Thanks @softenhard. This has been on my list to fix, but I hadn't yet thought about how to handle some of the double byte characters like emoji. I know relying on NSString length and enumeration can result in a split character. Any thoughts on that?

@kcharwood Oh yes, forgot about that while fast-fixing my project :)
So I've added a couple of lines to support multibyte characters.
Check it out:

static NSUInteger const batchSize = 50;

    NSInteger index = 0;
    NSMutableString *escaped = @"".mutableCopy;

    while (index < string.length) {
        NSUInteger length = MIN(string.length - index, batchSize);
        NSRange range = NSMakeRange(index, length);

        // To avoid breaking up character sequences such as 👴🏿
        range = [string rangeOfComposedCharacterSequencesForRange:range];

        NSString *substring = [string substringWithRange:range];
        NSString *encoded = [substring stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];
        [escaped appendString:encoded];

        index += range.length;
    }

What happens if the split is on the mutlibyte character? Is the character included in both results?

Could you add some unit tests demonstrating the fix? Thanks!

Updated in 6b6d41d

Merged with 6b6d41d

Merged in 3_0_0 with 039a317

As AFNetworking code is referencing this issue in https://github.com/AFNetworking/AFNetworking/blob/master/AFNetworking/AFURLRequestSerialization.m#L54, I'd like to quote in this pull request the details of this issue.

The reason and the workaround was discovered by @PrideChung and is a memory crash issue in stringByAddingPercentEncodingWithAllowedCharacters, reported in Alamofire/Alamofire#206. Scope of this issue was refined by @cnoon as only affecting iOS7 and iOS8, not affecting iOS9:

Batching is required for escaping due to an internal bug in iOS 8.1 and 8.2. Encoding more than a few hundred Chinese characters causes various malloc error crashes. To avoid this issue until iOS 8 is no longer supported, batching MUST be used for encoding. This introduces roughly a 20% overhead.

nice

I get a crash in my application. like this
| Application Specific Information: *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString appendString:]: nil argument'
-- | --
0 | CoreFoundation | 0x0000000202a74ec4 ___exceptionPreprocess + 228
1 | libobjc.A.dylib | 0x0000000201c45a40 _objc_exception_throw + 56
2 | CoreFoundation | 0x000000020297b594 +[NSException raise:format:] + 116
3 | CoreFoundation | 0x00000002029ea7d8 _mutateError + 204
4 | homework | 0x0000000102ae95dc AFPercentEscapedStringFromString (AFURLRequestSerialization.m:73)
5 | homework | 0x0000000102ae9880 -[AFQueryStringPair URLEncodedStringValue] (AFURLRequestSerialization.m:108)
6 | homework | 0x0000000102ae9a8c AFQueryStringFromParameters (AFURLRequestSerialization.m:0)
7 | homework | 0x0000000102aec560 -[AFHTTPRequestSerializer requestBySerializingRequest:withParameters:error:] (AFURLRequestSerialization.m:0)
8 | homework | 0x0000000102aeb878 -[AFHTTPRequestSerializer requestWithMethod:URLString:parameters:error:] (AFURLRequestSerialization.m:376)