esp-idf/components/nghttp/nghttp.rst

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The nghttp Instruction
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This is an implementation of the Hypertext Transfer Protocol version 2 in C.
The framing layer of HTTP/2 is implemented as a reusable C library.
An HPACK encoder and decoder are available as a public API.
- The nghttp support many different processor, But for the most part function you only need the function as follows:
*nghttp2_session_callbacks_new:* Initializes *callbacks_ptr with NULL values
*nghttp2_session_client_new:* Initializes *session_ptr for client use
*nghttp2_session_callbacks_del:* Frees any resources allocated for callbacks
*nghttp2_submit_settings:* Stores local settings and submits SETTINGS frame
*nghttp2_submit_request:* Submits HEADERS frame and optionally one or more DATA frames
*nghttp2_session_want_read:* Returns nonzero value if session wants to receive data from the remote peer
*nghttp2_session_want_write:* Returns nonzero value if session wants to send data to the remote peer
*nghttp2_session_recv:* Receives frames from the remote peer
*nghttp2_session_send:* Sends pending frames to the remote peer
*nghttp2_session_del:* Frees any resources allocated for session
If you are following TLS related RFC, you know that NPN is not the standardized way to negotiate HTTP/2. NPN itself is not event published as RFC.
The standard way to negotiate HTTP/2 is ALPN, Application-Layer Protocol Negotiation Extension, defined in RFC 7301.
- The following endpoints are available to try out the nghttp2 implementation:
https://nghttp2.org/ (TLS + ALPN/NPN)
This endpoint supports h2, h2-16, h2-14, spdy/3.1 and http/1.1 via ALPN/NPN and requires TLSv1.2 for HTTP/2 connection.
More information about nghttp library will show them on https://nghttp2.org
An introductory article on protocol is available on RFC 7540 HTTP/2 and RFC 7541 HPACK - Header Compression for HTTP/2