Allow ProtobufHttpMessageConverter extensions

Make ProtobufFormatDelegate protected and visible to subclasses.
Expose constructor that allows passing the delegate in.

See spring-projectsgh-35403

Author: rstoyanchev

spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverter.java

@@ -17,9 +17,7 @@
 package org.springframework.http.converter.protobuf;
 
 import java.io.IOException;
-import java.io.InputStream;
 import java.io.InputStreamReader;
-import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.lang.reflect.Method;
 import java.nio.charset.Charset;
@@ -105,7 +103,7 @@ public class ProtobufHttpMessageConverter extends AbstractHttpMessageConverter<M
 
 	final ExtensionRegistry extensionRegistry;
 
-	private final @Nullable ProtobufFormatSupport protobufFormatSupport;
+	private final ProtobufHttpMessageConverter.@Nullable ProtobufFormatDelegate protobufFormatDelegate;
 
 
 	/**
@@ -124,21 +122,27 @@ public ProtobufHttpMessageConverter(ExtensionRegistry extensionRegistry) {
 		this(null, extensionRegistry);
 	}
 
-	ProtobufHttpMessageConverter(@Nullable ProtobufFormatSupport formatSupport,
+	/**
+	 * Constructor for a subclass that supports additional formats.
+	 * @param formatDelegate delegate to read and write additional formats
+	 * @param extensionRegistry the registry to populate
+	 */
+	protected ProtobufHttpMessageConverter(
+			ProtobufHttpMessageConverter.@Nullable ProtobufFormatDelegate formatDelegate,
 			@Nullable ExtensionRegistry extensionRegistry) {
 
-		if (formatSupport != null) {
-			this.protobufFormatSupport = formatSupport;
+		if (formatDelegate != null) {
+			this.protobufFormatDelegate = formatDelegate;
 		}
 		else if (PROTOBUF_JSON_FORMAT_PRESENT) {
-			this.protobufFormatSupport = new ProtobufJavaUtilSupport(null, null);
+			this.protobufFormatDelegate = new ProtobufJavaUtilDelegate(null, null);
 		}
 		else {
-			this.protobufFormatSupport = null;
+			this.protobufFormatDelegate = null;
 		}
 
-		setSupportedMediaTypes(Arrays.asList(this.protobufFormatSupport != null ?
-				this.protobufFormatSupport.supportedMediaTypes() : new MediaType[] {PROTOBUF, PLUS_PROTOBUF, TEXT_PLAIN}));
+		setSupportedMediaTypes(Arrays.asList(this.protobufFormatDelegate != null ?
+				this.protobufFormatDelegate.supportedMediaTypes() : new MediaType[] {PROTOBUF, PLUS_PROTOBUF, TEXT_PLAIN}));
 
 		this.extensionRegistry = (extensionRegistry == null ? ExtensionRegistry.newInstance() : extensionRegistry);
 	}
@@ -172,13 +176,13 @@ protected Message readInternal(Class<? extends Message> clazz, HttpInputMessage
 				PLUS_PROTOBUF.isCompatibleWith(contentType)) {
 			builder.mergeFrom(inputMessage.getBody(), this.extensionRegistry);
 		}
-		else if (TEXT_PLAIN.isCompatibleWith(contentType)) {
+		else if (MediaType.TEXT_PLAIN.isCompatibleWith(contentType)) {
 			InputStreamReader reader = new InputStreamReader(inputMessage.getBody(), charset);
 			TextFormat.merge(reader, this.extensionRegistry, builder);
 		}
-		else if (this.protobufFormatSupport != null) {
-			this.protobufFormatSupport.merge(
-					inputMessage.getBody(), charset, contentType, this.extensionRegistry, builder);
+		else if (this.protobufFormatDelegate != null) {
+			this.protobufFormatDelegate.merge(
+					inputMessage, contentType, charset, builder, this.extensionRegistry);
 		}
 		return builder.build();
 	}
@@ -206,7 +210,7 @@ private Message.Builder getMessageBuilder(Class<? extends Message> clazz) {
 	@Override
 	protected boolean canWrite(@Nullable MediaType mediaType) {
 		return (super.canWrite(mediaType) ||
-				(this.protobufFormatSupport != null && this.protobufFormatSupport.supportsWriteOnly(mediaType)));
+				(this.protobufFormatDelegate != null && this.protobufFormatDelegate.supportsWriteOnly(mediaType)));
 	}
 
 	@Override
@@ -235,8 +239,8 @@ else if (TEXT_PLAIN.isCompatibleWith(contentType)) {
 			outputStreamWriter.flush();
 			outputMessage.getBody().flush();
 		}
-		else if (this.protobufFormatSupport != null) {
-			this.protobufFormatSupport.print(message, outputMessage.getBody(), contentType, charset);
+		else if (this.protobufFormatDelegate != null) {
+			this.protobufFormatDelegate.print(message, outputMessage, contentType, charset);
 			outputMessage.getBody().flush();
 		}
 	}
@@ -259,34 +263,51 @@ protected boolean supportsRepeatableWrites(Message message) {
 
