I wrote some Swift 2.2 code to interact with OpenSSL C APIs and now I'm trying to convert it to Swift 3.
In Swift 2
let octets = pkcs7_d_data(pkcs7_d_sign(receiptPKCS7).memory.contents)
var ptr = UnsafePointer<UInt8>(octets.memory.data)
// now pass pointer by reference
ASN1_get_object(&ptr, &length, &type, &xclass, end - ptr)
In Swift 3, I've had to make a couple changes
// use guard so i dont have to constantly unwrap these values
guard let octets = pkcs7_d_data(pkcs7_d_sign(receiptPKCS7).pointee.contents),
var ptr = UnsafePointer<UInt8>(octets.pointee.data) else {
return nil
}
ASN1_get_object(&ptr, &length, &type, &xclass, end - ptr)
// ^^^ this is now a compiler error
Unfortunately, I can no longer pass ptr to ASN1_get_object by reference, due to this error:
Cannot pass immutable value as inout argument: Implicit conversion from UnsafePointer<UInt8> to UnsafePointer<UInt8>? requires a temporary
and then the rest of the error is cut off (there's no expand arrow).
What I've tried:
changing the ptr assignment to UnsafePointer<UInt8>(octets.pointee.data)? but then I'm told that my existing assignment already produces an optional
changed the UnsafePointer to UnsafeMutablePointer
What needs to change here?
The problem seems to be that octets.pointee.data is a
UnsafeMutablePointer<UInt8>!, but ASN1_get_object expects
the address of a UnsafePointer<UInt8>?.
The following code compiles, but I could not test it:
if
let octets = pkcs7_d_data(pkcs7_d_sign(receiptPKCS7).pointee.contents),
let data = octets.pointee.data {
var ptr: UnsafePointer? = UnsafePointer(data) // (*)
var length = 0
var tag: Int32 = 0
var xclass: Int32 = 0
ASN1_get_object(&ptr, &length, &tag, &xclass, Int(octets.pointee.length))
}
(*) is the pointer conversion which makes it compile.
Related
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?
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)
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.
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)
}
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>
}
I am maintaining a set of data obtained from a AVCaptureSynchronizedData. One of the methods I use modifies the CVPixelBuffers obtained from the AVCaptureSynchronizedData. While modifying. the CVPixelBuffer, I create a copy of the CVPixelBuffer via
let status = CVPixelBufferCreateWithBytes(nil, scaleWidth, scaleHeight,
pixelFormat, destData,
destBytesPerRow, releaseCallback,
nil, nil, &dstPixelBuffer)
The releaseCallBack is referenced as
let releaseCallback: CVPixelBufferReleaseBytesCallback = { _, ptr in
if let ptr = ptr {
free(UnsafeMutableRawPointer(mutating: ptr))
}
}
However, I would like to be able to keep up with how many times this is called. But, if I add something like
var num:Int = 0
let releaseCallback: CVPixelBufferReleaseBytesCallback = { _, ptr in
if let ptr = ptr {
num += 1
free(UnsafeMutableRawPointer(mutating: ptr))
}
}
I get the error
A C function pointer cannot be formed from a closure that captures context
Not sure if it is possible, but it would be incredibly useful to be able to keep count of the number of times a pointer is destroyed
Referencing the instance variable num in the closure captures self and that is not possible in the callback which is a pure C function.
Similarly as in How to use instance method as callback for function which takes only func or literal closure you have to use that a custom pointer (here: releaseRefCon) can be passed to the callback:
let releaseCallback: CVPixelBufferReleaseBytesCallback = { releaseRefCon, ptr in
let mySelf = Unmanaged<YourClass>.fromOpaque(releaseRefCon!).takeUnretainedValue()
if let ptr = ptr {
free(UnsafeMutableRawPointer(mutating: ptr))
mySelf.num += 1
}
}
let releaseRefCon = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())
let status = CVPixelBufferCreateWithBytes(nil, scaleWidth, scaleHeight,
pixelFormat, destData,
destBytesPerRow,
releaseCallback, releaseRefCon,
nil, &dstPixelBuffer)
For the conversions from an instance pointer (here: self) to a void pointer and back to an instance pointer (here: mySelf) see How to cast self to UnsafeMutablePointer<Void> type in swift.
I have a C struct like this.
struct someStruct {
char path[10][MAXPATHLEN];
};
I'd like to copy a list of Swift strings into the char[10][] array.
For me it's very challenging to handle c two-dimensional char array in Swift. Could anyone share some code which can work with Swift 5? Thanks!
C Arrays are imported to Swift as tuples. Here we have a two-dimensional C array, which becomes a nested tuple in Swift:
public struct someStruct {
public var path: (
(Int8, ..., Int8),
(Int8, ..., Int8),
...
