fatalError when trying to send a message using URLSessionWebSocketTask

[LosFarmosCTL]

Hey, I am trying to get a WebSocket connection running on Linux using FoundationNetworking, I am using the nightly-5.8-jammy docker image inside of a devcontainer:

Swift version 5.8-dev (LLVM f0fb631dd1a3a29, Swift ef7a6b85c8f7360)
Target: x86_64-unknown-linux-gnu

Everything compiles correctly but when I try to actually send a message (UPDATE: also happens when calling receive()), I get a fatalError, saying that the URL is invalid:

Swift/ErrorType.swift:200: Fatal error: Error raised at top level: Error Domain=NSURLErrorDomain Code=-1002 "(null)"
Current stack trace:
0    libswiftCore.so                    0x00007fda5194db10 _swift_stdlib_reportFatalErrorInFile + 112
1    libswiftCore.so                    0x00007fda5163f40f <unavailable> + 1442831
2    libswiftCore.so                    0x00007fda5163f227 <unavailable> + 1442343
3    libswiftCore.so                    0x00007fda5163e030 _assertionFailure(_:_:file:line:flags:) + 364
4    libswiftCore.so                    0x00007fda5169ce96 <unavailable> + 1826454
5    Test                               0x000055df55764eed <unavailable> + 57069
6    libswift_Concurrency.so            0x00007fda51b5d0ee <unavailable> + 274670
7    libswift_Concurrency.so            0x00007fda51b5d860 swift_job_run + 92
8    libdispatch.so                     0x00007fda51d9bf45 <unavailable> + 192325
9    libdispatch.so                     0x00007fda51d9cbbd <unavailable> + 195517
10   libdispatch.so                     0x00007fda51da4002 <unavailable> + 225282
11   libc.so.6                          0x00007fda5130ab43 <unavailable> + 609091
12   libc.so.6                          0x00007fda5139ca00 <unavailable> + 1206784
Illegal instruction (core dumped)

I attempt to connect to Twitch Chat, I've made a very simple test that just tries to send a single message to their server:

import Foundation

#if canImport(FoundationNetworking)
  import FoundationNetworking
#endif

@main public struct Test {
  public static func main() async throws {
    let url = URL(string: "wss://irc-ws.chat.twitch.tv:443")!

    let ws = URLSession.shared.webSocketTask(with: url)

    ws.resume()

    try await ws.send(.string("CAP REQ :twitch.tv/tags"))
  }
}

That code runs perfectly fine under macOS (using Swift 5.7), but as soon as it's run on Linux I get the error from above.

I've tried using different WebSocket URLs, but everything yields the same result.

[monsieurjonees]

I'm having this same problem

[monsieurjonees]

I've been having issues with receive(): I'm using Swift 5.8-dev on Ubuntu 22.04 LTS

import Foundation

// Import URL Session on Linux:
#if canImport(FoundationNetworking)
import FoundationNetworking
#endif

@main
public struct Test {
    public private(set) var text = "Hello, World!"

    public static func main() async throws {
        let ws = URLSession.shared.webSocketTask(with: URL(string: "wss://gateway.discord.gg/?v=10&encoding=json")!)
        ws.resume()
        
        _ = try await ws.receive()
    }
}

And:

Swift/ErrorType.swift:200: Fatal error: Error raised at top level: Error Domain=NSURLErrorDomain Code=-1002 "(null)"
Current stack trace:
0    libswiftCore.so                    0x00007fc021177b10 _swift_stdlib_reportFatalErrorInFile + 112
1    libswiftCore.so                    0x00007fc020e6940f <unavailable> + 1442831
2    libswiftCore.so                    0x00007fc020e69227 <unavailable> + 1442343
3    libswiftCore.so                    0x00007fc020e68030 _assertionFailure(_:_:file:line:flags:) + 364
4    libswiftCore.so                    0x00007fc020ec6e96 <unavailable> + 1826454
5    PhloydBot                          0x000055901c4322cd <unavailable> + 123597
6    libswift_Concurrency.so            0x00007fc0213870ee <unavailable> + 274670
7    libswift_Concurrency.so            0x00007fc021387860 swift_job_run + 92
8    libdispatch.so                     0x00007fc021715f45 <unavailable> + 192325
9    libdispatch.so                     0x00007fc021716bbd <unavailable> + 195517
10   libdispatch.so                     0x00007fc02171e002 <unavailable> + 225282
11   libc.so.6                          0x00007fc020b34b43 <unavailable> + 609091
12   libc.so.6                          0x00007fc020bc6a00 <unavailable> + 1206784
Illegal instruction (core dumped)

Specifically on Linux--no errors if run from Xcode/on macOS.

[LosFarmosCTL]

I've been having issues with receive()

Yup, I didn't even think to test receive() since Twitch doesn't send anything without the client authenticating explicitly with NICK + PASS, but I can confirm this is also the case for me.

Updated the main issue as well to reflect that.

Only an issue on Linux, using macOS everything works as expected.

[LosFarmosCTL]

This is still happening on the official swift:5.8 release image.

[tkrajacic]

To be honest it seems the WebSocket implementation can never work, as libcurl4 doesn't report supporting the protocols. At least in all of my experiments with even the most recent versions, curl-config --protocols never lists ws or wss.

