Lesson 41 · Capstone: follow a redirect carrying a cookie

Capstone: follow a redirect carrying a cookie

The whole client in one exchange - a request gets a 302 that both sets a cookie and points elsewhere, and the follow-up request lands at the new location carrying that cookie. This is a real session in miniature.

The goal

Follow a redirect that sets a cookie, producing a follow-up request to the new location carrying the Cookie header.

Start here - the target

TO DO

Scenario: A redirect-and-cookie round-trip

Givenan empty jar and a GET to "http://example.com/login" whose stream returns "HTTP/1.1 302 Found\r\nLocation: /home\r\nSet-Cookie: sid=xyz; Path=/\r\nContent-Length: 0\r\n\r\n"

Whenthe client follows the redirect

Thenit stores sid=xyz, resolves the Location to "http://example.com/home", and the follow-up is a GET carrying header Cookie "sid=xyz"

Andthe follow-up request bytes are exactly "GET /home HTTP/1.1\r\nCookie: sid=xyz\r\nHost: example.com\r\n\r\n"

Background

This is the promise the whole project was built to keep: a client that holds a real conversation with a server. The login response does two things at once - it sets a cookie (sid=xyz) and redirects you (Location: /home) - and a working client has to honor both. It parses the Set-Cookie into its jar, resolves /home against the current host, keeps the method a GET per the 302 rule, and issues the follow-up request carrying the cookie it was just handed: GET /home with Cookie: sid=xyz.

Every layer is doing its job. The URL parser resolved the relative location, the request builder framed the follow-up with sorted headers, the redirect rule chose the method, and the cookie jar carried the session forward. From parsing a scheme off a string you have built the honest core of an HTTP/1.1 client - request serialization, response parsing, chunked and length framing, keep-alive, encodings, redirects, and cookies - all verified against exact bytes. The finalize wraps this unchanged core in a real socket to fetch a live page. That is a real client, and it is yours.

Make it work

// 1. Do the login request; get the 302 response
// 2. parse Set-Cookie into the jar (SetCookie)
// 3. resolveLocation(current, resp.Get("Location")) -> /home
// 4. redirectMethod(302, "GET") -> GET
// 5. build the follow-up; set Cookie header from jar.header()
// 6. assert its bytes match exactly

CheckpointDONE

Your client follows a redirect while carrying a server-set cookie. The project is complete - commit and stop here.