Decouple the different contexts from each other (#24786)

Replace #16455

Close #21803

Mixing different Gitea contexts together causes some problems:

1. Unable to respond proper content when error occurs, eg: Web should
respond HTML while API should respond JSON
2. Unclear dependency, eg: it's unclear when Context is used in
APIContext, which fields should be initialized, which methods are
necessary.


To make things clear, this PR introduces a Base context, it only
provides basic Req/Resp/Data features.

This PR mainly moves code. There are still many legacy problems and
TODOs in code, leave unrelated changes to future PRs.

modules/web/handler.go

@@ -10,6 +10,7 @@ import (
 	"reflect"
 
 	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/web/routing"
 )
 
@@ -25,6 +26,10 @@ var argTypeProvider = map[reflect.Type]func(req *http.Request) ResponseStatusPro
 	reflect.TypeOf(&context.PrivateContext{}): func(req *http.Request) ResponseStatusProvider { return context.GetPrivateContext(req) },
 }
 
+func RegisterHandleTypeProvider[T any](fn func(req *http.Request) ResponseStatusProvider) {
+	argTypeProvider[reflect.TypeOf((*T)(nil)).Elem()] = fn
+}
+
 // responseWriter is a wrapper of http.ResponseWriter, to check whether the response has been written
 type responseWriter struct {
 	respWriter http.ResponseWriter
@@ -78,7 +83,13 @@ func preCheckHandler(fn reflect.Value, argsIn []reflect.Value) {
 	}
 }
 
-func prepareHandleArgsIn(resp http.ResponseWriter, req *http.Request, fn reflect.Value) []reflect.Value {
+func prepareHandleArgsIn(resp http.ResponseWriter, req *http.Request, fn reflect.Value, fnInfo *routing.FuncInfo) []reflect.Value {
+	defer func() {
+		if err := recover(); err != nil {
+			log.Error("unable to prepare handler arguments for %s: %v", fnInfo.String(), err)
+			panic(err)
+		}
+	}()
 	isPreCheck := req == nil
 
 	argsIn := make([]reflect.Value, fn.Type().NumIn())
@@ -155,7 +166,7 @@ func toHandlerProvider(handler any) func(next http.Handler) http.Handler {
 			}
 
 			// prepare the arguments for the handler and do pre-check
-			argsIn := prepareHandleArgsIn(resp, req, fn)
+			argsIn := prepareHandleArgsIn(resp, req, fn, funcInfo)
 			if req == nil {
 				preCheckHandler(fn, argsIn)
 				return // it's doing pre-check, just return