Fix binding mixed attributes to body parameters (#6764)

`NettyHttpRequest.buildBody` distinguishes between requests with "received data" and "received content", where the former only applies when `AbstractHttpData` instances are present. `AbstractHttpData` is a base class of both `DiskAttribute` and `MemoryAttribute`, but not of `MixedAttribute`. This makes `buildBody` use the "content" path for mixed requests.

This change adds an exception for `MixedAttribute` so that it is also covered by the "data" path.

Fixes #6705

http-server-netty/src/main/java/io/micronaut/http/server/netty/NettyHttpRequest.java

@@ -61,6 +61,8 @@
 import io.netty.handler.codec.http.QueryStringDecoder;
 import io.netty.handler.codec.http.cookie.ClientCookieEncoder;
 import io.netty.handler.codec.http.multipart.AbstractHttpData;
+import io.netty.handler.codec.http.multipart.HttpData;
+import io.netty.handler.codec.http.multipart.MixedAttribute;
 import io.netty.handler.codec.http2.Http2ConnectionHandler;
 import io.netty.handler.codec.http2.HttpConversionUtil;
 import io.netty.handler.ssl.SslHandler;
@@ -144,7 +146,7 @@ public class NettyHttpRequest<T> extends AbstractNettyHttpRequest<T> implements
     private MutableConvertibleValues<Object> attributes;
     private NettyCookies nettyCookies;
     private List<ByteBufHolder> receivedContent = new ArrayList<>();
-    private Map<IdentityWrapper, AbstractHttpData> receivedData = new LinkedHashMap<>();
+    private Map<IdentityWrapper, HttpData> receivedData = new LinkedHashMap<>();
 
     private Supplier<Optional<T>> body;
     private RouteMatch<?> matchedRoute;
@@ -297,7 +299,7 @@ protected Object buildBody() {
         if (!receivedData.isEmpty()) {
             Map body = new LinkedHashMap(receivedData.size());
 
-            for (AbstractHttpData data: receivedData.values()) {
+            for (HttpData data: receivedData.values()) {
                 String newValue = getContent(data);
                 //noinspection unchecked
                 body.compute(data.getName(), (key, oldValue) -> {
@@ -332,7 +334,7 @@ protected Object buildBody() {
         }
     }
 
-    private String getContent(AbstractHttpData data) {
+    private String getContent(HttpData data) {
         String newValue;
         try {
             newValue = data.getString(serverConfiguration.getDefaultCharset());
@@ -412,10 +414,10 @@ public RouteMatch<?> getMatchedRoute() {
      */
     @Internal
     public void addContent(ByteBufHolder httpContent) {
-        if (httpContent instanceof AbstractHttpData) {
+        if (httpContent instanceof AbstractHttpData || httpContent instanceof MixedAttribute) {
             receivedData.computeIfAbsent(new IdentityWrapper(httpContent), key -> {
                 httpContent.retain();
-                return (AbstractHttpData) httpContent;
+                return (HttpData) httpContent;
             });
         } else {
             receivedContent.add(httpContent.retain());

test-suite/src/test/groovy/io/micronaut/upload/MixedUploadSpec.groovy

@@ -430,6 +430,28 @@ class MixedUploadSpec extends AbstractMicronautSpec {
         result == 'data.json: 16'
     }
 
+    void "test normal form items"() {
+        given:
+        MultipartBody requestBody = MultipartBody.builder()
+                .addPart("title", "foo")
+                .build()
+
+
+        when:
+        Mono<HttpResponse<String>> flowable = Mono.from(client.exchange(
+                HttpRequest.POST("/upload/receive-multipart", requestBody)
+                        .contentType(MediaType.MULTIPART_FORM_DATA_TYPE)
+                        .accept(MediaType.TEXT_PLAIN_TYPE),
+                String
+        ))
+        HttpResponse<String> response = flowable.block()
+        def result = response.getBody().get()
+
+        then:
+        response.code() == HttpStatus.OK.code
+        result == "Data{title='foo'}"
+    }
+
     @Override
     Map<String, Object> getConfiguration() {
         super.getConfiguration() << ['micronaut.http.client.read-timeout': 300,

test-suite/src/test/groovy/io/micronaut/upload/UploadController.java

@@ -75,6 +75,11 @@ public String receiveBytes(byte[] data, String title) {
         return title + ": " + data.length;
     }
 
+    @Post(value = "/receive-multipart", consumes = MediaType.MULTIPART_FORM_DATA, produces = MediaType.TEXT_PLAIN)
+    public String receiveMultipart(@Body Data data) {
+        return data.toString();
+    }
+
     @Post(value = "/receive-file-upload", consumes = MediaType.MULTIPART_FORM_DATA, produces = MediaType.TEXT_PLAIN)
     public Publisher<MutableHttpResponse<?>> receiveFileUpload(StreamingFileUpload data, String title) {
         long size = data.getDefinedSize();