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// Copyright 2023 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package web
import (
goctx "context"
"fmt"
"net/http"
"reflect"
"code.gitea.io/gitea/modules/context"
"code.gitea.io/gitea/modules/web/routing"
)
// ResponseStatusProvider is an interface to check whether the response has been written by the handler
type ResponseStatusProvider interface {
Written() bool
}
// TODO: decouple this from the context package, let the context package register these providers
var argTypeProvider = map[reflect.Type]func(req *http.Request) ResponseStatusProvider{
reflect.TypeOf(&context.APIContext{}): func(req *http.Request) ResponseStatusProvider { return context.GetAPIContext(req) },
reflect.TypeOf(&context.Context{}): func(req *http.Request) ResponseStatusProvider { return context.GetContext(req) },
reflect.TypeOf(&context.PrivateContext{}): func(req *http.Request) ResponseStatusProvider { return context.GetPrivateContext(req) },
}
// responseWriter is a wrapper of http.ResponseWriter, to check whether the response has been written
type responseWriter struct {
respWriter http.ResponseWriter
status int
}
var _ ResponseStatusProvider = (*responseWriter)(nil)
func (r *responseWriter) Written() bool {
return r.status > 0
}
func (r *responseWriter) Header() http.Header {
return r.respWriter.Header()
}
func (r *responseWriter) Write(bytes []byte) (int, error) {
if r.status == 0 {
r.status = http.StatusOK
}
return r.respWriter.Write(bytes)
}
func (r *responseWriter) WriteHeader(statusCode int) {
r.status = statusCode
r.respWriter.WriteHeader(statusCode)
}
var (
httpReqType = reflect.TypeOf((*http.Request)(nil))
respWriterType = reflect.TypeOf((*http.ResponseWriter)(nil)).Elem()
cancelFuncType = reflect.TypeOf((*goctx.CancelFunc)(nil)).Elem()
)
// preCheckHandler checks whether the handler is valid, developers could get first-time feedback, all mistakes could be found at startup
func preCheckHandler(fn reflect.Value, argsIn []reflect.Value) {
hasStatusProvider := false
for _, argIn := range argsIn {
if _, hasStatusProvider = argIn.Interface().(ResponseStatusProvider); hasStatusProvider {
break
}
}
if !hasStatusProvider {
panic(fmt.Sprintf("handler should have at least one ResponseStatusProvider argument, but got %s", fn.Type()))
}
if fn.Type().NumOut() != 0 && fn.Type().NumIn() != 1 {
panic(fmt.Sprintf("handler should have no return value or only one argument, but got %s", fn.Type()))
}
if fn.Type().NumOut() == 1 && fn.Type().Out(0) != cancelFuncType {
panic(fmt.Sprintf("handler should return a cancel function, but got %s", fn.Type()))
}
}
func prepareHandleArgsIn(resp http.ResponseWriter, req *http.Request, fn reflect.Value) []reflect.Value {
isPreCheck := req == nil
argsIn := make([]reflect.Value, fn.Type().NumIn())
for i := 0; i < fn.Type().NumIn(); i++ {
argTyp := fn.Type().In(i)
switch argTyp {
case respWriterType:
argsIn[i] = reflect.ValueOf(resp)
case httpReqType:
argsIn[i] = reflect.ValueOf(req)
default:
if argFn, ok := argTypeProvider[argTyp]; ok {
if isPreCheck {
argsIn[i] = reflect.ValueOf(&responseWriter{})
} else {
argsIn[i] = reflect.ValueOf(argFn(req))
}
} else {
panic(fmt.Sprintf("unsupported argument type: %s", argTyp))
}
}
}
return argsIn
}
func handleResponse(fn reflect.Value, ret []reflect.Value) goctx.CancelFunc {
if len(ret) == 1 {
if cancelFunc, ok := ret[0].Interface().(goctx.CancelFunc); ok {
return cancelFunc
}
panic(fmt.Sprintf("unsupported return type: %s", ret[0].Type()))
} else if len(ret) > 1 {
panic(fmt.Sprintf("unsupported return values: %s", fn.Type()))
}
return nil
}
func hasResponseBeenWritten(argsIn []reflect.Value) bool {
for _, argIn := range argsIn {
if statusProvider, ok := argIn.Interface().(ResponseStatusProvider); ok {
if statusProvider.Written() {
return true
}
}
}
return false
}
// toHandlerProvider converts a handler to a handler provider
// A handler provider is a function that takes a "next" http.Handler, it can be used as a middleware
func toHandlerProvider(handler any) func(next http.Handler) http.Handler {
funcInfo := routing.GetFuncInfo(handler)
fn := reflect.ValueOf(handler)
if fn.Type().Kind() != reflect.Func {
panic(fmt.Sprintf("handler must be a function, but got %s", fn.Type()))
}
if hp, ok := handler.(func(next http.Handler) http.Handler); ok {
return func(next http.Handler) http.Handler {
h := hp(next) // this handle could be dynamically generated, so we can't use it for debug info
return http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
routing.UpdateFuncInfo(req.Context(), funcInfo)
h.ServeHTTP(resp, req)
})
}
}
provider := func(next http.Handler) http.Handler {
return http.HandlerFunc(func(respOrig http.ResponseWriter, req *http.Request) {
// wrap the response writer to check whether the response has been written
resp := respOrig
if _, ok := resp.(ResponseStatusProvider); !ok {
resp = &responseWriter{respWriter: resp}
}
// prepare the arguments for the handler and do pre-check
argsIn := prepareHandleArgsIn(resp, req, fn)
if req == nil {
preCheckHandler(fn, argsIn)
return // it's doing pre-check, just return
}
routing.UpdateFuncInfo(req.Context(), funcInfo)
ret := fn.Call(argsIn)
// handle the return value, and defer the cancel function if there is one
cancelFunc := handleResponse(fn, ret)
if cancelFunc != nil {
defer cancelFunc()
}
// if the response has not been written, call the next handler
if next != nil && !hasResponseBeenWritten(argsIn) {
next.ServeHTTP(resp, req)
}
})
}
provider(nil).ServeHTTP(nil, nil) // do a pre-check to make sure all arguments and return values are supported
return provider
}
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