feat(function-aws-api-proxy): add multipart/form-data support to ApiGatewayServletRequest

This adds support for parsing multipart/form-data in AWS API Gateway proxy requests.
The implementation handles boundary extraction, part parsing, and field name extraction
while maintaining compatibility with existing form handling.

Co-Authored-By: Claude <[email protected]>

Author: nanodeath

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

@@ -18,6 +18,9 @@
 import io.micronaut.context.annotation.Replaces;
 import io.micronaut.core.annotation.Internal;
 import io.micronaut.core.convert.ConversionService;
+import io.micronaut.function.aws.proxy.multipart.CompletedFileUploadBinder;
+import io.micronaut.function.aws.proxy.multipart.PartAnnotationRequestArgumentBinder;
+import io.micronaut.http.annotation.Part;
 import io.micronaut.http.bind.DefaultRequestBinderRegistry;
 import io.micronaut.http.bind.binders.DefaultBodyAnnotationBinder;
 import io.micronaut.http.bind.binders.RequestArgumentBinder;
@@ -39,5 +42,8 @@ class ApiGatewayBinderRegistry<T> extends ServletBinderRegistry<T> {
         DefaultBodyAnnotationBinder<T> defaultBodyAnnotationBinder
     ) {
         super(mediaTypeCodecRegistry, conversionService, binders, defaultBodyAnnotationBinder);
+
+        CompletedFileUploadBinder completedFileUploadBinder = new CompletedFileUploadBinder();
+        byAnnotation.put(Part.class, new PartAnnotationRequestArgumentBinder<>(conversionService, completedFileUploadBinder));
     }
 }

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

@@ -29,6 +29,7 @@
 import io.micronaut.core.util.CollectionUtils;
 import io.micronaut.core.util.StringUtils;
 import io.micronaut.core.util.SupplierUtil;
+import io.micronaut.function.aws.proxy.multipart.MultipartDataDecoder;
 import io.micronaut.http.CaseInsensitiveMutableHttpHeaders;
 import io.micronaut.http.FullHttpRequest;
 import io.micronaut.http.HttpMethod;
@@ -41,6 +42,7 @@
 import io.micronaut.http.body.stream.AvailableByteArrayBody;
 import io.micronaut.http.cookie.Cookie;
 import io.micronaut.http.cookie.Cookies;
+import io.micronaut.http.multipart.CompletedFileUpload;
 import io.micronaut.http.uri.UriBuilder;
 import io.micronaut.servlet.http.ByteArrayByteBuffer;
 import io.micronaut.servlet.http.MutableServletHttpRequest;
@@ -91,6 +93,8 @@ public abstract class ApiGatewayServletRequest<T, REQ, RES> implements MutableSe
     private Supplier<Optional<T>> body;
     private T parsedBody;
     private T overriddenBody;
+    private final Supplier<Optional<MultipartDataDecoder>> multipartDataDecoder;
+    private Map<String, CompletedFileUpload> fileUploads;
 
     private ByteArrayByteBuffer<T> servletByteBuffer;
 
@@ -111,6 +115,19 @@ protected ApiGatewayServletRequest(
             T built = parsedBody != null ? parsedBody :  (T) bodyBuilder.buildBody(this::getInputStream, this);
             return Optional.ofNullable(built);
         });
+        this.multipartDataDecoder = SupplierUtil.memoized(() -> {
+            try {
+                MediaType contentType = getContentType().orElse(null);
+                if (MediaType.MULTIPART_FORM_DATA_TYPE.equals(contentType)) {
+                    return Optional.of(new MultipartDataDecoder(getBodyBytes(), getHeaders(), getCharacterEncoding()));
+                }
+            } catch (IOException e) {
+                if (log.isDebugEnabled()) {
+                    log.debug("Error decoding multipart form data: {}", e.getMessage(), e);
+                }
+            }
+            return Optional.empty();
+        });
     }
 
