with absent names reading empty. Commit.