HTTP

Core Idea

HTTP is a request-response protocol: a client asks for a resource, and a server returns a status line, headers, and usually a body.

Commands To Try

curl -I https://lf2607.kolamayermakers.org/~username/
curl -L https://lf2607.kolamayermakers.org/~username/
curl -v https://lf2607.kolamayermakers.org/~username/

curl -I shows headers. Plain curl shows the body. curl -v shows the client-server conversation.

Response Shape

HTTP/2 200
server: Caddy
content-type: text/html; charset=utf-8

<html>...</html>

Status line: whether the request succeeded or failed.
Headers: metadata about the response.
Blank line: separates headers from the body.
Body: the resource content, if there is one.

Status Codes To Know

Code	Meaning
`200`	OK. The resource was returned.
`301` or `302`	Redirect. Try `curl -L`.
`404`	Not found. The server could not find that path.
`500`	Server error. The server failed while handling the request.
`502`	Bad gateway. A proxy could not reach or use its backend.

Methods

This course mostly uses GET and header-only inspection. curl -I sends a HEAD request, which asks for headers without the body.

HTTP Versus HTTPS

HTTP is the protocol. HTTPS is HTTP carried inside TLS encryption. HTTPS protects the request and response in transit and lets the client verify the server certificate.

Common Failures

404: rebuild the site or check the path and filename.
502: check the backend service with systemctl --user status site.service.
Redirect loop or surprise redirect: inspect with curl -L -I and read each location header.
Certificate error: read the hostname and certificate message; do not bypass it blindly.

Proof Check

Fetch your static site with curl -I. Identify the status code, server header, and content type.