reverseproxy: Rewrite requests and responses for websocket over http2 (#6567)

* reverse proxy: rewrite requests and responses for websocket over http2

* delete protocol pseudo-header

* modify cloned requests

* set request variable to track if it's a h2 websocket

* use request bodu

* rewrite request body

* use WebSocket instead of Websocket in the headers

* use logger check for zap loggers

* fix lint

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -17,6 +17,8 @@ package reverseproxy
 import (
 	"bytes"
 	"context"
+	"crypto/rand"
+	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -394,6 +396,23 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyht
 		return caddyhttp.Error(http.StatusInternalServerError,
 			fmt.Errorf("preparing request for upstream round-trip: %v", err))
 	}
+	// websocket over http2, assuming backend doesn't support this, the request will be modified to http1.1 upgrade
+	// TODO: once we can reliably detect backend support this, it can be removed for those backends
+	if r.ProtoMajor == 2 && r.Method == http.MethodConnect && r.Header.Get(":protocol") != "" {
+		clonedReq.Header.Del(":protocol")
+		// keep the body for later use. http1.1 upgrade uses http.NoBody
+		caddyhttp.SetVar(clonedReq.Context(), "h2_websocket_body", clonedReq.Body)
+		clonedReq.Body = http.NoBody
+		clonedReq.Method = http.MethodGet
+		clonedReq.Header.Set("Upgrade", r.Header.Get(":protocol"))
+		clonedReq.Header.Set("Connection", "Upgrade")
+		key := make([]byte, 16)
+		_, randErr := rand.Read(key)
+		if randErr != nil {
+			return randErr
+		}
+		clonedReq.Header["Sec-WebSocket-Key"] = []string{base64.StdEncoding.EncodeToString(key)}
+	}
 
 	// we will need the original headers and Host value if
 	// header operations are configured; this is so that each