Lesson 19 · Serialize response headers

Serialize response headers

A response carries headers just like a request does, written one per line. Today you turn a header map into that wire text, the inverse of the parsing you did earlier.

The goal

Serialize a set of response headers into CRLF-terminated "Name: Value" lines.

Start here - the target

TO DO

Scenario: Writing headers to the wire

Givena response header "Content-Type" with value "text/plain"

Whenthe headers are serialized

Thenthe output contains the line "Content-Type: text/plain\r\n"

Background

Writing headers is the mirror image of parsing them: each entry becomes one Name: Value line ending in CRLF. Where parsing split on the first colon and trimmed whitespace, serializing joins with ": " and terminates with \r\n.

Keep the response’s header names in the exact case you want on the wire — clients do not care, but Content-Type reads better than content-type in a debugger. Emit the lines in a stable order — sorting by name is simplest — so that once a response carries several headers it serializes to predictable bytes you can check exactly. This block sits between the status line and the body; the blank line that separates headers from body comes when you assemble the whole response next.

Make it work

var b strings.Builder
for name, value := range headers {
    fmt.Fprintf(&b, "%s: %s\r\n", name, value)
}

CheckpointDONE

Response headers serialize to CRLF-terminated lines. Commit.