Support CORS

README.md

@@ -8,6 +8,7 @@ A lightweight Docker image to emulate **AWS Lambda Function URLs** locally. It w
 - Automatically forwards HTTP requests to a locally running Lambda function to work with the AWS Lambda Runtime Interface Emulator.
 - Supports `APIGatewayProxyEventV2` for HTTP API requests.
 - Handles `isBase64Encoded` for binary data.
+- Supports enabling CORS via an environment variable, allowing cross-origin requests.
 
 ## Getting Started
 
@@ -49,9 +50,10 @@ RIE_ENDPOINT=http://custom-host:9000/2015-03-31/functions/function/invocations a
 
 ## Environment Variables
 
-| Variable       | Description                                         | Default Value                                                     |
-| -------------- | --------------------------------------------------- | ----------------------------------------------------------------- |
-| `RIE_ENDPOINT` | URL for the Lambda Runtime Interface Emulator (RIE) | `http://localhost:9000/2015-03-31/functions/function/invocations` |
+| Variable       | Description                                                                                                                                                  | Default Value                                                     |
+| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------- |
+| `RIE_ENDPOINT` | URL for the Lambda Runtime Interface Emulator (RIE)                                                                                                          | `http://localhost:9000/2015-03-31/functions/function/invocations` |
+| `ENABLE_CORS`  | Set this to `"true"` to enable CORS for all origins, methods, and headers.<br>**Warning:** Please be aware that this options may have security implications. | `"false"`                                                         |
 
 ## License
 

go.mod

@@ -2,4 +2,7 @@ module github.com/daido1976/aws-lambda-function-url-emulator
 
 go 1.23.3
 
-require github.com/aws/aws-lambda-go v1.47.0 // indirect
+require (
+	github.com/aws/aws-lambda-go v1.47.0 // indirect
+	github.com/rs/cors v1.11.1 // indirect
+)

go.sum

@@ -1,2 +1,4 @@
 github.com/aws/aws-lambda-go v1.47.0 h1:0H8s0vumYx/YKs4sE7YM0ktwL2eWse+kfopsRI1sXVI=
 github.com/aws/aws-lambda-go v1.47.0/go.mod h1:dpMpZgvWx5vuQJfBt0zqBha60q7Dd7RfgJv23DymV8A=
+github.com/rs/cors v1.11.1 h1:eU3gRzXLRK57F5rKMGMZURNdIG4EoAmX8k94r9wXWHA=
+github.com/rs/cors v1.11.1/go.mod h1:XyqrcTp5zjWr1wsJ8PIRZssZ8b/WMcMf71DJnit4EMU=

main.go

@@ -12,10 +12,12 @@ import (
 	"time"
 
 	"github.com/aws/aws-lambda-go/events"
+	"github.com/rs/cors"
 )
 
 var port = getEnv("PORT", "8080")
 var rieEndpoint = getEnv("RIE_ENDPOINT", "http://localhost:9000/2015-03-31/functions/function/invocations")
+var enableCors = getEnv("ENABLE_CORS", "false")
 
 func getEnv(key, fallback string) string {
 	if value, exists := os.LookupEnv(key); exists {
@@ -25,12 +27,21 @@ func getEnv(key, fallback string) string {
 }
 
 func main() {
-	http.HandleFunc("/", handler)
+	var rootHandler http.Handler
+
+	if enableCors == "true" {
+		rootHandler = cors.AllowAll().Handler(http.HandlerFunc(lambdaUrlProxyHandler))
+		log.Println("[Lambda URL Proxy] CORS enabled")
+	} else {
+		rootHandler = http.HandlerFunc(lambdaUrlProxyHandler)
+	}
+
+	http.Handle("/", rootHandler)
 	log.Printf("[Lambda URL Proxy] Listening on http://localhost:%s\n", port)
 	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s", port), nil))
 }
 
-func handler(w http.ResponseWriter, r *http.Request) {
+func lambdaUrlProxyHandler(w http.ResponseWriter, r *http.Request) {
 	// Log the incoming request
 	log.Printf("[Lambda URL Proxy] %s %s\n", r.Method, r.URL.String())
 

main_test.go

@@ -37,7 +37,7 @@ func TestHandler(t *testing.T) {
 
 	rieEndpoint = mockRieServer.URL
 
-	server := httptest.NewServer(http.HandlerFunc(handler))
+	server := httptest.NewServer(http.HandlerFunc(lambdaUrlProxyHandler))
 	defer server.Close()
 
 	req, _ := http.NewRequest("POST", server.URL+"/foo/bar?testkey=testvalue", strings.NewReader("test body"))

test/compose.yaml

@@ -7,6 +7,8 @@ services:
       - "8080:8080"
     environment:
       RIE_ENDPOINT: "http://test-lambda-rie:8080/2015-03-31/functions/function/invocations"
+      # Uncomment out when testing for CORS.
+      # ENABLE_CORS: "true"
   test-lambda-rie:
     build:
       context: ./lambda