fix: Populate AWSProxyResponse headers with multi

function-aws-api-proxy/src/main/java/io/micronaut/function/aws/proxy/MicronautResponseWriter.java

@@ -20,6 +20,7 @@
 import com.amazonaws.serverless.proxy.internal.testutils.Timer;
 import com.amazonaws.serverless.proxy.model.RequestSource;
 import com.amazonaws.serverless.proxy.model.AwsProxyResponse;
+import com.amazonaws.serverless.proxy.model.Headers;
 import com.amazonaws.services.lambda.runtime.Context;
 import io.micronaut.core.annotation.Internal;
 import io.micronaut.core.io.Writable;
@@ -37,6 +38,7 @@
 import java.io.IOException;
 import java.nio.charset.Charset;
 import java.util.Base64;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -67,6 +69,7 @@ public AwsProxyResponse writeResponse(
             Context lambdaContext) throws InvalidResponseObjectException {
         Timer.start(TIMER_NAME);
         AwsProxyResponse awsProxyResponse = containerResponse.getAwsResponse();
+
         final Map<String, Cookie> cookies = containerResponse.getAllCookies();
         if (CollectionUtils.isNotEmpty(cookies)) {
             final List<String> values = ServerCookieEncoder.LAX.encode(cookies.values());
@@ -110,8 +113,21 @@ public AwsProxyResponse writeResponse(
                     status + " " +
                             Response.Status.fromStatusCode(status.getCode()).getReasonPhrase());
         }
-
+        awsProxyResponse.setHeaders(getHeaders(awsProxyResponse));
         Timer.stop(TIMER_NAME);
         return awsProxyResponse;
     }
+
+    private static Map<String, String> getHeaders(AwsProxyResponse awsProxyResponse) {
+        Headers multiValueHeaders = awsProxyResponse.getMultiValueHeaders();
+        Map<String, String> headers = new LinkedHashMap<>();
+        for (Map.Entry<String, List<String>> entry : multiValueHeaders.entrySet()) {
+      Optional.ofNullable(entry.getValue())
+          .filter(not(List::isEmpty))
+          .map(List::stream)
+          .flatMap(Stream::findFirst)
+          .ifPresent(value -> headers.put(entry.getKey(), value));
+        }
+        return headers;
+    }
 }

function-aws-api-proxy/src/test/groovy/io/micronaut/function/aws/proxy/ContentTypeSpec.groovy

@@ -0,0 +1,77 @@
+package io.micronaut.function.aws.proxy
+
+import com.amazonaws.serverless.proxy.internal.testutils.AwsProxyRequestBuilder
+import com.amazonaws.serverless.proxy.internal.testutils.MockLambdaContext
+import com.amazonaws.serverless.proxy.model.AwsProxyResponse
+import com.amazonaws.services.lambda.runtime.Context
+import io.micronaut.context.ApplicationContext
+import io.micronaut.context.annotation.Requires
+import io.micronaut.http.HttpHeaders
+import io.micronaut.http.HttpMethod
+import io.micronaut.http.HttpStatus
+import io.micronaut.http.MediaType
+import io.micronaut.http.annotation.Controller
+import io.micronaut.http.annotation.Get
+import io.micronaut.http.annotation.Status
+import spock.lang.AutoCleanup
+import spock.lang.Issue
+import spock.lang.Shared
+import spock.lang.Specification
+
+class ContentTypeSpec extends Specification {
+    @Shared
+    @AutoCleanup
+    MicronautLambdaContainerHandler handler = new MicronautLambdaContainerHandler(
+            ApplicationContext.builder().properties([
+                    'spec.name'                 : 'ContentTypeSpec',
+                    'micronaut.security.enabled': false,
+            ])
+    )
+    @Shared
+    Context lambdaContext = new MockLambdaContext()
+
+    void "verify controllers return json by default and mulitvalue headers are populated"() {
+        given:
+        AwsProxyRequestBuilder builder = new AwsProxyRequestBuilder('/json/bydefault', HttpMethod.GET.toString())
+        builder.header(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON)
+
+        when:
+        AwsProxyResponse response = handler.proxy(builder.build(), lambdaContext)
+
+        then:
+        response.statusCode == 200
+        response.body == '{"msg":"Hello world"}'
+
+        and: 'works with multivalue headers'
+        response.multiValueHeaders
+        ["application/json"] == response.getMultiValueHeaders().get("Content-Type")
+    }
+
+    @Issue("https://github.com/micronaut-projects/micronaut-aws/issues/1330")
+    void "verify controllers return json by default and headers are populated"() {
+        given:
+        AwsProxyRequestBuilder builder = new AwsProxyRequestBuilder('/json/bydefault', HttpMethod.GET.toString())
+        builder.header(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON)
+
+        when:
+        AwsProxyResponse response = handler.proxy(builder.build(), lambdaContext)
+
+        then:
+        response.statusCode == 200
+        response.body == '{"msg":"Hello world"}'
+
+        response.headers
+        "application/json" == response.getHeaders().get("Content-Type")
+    }
+
+    @Controller('/json')
+    @Requires(property = 'spec.name', value = 'ContentTypeSpec')
+    static class BodyController {
+
+        @Get("/bydefault")
+        @Status(HttpStatus.OK)
+        Map<String, Object> index() {
+            [msg: "Hello world"]
+        }
+    }
+}