Created
April 10, 2024 21:34
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package tmp | |
import ( | |
"context" | |
"encoding/json" | |
"fmt" | |
"os" | |
"reflect" | |
"github.com/go-kit/log" | |
) | |
func errorHandler(e error) func(context.Context, interface{}) (interface{}, error) { | |
return func(context.Context, interface{}) (interface{}, error) { | |
return nil, e | |
} | |
} | |
func WrapHandler(handlerFunc interface{}) interface{} { | |
if handlerFunc == nil { | |
return errorHandler(fmt.Errorf("handler is nil")) | |
} | |
handlerType := reflect.TypeOf(handlerFunc) | |
if handlerType.Kind() != reflect.Func { | |
return errorHandler(fmt.Errorf("handler kind %s is not %s", handlerType.Kind(), reflect.Func)) | |
} | |
takesContext, err := validateArguments(handlerType) | |
if err != nil { | |
return errorHandler(err) | |
} | |
if handlerType.NumIn() == 0 || handlerType.NumIn() == 1 && takesContext { | |
return func(ctx context.Context) (interface{}, error) { | |
var temp *interface{} | |
event := reflect.ValueOf(temp) | |
return wrap(ctx, handlerFunc, []byte{}, event, takesContext) | |
} | |
} | |
return func(ctx context.Context, payload interface{}) (interface{}, error) { | |
event := reflect.New(handlerType.In(handlerType.NumIn() - 1)) | |
remarshalledPayload, err := json.Marshal(payload) | |
if err != nil { | |
return nil, err | |
} | |
if err := json.Unmarshal(remarshalledPayload, event.Interface()); err != nil { | |
return nil, err | |
} | |
return wrap(ctx, handlerFunc, remarshalledPayload, event.Elem(), takesContext) | |
} | |
} | |
func validateArguments(handler reflect.Type) (bool, error) { | |
handlerTakesContext := false | |
if handler.NumIn() > 2 { | |
return false, fmt.Errorf("handlers may not take more than two arguments, but handler takes %d", handler.NumIn()) | |
} else if handler.NumIn() > 0 { | |
contextType := reflect.TypeOf((*context.Context)(nil)).Elem() | |
argumentType := handler.In(0) | |
handlerTakesContext = argumentType.Implements(contextType) | |
if handler.NumIn() > 1 && !handlerTakesContext { | |
return false, fmt.Errorf("handler takes two arguments, but the first is not Context. got %s", argumentType.Kind()) | |
} | |
} | |
return handlerTakesContext, nil | |
} | |
func eventExists(event interface{}) bool { | |
if event == nil { | |
return false | |
} | |
// reflect.Value.isNil() can only be called on Values of certain Kinds. | |
// Unsupported Kinds will panic rather than return false | |
switch reflect.TypeOf(event).Kind() { | |
case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.UnsafePointer, reflect.Interface, reflect.Slice: | |
return !reflect.ValueOf(event).IsNil() | |
} | |
return true | |
} | |
func wrapper(handlerFunc interface{}) func(ctx context.Context, eventJSON []byte, event interface{}, takesContext bool) []reflect.Value { | |
return func(ctx context.Context, eventJSON []byte, event interface{}, takesContext bool) []reflect.Value { | |
handler := reflect.ValueOf(handlerFunc) | |
var args []reflect.Value | |
if takesContext { | |
args = append(args, reflect.ValueOf(ctx)) | |
} | |
if eventExists(event) { | |
args = append(args, reflect.ValueOf(event)) | |
} | |
response := handler.Call(args) | |
return response | |
} | |
} | |
func wrap(ctx context.Context, handlerFunc interface{}, eventJSON []byte, event reflect.Value, takesContext bool) (interface{}, error) { | |
wrappedLambdaHandler := reflect.ValueOf(wrapper(handlerFunc)) | |
ctx = SetLogger(ctx, log.NewLogfmtLogger(os.Stderr)) | |
argsWrapped := []reflect.Value{reflect.ValueOf(ctx), reflect.ValueOf(eventJSON), event, reflect.ValueOf(takesContext)} | |
response := wrappedLambdaHandler.Call(argsWrapped)[0].Interface().([]reflect.Value) | |
var err error | |
if len(response) > 0 { | |
if errVal, ok := response[len(response)-1].Interface().(error); ok { | |
err = errVal | |
} | |
} | |
var val interface{} | |
if len(response) > 1 { | |
val = response[0].Interface() | |
} | |
return val, err | |
} |
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package tmp_test | |
import ( | |
"context" | |
"fmt" | |
"os" | |
"reflect" | |
"testing" | |
"tmp" | |
"github.com/aws/aws-lambda-go/lambdacontext" | |
"github.com/stretchr/testify/assert" | |
) | |
var mockContext = lambdacontext.NewContext(context.Background(), &lambdacontext.LambdaContext{}) | |
func TestLambdaHandlerSignatures(t *testing.T) { | |
setEnvVars() | |
testCases := []struct { | |
name string | |
handler interface{} | |
expected error | |
args []reflect.Value | |
}{ | |
{ | |
name: "simple handler", | |
expected: nil, | |
handler: func(ctx context.Context, in string) (string, error) { | |
l := tmp.GetLogger(ctx) | |
l.Log("hello", "world") | |
return fmt.Sprintf("Hello, %s", in), nil | |
}, | |
args: []reflect.Value{reflect.ValueOf(mockContext), reflect.ValueOf("")}, | |
}, | |
} | |
for i, testCase := range testCases { | |
testCase := testCase | |
t.Run(fmt.Sprintf("testCase[%d] %s", i, testCase.name), func (t *testing.T) { | |
lambdaHandler := tmp.WrapHandler(testCase.handler) | |
handler := reflect.ValueOf(lambdaHandler) | |
resp := handler.Call(testCase.args) | |
assert.Equal(t, 2, len(resp)) | |
assert.Equal(t, testCase.expected, resp[1].Interface()) | |
}) | |
} | |
} | |
func setEnvVars() { | |
_ = os.Setenv("AWS_LAMBDA_FUNCTION_NAME", "testFunction") | |
_ = os.Setenv("AWS_REGION", "us-texas-1") | |
_ = os.Setenv("AWS_LAMBDA_FUNCTION_VERSION", "$LATEST") | |
_ = os.Setenv("AWS_LAMBDA_LOG_STREAM_NAME", "2023/01/01/[$LATEST]5d1edb9e525d486696cf01a3503487bc") | |
_ = os.Setenv("AWS_LAMBDA_FUNCTION_MEMORY_SIZE", "128") | |
_ = os.Setenv("_X_AMZN_TRACE_ID", "Root=1-5759e988-bd862e3fe1be46a994272793;Parent=53995c3f42cd8ad8;Sampled=1") | |
} |
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package tmp | |
import ( | |
"context" | |
"os" | |
"github.com/go-kit/log" | |
) | |
type loggerContextKeyType int | |
const loggerContextKey loggerContextKeyType = iota | |
func SetLogger(ctx context.Context, logger log.Logger) context.Context { | |
return context.WithValue(ctx, loggerContextKey, logger) | |
} | |
func GetLogger(ctx context.Context) log.Logger { | |
logger, ok := ctx.Value(loggerContextKey).(log.Logger) | |
if !ok { | |
logger = log.NewLogfmtLogger(os.Stderr) | |
} | |
return logger | |
} |
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