     @Override
@@ -266,16 +283,38 @@ public <B> MutableHttpRequest<B> body(B body) {
      */
     protected MapListOfStringAndMapStringMutableHttpParameters getParametersFromBody(Map<String, String> queryStringParameters) {
         Map<String, List<String>> parameters = null;
-        try {
-            parameters = new QueryStringDecoder(new String(getBodyBytes(), getCharacterEncoding()), false).parameters();
-        } catch (IOException ex) {
-            if (log.isDebugEnabled()) {
-                log.debug("Error decoding form data: " + ex.getMessage(), ex);
+        MediaType contentType = getContentType().orElse(MediaType.APPLICATION_JSON_TYPE);
+
+        if (MediaType.APPLICATION_FORM_URLENCODED_TYPE.equals(contentType)) {
+            try {
+                parameters = new QueryStringDecoder(new String(getBodyBytes(), getCharacterEncoding()), false).parameters();
+            } catch (IOException ex) {
+                if (log.isDebugEnabled()) {
+                    log.debug("Error decoding form data: {}", ex.getMessage(), ex);
+                }
             }
+        } else if (MediaType.MULTIPART_FORM_DATA_TYPE.equals(contentType)) {
+            parameters = multipartDataDecoder.get()
+                .map(MultipartDataDecoder::parameters)
+                .orElse(Collections.emptyMap());
         }
+
         return new MapListOfStringAndMapStringMutableHttpParameters(conversionService, parameters, queryStringParameters);
     }
 
+    /**
+     * Gets a map of uploaded files from the multipart request.
+     * @return A map of field names to file uploads
+     */
+    public Map<String, CompletedFileUpload> getFileUploads() {
+        if (fileUploads != null) {
+            log.trace("Skipping decoding file uploads as they have already been processed");
+        } else {
+            fileUploads = multipartDataDecoder.get().map(MultipartDataDecoder::fileUploads).orElse(Collections.emptyMap());
+        }
+        return Collections.unmodifiableMap(fileUploads);
+    }
+
     @Override
     public void setConversionService(ConversionService conversionService) {
         this.conversionService = conversionService;
@@ -355,6 +394,7 @@ protected MutableHttpParameters getParameters(@NonNull Supplier<Map<String, Stri
         Map<String, List<String>> multi = multiQueryStringParametersSupplier.get();
         Map<String, String> single = queryStringParametersSupplier.get();
         MediaType mediaType = getContentType().orElse(MediaType.APPLICATION_JSON_TYPE);
+
         if (isFormSubmission(mediaType)) {
             return getParametersFromBody(MapCollapseUtils.collapse(MapCollapseUtils.collapse(multi, single)));
         } else {

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

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2017-2025 original authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.micronaut.function.aws.proxy.multipart;
+
+import io.micronaut.core.annotation.Internal;
+import io.micronaut.core.bind.annotation.Bindable;
+import io.micronaut.core.convert.ArgumentConversionContext;
+import io.micronaut.core.type.Argument;
+import io.micronaut.function.aws.proxy.ApiGatewayServletRequest;
+import io.micronaut.http.HttpRequest;
+import io.micronaut.http.bind.binders.TypedRequestArgumentBinder;
+import io.micronaut.http.multipart.CompletedFileUpload;
+
+import java.util.Optional;
+
+/**
+ * Binds {@link CompletedFileUpload} arguments from multipart requests in the AWS API Gateway context.
+ */
+@Internal
+public class CompletedFileUploadBinder implements TypedRequestArgumentBinder<CompletedFileUpload> {
+
+    static final Argument<CompletedFileUpload> TYPE = Argument.of(CompletedFileUpload.class);
+
+    @Override
+    public Argument<CompletedFileUpload> argumentType() {
+        return TYPE;
+    }
+
+    @Override
+    public BindingResult<CompletedFileUpload> bind(
+            ArgumentConversionContext<CompletedFileUpload> context,
+            HttpRequest<?> source) {
+
+        if (!(source instanceof ApiGatewayServletRequest)) {
+            return BindingResult.UNSATISFIED;
+        }
+
+        ApiGatewayServletRequest<?, ?, ?> request = (ApiGatewayServletRequest<?, ?, ?>) source;
+
+        // Get the parameter name to bind
+        String paramName = context.getArgument()
+                .getAnnotationMetadata()
+                .stringValue(Bindable.class)
+                .orElse(context.getArgument().getName());
+
+        // Try to find a file upload with the matching name
+        final CompletedFileUpload fileUpload = request.getFileUploads().get(paramName);
+        if (fileUpload != null) {
+            return () -> Optional.of(fileUpload);
+        }
+
+        return BindingResult.UNSATISFIED;
+    }
+}