[BUG] MultipartFile mapping issue with Spring Boot 3 and binary media types

示されている LambdaHandler の設定と StageAwareAwsProxyHttpServletRequestReader から始め、aws-serverless-java-container-springboot3 が multipart リクエストと image/jpeg コンテンツタイプを Spring Boot に渡す仕組みを追跡します。API Gateway/Lambda のアップロードを再現し、415 エラーを返すことなくコントローラーが画像を MultipartFile にバインドすることを確認します。

Description:

I am encountering an issue when trying to upload images from my client to a Spring Boot 3 application deployed as a Lambda function using aws-serverless-java-container-springboot3.

Problem:

Despite configuring API Gateway with multipart/form-data as a binary media type, and observing the binary data successfully reaching the Lambda handler, the Spring controller fails to map the incoming request to a MultipartFile argument. Instead, a GlobalException is triggered with the message:

415 UNSUPPORTED_MEDIA_TYPE "Content type 'image/jpeg' not supported for bodyType=org.springframework.web.multipart.MultipartFile"

Setup:

Framework: Spring Boot 3

Serverless Java Container Dependency:

<dependency>
    <groupId>com.amazonaws.serverless</groupId>
    <artifactId>aws-serverless-java-container-springboot3</artifactId>
    <version>2.1.4</version>
</dependency>

LambdaHandler:

package net.myApp.lambda.handler;

import com.amazonaws.serverless.exceptions.ContainerInitializationException;
import com.amazonaws.serverless.proxy.AsyncInitializationWrapper;
import com.amazonaws.serverless.proxy.AwsProxyExceptionHandler;
import com.amazonaws.serverless.proxy.AwsProxySecurityContextWriter;
import com.amazonaws.serverless.proxy.internal.servlet.AwsProxyHttpServletResponseWriter;
import com.amazonaws.serverless.proxy.model.AwsProxyRequest;
import com.amazonaws.serverless.proxy.model.AwsProxyResponse;
import com.amazonaws.serverless.proxy.spring.SpringBootLambdaContainerHandler;
import com.amazonaws.serverless.proxy.spring.SpringBootProxyHandlerBuilder;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestStreamHandler;
import jakarta.ws.rs.core.MediaType;
import net.myApp.lambda.StageAwareAwsProxyHttpServletRequestReader;
import net.myApp.rest.MyApp;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

@Component
public class LambdaHandler implements RequestStreamHandler {
  private static final Logger logger = LoggerFactory.getLogger(LambdaHandler.class);
  private static SpringBootLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler;

  static {
    try {
      handler =
          new SpringBootProxyHandlerBuilder<AwsProxyRequest>()
              .initializationWrapper(new AsyncInitializationWrapper())
              .requestReader(new StageAwareAwsProxyHttpServletRequestReader())
              .responseWriter(new AwsProxyHttpServletResponseWriter())
              .securityContextWriter(new AwsProxySecurityContextWriter())
              .exceptionHandler(new AwsProxyExceptionHandler())
              .requestTypeClass(AwsProxyRequest.class)
              .responseTypeClass(AwsProxyResponse.class)
              .springBootApplication(MyApp.class)
              .buildAndInitialize();
      handler.getContainerConfig().addBinaryContentTypes(MediaType.MULTIPART_FORM_DATA, "image/jpeg", "image/png", "image/jpg");
    } catch (ContainerInitializationException e) {
      logger.error("FATAL: Failed to initialize Spring Boot application container. This will cause cold starts.", e);
      throw new RuntimeException("Could not initialize Spring Boot application", e);
    }
  }

  @Override
  public void handleRequest(InputStream input, OutputStream output, Context context) throws IOException {
    try {
      handler.proxyStream(input, output, context);
    } catch (Exception ex) {
      logger.error("Error processing Lambda request: {}", ex.getMessage());
      throw ex;
    }
  }
}

API Gateway Configuration: multipart/form-data has been added to the "Binary Media Types" in the API Gateway settings.

Steps Taken (and observations):

Client-side upload: Attempting to upload an image/jpeg file from the client.

API Gateway: Configured multipart/form-data as a binary media type.

Lambda Handler: Logs within the Lambda handler confirm that the binary data is indeed present and being received by the Lambda function.

Spring Controller: The request does not successfully map to a MultipartFile parameter in my Spring controller. Error: The GlobalException handler in my Spring application catches a 415 UNSUPPORTED_MEDIA_TYPE error, specifically stating that image/jpeg is not supported for MultipartFile.

Expected Behavior:

The aws-serverless-java-container should correctly handle the multipart/form-data request, allowing Spring Boot to bind the uploaded file to a MultipartFile object in the controller method.

Actual Behavior:

The request fails with a 415 UNSUPPORTED_MEDIA_TYPE error, indicating that the image/jpeg content type is not being correctly processed for MultipartFile binding within the Spring application, despite the data reaching the Lambda handler as binary.

Possible Cause/Request for Help:

It appears there might be an issue with how aws-serverless-java-container-springboot3 (version 2.1.4) or its underlying dependencies are processing multipart/form-data requests, preventing Spring's MultipartFile resolver from recognizing the incoming binary data as a valid file upload.

Any guidance or a fix for this issue would be greatly appreciated.