[SR-2514] Add a "hex dump" method to Data

[martinr448]

Previous ID	SR-2514
Radar	None
Original Reporter	@martinr448
Type	Improvement

Additional Detail from JIRA

Votes	1
Component/s	Foundation
Labels	Improvement
Assignee	None
Priority	Medium

md5: 641850a22679507d5d233e1d7021576d

Issue Description:

There should be a way to get the contents of a Data object in hexadecimal form.
The description methods do not provide that, as it was the case with NSData:

let data = Data(bytes: [1, 2, 3])
print(data) // 3 bytes
print(data.debugDescription) // 3 bytes

Of course I can cast to NSData

print(data as NSData) // <010203>

but it would be nice to have a "native" method. Suggestions:

• description returns a hex dump, or

• debugDescription returns a hex dump, or

• a new hexEncodedString method, similar to the existing Base64 methods.

[beccadax]

It's worth noting that, if Data.description returned a hex dump (or some other complete representation of the instance's contents), then we could provide a compatible Data.init(_: String) and then conform Data to LosslessStringConvertible.

[parkera]

We do have a bug in radar for this (15719610).

[martinr448]

Casting to NSData does not help any more in Xcode 10/Swift 4.2:

    let data1 = Data(bytes: [1, 2, 3])
    print(data1 as NSData) // Foundation._NSSwiftData
    
    let data2 = "Hello world".data(using: .utf8)!
    print(data2 as NSData) // _NSInlineData

[parkera]

I'd be open to accepting a PR that improves struct Data's debugDescription to print out some actual bytes.

[martinr448]

On macOS 10.15 (Catalina) beta, the NSData output is now truncated:

let data = Data(1...255)
// 255 bytes
print(data as NSData)
// {length = 255, bytes = 0x01020304 05060708 090a0b0c 0d0e0f10 ... f8f9fafb fcfdfeff }

so that this workaround does not help anymore to get the (full) content of a Data value (for debugging purposes).