HTTP/1.1 coverage

LWHTTP is a client. Message syntax and framing follow RFC 9112, semantics follow RFC 9110, and URLs follow RFC 3986.

Implemented

Area	Behaviour
Status line	HTTP/1.x, three-digit status, optional reason phrase. Other major versions fail with LWHTTP_ERR_VERSION.
Field syntax	Token names, OWS trimming, obs-fold replaced by a space, bare LF line endings accepted, CR, NUL and other control characters rejected, whitespace before the colon tolerated.
Message length	HEAD, 1xx, 204 and 304 have no body. 101 and 2xx to CONNECT switch protocols. Transfer-Encoding overrides Content-Length and disables reuse. Repeated Content-Length values must agree.
Chunked transfer	Chunk extensions (including quoted strings) skipped, trailer fields collected, chunk sizes bounds-checked.
Interim responses	100 Continue releases a held body, other 1xx are skipped.
Persistent connections	Reuse per origin, Connection: close and keep-alive honoured, one automatic retry for idempotent requests on a dead reused connection.
Request bodies	Content-Length for known sizes, chunked for streamed bodies, Content-Length: 0 for empty POST, PUT, PATCH, Expect: 100-continue.
Early responses	A final response that arrives during the upload stops it and retires the connection.
Redirects	301, 302, 303, 307, 308, relative references, method rewriting, credential stripping across origins.
Request targets	origin form, authority form for CONNECT, asterisk and absolute form through target.
Content codings	Accept-Encoding: identity sent, encoded responses rejected unless the program opts in.
Upgrades	101 and CONNECT tunnels hand the socket over to the program.
HTTPS	TLS 1.3 through lwIP-CE, with SNI and certificate verification.

Not implemented

Area	Why
Content decoding (gzip, deflate, br)	A streaming inflater needs a 32 KB window, most of the calculator’s free RAM.
Caching	Belongs in the application on a device without storage to spare.
Cookies	A separate specification (RFC 6265) with state that applications manage better themselves.
Proxies	lwIP-CE cannot start TLS inside an existing TCP tunnel.
Pipelining	Optional in RFC 9112 and poorly supported by servers.
HTTP date helpers	Nothing in the client needs them; parsing Date or Last-Modified is left to applications.
Server role	LWHTTP is a client library.