HTTP 08: Everything

The finale board. No new mechanism: one ordinary request, followed through everything this build has already made, closing the build begun in Build Your Own HTTP Server - From Scratch.

Before you start. This series has been building a small HTTP server, a program that answers a browser’s request for a page the same way every real website does. By now it can do seven things, one per earlier lesson:

Hang up on a caller who never finishes asking, instead of waiting forever.
Find where a request’s opening line and labels end, even when the bytes (single characters, roughly) arrive in pieces.
Work out whether anything follows those labels, and how long it runs.
Send an address like /users/42 to the right piece of code.
Keep the line open and answer a second request on it.
Refuse to hold more than so many lines open, so a flood cannot sink it.
Send back a reply whose length it doesn’t know yet, piece by piece.

This lesson adds no new piece: it sends one ordinary request through all seven, in order.

The idea in 30 seconds

A server that hands out desks with no limit at all eventually runs out of room and crashes; checking a number before handing one out is the fix.
A clock, called a deadline, protects the server from a caller who never finishes talking.
Bytes arrive with no built-in edges, so the server searches for a fixed signal marking where one message ends.
Framing is the rule that says exactly how much more of a message is coming, even when the honest answer is “nothing.”
Routing sends an address to the most specific desk that matches it, not the first one written down.
A reply of unknown length goes out chunked, in labelled pieces, ending in an empty piece that ends the message without ending the call - which is what lets the call stay open, or keep-alive, for the next question.

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