Cracking the Dave & Buster’s anomaly

Let’s dive into a peculiar bug in iOS. And by that I mean, let’s follow along as Guilherme Rambo dives into a peculiar bug in iOS.

The bug is that, if you try to send an audio message using the Messages app to someone who’s also using the Messages app, and that message happens to include the name “Dave and Buster’s”, the message will never be received.

↫ Guilherme Rambo

As I read this first description of the bug, I had no idea what could possibly be causing this. However, once Rambo explained that every audio message is transcribed by Apple into a text version, I immediately assumed what was going on: that “and” is throwing up problems because the actual name of the brand is stylised with an ampersand, isn’t it? It’s always DNS HTML, isn’t it?

Yes. Yes it is.

MessagesBlastDoorService uses MBDXMLParserContext (via MBDHTMLToSuperParserContext) to parse XHTML for the audio message. Ampersands have special meaning in XML/HTML and must be escaped, so the correct way to represent the transcription in HTML would have been "Dave & Buster's". Apple’s transcription system is not doing that, causing the parser to attempt to detect a special code after the ampersand, and since there’s no valid special code nor semicolon terminating what it thinks is an HTML entity, it detects an error and stops parsing the content.

↫ Guilherme Rambo

It must be somewhat of a relief to programmers and developers the world over that even a company as large and filled with talented people as Apple can run into bugs like this.