withUnsafeBytes' is deprecated: use `withUnsafeBytes<R>(_: (UnsafeRawBufferPointer) throws -> R) rethrows -> R` instead [duplicate] - swift

Question

I previously used this code in Swift 4.2 to generate an id:
public static func generateId() throws -> UInt32 {
let data: Data = try random(bytes: 4)
let value: UInt32 = data.withUnsafeBytes { $0.pointee } // deprecated warning!
return value // + some other stuff
}
withUnsafeBytes is deprecated on Swift 5.0. How can I solve this?

Answer 1

In Swift 5 the withUnsafeBytes() method of Data calls the closure with an (untyped) UnsafeRawBufferPointer, and you can load() the value from the raw memory:
let value = data.withUnsafeBytes { $0.load(as: UInt32.self) }
(compare How to use Data.withUnsafeBytes in a well-defined manner? in the Swift forum). Note that this requires that the memory is aligned on a 4-byte boundary. For alternatives see round trip Swift number types to/from Data.
Note also that as of Swift 4.2 you can create a random 32-bit integer simply using the new Random API:
let randomId = UInt32.random(in: .min ... .max)

Answer 2

On Xcode 10.2, Swift 5, using $0.load(as:) didn't work for me, both when reading from the pointer or writing to it.
Instead, using $0.baseAddress?.assumingMemoryBound(to:) seems to work well.
Example reading from the pointer buffer (code is unrelated to the question):
var reachability: SCNetworkReachability?
data.withUnsafeBytes { ptr in
guard let bytes = ptr.baseAddress?.assumingMemoryBound(to: Int8.self) else {
return
}
reachability = SCNetworkReachabilityCreateWithName(nil, bytes)
}
Example writing to the buffer pointer (code is unrelated to the question):
try outputData.withUnsafeMutableBytes { (outputBytes: UnsafeMutableRawBufferPointer) in
let status = CCKeyDerivationPBKDF(CCPBKDFAlgorithm(kCCPBKDF2),
passphrase,
passphrase.utf8.count,
salt,
salt.utf8.count,
CCPseudoRandomAlgorithm(kCCPRFHmacAlgSHA1),
rounds,
outputBytes.baseAddress?.assumingMemoryBound(to: UInt8.self),
kCCKeySizeAES256)
guard status == kCCSuccess else {
throw Error.keyDerivationError
}
}
The code from the question would look like:
let value = data.withUnsafeBytes {
$0.baseAddress?.assumingMemoryBound(to: UInt32.self)
}
In cases where the 'withUnsafeBytes' is deprecated: use withUnsafeBytes<R>(…) warning persists, it seems like the compiler can get confused when the closure has only one line. Making the closure have two or more lines might remove the ambiguity.

Answer 3

One more way to fix this warning to use bindMemory(to:).
var rawKey = Data(count: rawKeyLength)
let status = rawKey.withUnsafeMutableBytes { rawBytes -> Int32 in
guard let rawBytes = rawBytes.bindMemory(to: UInt8.self).baseAddress else {
return Int32(kCCMemoryFailure)
}
return CCSymmetricKeyUnwrap(alg, ivBytes, iv.count, keyBytes, key.count, wrappedKeyBytes, wrappedKey.count, rawBytes, &rawKeyLength)
}

Answer 4

I got this error as I was trying to figure out a compression stream tutorial. To get it to work, I added a step of converting the raw buffer pointer to a UnsafePointer
Original code from a tutorial I was working on.
--> where input: Data
--> where stream: compression_stream
//Method that shows the deprecation alert
return input.withUnsafeBytes { (srcPointer: UnsafePointer<UInt8>) in
//holder
var output = Data()
//Source and destination buffers
stream.src_ptr = srcPointer //UnsafePointer<UInt8>
stream.src_size = input.count
… etc.
}
Code with a conversion to make the above code work with a valid method
return input.withUnsafeBytes { bufferPtr in
//holder
var output = Data()
//Get the Raw pointer at the initial position of the UnsafeRawBuffer
let base: UnsafeRawPointer? = bufferPtr.baseAddress
//Unwrap (Can be combined with above, but kept it separate for clarity)
guard let srcPointer = base else {
return output
}
//Bind the memory to the type
let count = bufferPtr.count
let typedPointer: UnsafePointer<UInt8> = srcPointer.bindMemory(to: UInt8.self, capacity: count)
// Jump back into the original method
stream.src_ptr = typedPointer //UnsafePointer<UInt8>
}