Reject duplicate MIME type parameters

Prior to this commit, MIME type parsing in Spring would allow duplicate
parameters like "text/plain; dupe=1; dupe=2", effectively retaining the
latest value and ignoring the first.

RFC 6838 4.3 states that this should be treated as an error and this
commit ensures that this is the case.

Closes gh-36841

Author: bclozel

spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java

@@ -252,7 +252,9 @@ else if (ch == '"' && mimeType.charAt(nextIndex - 1) != '\\') {
 				if (eqIndex >= 0) {
 					String attribute = parameter.substring(0, eqIndex).trim();
 					String value = parameter.substring(eqIndex + 1).trim();
-					parameters.put(attribute, value);
+					if (parameters.put(attribute, value) != null) {
+						throw new InvalidMimeTypeException(mimeType, "duplicate parameter '" + parameter + "'");
+					}
 				}
 			}
 			index = nextIndex;

spring-core/src/test/java/org/springframework/util/MimeTypeTests.java

@@ -32,6 +32,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 /**
  * Tests for {@link MimeType}.
@@ -116,6 +117,13 @@ void parseParameterWithQuotedPair() {
 		assertThat(mimeType.getParameter("twelve")).isEqualTo("\"1\\\"2\"");
 	}
 
+	@Test
+	void rejectsDuplicateParameter() {
+		String s = "text/plain;dupe=\"1\";dupe=\"2\"";
+		assertThatThrownBy(() -> MimeType.valueOf(s)).isInstanceOf(InvalidMimeTypeException.class)
+				.hasMessageContaining("Invalid mime type \"text/plain;dupe=\"1\";dupe=\"2\"\": duplicate parameter 'dupe=\"2\"'");
+	}
+
 	@Test
 	void withConversionService() {
 		ConversionService conversionService = new DefaultConversionService();

spring-test/src/test/java/org/springframework/mock/web/MockHttpServletRequestTests.java

@@ -237,7 +237,7 @@ void contentTypeMultipleCalls() {
 
 	@Test  // SPR-12677
 	void setContentTypeHeaderWithMoreComplexCharsetSyntax() {
-		String contentType = "test/plain;charset=\"utf-8\";foo=\"charset=bar\";foocharset=bar;foo=bar";
+		String contentType = "test/plain;charset=\"utf-8\";foo=\"charset=bar\";foocharset=bar;foobar=bar";
 		request.addHeader(HttpHeaders.CONTENT_TYPE, contentType);
 		assertThat(request.getContentType()).isEqualTo(contentType);
 		assertThat(request.getHeader(HttpHeaders.CONTENT_TYPE)).isEqualTo(contentType);

spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java

@@ -116,7 +116,7 @@ void shouldSetUtf8EncodingForJson() {
 
 		@Test // SPR-12677
 		void shouldSetEncodingWithComplexContentTypeSyntax() {
-			String contentType = "test/plain;charset=\"utf-8\";foo=\"charset=bar\";foocharset=bar;foo=bar";
+			String contentType = "test/plain;charset=\"utf-8\";foo=\"charset=bar\";foocharset=bar;foobar=bar";
 			response.setHeader(HttpHeaders.CONTENT_TYPE, contentType);
 			assertThat(response.getContentType()).isEqualTo(contentType);
 			assertThat(response.getHeader(HttpHeaders.CONTENT_TYPE)).isEqualTo(contentType);