add s3 head bucket call

Author: srprash

sample-apps/apigateway-lambda/build.gradle.kts

@@ -16,7 +16,9 @@ java {
 dependencies {
   implementation("com.amazonaws:aws-lambda-java-core:1.2.2")
   implementation("com.squareup.okhttp3:okhttp:4.11.0")
+  implementation("software.amazon.awssdk:s3:2.29.23")
   implementation("org.json:json:20240303")
+  implementation("org.slf4j:jcl-over-slf4j:2.0.16")
   testImplementation("org.junit.jupiter:junit-jupiter:5.10.0")
 }
 

sample-apps/apigateway-lambda/src/main/java/com/amazon/sampleapp/LambdaHandler.java

@@ -8,10 +8,14 @@
 import okhttp3.Request;
 import okhttp3.Response;
 import org.json.JSONObject;
+import software.amazon.awssdk.services.s3.S3Client;
+import software.amazon.awssdk.services.s3.model.HeadBucketRequest;
+import software.amazon.awssdk.services.s3.model.S3Exception;
 
 public class LambdaHandler implements RequestHandler<Object, Map<String, Object>> {
 
   private final OkHttpClient client = new OkHttpClient();
+  private final S3Client s3Client = S3Client.create();
 
   @Override
   public Map<String, Object> handleRequest(Object input, Context context) {
@@ -28,14 +32,14 @@ public Map<String, Object> handleRequest(Object input, Context context) {
 
     System.out.println("Trace ID: " + traceId);
 
+    JSONObject responseBody = new JSONObject();
+    responseBody.put("traceId", traceId);
+
     // Make a remote call using OkHttp
     System.out.println("Making a remote call using OkHttp");
     String url = "https://www.amazon.com";
     Request request = new Request.Builder().url(url).build();
 
-    JSONObject responseBody = new JSONObject();
-    responseBody.put("traceId", traceId);
-
     try (Response response = client.newCall(request).execute()) {
       responseBody.put("httpRequest", "Request successful");
     } catch (IOException e) {
@@ -44,6 +48,26 @@ public Map<String, Object> handleRequest(Object input, Context context) {
     }
     System.out.println("Remote call done");
 
+    // Make a S3 HeadBucket call to check whether the bucket exists
+    System.out.println("Making a S3 HeadBucket call");
+    String bucketName = "SomeDummyBucket";
+    try {
+      HeadBucketRequest headBucketRequest = HeadBucketRequest.builder().bucket(bucketName).build();
+      s3Client.headBucket(headBucketRequest);
+      responseBody.put("s3Request", "Bucket exists and is accessible: " + bucketName);
+    } catch (S3Exception e) {
+      if (e.statusCode() == 403) {
+        responseBody.put("s3Request", "Access denied to bucket: " + bucketName);
+      } else if (e.statusCode() == 404) {
+        responseBody.put("s3Request", "Bucket does not exist: " + bucketName);
+      } else {
+        System.err.println("Error checking bucket: " + e.awsErrorDetails().errorMessage());
+        responseBody.put(
+            "s3Request", "Error checking bucket: " + e.awsErrorDetails().errorMessage());
+      }
+    }
+    System.out.println("S3 HeadBucket call done");
+
     // return a response in the ApiGateway proxy format
     return Map.of(
         "isBase64Encoded",

sample-apps/apigateway-lambda/terraform/main.tf

@@ -16,13 +16,13 @@ resource "aws_iam_role" "lambda_role" {
 }
 
 resource "aws_iam_policy" "s3_access" {
-  name        = "S3ListBucketsPolicy"
-  description = "Allow Lambda to list S3 buckets"
+  name        = "S3ListBucketPolicy"
+  description = "Allow Lambda to check a given S3 bucket exists"
   policy      = jsonencode({
     Version = "2012-10-17",
     Statement = [{
       Effect   = "Allow",
-      Action   = ["s3:ListAllMyBuckets"],
+      Action   = ["s3:ListBucket"],
       Resource = "*"
     }]
   })