Filter unicode ordering letters.

Signal/test/util/UtilTest.m

@@ -1,5 +1,5 @@
 //
-//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
 //
 
 #import "UtilTest.h"
@@ -11,6 +11,8 @@
 
 - (NSString *)removeAllCharactersIn:(NSCharacterSet *)characterSet;
 
+- (NSString *)filterUnsafeCharacters;
+
 @end
 
 #pragma mark -
@@ -69,4 +71,16 @@
     test([@"(555) 235-7111".digitsOnly isEqual:@"5552357111"]);
 }
 
+- (void)testFilterUnsafeCharacters
+{
+    XCTAssertEqualObjects(@"1".filterUnsafeCharacters, @"1");
+    XCTAssertEqualObjects(@"alice\u202Dbob".filterUnsafeCharacters, @"alice\uFFFDbob");
+    XCTAssertEqualObjects(@"\u202Dalicebob".filterUnsafeCharacters, @"\uFFFDalicebob");
+    XCTAssertEqualObjects(@"alicebob\u202D".filterUnsafeCharacters, @"alicebob\uFFFD");
+    XCTAssertEqualObjects(@"alice\u202Ebob".filterUnsafeCharacters, @"alice\uFFFDbob");
+    XCTAssertEqualObjects(@"\u202Ealicebob".filterUnsafeCharacters, @"\uFFFDalicebob");
+    XCTAssertEqualObjects(@"alicebob\u202E".filterUnsafeCharacters, @"alicebob\uFFFD");
+    XCTAssertEqualObjects(@"alice\u202Dbobalice\u202Ebob".filterUnsafeCharacters, @"alice\uFFFDbobalice\uFFFDbob");
+}
+
 @end

SignalServiceKit/src/Util/NSString+SSK.m

@@ -103,10 +103,7 @@ NS_ASSUME_NONNULL_BEGIN
     static NSCharacterSet *characterSet;
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
-        UniChar chars[] = { 0x200C };
-        NSString *characterSetString =
-            [[NSString alloc] initWithCharacters:chars length:sizeof(chars) / sizeof(UniChar)];
-        characterSet = [NSCharacterSet characterSetWithCharactersInString:characterSetString];
+        characterSet = [NSCharacterSet characterSetWithCharactersInString:@"\u200C"];
     });
 
     return characterSet;
@@ -147,9 +144,42 @@ NS_ASSUME_NONNULL_BEGIN
     return [filteredForIndic copy];
 }
 
++ (NSCharacterSet *)unsafeCharacterSet
+{
+    static NSCharacterSet *characterSet;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        characterSet = [NSCharacterSet characterSetWithCharactersInString:@"\u202D\u202E"];
+    });
+
+    return characterSet;
+}
+
+- (NSString *)filterUnsafeCharacters
+{
+    NSCharacterSet *unsafeCharacterSet = [[self class] unsafeCharacterSet];
+    NSRange range = [self rangeOfCharacterFromSet:unsafeCharacterSet];
+    if (range.location == NSNotFound) {
+        return self;
+    }
+    NSMutableString *filtered = [NSMutableString new];
+    NSString *remainder = [self copy];
+    while (range.location != NSNotFound) {
+        if (range.location > 0) {
+            [filtered appendString:[remainder substringToIndex:range.location]];
+        }
+        // The "replacement" code point.
+        [filtered appendString:@"\uFFFD"];
+        remainder = [remainder substringFromIndex:range.location + range.length];
+        range = [remainder rangeOfCharacterFromSet:unsafeCharacterSet];
+    }
+    [filtered appendString:remainder];
+    return filtered;
+}
+
 - (NSString *)filterStringForDisplay
 {
-    return self.ows_stripped.filterForIndicScripts.filterForExcessiveDiacriticals;
+    return self.ows_stripped.filterForIndicScripts.filterForExcessiveDiacriticals.filterUnsafeCharacters;
 }
 
 - (NSString *)filterForExcessiveDiacriticals