(Int8, ..., Int8)
)
}
There is no really “nice” solution that I am aware of, but using the fact that Swift preserves the memory layout of imported C structures (source), one can achive the goal with some pointer magic:
var s = someStruct()
let totalSize = MemoryLayout.size(ofValue: s.path)
let itemSize = MemoryLayout.size(ofValue: s.path.0)
let numItems = totalSize / itemSize
withUnsafeMutablePointer(to: &s.path) {
$0.withMemoryRebound(to: Int8.self, capacity: totalSize) { ptr in
for i in 0..<numItems {
let itemPtr = ptr + i * itemSize
strlcpy(itemPtr, "String \(i)", itemSize)
}
print(ptr)
}
}
ptr is a pointer to s.path, and itemPtr is pointer to s.path[i]. strlcpy copies the string, here we use the fact that one can pass a Swift string directly to a C function taking a const char* argument (and a temporary null-terminated UTF-8 representation is created automatically).
I strongly encourage you to use some kind of helper methods.
Example:
/* writes str to someStruct instance at index */
void writePathToStruct(struct someStruct* s, size_t index, const char* str) {
assert(index < 10 && "Specified index is out of bounds");
strcpy(s->path[index], str);
}
Now, when calling this function, filling the array looks much cleaner:
var someStructInstance = someStruct()
let pathIndex: Int = 3
let path = "/dev/sda1"
let encoding = String.Encoding.ascii
withUnsafeMutablePointer(to: &someStructInstance) { pointer -> Void in
writePathToStruct(pointer, pathIndex, path.cString(using: encoding)!)
}
By design, tuples can not be accessed by variable index. Reading statically can thus be done without a helper function.
let pathRead = withUnsafeBytes(of: &someStructInstance.path.3) { pointer -> String? in
return String(cString: pointer.baseAddress!.assumingMemoryBound(to: CChar.self), encoding: encoding)
}
print(pathRead ?? "<Empty path>")
However, I assume you will definitely have to read the array with a dynamic index.
In that case, I encourage you to use a helper method as well:
const char* readPathFromStruct(const struct someStruct* s, size_t index) {
assert(index < 10 && "Specified index is out of bounds");
return s->path[index];
}
which will result in a much cleaner Swift code:
pathRead = withUnsafePointer(to: &someStructInstance) { pointer -> String? in
return String(cString: readPathFromStruct(pointer, 3), encoding: encoding)
}
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?
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)
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.
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)
}
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>
}
Up to Xcode 8 beta 5, I could access the event info in a MusicEventIterator, using something like:
var type: MusicEventType = 0
var stamp: MusicTimeStamp = 0
var data: UnsafePointer<()>? = nil
var size: UInt32 = 0
while(hasCurrentEvent != false) {
MusicEventIteratorGetEventInfo(iterator!, &stamp, &type,
&data, &size)
// do stuff with stamp, type, data...
}
I managed to get some help at the Apple dev site on dealing with "data", but getting data in the first place is also broken. I get a warning about using "UnsafeRawPointer" in the declaration of "data", and an error about not being able to use data as an inout argument in the call to MusicEventIteratorGetEventInfo()...
Though I know they're making things more deterministic and future-proof (i.e., for the compiler), it's incredibly frustrating to have the C-interop stuff changing every few months. My MIDI file parser code has already changed 3 times...
For reference, MusicEventIteratorGetEventInfo has the signature:
func MusicEventIteratorGetEventInfo(_ inIterator: MusicEventIterator,
_ outTimeStamp: UnsafeMutablePointer<MusicTimeStamp>,
_ outEventType: UnsafeMutablePointer<MusicEventType>,
_ outEventData: UnsafeMutablePointer<UnsafePointer<Void>>,
_ outEventDataSize: UnsafeMutablePointer<UInt32>) -> OSStatus
Any help greatly appreciated.
The latest reference of MusicEventIteratorGetEventInfo shows this:
Declaration
func MusicEventIteratorGetEventInfo(_ inIterator: MusicEventIterator,
_ outTimeStamp: UnsafeMutablePointer<MusicTimeStamp>,
_ outEventType: UnsafeMutablePointer<MusicEventType>,
_ outEventData: UnsafeMutablePointer<UnsafeRawPointer?>,
_ outEventDataSize: UnsafeMutablePointer<UInt32>) -> OSStatus
The third parameter outEventData is of type UnsafeMutablePointer<UnsafeRawPointer?>.
Generally, when an API claims UnsafeMutablePointer<T>, you declare a variable of type T, and pass it as an inout argument.
So, this should work:
var type: MusicEventType = 0
var stamp: MusicTimeStamp = 0
var data: UnsafeRawPointer? = nil //<- Declare a variable of type `UnsafeRawPointer?`.
var size: UInt32 = 0
while hasCurrentEvent != false {
MusicEventIteratorGetEventInfo(iterator!, &stamp, &type,
&data, &size) //<- Pass it as an inout argument.
// do stuff with stamp, type, data...
}
In case anyone else has the same problem, this seems to work:
// Somewhere to put the raw midi data
var type: MusicEventType = 0
var stamp: MusicTimeStamp = -1
let data: UnsafeMutablePointer<UnsafeRawPointer?> = UnsafeMutablePointer<UnsafeRawPointer?>.allocate(capacity: MemoryLayout<MusicEventType>.size)
var size: UInt32 = 0
var tsChangeStamp: MusicTimeStamp = 0
while(hasCurrentEvent != false) {
MusicEventIteratorGetEventInfo(iterator!, &stamp, &type, data, &size)
// do stuff...
}