 
 	/**
-	 * Protobuf format support.
+	 * Contract to enable subclasses to plug in support for additional formats.
 	 */
-	interface ProtobufFormatSupport {
-
+	protected interface ProtobufFormatDelegate {
+
+		/**
+		 * Return the supported media types for the converter.
+		 * <p>Note that {@link #PROTOBUF}, {@link #PLUS_PROTOBUF}, and {@link MediaType#TEXT_PLAIN}
+		 * have built-in support and can be listed in addition to formats
+		 * specific to this delegate.
+		 */
 		MediaType[] supportedMediaTypes();
 
+		/**
+		 * Whether the media type is supported for writing.
+		 */
 		boolean supportsWriteOnly(@Nullable MediaType mediaType);
 
-		void merge(InputStream input, Charset charset, MediaType contentType,
-				ExtensionRegistry extensionRegistry, Message.Builder builder)
+		/**
+		 * Use merge methods on {@link Message.Builder} to read a message from
+		 * the given {@code HttpInputMessage}.
+		 */
+		void merge(HttpInputMessage inputMessage, MediaType contentType, Charset charset,
+				Message.Builder builder, ExtensionRegistry extensionRegistry)
 				throws IOException, HttpMessageConversionException;
 
-		void print(Message message, OutputStream output, MediaType contentType, Charset charset)
+		/**
+		 * Use print methods on {@link Message.Builder} to write the message to
+		 * the given {@code HttpOutputMessage}.
+		 */
+		void print(Message message, HttpOutputMessage outputMessage, MediaType contentType, Charset charset)
 				throws IOException, HttpMessageConversionException;
 	}
 
 
 	/**
-	 * {@link ProtobufFormatSupport} implementation used when
+	 * {@link ProtobufFormatDelegate} implementation used when
 	 * {@code com.google.protobuf.util.JsonFormat} is available.
 	 */
-	static class ProtobufJavaUtilSupport implements ProtobufFormatSupport {
+	static class ProtobufJavaUtilDelegate implements ProtobufFormatDelegate {
 
 		private final JsonFormat.Parser parser;
 
 		private final JsonFormat.Printer printer;
 
-		public ProtobufJavaUtilSupport(JsonFormat.@Nullable Parser parser, JsonFormat.@Nullable Printer printer) {
+		public ProtobufJavaUtilDelegate(JsonFormat.@Nullable Parser parser, JsonFormat.@Nullable Printer printer) {
 			this.parser = (parser != null ? parser : JsonFormat.parser());
 			this.printer = (printer != null ? printer : JsonFormat.printer());
 		}
@@ -302,12 +323,12 @@ public boolean supportsWriteOnly(@Nullable MediaType mediaType) {
 		}
 
 		@Override
-		public void merge(InputStream input, Charset charset, MediaType contentType,
-				ExtensionRegistry extensionRegistry, Message.Builder builder)
+		public void merge(HttpInputMessage inputMessage, MediaType contentType, Charset charset,
+				Message.Builder builder, ExtensionRegistry extensionRegistry)
 				throws IOException, HttpMessageConversionException {
 
 			if (contentType.isCompatibleWith(APPLICATION_JSON)) {
-				InputStreamReader reader = new InputStreamReader(input, charset);
+				InputStreamReader reader = new InputStreamReader(inputMessage.getBody(), charset);
 				this.parser.merge(reader, builder);
 			}
 			else {
@@ -317,11 +338,11 @@ public void merge(InputStream input, Charset charset, MediaType contentType,
 		}
 
 		@Override
-		public void print(Message message, OutputStream output, MediaType contentType, Charset charset)
+		public void print(Message message, HttpOutputMessage outputMessage, MediaType contentType, Charset charset)
 				throws IOException, HttpMessageConversionException {
 
 			if (contentType.isCompatibleWith(APPLICATION_JSON)) {
-				OutputStreamWriter writer = new OutputStreamWriter(output, charset);
+				OutputStreamWriter writer = new OutputStreamWriter(outputMessage.getBody(), charset);
 				this.printer.appendTo(message, writer);
 				writer.flush();
 			}

spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufJsonFormatHttpMessageConverter.java

@@ -71,7 +71,7 @@ public ProtobufJsonFormatHttpMessageConverter(
 	public ProtobufJsonFormatHttpMessageConverter(JsonFormat.@Nullable Parser parser,
 			JsonFormat.@Nullable Printer printer, @Nullable ExtensionRegistry extensionRegistry) {
 
-		super(new ProtobufJavaUtilSupport(parser, printer), extensionRegistry);
+		super(new ProtobufJavaUtilDelegate(parser, printer), extensionRegistry);
 	}
 
 }

spring-web/src/test/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverterTests.java

@@ -107,7 +107,7 @@ void writeProtobuf() throws IOException {
 	@Test
 	void writeJsonWithGoogleProtobuf() throws IOException {
 		this.converter = new ProtobufHttpMessageConverter(
-				new ProtobufHttpMessageConverter.ProtobufJavaUtilSupport(null, null),
+				new ProtobufHttpMessageConverter.ProtobufJavaUtilDelegate(null, null),
 				this.extensionRegistry);
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
 		MediaType contentType = MediaType.APPLICATION_JSON;