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Adopt DispatchData in URLSessionHTTPClient #167

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Adopt DispatchData in URLSessionHTTPClient
guoye-zhang May 15, 2026
40e4b20
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guoye-zhang May 21, 2026
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8 changes: 5 additions & 3 deletions Sources/URLSessionHTTPClient/URLSessionHTTPClient.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -84,9 +84,9 @@ public final class URLSessionHTTPClient: HTTPClient, IdleTimerEntryProvider {
public mutating func read<Return: ~Copyable, Failure>(
body: (inout UniqueArray<UInt8>) async throws(Failure) -> Return
) async throws(AsyncStreaming.EitherError<any Error, Failure>) -> Return where Failure: Error {
let data: Data?
let data: DispatchData?
do {
data = try await self.actual.data(maximumCount: nil)
data = try await self.actual.data()
} catch {
throw .first(error)
}
Expand All @@ -95,7 +95,9 @@ public final class URLSessionHTTPClient: HTTPClient, IdleTimerEntryProvider {
var buffer = self.buffer.take()!
if let data, !data.isEmpty {
buffer.reserveCapacity(data.count)
buffer.append(copying: data.span)
for region in data.regions {
buffer.append(copying: region)
}
}

let result: Return
Expand Down
69 changes: 42 additions & 27 deletions Sources/URLSessionHTTPClient/URLSessionTaskDelegateBridge.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ import HTTPTypesFoundation
import Synchronization

@available(anyAppleOS 26.0, *)
final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDelegate {
final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionTaskDelegate {
private enum Callback: Sendable {
case response(URLResponse)
case redirection(
Expand Down Expand Up @@ -66,10 +66,10 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
// The client is waiting on URLSession. The client is expecting response body data,
// but URLSession has not received any that it can send out to the client. When
// URLSession does receive an update, the provided continuation must be fired.
case awaitingData(CheckedContinuation<(Bool, Data?), any Error>)
case awaitingData(CheckedContinuation<(Bool, DispatchData?), any Error>)
// URLSession is waiting for the client. URLSession has updated the response body
// with more data/completion/error but the client has not consumed/processed this.
case awaitingConsumption(Data, complete: Bool, error: (any Error)?, suspendedTask: URLSessionTask?)
case awaitingConsumption(DispatchData, complete: Bool, error: (any Error)?, suspendedTask: URLSessionTask?)
}
var state: State = .awaitingResponse
var completionContinuation: CheckedContinuation<Void, Never>? = nil
Expand All @@ -82,6 +82,8 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
self.state.withLock { $0.responseTrailerFields }
}

// Manually specifying the selector without conforming to `URLSessionDataDelegate` to avoid Data bridging
@objc(URLSession:dataTask:didReceiveResponse:completionHandler:)
func urlSession(
_ session: URLSession,
dataTask: URLSessionDataTask,
Expand All @@ -92,7 +94,7 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
defer {
switch state.state {
case .awaitingResponse:
state.state = .awaitingConsumption(Data(), complete: false, error: nil, suspendedTask: nil)
state.state = .awaitingConsumption(.empty, complete: false, error: nil, suspendedTask: nil)
case .awaitingData, .awaitingConsumption:
break
}
Expand All @@ -108,23 +110,27 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
completionHandler(.allow)
}

func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
// Manually specifying the selector without conforming to `URLSessionDataDelegate` to avoid Data bridging
@objc(URLSession:dataTask:didReceiveData:)
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: NSData) {
// URLSession usually vends dispatch_data_t as NSData
let data = DispatchData(data)
let oldState = self.state.withLock { state in
defer {
switch state.state {
case .awaitingData:
state.state = .awaitingConsumption(data, complete: false, error: nil, suspendedTask: nil)
case .awaitingResponse:
// We don't support data before response
state.state = .awaitingConsumption(Data(), complete: true, error: nil, suspendedTask: nil)
case .awaitingConsumption(let existingData, let complete, let error, var suspendedTask):
let newData = existingData + data
if newData.count > Self.highWatermark && suspendedTask == nil {
state.state = .awaitingConsumption(.empty, complete: true, error: nil, suspendedTask: nil)
case .awaitingConsumption(var existingData, let complete, let error, var suspendedTask):
existingData.append(data)
if existingData.count > Self.highWatermark && suspendedTask == nil {
dataTask.suspend()
suspendedTask = dataTask
}
state.state = .awaitingConsumption(
newData,
existingData,
complete: complete,
error: error,
suspendedTask: suspendedTask
Expand All @@ -150,9 +156,9 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
defer {
switch state.state {
case .awaitingData:
state.state = .awaitingConsumption(Data(), complete: true, error: error, suspendedTask: nil)
state.state = .awaitingConsumption(.empty, complete: true, error: error, suspendedTask: nil)
case .awaitingResponse:
state.state = .awaitingConsumption(Data(), complete: true, error: nil, suspendedTask: nil)
state.state = .awaitingConsumption(.empty, complete: true, error: nil, suspendedTask: nil)
case .awaitingConsumption(let existingData, _, _, _):
state.state = .awaitingConsumption(existingData, complete: true, error: error, suspendedTask: nil)
}
Expand Down Expand Up @@ -181,35 +187,26 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
self.continuation.finish()
}

func data(maximumCount: Int?) async throws -> Data? {
func data() async throws -> DispatchData? {
try await withTaskCancellationHandler {
// Keep waiting on continuations until:
// a) data is returned
// b) no more data can be returned (complete)
// c) an error occurred
while true {
let (shouldReturn, result): (Bool, Data?) = try await withCheckedThrowingContinuation { continuation in
let (shouldReturn, result): (Bool, DispatchData?) = try await withCheckedThrowingContinuation { continuation in
self.state.withLock { state in
switch state.state {
case .awaitingConsumption(let existingData, let complete, let error, let suspendedTask):
if !existingData.isEmpty {
let (dataToReturn, remainingData) =
if let maximumCount, existingData.count > maximumCount {
(existingData.prefix(maximumCount), existingData.dropFirst(maximumCount))
} else {
(existingData, Data())
}
let shouldResume = remainingData.count <= Self.highWatermark
state.state = .awaitingConsumption(
remainingData,
.empty,
complete: complete,
error: existingData.isEmpty ? nil : error,
suspendedTask: shouldResume ? nil : suspendedTask
suspendedTask: nil
)
if shouldResume {
suspendedTask?.resume()
}
continuation.resume(returning: (true, dataToReturn))
suspendedTask?.resume()
continuation.resume(returning: (true, existingData))
} else if let error, complete {
continuation.resume(throwing: error)
} else if complete {
Expand Down Expand Up @@ -462,4 +459,22 @@ final class URLSessionTaskDelegateBridge: NSObject, Sendable, URLSessionDataDele
}
}
}

extension DispatchData {
init(_ data: NSData) {
// If the NSData is already dispatch_data_t
if let dispatchData = data as AnyObject as? __DispatchData {
self = dispatchData as DispatchData
} else {
// This doesn't actually make a copy if the data is immutable
nonisolated(unsafe) let data = data.copy() as! NSData
self = unsafe DispatchData(
bytesNoCopy: UnsafeRawBufferPointer(start: data.bytes, count: data.count),
deallocator: .custom(nil) {
unsafe withExtendedLifetime(data) {}
}
)
}
}
}
#endif
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