And if I am not mistaken, that's what is checked here in CFURLSessionInterface.c

Boolean CFURLSessionWebSocketsSupported(void) {
    curl_version_info_data *info = curl_version_info(CURLVERSION_NOW);
    for (int i = 0; ; i++) {
        const char * const protocol = info->protocols[i];
        if (protocol == NULL) {
            break;
        }
        if ((0 == strncmp(protocol, "ws", 2)) ||
            (0 == strncmp(protocol, "wss", 3))) {
            return true;
        }
    }
    return false;
}

But maybe I am just holding it wrong™ 🤷‍♂️

[rojvv]

You are holding it right :(

]

Image Source

[kevinrpb]

Just for reference: Even when compiling libcurl from source with websocket support, WebSocketURLProtocol throws a fatal error (this is Swift 6.0).

FoundationNetworking/WebSocketURLProtocol.swift:134: Fatal error: WebSocket internal invariant violated

*** Signal 5: Backtracing from 0xaaaab72d80cc... done ***

*** Program crashed: System trap at 0x0000aaaab72d80cc ***

Thread 0 crashed:

 0              0x0000aaaab72d80cc _assertionFailure(_:_:file:line:flags:) + 252 in libcurl-websocket-testapp
 1 [ra]         0x0000aaaab77c3354 _WebSocketURLProtocol.notifyTask(aboutReceivedData:flags:) + 3635 in libcurl-websocket-testapp
 2 [ra]         0x0000aaaab77c2254 _WebSocketURLProtocol.didReceive(data:) + 731 in libcurl-websocket-testapp
 3 [ra]         0x0000aaaab7800048 _EasyHandle.didReceive(data:size:nmemb:) + 95 in libcurl-websocket-testapp
 4 [ra]         0x0000aaaab78001c4 @objc closure #1 in _EasyHandle.setupCallbacks() + 67 in libcurl-websocket-testapp
 5 [ra]         0x0000ffff8903cfa8 cw_out_ptr_flush + 263 in libcurl.so.4.8.0
 6 [ra]         0x0000ffff8903d630 cw_out_do_write + 239 in libcurl.so.4.8.0
 7 [ra]         0x0000ffff8903d748 cw_out_write + 119 in libcurl.so.4.8.0
 8 [ra]         0x0000ffff89093020 ws_cw_dec_next + 299 in libcurl.so.4.8.0
 9 [ra]         0x0000ffff89091c68 ws_dec_pass + 515 in libcurl.so.4.8.0
10 [ra]         0x0000ffff89091fec ws_cw_write + 155 in libcurl.so.4.8.0
11 [ra]         0x0000ffff8907818c cw_download_write + 199 in libcurl.so.4.8.0
12 [ra]         0x0000ffff890795cc Curl_client_write + 71 in libcurl.so.4.8.0
13 [ra]         0x0000ffff89088a84 Curl_xfer_write_resp + 51 in libcurl.so.4.8.0
14 [ra]         0x0000ffff89088d94 Curl_sendrecv + 591 in libcurl.so.4.8.0
15 [ra]         0x0000ffff8906c348 multi_runsingle + 1831 in libcurl.so.4.8.0
16 [ra]         0x0000ffff8906d070 multi_run_expired + 191 in libcurl.so.4.8.0
17 [ra]         0x0000ffff8906dfbc multi_socket + 171 in libcurl.so.4.8.0
18 [ra]         0x0000aaaab780291c URLSession._MultiHandle.readAndWriteAvailableData(on:) + 67 in libcurl-websocket-testapp
19 [ra]         0x0000aaaab7802170 closure #1 in URLSession._MultiHandle.register(socket:for:what:socketSourcePtr:) + 75 in libcurl-websocket-testapp
20 [ra] [thunk] 0x0000aaaab5aedc94 thunk for @escaping @callee_guaranteed () -> () + 47 in libcurl-websocket-testapp at //<compiler-generated>
21 [ra]         0x0000aaaab760f80c _dispatch_block_async_invoke2 + 103 in libcurl-websocket-testapp
22 [ra]         0x0000aaaab7606b18 _dispatch_continuation_pop + 235 in libcurl-websocket-testapp
23 [ra]         0x0000aaaab7614474 _dispatch_source_invoke + 1679 in libcurl-websocket-testapp
24 [ra]         0x0000aaaab760a420 _dispatch_lane_serial_drain + 315 in libcurl-websocket-testapp
25 [ra]         0x0000aaaab760b1c8 _dispatch_lane_invoke + 999 in libcurl-websocket-testapp
26 [ra]         0x0000aaaab760a420 _dispatch_lane_serial_drain + 315 in libcurl-websocket-testapp
27 [ra]         0x0000aaaab760b1c8 _dispatch_lane_invoke + 999 in libcurl-websocket-testapp
28 [ra]         0x0000aaaab760a420 _dispatch_lane_serial_drain + 315 in libcurl-websocket-testapp
29 [ra]         0x0000aaaab760b1c8 _dispatch_lane_invoke + 999 in libcurl-websocket-testapp
30 [ra]         0x0000aaaab7611a00 _dispatch_worker_thread + 431 in libcurl-websocket-testapp
31 [ra]         0x0000ffff889a597c <unknown> in libc.so.6

Even if the support is experimental in curl, this is maybe actionable by the team here?