micro/server/subscriber.go

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package server
import (
"fmt"
"reflect"
"unicode"
"unicode/utf8"
)
const (
subSig = "func(context.Context, interface{}) error"
)
// Precompute the reflect type for error. Can't use error directly
// because Typeof takes an empty interface value. This is annoying.
var typeOfError = reflect.TypeOf((*error)(nil)).Elem()
// Is this an exported - upper case - name?
func isExported(name string) bool {
r, _ := utf8.DecodeRuneInString(name)
return unicode.IsUpper(r)
}
// Is this type exported or a builtin?
func isExportedOrBuiltinType(t reflect.Type) bool {
for t.Kind() == reflect.Ptr {
t = t.Elem()
}
// PkgPath will be non-empty even for an exported type,
// so we need to check the type name as well.
return isExported(t.Name()) || t.PkgPath() == ""
}
// ValidateSubscriber func signature
func ValidateSubscriber(sub Subscriber) error {
typ := reflect.TypeOf(sub.Subscriber())
var argType reflect.Type
switch typ.Kind() {
case reflect.Func:
name := "Func"
switch typ.NumIn() {
case 2:
argType = typ.In(1)
default:
return fmt.Errorf("subscriber %v takes wrong number of args: %v required signature %s", name, typ.NumIn(), subSig)
}
if !isExportedOrBuiltinType(argType) {
return fmt.Errorf("subscriber %v argument type not exported: %v", name, argType)
}
if typ.NumOut() != 1 {
return fmt.Errorf("subscriber %v has wrong number of return values: %v require signature %s",
name, typ.NumOut(), subSig)
}
if returnType := typ.Out(0); returnType != typeOfError {
return fmt.Errorf("subscriber %v returns %v not error", name, returnType.String())
}
default:
hdlr := reflect.ValueOf(sub.Subscriber())
name := reflect.Indirect(hdlr).Type().Name()
for m := 0; m < typ.NumMethod(); m++ {
method := typ.Method(m)
switch method.Type.NumIn() {
case 3:
argType = method.Type.In(2)
default:
return fmt.Errorf("subscriber %v.%v takes wrong number of args: %v required signature %s",
name, method.Name, method.Type.NumIn(), subSig)
}
if !isExportedOrBuiltinType(argType) {
return fmt.Errorf("%v argument type not exported: %v", name, argType)
}
if method.Type.NumOut() != 1 {
return fmt.Errorf(
"subscriber %v.%v has wrong number of return values: %v require signature %s",
name, method.Name, method.Type.NumOut(), subSig)
}
if returnType := method.Type.Out(0); returnType != typeOfError {
return fmt.Errorf("subscriber %v.%v returns %v not error", name, method.Name, returnType.String())
}
}
}
return nil
}