Polishing contribution

Closes gh-26463

spring-web/src/main/java/org/springframework/http/ContentDisposition.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -48,6 +48,9 @@ import static java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME;
  */
 public final class ContentDisposition {
 
+	private final static Pattern BASE64_ENCODED_PATTERN =
+			Pattern.compile("=\\?([0-9a-zA-Z-_]+)\\?B\\?([+/0-9a-zA-Z]+=*)\\?=");
+
 	private static final String INVALID_HEADER_FIELD_PARAMETER_FORMAT =
 			"Invalid header field parameter format (as defined in RFC 5987)";
 
@@ -139,8 +142,9 @@ public final class ContentDisposition {
 	}
 
 	/**
-	 * Return the value of the {@literal filename} parameter (or the value of the
-	 * {@literal filename*} one decoded as defined in the RFC 5987), or {@code null} if not defined.
+	 * Return the value of the {@literal filename} parameter, possibly decoded
+	 * from BASE64 encoding based on RFC 2047, or of the {@literal filename*}
+	 * parameter, possibly decoded as defined in the RFC 5987.
 	 */
 	@Nullable
 	public String getFilename() {
@@ -323,7 +327,6 @@ public final class ContentDisposition {
 		return new ContentDisposition("", null, null, null, null, null, null, null);
 	}
 
-	private final static Pattern BASE64_ENCODED_PATTERN = Pattern.compile("=\\?([0-9a-zA-Z-_]+)\\?B\\?([+/0-9a-zA-Z]+=*)\\?=");
 	/**
 	 * Parse a {@literal Content-Disposition} header value as defined in RFC 2183.
 	 * @param contentDisposition the {@literal Content-Disposition} header value
@@ -366,12 +369,18 @@ public final class ContentDisposition {
 					}
 				}
 				else if (attribute.equals("filename") && (filename == null)) {
-					final Matcher matcher = BASE64_ENCODED_PATTERN.matcher(value);
-					if (matcher.find()) {
-						String charsetName = matcher.group(1);
-						String encoded = matcher.group(2);
-						filename = new String(Base64.getDecoder().decode(encoded), Charset.forName(charsetName));
-					} else {
+					if (value.startsWith("=?") ) {
+						Matcher matcher = BASE64_ENCODED_PATTERN.matcher(value);
+						if (matcher.find()) {
+							String match1 = matcher.group(1);
+							String match2 = matcher.group(2);
+							filename = new String(Base64.getDecoder().decode(match2), Charset.forName(match1));
+						}
+						else {
+							filename = value;
+						}
+					}
+					else {
 						filename = value;
 					}
 				}

spring-web/src/test/java/org/springframework/http/ContentDispositionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -80,16 +80,16 @@ class ContentDispositionTests {
 						.build());
 	}
 
-	@Test
-	void parseBase64EncodedUTF8Filename() {
-		assertThat(parse("attachment; filename=\"=?UTF-8?B?5pel5pys6KqeLmNzdg==?=\"").getFilename())
-				.isEqualTo("日本語.csv");
+	@Test // gh-26463
+	void parseBase64EncodedFilename() {
+		String input = "attachment; filename=\"=?UTF-8?B?5pel5pys6KqeLmNzdg==?=\"";
+		assertThat(parse(input).getFilename()).isEqualTo("日本語.csv");
 	}
 
-	@Test
+	@Test // gh-26463
 	void parseBase64EncodedShiftJISFilename() {
-		assertThat(parse("attachment; filename=\"=?SHIFT_JIS?B?k/qWe4zqLmNzdg==?=\"").getFilename())
-				.isEqualTo("日本語.csv");
+		String input = "attachment; filename=\"=?SHIFT_JIS?B?k/qWe4zqLmNzdg==?=\"";
+		assertThat(parse(input).getFilename()).isEqualTo("日本語.csv");
 	}
 
 	@Test