Ensure parsing/tostring symmetry in ContentDisposition

Prior to this commit, building a "Content-Disposition" header to a
String and then parsing it back would not always result in the original
header.

This commit ensures that ContentDisposition guarantees this and honors
the "equals" contract.

Fixes gh-37064

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

@@ -172,17 +172,17 @@ public final class ContentDisposition {
 			sb.append(this.type);
 		}
 		if (this.name != null) {
-			sb.append("; name=\"").append(this.name).append('\"');
+			sb.append("; name=\"");
+			appendName(sb, this.name).append('\"');
 		}
 		if (this.filename != null) {
 			if (this.charset == null || StandardCharsets.US_ASCII.equals(this.charset)) {
-				sb.append("; filename=\"")
-						.append(encodeQuotedPairs(this.filename))
-						.append('\"');
+				sb.append("; filename=\"");
+				appendName(sb, this.filename).append('\"');
 			}
 			else {
 				sb.append("; filename=\"")
-						.append(transliterateToAscii(encodeQuotedPairs(this.filename)))
+						.append(transliterateToAscii(appendName(new StringBuilder(), this.filename).toString()))
 						.append("\"; filename*=")
 						.append(encodeRfc5987Filename(this.filename, this.charset));
 			}
@@ -253,7 +253,7 @@ public final class ContentDisposition {
 						part.substring(eqIndex + 2, part.length() - 1) :
 						part.substring(eqIndex + 1));
 				if (attribute.equals("name") ) {
-					name = value;
+					name = (value.indexOf('\\') != -1 ? decodeQuotedPairs(value) : value);
 				}
 				else if (attribute.equals("filename*") ) {
 					int idx1 = value.indexOf('\'');
@@ -503,19 +503,20 @@ public final class ContentDisposition {
 		return sb.toString();
 	}
 
-	private static String encodeQuotedPairs(String filename) {
-		if (filename.indexOf('"') == -1 && filename.indexOf('\\') == -1) {
-			return filename;
-		}
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < filename.length() ; i++) {
-			char c = filename.charAt(i);
-			if (c == '"' || c == '\\') {
-				sb.append('\\');
+	private static StringBuilder appendName(StringBuilder buffer, String name) {
+		for (int i = 0; i < name.length() ; i++) {
+			char c = name.charAt(i);
+			// strip control characters
+			if (c <= 0x1F || c == 0x7F) {
+				continue;
 			}
-			sb.append(c);
+			// encode quoted pairs
+			if (c == '"' || c == '\\') {
+				buffer.append('\\');
+			}
+			buffer.append(c);
 		}
-		return sb.toString();
+		return buffer;
 	}
 
 	private static String decodeQuotedPairs(String filename) {

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

@@ -181,6 +181,15 @@ class ContentDispositionTests {
 			assertThat(cd.getFilename()).isEqualTo("foo\\bar \"baz\" qux \\\" quux.txt");
 		}
 
+		@Test
+		void parseBackslashInName() {
+			String s = "form-data; name=\"foo\\\"bar\"; filename=\"foo.txt\"";
+			ContentDisposition cd = ContentDisposition.parse(s);
+			assertThat(cd.getName()).isEqualTo("foo\"bar");
+			assertThat(cd.getFilename()).isEqualTo("foo.txt");
+			assertThat(cd.toString()).isEqualTo(s);
+		}
+
 		@Test
 		void parseBackslashInLastPosition() {
 			ContentDisposition cd = ContentDisposition.parse("form-data; name=\"foo\"; filename=\"bar\\\"");