feat: add experimental warning

docs/api/Client.md

@@ -17,6 +17,8 @@ Returns: `Client`
 
 ### Parameter: `ClientOptions`
 
+> ⚠️ Warning: The `H2` support is experimental.
+
 * **bodyTimeout** `number | null` (optional) - Default: `300e3` - The timeout after which a request will time out, in milliseconds. Monitors time between receiving body data. Use `0` to disable it entirely. Defaults to 300 seconds.
 * **headersTimeout** `number | null` (optional) - Default: `300e3` - The amount of time the parser will wait to receive the complete HTTP headers while not sending the request. Defaults to 300 seconds.
 * **keepAliveMaxTimeout** `number | null` (optional) - Default: `600e3` - The maximum allowed `keepAliveTimeout` when overridden by *keep-alive* hints from the server. Defaults to 10 minutes.

lib/client.js

@@ -90,6 +90,9 @@ const {
   }
 } = http2
 
+// Experimental
+let h2ExperimentalWarned = false
+
 const FastBuffer = Buffer[Symbol.species]
 
 const kClosedResolve = Symbol('kClosedResolve')
@@ -344,9 +347,9 @@ class Client extends DispatcherBase {
   [kDispatch] (opts, handler) {
     const origin = opts.origin || this[kUrl].origin
 
-    let request
-    if (this[kHTTPConnVersion] === 'h2') request = Request[kHTTP2BuildRequest](origin, opts, handler)
-    else request = Request[kHTTP1BuildRequest](origin, opts, handler)
+    const request = this[kHTTPConnVersion] === 'h2'
+      ? Request[kHTTP2BuildRequest](origin, opts, handler)
+      : Request[kHTTP1BuildRequest](origin, opts, handler)
 
     this[kQueue].push(request)
     if (this[kResuming]) {
@@ -1214,6 +1217,13 @@ async function connect (client) {
 
     const isH2 = socket.alpnProtocol === 'h2'
     if (isH2) {
+      if (!h2ExperimentalWarned) {
+        h2ExperimentalWarned = true
+        process.emitWarning('H2 support is experimental, expect them to change at any time.', {
+          code: 'UNDICI-H2'
+        })
+      }
+
       const session = http2.connect(client[kUrl], {
         createConnection: () => socket,
         peerMaxConcurrentStreams: client[kHTTP2SessionState].maxConcurrentStreams