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