HTTP

Requests and responses

HTTP is a request/response protocol. The client sends a method, a path, headers and an optional body; the server answers with a status code, headers and a body. HTTP/1.1 messages are plain text:

GET /api/orders/42 HTTP/1.1
Host: shop.example.com
Accept: application/json
Authorization: Bearer eyJhbGciOi...

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Content-Length: 28

{"id": 42, "status": "paid"}

raw = (
    "HTTP/1.1 200 OK\r\n"
    "Content-Type: application/json\r\n"
    "Cache-Control: no-store\r\n"
    "Content-Length: 28\r\n"
    "\r\n"
    '{"id": 42, "status": "paid"}'
)

head, body = raw.split("\r\n\r\n", 1)
status_line, *header_lines = head.split("\r\n")
version, code, reason = status_line.split(" ", 2)
headers = {k.lower(): v for k, v in (line.split(": ", 1) for line in header_lines)}
print("status:", code, reason)
print("headers:", headers)
print("body:", body)

status: 200 OK
headers: {'content-type': 'application/json', 'cache-control': 'no-store', 'content-length': '28'}
body: {"id": 42, "status": "paid"}

Methods

GET reads, POST creates or triggers, PUT replaces, PATCH partially updates, DELETE deletes. GET, PUT and DELETE are idempotent: repeating them has the same effect, so clients and proxies may retry them.

Status code families

502 and 504 come from a proxy or load balancer in front of your app: 502 means it got a bad or no response (for example the app closed the connection), 504 means the app didn't answer in time.

Try it

$ curl -i https://example.com          # show response headers
$ curl -v https://example.com          # show the whole conversation, including TLS