{"id":26629,"date":"2019-09-17T16:10:07","date_gmt":"2019-09-17T20:10:07","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=26629"},"modified":"2019-12-23T16:34:01","modified_gmt":"2019-12-23T21:34:01","slug":"breaking-the-nsdata-description-contract","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2019\/09\/17\/breaking-the-nsdata-description-contract\/","title":{"rendered":"Breaking the NSData.description Contract"},"content":{"rendered":"

Mattt Thompson<\/a> (tweet<\/a> via Cédric Luthi<\/a>):<\/p>\n

\n

iOS 13 changes the format of descriptions for Foundation objects, including NSData:<\/p>\n

\/\/ iOS 12\n(deviceToken as NSData).description \/\/ \"<965b251c 6cb1926d e3cb366f dfb16ddd e6b9086a 8a3cac9e 5f857679 376eab7C>\"\n\n\/\/ iOS 13\n(deviceToken as NSData).description \/\/ \"{length = 32, bytes = 0x965b251c 6cb1926d e3cb366f dfb16ddd ... 5f857679 376eab7c }\"<\/pre>\n
Whereas previously, you could coerce NSData<\/code> to spill its entire contents by converting it into a String<\/code>, it now reports its length and a truncated summary of its internal bytes.<\/p>\n
[…]<\/p>\n
Was Apple irresponsible in making this particular change?<\/p>\n
No, not really — developers shouldn’t have relied on a specific format for an object’s description<\/code><\/a>.<\/p>\n<\/blockquote>\n
The documentation<\/a> promises—still, as of this writing—that description<\/code> returns:<\/p>\n
A string that contains a hexadecimal representation of the data object’s contents in a property list format.<\/p><\/blockquote>\n
Perhaps it would be a mistake to rely on the exact format of the string, e.g. where the spaces are inserted. But, clearly, it is supposed to contain the entire data’s contents, in a format that can be reconstituted by the property list API<\/a>. That is no longer the case, and the fault for any resulting breakage lies with Apple, not with developers who were relying on the API to do what it said it would do.<\/p>\n
Apple hasn’t explained why it made the change, or even documented it in the release notes<\/a>. In fact, there don’t even seem to be Foundation release notes yet.<\/p>\n\n
Previously:<\/p>\n