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Implement FileHandle#waitForDataInBackgroundAndNotify #1427

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Implement FileHandle#waitForDataInBackgroundAndNotify #1427

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15 changes: 14 additions & 1 deletion Foundation/FileHandle.swift
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Expand Up @@ -8,6 +8,7 @@
//

import CoreFoundation
import Dispatch

#if os(OSX) || os(iOS)
import Darwin
Expand Down Expand Up @@ -345,7 +346,19 @@ extension FileHandle {
}

open func waitForDataInBackgroundAndNotify() {
NSUnimplemented()
let global = DispatchQueue.global(qos: .background)
let channel = DispatchIO(type: .stream, fileDescriptor: fileDescriptor, queue: global) { _ in }

// The desire is to trigger the handler blocka as soon as there is any data in the channel.
channel.setLimit(lowWater: 1)

channel.read(offset: 0, length: Int.max, queue: global) { (_, _, error) in
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  • this reads all the data for no reason
  • also if this is a socket/pipe this is a permanent leak of a file descriptor
  • you could just use a DispatchSource.makeReadSource and get the notifications but not the reading. As soon as you get the first notification you then want to .cancel the DispatchSource as you only want to get notified once.

var notification = Notification(name: .NSFileHandleDataAvailable, object: nil, userInfo: nil)
if error != 0 {
notification.userInfo = ["NSFileHandleError": NSNumber(value: error)]
}
NotificationCenter.default.post(notification)
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doesn't that need to happen on the main thread? CC @parkera

}
}

open var readabilityHandler: ((FileHandle) -> Void)? {
Expand Down
18 changes: 18 additions & 0 deletions TestFoundation/TestFileHandle.swift
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Expand Up @@ -21,6 +21,7 @@ class TestFileHandle : XCTestCase {
("test_constants", test_constants),
("test_pipe", test_pipe),
("test_nullDevice", test_nullDevice),
("test_waitForDataInBackgroundAndNotify", test_waitForDataInBackgroundAndNotify),
]
}

Expand Down Expand Up @@ -64,4 +65,21 @@ class TestFileHandle : XCTestCase {
fh.seek(toFileOffset: 0)
XCTAssertEqual(fh.readDataToEndOfFile().count, 0)
}

func test_waitForDataInBackgroundAndNotify() {
let expect = expectation(description: "Receiving asynchronous data from pipe")
let pipe = Pipe()
pipe.fileHandleForReading.waitForDataInBackgroundAndNotify()

NotificationCenter.default.addObserver(forName: .NSFileHandleDataAvailable, object: nil, queue: nil) { (notification) in
XCTAssertEqual(notification.name, .NSFileHandleDataAvailable)
XCTAssertNil(notification.userInfo)
expect.fulfill()
}

let data = Data(bytes: [0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x2c, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x21])
pipe.fileHandleForWriting.write(data)

waitForExpectations(timeout: 2)
}
}