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Use reflection to invoke receiver fn from client. (#67)
Signed-off-by: Scott Nichols <nicholss@google.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,187 @@ | ||
| package client | ||
|
|
||
| import ( | ||
| "context" | ||
| "errors" | ||
| "fmt" | ||
| "github.com/cloudevents/sdk-go/pkg/cloudevents" | ||
| "reflect" | ||
| ) | ||
|
|
||
| // Receive is the signature of a fn to be invoked for incoming cloudevents. | ||
| // If fn returns an error, EventResponse will not be considered by the client or | ||
| // or transport. | ||
| // This is just an FYI: | ||
| type ReceiveFull func(context.Context, cloudevents.Event, *cloudevents.EventResponse) error | ||
|
|
||
| type receiverFn struct { | ||
| numIn int | ||
| fnValue reflect.Value | ||
|
|
||
| hasContextIn bool | ||
| hasEventIn bool | ||
| hasEventResponseIn bool | ||
|
|
||
| hasErrorOut bool | ||
| } | ||
|
|
||
| const ( | ||
| inParamUsage = "expected a function taking either no parameters, one or more of (context.Context, cloudevents.Event, *cloudevents.EventResponse) ordered" | ||
| outParamUsage = "expected a function returning either nothing or an error" | ||
| ) | ||
|
|
||
| var ( | ||
| contextType = reflect.TypeOf((*context.Context)(nil)).Elem() | ||
| eventType = reflect.TypeOf((*cloudevents.Event)(nil)).Elem() | ||
| eventResponseType = reflect.TypeOf((*cloudevents.EventResponse)(nil)) // want the ptr type | ||
| errorType = reflect.TypeOf((*error)(nil)).Elem() | ||
| ) | ||
|
|
||
| // receiver creates a receiverFn wrapper class that is used by the client to | ||
| // validate and invoke the provided function. | ||
| // Valid fn signatures are: | ||
| // * func() | ||
| // * func() error | ||
| // * func(context.Context) | ||
| // * func(context.Context) error | ||
| // * func(cloudevents.Event) | ||
| // * func(cloudevents.Event) error | ||
| // * func(context.Context, cloudevents.Event) | ||
| // * func(context.Context, cloudevents.Event) error | ||
| // * func(cloudevents.Event, *cloudevents.EventResponse) | ||
| // * func(cloudevents.Event, *cloudevents.EventResponse) error | ||
| // * func(context.Context, cloudevents.Event, *cloudevents.EventResponse) | ||
| // * func(context.Context, cloudevents.Event, *cloudevents.EventResponse) error | ||
| // | ||
| func receiver(fn interface{}) (*receiverFn, error) { | ||
| fnType := reflect.TypeOf(fn) | ||
| if fnType.Kind() != reflect.Func { | ||
| return nil, errors.New("must pass a function to handle events") | ||
| } | ||
|
|
||
| r := &receiverFn{ | ||
| fnValue: reflect.ValueOf(fn), | ||
| numIn: fnType.NumIn(), | ||
| } | ||
| if err := r.validate(fnType); err != nil { | ||
| return nil, err | ||
| } | ||
|
|
||
| return r, nil | ||
| } | ||
|
|
||
| func (r *receiverFn) invoke(ctx context.Context, event cloudevents.Event, resp *cloudevents.EventResponse) error { | ||
| args := make([]reflect.Value, 0, r.numIn) | ||
|
|
||
| if r.numIn > 0 { | ||
| if r.hasContextIn { | ||
| args = append(args, reflect.ValueOf(ctx)) | ||
| } | ||
| if r.hasEventIn { | ||
| args = append(args, reflect.ValueOf(event)) | ||
| } | ||
| if r.hasEventResponseIn { | ||
| args = append(args, reflect.ValueOf(resp)) | ||
| } | ||
| } | ||
| v := r.fnValue.Call(args) | ||
| if r.hasErrorOut && len(v) >= 1 { | ||
| if err, ok := v[0].Interface().(error); ok { | ||
| return err | ||
| } | ||
| } | ||
| return nil | ||
| } | ||
|
|
||
| // Verifies that the inputs to a function have a valid signature | ||
| // Valid input is to be [0, all] of | ||
