Different console output data via NSData and Data (Xcode 8 beta 6, Swift 3)

Question

I write a little snippet of usual code but found that my code don't return hex data from server with this line of code:

let currentData = try! Data(contentsOf: fullURL!)
print("currentData=", currentData)

And the output:

currentData= 24419 bytes

I tried to use Leo's comment link:

stackoverflow.com/q/39075043/2303865

I got something hex data without spaces, and validator (http://jsonprettyprint.com) can't recognise it and returns null.

You were probably (ab)using the fact that the description method of NSData returns a "hex dump", which is no longer true for Data. But the data is there. Why do you think it isn't, and what do you actually want to achieve? — Martin R, Aug 27 '16 at 06:36
@MartinR I just want to get data and then use JSONSerialization to get it into JSON format. — wm.p1us, Aug 27 '16 at 06:59
And `JSONSerialization.jsonObject(with: currentData)` does not work? What result do you get and what do you expect? — Martin R, Aug 27 '16 at 07:02
Serialisation is ok. But want to see output and try to print currentData (with Data()) but console shows kind of garbage. — wm.p1us, Aug 27 '16 at 07:05
@LeoDabus: This looks more like an XY-problem to me. If OP wants to deserialize JSON data then the hex dump is irrelevant. — Martin R, Aug 27 '16 at 07:09
@wm.p1us: Your update does not help. There is no `print` statement in your code, therefore we cannot answer why you don't see any print data in the console. — Martin R, Aug 27 '16 at 07:14
@wm.p1us: Can you remove the unrelated stuff? Have you checked if the link that Leo pointed to answers your question? What does `print("currentData=", currentData)` show? — Martin R, Aug 27 '16 at 07:18
Can you post your actual code? As Martin already mentioned you need to use JSONObjectWithData to serialize your data — Leo Dabus, Aug 27 '16 at 07:35
I can serialise it so I got correct JSON. But I want to understand why hex data which I can get with your link returns nil in jsonprettyprint.com — wm.p1us, Aug 27 '16 at 07:37
You can print the returned data using `String(data: currentData, encoding: .utf8)` — Leo Dabus, Aug 27 '16 at 07:39
Your first link make hex data in the console appear. So I think that was correct way to do things. But now I try to figure out why that hex data I can't convert to normal JSON format with online services. — wm.p1us, Aug 27 '16 at 07:45
@LeoDabus I know this is just test new classes code. It's unsafe. — wm.p1us, Aug 27 '16 at 07:46
@wm.p1us: http://jsonprettyprint.com requires the JSON as a string, not as hex data. It wouldn't work with the hex output from NSData either. — Martin R, Aug 27 '16 at 07:51
Omg I understand it at the same time you wrote. Have to sleep :( Please wrote some answer about console output and I accept it. — wm.p1us, Aug 27 '16 at 07:53

score 5 · Accepted Answer · edited May 23 '17 at 11:48

Let's try to sort out the different issues here and summarize the above comments.

The description method of Data prints only a short summary "NNN bytes", and not a hex dump as NSData did:

let o = ["foo": "bar"]
let jsonData = try! JSONSerialization.data(withJSONObject: o)

print(jsonData) // 13 bytes

You can get a hex dump by bridging to NSData (source):

print(jsonData as NSData) // <7b22666f 6f223a22 62617222 7d>

or by writing an extension method for Data (How to convert Data to hex string in swift).

But that is actually not the real problem. The JSON validator needs the JSON as a string, not as a hex dump (source):

print(String(data: jsonData, encoding: .utf8)!) // {"foo":"bar"}

And to de-serialize the JSON data into an object you would need none of the above and just call

let obj = try JSONSerialization.jsonObject(with: jsonData)

Different console output data via NSData and Data (Xcode 8 beta 6, Swift 3)

1 Answers1