Decode quoted pairs in ContentDisposition

This commit makes sure that quoted pairs, as used in Content-Disposition
header file names (i.e. \" and \\), are properly decoded, whereas before
they were stored as is.

Closes spring-projectsgh-28837

Author: poutsma

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

@@ -259,7 +259,7 @@ public String toString() {
 		if (this.filename != null) {
 			if (this.charset == null || StandardCharsets.US_ASCII.equals(this.charset)) {
 				sb.append("; filename=\"");
-				sb.append(escapeQuotationsInFilename(this.filename)).append('\"');
+				sb.append(encodeQuotedPairs(this.filename)).append('\"');
 			}
 			else {
 				sb.append("; filename*=");
@@ -404,6 +404,9 @@ else if (attribute.equals("filename") && (filename == null)) {
 							}
 						}
 					}
+					else if (value.indexOf('\\') != -1) {
+						filename = decodeQuotedPairs(value);
+					}
 					else {
 						filename = value;
 					}
@@ -560,25 +563,33 @@ else if (b == '=' && index < value.length - 2) {
 		return StreamUtils.copyToString(baos, charset);
 	}
 
-	private static String escapeQuotationsInFilename(String filename) {
+	private static String encodeQuotedPairs(String filename) {
 		if (filename.indexOf('"') == -1 && filename.indexOf('\\') == -1) {
 			return filename;
 		}
-		boolean escaped = false;
 		StringBuilder sb = new StringBuilder();
 		for (int i = 0; i < filename.length() ; i++) {
 			char c = filename.charAt(i);
-			if (!escaped && c == '"') {
-				sb.append("\\\"");
+			if (c == '"' || c == '\\') {
+				sb.append('\\');
+			}
+			sb.append(c);
+		}
+		return sb.toString();
+	}
+
+	private static String decodeQuotedPairs(String filename) {
+		StringBuilder sb = new StringBuilder();
+		int length = filename.length();
+		for (int i = 0; i < length; i++) {
+			char c = filename.charAt(i);
+			if (filename.charAt(i) == '\\' && i + 1 < length) {
+				i++;
+				sb.append(filename.charAt(i));
 			}
 			else {
 				sb.append(c);
 			}
-			escaped = (!escaped && c == '\\');
-		}
-		// Remove backslash at the end.
-		if (escaped) {
-			sb.deleteCharAt(sb.length() - 1);
 		}
 		return sb.toString();
 	}

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

@@ -149,27 +149,25 @@ void parseEncodedFilenameWithInvalidName() {
 				.isThrownBy(() -> parse("form-data; name=\"name\"; filename*=UTF-8''%A.txt"));
 	}
 
-	@Test // gh-23077
-	@SuppressWarnings("deprecation")
-	void parseWithEscapedQuote() {
-		BiConsumer<String, String> tester = (description, filename) ->
-			assertThat(parse("form-data; name=\"file\"; filename=\"" + filename + "\"; size=123"))
-					.as(description)
-					.isEqualTo(ContentDisposition.formData().name("file").filename(filename).size(123L).build());
-
-		tester.accept("Escaped quotes should be ignored",
-				"\\\"The Twilight Zone\\\".txt");
-
-		tester.accept("Escaped quotes preceded by escaped backslashes should be ignored",
-				"\\\\\\\"The Twilight Zone\\\\\\\".txt");
-
-		tester.accept("Escaped backslashes should not suppress quote",
-				"The Twilight Zone \\\\");
+	@Test
+	void parseBackslash() {
+		String s = "form-data; name=\"foo\"; filename=\"foo\\\\bar \\\"baz\\\" qux \\\\\\\" quux.txt\"";
+		ContentDisposition cd = ContentDisposition.parse(
+				s);
+		assertThat(cd.getName()).isEqualTo("foo");
+		assertThat(cd.getFilename()).isEqualTo("foo\\bar \"baz\" qux \\\" quux.txt");
+		assertThat(cd.toString()).isEqualTo(s);
+	}
 
-		tester.accept("Escaped backslashes should not suppress quote",
-				"The Twilight Zone \\\\\\\\");
+	@Test
+	void parseBackslashInLastPosition() {
+		ContentDisposition cd = ContentDisposition.parse("form-data; name=\"foo\"; filename=\"bar\\\"");
+		assertThat(cd.getName()).isEqualTo("foo");
+		assertThat(cd.getFilename()).isEqualTo("bar\\");
+		assertThat(cd.toString()).isEqualTo("form-data; name=\"foo\"; filename=\"bar\\\\\"");
 	}
 
+
 	@Test
 	@SuppressWarnings("deprecation")
 	void parseWithExtraSemicolons() {
@@ -281,26 +279,26 @@ void formatWithFilenameWithQuotes() {
 		};
 
 		String filename = "\"foo.txt";
-		tester.accept(filename, "\\" + filename);
+		tester.accept(filename, "\\\"foo.txt");
 
 		filename = "\\\"foo.txt";
-		tester.accept(filename, filename);
+		tester.accept(filename, "\\\\\\\"foo.txt");
 
 		filename = "\\\\\"foo.txt";
-		tester.accept(filename, "\\" + filename);
+		tester.accept(filename, "\\\\\\\\\\\"foo.txt");
 
 		filename = "\\\\\\\"foo.txt";
-		tester.accept(filename, filename);
+		tester.accept(filename, "\\\\\\\\\\\\\\\"foo.txt");
 
 		filename = "\\\\\\\\\"foo.txt";
-		tester.accept(filename, "\\" + filename);
+		tester.accept(filename, "\\\\\\\\\\\\\\\\\\\"foo.txt");
 
 		tester.accept("\"\"foo.txt", "\\\"\\\"foo.txt");
 		tester.accept("\"\"\"foo.txt", "\\\"\\\"\\\"foo.txt");
 
-		tester.accept("foo.txt\\", "foo.txt");
-		tester.accept("foo.txt\\\\", "foo.txt\\\\");
-		tester.accept("foo.txt\\\\\\", "foo.txt\\\\");
+		tester.accept("foo.txt\\", "foo.txt\\\\");
+		tester.accept("foo.txt\\\\", "foo.txt\\\\\\\\");
+		tester.accept("foo.txt\\\\\\", "foo.txt\\\\\\\\\\\\");
 	}
 
 	@Test
@@ -313,4 +311,14 @@ void formatWithEncodedFilenameUsingInvalidCharset() {
 						.toString());
 	}
 
+	@Test
+	void parseFormatted() {
+		ContentDisposition cd = ContentDisposition.builder("form-data")
+				.name("foo")
+				.filename("foo\\bar \"baz\" qux \\\" quux.txt").build();
+		ContentDisposition parsed = ContentDisposition.parse(cd.toString());
+		assertThat(parsed).isEqualTo(cd);
+		assertThat(parsed.toString()).isEqualTo(cd.toString());
+	}
+
 }