/
handler.go
94 lines (77 loc) · 2.48 KB
/
handler.go
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package rest
import (
"bytes"
"github.com/AlexanderFadeev/myerrors"
"io"
"net/http"
"reflect"
)
type (
GenericHandler interface{} // TODO: Go2: func(type ArgsType, ReplyType)(*ArgsType) (*ReplyType, error)
Handler func(Request) Reply
)
var errorInterface = reflect.TypeOf((*error)(nil)).Elem()
func WrapGenericHandler(genericHandler GenericHandler, translator ErrorTranslator, errHandler myerrors.Handler) (http.HandlerFunc, error) {
rv := reflect.ValueOf(genericHandler)
rt := rv.Type()
if rk := rt.Kind(); rk != reflect.Func {
return nil, myerrors.Errorf("expected function, got %s", rk.String())
}
if numIn := rt.NumIn(); numIn != 1 {
return nil, myerrors.Errorf("expected function with 1 argument, got %d", numIn)
}
if numOut := rt.NumOut(); numOut != 2 {
return nil, myerrors.Errorf("expected function with 2 return values, got %d)", numOut)
}
if !rt.Out(1).Implements(errorInterface) {
return nil, myerrors.Errorf("expected second return value to implement error interface, got %s", rt.Out(1).Name())
}
handler := func(req Request) Reply {
in := reflect.New(rt.In(0).Elem())
err := req.Decode(in.Interface())
if err != nil {
err = myerrors.Wrap(err, "failed to decode request")
return NewError(err, http.StatusBadRequest)
}
ret := rv.Call([]reflect.Value{in})
iErr := ret[1].Interface()
if iErr != nil {
return translator.TranslateError(iErr.(error))
}
out := ret[0].Elem().Interface()
return NewOKReply(out)
}
return WrapHandler(handler, errHandler), nil
}
func MustWrapGenericHandler(genericHandler GenericHandler, translator ErrorTranslator, errHandler myerrors.Handler) http.HandlerFunc {
handler, err := WrapGenericHandler(genericHandler, translator, errHandler)
if err != nil {
panic(err.Error())
}
return handler
}
func WrapHandler(handler Handler, errHandler myerrors.Handler) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
request := request{httpRequest: r}
reply := handler(&request)
err := encodeReply(w, reply)
if err != nil {
err = myerrors.Wrap(err, "failed to handle HTTP request")
errHandler.Handle(err)
}
}
}
func encodeReply(w http.ResponseWriter, reply Reply) error {
var buf bytes.Buffer
err := reply.Encode(&buf)
if err != nil {
w.WriteHeader(http.StatusInternalServerError)
return myerrors.Errorf("failed to encode reply")
}
w.WriteHeader(reply.StatusCode())
_, err = io.Copy(w, &buf)
if err != nil {
return myerrors.Wrap(err, "failed to write reply")
}
return nil
}