Always specify charset for form data requests

Issue: SPR-16613

spring-web/src/main/java/org/springframework/http/codec/FormHttpMessageWriter.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -61,12 +61,15 @@ public class FormHttpMessageWriter implements HttpMessageWriter<MultiValueMap<St
 
 	public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;
 
-	private static final ResolvableType MULTIVALUE_TYPE =
-			ResolvableType.forClassWithGenerics(MultiValueMap.class, String.class, String.class);
+	private static final MediaType DEFAULT_FORM_DATA_MEDIA_TYPE =
+			new MediaType(MediaType.APPLICATION_FORM_URLENCODED, DEFAULT_CHARSET);
 
 	private static final List<MediaType> MEDIA_TYPES =
 			Collections.singletonList(MediaType.APPLICATION_FORM_URLENCODED);
 
+	private static final ResolvableType MULTIVALUE_TYPE =
+			ResolvableType.forClassWithGenerics(MultiValueMap.class, String.class, String.class);
+
 
 	private Charset defaultCharset = DEFAULT_CHARSET;
 
@@ -117,13 +120,16 @@ public class FormHttpMessageWriter implements HttpMessageWriter<MultiValueMap<St
 			ResolvableType elementType, @Nullable MediaType mediaType, ReactiveHttpOutputMessage message,
 			Map<String, Object> hints) {
 
-		MediaType contentType = message.getHeaders().getContentType();
-		if (contentType == null) {
-			contentType = MediaType.APPLICATION_FORM_URLENCODED;
-			message.getHeaders().setContentType(contentType);
+		mediaType = (mediaType != null ? mediaType : DEFAULT_FORM_DATA_MEDIA_TYPE);
+		Charset charset;
+		if (mediaType.getCharset() == null) {
+			charset = getDefaultCharset();
+			mediaType = new MediaType(mediaType, charset);
 		}
-
-		Charset charset = getMediaTypeCharset(contentType);
+		else {
+			charset = mediaType.getCharset();
+		}
+		message.getHeaders().setContentType(mediaType);
 
 		return Mono.from(inputStream).flatMap(form -> {
 					String value = serializeForm(form, charset);

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

@@ -96,6 +96,9 @@ public class FormHttpMessageConverter implements HttpMessageConverter<MultiValue
 
 	public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;
 
+	private static final MediaType DEFAULT_FORM_DATA_MEDIA_TYPE =
+			new MediaType(MediaType.APPLICATION_FORM_URLENCODED, DEFAULT_CHARSET);
+
 
 	private List<MediaType> supportedMediaTypes = new ArrayList<>();
 
@@ -290,15 +293,14 @@ public class FormHttpMessageConverter implements HttpMessageConverter<MultiValue
 	private void writeForm(MultiValueMap<String, String> form, @Nullable MediaType contentType,
 			HttpOutputMessage outputMessage) throws IOException {
 
-		Charset charset;
-		if (contentType != null) {
-			outputMessage.getHeaders().setContentType(contentType);
-			charset = (contentType.getCharset() != null ? contentType.getCharset() : this.charset);
-		}
-		else {
-			outputMessage.getHeaders().setContentType(MediaType.APPLICATION_FORM_URLENCODED);
+		contentType = (contentType != null ? contentType : DEFAULT_FORM_DATA_MEDIA_TYPE);
+		Charset charset = contentType.getCharset();
+		if (charset == null) {
 			charset = this.charset;
+			contentType = new MediaType(contentType, charset);
 		}
+		outputMessage.getHeaders().setContentType(contentType);
+
 		StringBuilder builder = new StringBuilder();
 		for (Iterator<String> nameIterator = form.keySet().iterator(); nameIterator.hasNext();) {
 			String name = nameIterator.next();

spring-web/src/test/java/org/springframework/http/codec/FormHttpMessageWriterTests.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import org.junit.Test;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.ResolvableType;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
 import org.springframework.mock.http.server.reactive.test.MockServerHttpResponse;
 import org.springframework.util.LinkedMultiValueMap;
@@ -79,8 +80,9 @@ public class FormHttpMessageWriterTests {
 
 		String responseBody = response.getBodyAsString().block();
 		assertEquals("name+1=value+1&name+2=value+2%2B1&name+2=value+2%2B2&name+3", responseBody);
-		assertEquals(MediaType.APPLICATION_FORM_URLENCODED, response.getHeaders().getContentType());
-		assertEquals(responseBody.getBytes().length, response.getHeaders().getContentLength());
+		HttpHeaders headers = response.getHeaders();
+		assertEquals("application/x-www-form-urlencoded;charset=UTF-8", headers.getContentType().toString());
+		assertEquals(responseBody.getBytes().length, headers.getContentLength());
 	}
 
 }

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

 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -112,8 +112,8 @@ public class FormHttpMessageConverterTests {
 
 		assertEquals("Invalid result", "name+1=value+1&name+2=value+2%2B1&name+2=value+2%2B2&name+3",
 				outputMessage.getBodyAsString(StandardCharsets.UTF_8));
-		assertEquals("Invalid content-type", new MediaType("application", "x-www-form-urlencoded"),
-				outputMessage.getHeaders().getContentType());
+		assertEquals("Invalid content-type", "application/x-www-form-urlencoded;charset=UTF-8",
+				outputMessage.getHeaders().getContentType().toString());
 		assertEquals("Invalid content-length", outputMessage.getBodyAsBytes().length,
 				outputMessage.getHeaders().getContentLength());
 	}

spring-web/src/test/java/org/springframework/web/client/AbstractMockWebServerTestCase.java

@@ -165,7 +165,7 @@ public class AbstractMockWebServerTestCase {
 	}
 
 	private MockResponse formRequest(RecordedRequest request) {
-		assertEquals("application/x-www-form-urlencoded", request.getHeader("Content-Type"));
+		assertEquals("application/x-www-form-urlencoded;charset=UTF-8", request.getHeader("Content-Type"));
 		String body = request.getBody().readUtf8();
 		assertThat(body, Matchers.containsString("name+1=value+1"));
 		assertThat(body, Matchers.containsString("name+2=value+2%2B1"));