Fixed a Task cancellation bug.

A misleading error was being thrown if the Task performing a WebSocket handshake
was canceled. Added WebSocketError.canceled to address this case.

Sources/WebSockets/WebSocket.swift

@@ -571,6 +571,12 @@ private extension WebSocket {
             continue
         }
       }
+      // The `AsyncThrowingStream` used by Connection finishes the stream (yielding `nil`) if the Task is
+      // canceled. However, we want an error to be thrown in this instance so that it's not confused with
+      // the server simply dropping the connection.
+      if Task.isCancelled {
+        throw WebSocketError.canceled
+      }
       if openingHandshakeDidExpire {
         throw WebSocketError.timeout
       }

Sources/WebSockets/WebSocketError.swift

@@ -53,6 +53,9 @@ public enum WebSocketError: Error {
   /// The handshake did not complete within the specified timeframe.
   case timeout
 
+  /// The `Task` performing the handshake was canceled.
+  case canceled
+
   /// The redirect limit was exceeded. This usually indicates a redirect loop.
   case maximumRedirectsExceeded
 
@@ -99,6 +102,8 @@ extension WebSocketError: CustomDebugStringConvertible {
         return "Unexpected disconnect"
       case .timeout:
         return "WebSocket handshake timed out"
+      case .canceled:
+        return "The task performing the WebSocket handshake was canceled"
       case .maximumRedirectsExceeded:
         return "Maximum number of HTTP redirects exceeded"
       case .invalidRedirectLocation(let location):

Tests/WebSocketsTests/WebSocketTests.swift

@@ -550,6 +550,27 @@ class WebSocketTests: XCTestCase {
     XCTAssert(events == expected)
   }
 
+  func testHandshakeCancellation() async throws {
+    let server = TestServer()
+    defer {
+      Task {
+        await server.stop()
+      }
+    }
+    let socket = WebSocket(url: try await server.start(path: "/test"))
+    let t = Task {
+      await socket.send(text: "Hello")
+    }
+    t.cancel()
+    let _ = await t.value
+    do {
+      for try await _ in socket {
+      }
+      XCTFail("Expected an exception ")
+    } catch WebSocketError.canceled {
+    }
+  }
+
   func expectCloseCode(quirk: QuirkyTestServer.Quirk, code: WebSocket.CloseCode, reason: String? = nil) async throws {
     let server = QuirkyTestServer(with: quirk)
     defer {