Strip bad ASCII chars from Content-Disposition (#13)

Not all ASCII chars are even supported in practice in filenames in a Content-Disposition header. Strip out these characters as well as non-ASCII ones. This is based on the advice in RFC 6266 for implementing this header.

src/main/java/com/widen/urlbuilder/HttpUtils.java

@@ -6,13 +6,17 @@
 
 public class HttpUtils
 {
+    // Guidelines for generating this header: https://tools.ietf.org/html/rfc6266#appendix-D
     public static String createContentDispositionHeader(String type, String filename)
     {
         // Most browsers don't normally support UTF-8 in HTTP headers (HTTP officially supports only ISO-8859-1). In
-        // practice, S3 only supports ASCII characters, so strip everything from the filename out not in the ASCII range.
+        // practice, S3 only supports ASCII characters, so strip everything from the filename out not in the ASCII
+        // range.
+        // In addition, many browsers do not support escape sequences or percent encoding properly either, so strip out
+        // the following characters: \ " %
         String asciiFilename = Normalizer
             .normalize(filename, Normalizer.Form.NFD)
-            .replaceAll("[^\\x20-\\x7E]", "");
+            .replaceAll("[^\\x20-\\x7E[\\\\\"%]]", "");
 
         // Create the base header value.
         String header = String.format("%s; filename=\"%s\"", type, asciiFilename);

src/test/java/com/widen/urlbuilder/HttpUtilsTest.java

@@ -13,6 +13,22 @@ public void testCreateContentDispositionHeader()
             "inline; filename=\"foo.jpg\"",
             HttpUtils.createContentDispositionHeader("inline", "foo.jpg")
         );
+        assertEquals(
+            "inline; filename=\"hello world.jpg\"",
+            HttpUtils.createContentDispositionHeader("inline", "hello world.jpg")
+        );
+        assertEquals(
+            "inline; filename=\"helloworld.jpg\"; filename*=UTF-8''hello%22world.jpg",
+            HttpUtils.createContentDispositionHeader("inline", "hello\"world.jpg")
+        );
+        assertEquals(
+            "inline; filename=\"helloworld.jpg\"; filename*=UTF-8''hello%5Cworld.jpg",
+            HttpUtils.createContentDispositionHeader("inline", "hello\\world.jpg")
+        );
+        assertEquals(
+            "inline; filename=\"helloworld.jpg\"; filename*=UTF-8''hello%25world.jpg",
+            HttpUtils.createContentDispositionHeader("inline", "hello%world.jpg")
+        );
         assertEquals(
             "attachment; filename=\"+oo.jpg\"; filename*=UTF-8''%2B%C6%92oo.jpg",
             HttpUtils.createContentDispositionHeader("attachment", "+ƒoo.jpg")