doc: add initial version of maintaining-http.md

doc/contributing/maintaining-http.md

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+# Maintaining HTTP
+
+Support for HTTP is a key priority in terms of ensuring the continued success of
+Node.js as captured in the project's
+[technical priorities](https://github.com/nodejs/node/blob/HEAD/doc/contributing/technical-priorities.md).
+
+The current high level strategy is based on the discussion in the
+[Next-10](https://github.com/nodejs/next-10)
+ [mini-summit](https://github.com/nodejs/next-10/blob/main/meetings/summit-jan-2022.md)
+on modern HTTP which was held on Jan 27 2022.
+
+## High level strategy
+
+The key elements of our strategy for future HTTP APIs are:
+
+* APIs should be HTTP protocol independent (support HTTP1, HTTP2, etc.).
+* APIs should be transport protocol independent (TCP, QUIC, etc.).
+* APIs should provide good defaults that perform well.
+* Client/server APIs should be consistent and allow easy integration.
+* Common requirements like piping out from client API to server APIs should be
+  easy.
+* For both the Client and Server there is a need for multiple APIs, with each
+  targeting a different level of abstraction.
+
+Unfortunately our existing HTTP APIs (
+[HTTP](https://nodejs.org/docs/latest/api/http.html),
+[HTTPS](https://nodejs.org/docs/latest/api/https.html), and
+[HTTP2](https://nodejs.org/docs/latest/api/http2.html))
+do not align with our high level strategy. While these APIs
+are widely used and we do not plan to deprecate or remove them,
+they are not the focus of active development or performance improvements.
+Bug fixes however are still important for all of these APIs.
+
+With respect to the HTTP protocols themselves, our current assessment in
+terms of priority within existing or new APIs is:
+
+* HTTP 2 is in “maintenance mode” for both protocol and APIs.
+* HTTP 1 is a stable protocol, but innovation is still possible with the APIs.
+* HTTP 3 is the future need to plan in support.
+
+The current strategy is to build out 2 new client APIs and 2 new Server APIs
+in line with the high level strategy above.
+
+While transport-level APIs are important (e.g. socket level), the HTTP APIs
+should not be tied to a specific transport-level API. Therefore,
+transport-level APIs are out of the scope of our HTTP strategy/maintenance
+information.
+
+### Client APIs
+
+For client APIs we want a high-level API and a low-level API when
+more control is required. The current plan is for the following APIs:
+
+* High-level API -
+  [Fetch](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API)
+  based API built on top of [undici](https://www.npmjs.com/package/undici).
+* Low-level API - a subset of the APIs exposed by
+  [undici](https://www.npmjs.com/package/undici). The exact shape and
+  set of these APIs is still to be worked out. The current plan is to
+  pull undici into Node.js core without exposing its APIs in the Node.js
+  API so that it can initially be used to support the higher level
+  Fetch-based API. As this gets worked out we will discuss which
+  APIs to expose in the Node.js API surface.
+
+### Server APIs
+
+For the server APIs we do not yet have a clear path, other than wanting
+to align them with the APIs built for the client.
+
+## Maintaining the HTTP APIs
+
+### HTTP, HTTPS
+
+The low-level implementation of the
+[HTTP](https://nodejs.org/docs/latest/api/http.html)
+and [HTTPS](https://nodejs.org/docs/latest/api/https.html) APIs
+are maintained in the [llttp](https://github.com/nodejs/llhttp)
+repository. Updates are pulled into Node.js under
+[deps/llhttp](https://github.com/nodejs/node/tree/HEAD/deps/llhttp)
+
+The low-level implementation is made available in the Node.js API through
+JavaScript code in the [lib](https://github.com/nodejs/node/tree/HEAD/lib)
+directory and C++ code in the
+[src](https://github.com/nodejs/node/tree/HEAD/src) directory.
+
+### HTTP2
+
+The low-level implementation of
+[HTTP2](https://nodejs.org/docs/latest/api/http2.html)
+is based on [nghttp2](https://nghttp2.org/). Updates are pulled into Node.js
+under [deps/nghttp2](https://github.com/nodejs/node/tree/HEAD/deps/nghttp2)
+as needed.
+
+The low-level implementation is made available in the Node.js API through
+JavaScript code in the [lib](https://github.com/nodejs/node/tree/HEAD/lib)
+directory and C++ code in the
+[src](https://github.com/nodejs/node/tree/HEAD/src) directory.