| // context.Context, cloudevents.Event, *cloudevents.EventResponse in this order. | ||
| func (r *receiverFn) validateInParamSignature(fnType reflect.Type) error { | ||
| r.hasContextIn = false | ||
| r.hasEventIn = false | ||
| r.hasEventResponseIn = false | ||
|
|
||
| switch fnType.NumIn() { | ||
| case 3: | ||
| // has to be cloudevents.Event, *cloudevents.EventResponse | ||
| if !fnType.In(2).ConvertibleTo(eventResponseType) { | ||
| return fmt.Errorf("%s; cannot convert parameter 2 from %s to *cloudevents.EventResponse", inParamUsage, fnType.In(2)) | ||
| } else { | ||
| r.hasEventResponseIn = true | ||
| } | ||
| fallthrough | ||
| case 2: | ||
| // can be cloudevents.Event or *cloudevents.EventResponse | ||
| if !fnType.In(1).ConvertibleTo(eventResponseType) { | ||
| if !fnType.In(1).ConvertibleTo(eventType) { | ||
| return fmt.Errorf("%s; cannot convert parameter 1 from %s to cloudevents.Event or *cloudevents.EventResponse", inParamUsage, fnType.In(1)) | ||
| } else { | ||
| r.hasEventIn = true | ||
| } | ||
| } else if r.hasEventResponseIn { | ||
| return fmt.Errorf("%s; duplicate parameter of type *cloudevents.EventResponse", inParamUsage) | ||
| } else { | ||
| r.hasEventResponseIn = true | ||
| } | ||
| fallthrough | ||
| case 1: | ||
| if !fnType.In(0).ConvertibleTo(contextType) { | ||
| if !fnType.In(0).ConvertibleTo(eventResponseType) { | ||
| if !fnType.In(0).ConvertibleTo(eventType) { | ||
| return fmt.Errorf("%s; cannot convert parameter 0 from %s to context.Context, cloudevents.Event or *cloudevents.EventResponse", inParamUsage, fnType.In(0)) | ||
| } else if r.hasEventIn { | ||
| return fmt.Errorf("%s; duplicate parameter of type cloudevents.Event", inParamUsage) | ||
| } else { | ||
| r.hasEventIn = true | ||
| } | ||
| } else if r.hasEventResponseIn { | ||
| return fmt.Errorf("%s; duplicate parameter of type *cloudevents.EventResponse", inParamUsage) | ||
| } else if r.hasEventIn { | ||
| return fmt.Errorf("%s; out of order parameter 0 for %s", inParamUsage, fnType.In(1)) | ||
| } else { | ||
| r.hasEventResponseIn = true | ||
| } | ||
| } else { | ||
| r.hasContextIn = true | ||
| } | ||
| fallthrough | ||
| case 0: | ||
| return nil | ||
| default: | ||
| return fmt.Errorf("%s; function has too many parameters (%d)", inParamUsage, fnType.NumIn()) | ||
| } | ||
| } | ||
|
|
||
| // Verifies that the outputs of a function have a valid signature | ||
| // Valid output signatures: | ||
| // (), (error) | ||
| func (r *receiverFn) validateOutParamSignature(fnType reflect.Type) error { | ||
| r.hasErrorOut = false | ||
| switch fnType.NumOut() { | ||
| case 1: | ||
| paramNo := fnType.NumOut() - 1 | ||
| paramType := fnType.Out(paramNo) | ||
| if !paramType.ConvertibleTo(errorType) { | ||
| return fmt.Errorf("%s; cannot convert return type %d from %s to error", outParamUsage, paramNo, paramType) | ||
| } else { | ||
| r.hasErrorOut = true | ||
| } | ||
| fallthrough | ||
| case 0: | ||
| return nil | ||
| default: | ||
| return fmt.Errorf("%s; function has too many return types (%d)", outParamUsage, fnType.NumOut()) | ||
| } | ||
| } | ||
|
|
||
| // validateReceiverFn validates that a function has the right number of in and | ||
| // out params and that they are of allowed types. | ||
| func (r *receiverFn) validate(fnType reflect.Type) error { | ||
| if err := r.validateInParamSignature(fnType); err != nil { | ||
| return err | ||
| } | ||
| if err := r.validateOutParamSignature(fnType); err != nil { | ||
| return err | ||
| } | ||
| return nil | ||
| } |
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