DNS query failure in async paradigm

[novi]

DNS request will failure with this async test as expected.

2019-09-17 15:14:22.499290+0900 xctest[7603:427732] [si_destination_compare] send failed: Invalid argument
2019-09-17 15:14:22.499516+0900 xctest[7603:427732] [si_destination_compare] send failed: Undefined error: 0
NioDNS/Tests/DNSClientTests/DNSClientTests.swift:54: error: -[DNSClientTests.DNSClientTests testSRVRecordsAsync] : Asynchronous wait failed: Exceeded timeout of 5 seconds, with unfulfilled expectations: "getSRVRecords".

No callback is called and it shows send failed error in console.

[Joannis]

I'm sorry that I missed this issue. Is this still an issue with the recent versions, since I am relying on this code.

[Joannis]

Closing this, as send failed is a known bug in SwiftNIO and doesn't affect NIODNS

[alessionossa]

I think the send failed error is unrelated to the issue reported by @novi , and that you can reproduce with his test.
The send failed issue is just a "false error", but the request is correctly sent to the server.
The error here, instead, is that for some reason the library doesn’t complete/return the Future when using asynchronous code instead of .wait().

I have faced the same issue and found this thread after I checked with Wireshark that the request was correctly sent to the server and the server responded correctly.

Please, reopen the issue.

It looks like the last code that gets executed is the following:
https://github.com/orlandos-nl/NioDNS/blob/de0b66fdedab85b4b84535df3efbef2e6605f89b/Sources/DNSClient/DNSClient%2BQuery.swift#L96-L109

The problem, in particular, is present only when the client connection is async like here:

DNSClient.connect(on: group, host: "8.8.8.8").flatMap({ client in
    client.getSRVRecords(from: "_mongodb._tcp.ok0-xkvc1.mongodb.net")
})

in fact, the following test succeed:

func testSRVRecordsSyncClient() throws {
    let expectation = self.expectation(description: "getSRVRecords")

    dnsClient.getSRVRecords(from: "_mongodb._tcp.ok0-xkvc1.mongodb.net")
    .whenComplete { (result) in
        switch result {
        case .failure(let error):
            XCTFail("\(error)")
        case .success(let answers):
            print(answers)
            XCTAssertGreaterThanOrEqual(answers.count, 1, "The returned answers should be greater than or equal to 1")
        }
        expectation.fulfill()
    }
    self.waitForExpectations(timeout: 5, handler: nil)
}

Probably, it all goes down to
https://github.com/apple/swift-nio/blob/19403414baa3f1c19a880154c81cbdeda9668acd/Sources/NIOCore/SocketAddresses.swift#L385-L394
which is suggested to be run outside an EventLoop

[Joannis]

@alessionossa might it be that Swift deallocated/deinit-ed the DNS client while waiting for a response?

[alessionossa]

I just read again Notes and this is probably the case. Thank you for the fast response!

I will open another issue related to ProtocolError as soon as I will reproduce the issue without sensitive data.

[alessionossa]

I think this issue can now be closed

[Joannis]

Thanks! Will do.