refactor(route): simplify context handling in RouteContext

- Removed unnecessary requestInternal struct and directly accessed the context field of http.Request.
- Simplified the initialization of ctxFieldOffset.

internal/route/routes/context.go

@@ -2,10 +2,6 @@ package routes
 
 import (
 	"context"
-	"crypto/tls"
-	"fmt"
-	"io"
-	"mime/multipart"
 	"net/http"
 	"net/url"
 	"reflect"
@@ -34,7 +30,8 @@ func (r *RouteContext) Value(key any) any {
 func WithRouteContext(r *http.Request, route types.HTTPRoute) *http.Request {
 	// we don't want to copy the request object every fucking requests
 	// return r.WithContext(context.WithValue(r.Context(), routeContextKey, route))
-	(*requestInternal)(unsafe.Pointer(r)).ctx = &RouteContext{
+	ctxFieldPtr := (*context.Context)(unsafe.Pointer(uintptr(unsafe.Pointer(r)) + ctxFieldOffset))
+	*ctxFieldPtr = &RouteContext{
 		Context: r.Context(),
 		Route:   route,
 	}
@@ -107,43 +104,12 @@ func TryGetUpstreamURL(r *http.Request) string {
 	return ""
 }
 
-type requestInternal struct {
-	Method           string
-	URL              *url.URL
-	Proto            string
-	ProtoMajor       int
-	ProtoMinor       int
-	Header           http.Header
-	Body             io.ReadCloser
-	GetBody          func() (io.ReadCloser, error)
-	ContentLength    int64
-	TransferEncoding []string
-	Close            bool
-	Host             string
-	Form             url.Values
-	PostForm         url.Values
-	MultipartForm    *multipart.Form
-	Trailer          http.Header
-	RemoteAddr       string
-	RequestURI       string
-	TLS              *tls.ConnectionState
-	Cancel           <-chan struct{}
-	Response         *http.Response
-	Pattern          string
-	ctx              context.Context
-}
+var ctxFieldOffset uintptr
 
 func init() {
-	// make sure ctx has the same offset as http.Request
-	f, ok := reflect.TypeFor[requestInternal]().FieldByName("ctx")
+	f, ok := reflect.TypeFor[http.Request]().FieldByName("ctx")
 	if !ok {
 		panic("ctx field not found")
 	}
-	f2, ok := reflect.TypeFor[http.Request]().FieldByName("ctx")
-	if !ok {
-		panic("ctx field not found")
-	}
-	if f.Offset != f2.Offset {
-		panic(fmt.Sprintf("ctx has different offset than http.Request: %d != %d", f.Offset, f2.Offset))
-	}
+	ctxFieldOffset = f.Offset
 }