testPlatformConnectErrorIsForwardedOnTimeout port reuse (#716)

Motivation:

The above test has been seen to fail with port already in use.
The test assumes that a port can be bound to twice in a row.
It's possible that another process takes the port between the two
binds - this can be stopped by binding a second time before stopping
the first.

Modifications:

Allow port reuse and reorder the test to bind a second time before
releasing the first.

Result:

Test should no longer be flaky.

Tests/AsyncHTTPClientTests/HTTP2ClientTests.swift

@@ -376,7 +376,7 @@ class HTTP2ClientTests: XCTestCase {
     }
 
     func testPlatformConnectErrorIsForwardedOnTimeout() {
-        let bin = HTTPBin(.http2(compress: false))
+        let bin = HTTPBin(.http2(compress: false), reusePort: true)
         let clientGroup = MultiThreadedEventLoopGroup(numberOfThreads: 2)
         let el1 = clientGroup.next()
         let el2 = clientGroup.next()
@@ -404,20 +404,22 @@ class HTTP2ClientTests: XCTestCase {
         XCTAssertEqual(.ok, response1?.status)
         XCTAssertEqual(response1?.version, .http2)
         let serverPort = bin.port
-        XCTAssertNoThrow(try bin.shutdown())
-        // client is now in HTTP/2 state and the HTTPBin is closed
-        // start a new server on the old port which closes all connections immediately
+
         let serverGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
         defer { XCTAssertNoThrow(try serverGroup.syncShutdownGracefully()) }
         var maybeServer: Channel?
         XCTAssertNoThrow(maybeServer = try ServerBootstrap(group: serverGroup)
             .serverChannelOption(ChannelOptions.socketOption(.so_reuseaddr), value: 1)
+            .serverChannelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEPORT), value: 1)
             .childChannelInitializer { channel in
                 channel.close()
             }
             .childChannelOption(ChannelOptions.socketOption(.so_reuseaddr), value: 1)
             .bind(host: "127.0.0.1", port: serverPort)
             .wait())
+        // shutting down the old server closes all connections immediately
+        XCTAssertNoThrow(try bin.shutdown())
+        // client is now in HTTP/2 state and the HTTPBin is closed
         guard let server = maybeServer else { return }
         defer { XCTAssertNoThrow(try server.close().wait()) }
 

Tests/AsyncHTTPClientTests/HTTPClientTestUtils.swift

@@ -438,6 +438,7 @@ internal final class HTTPBin<RequestHandler: ChannelInboundHandler> where
         _ mode: Mode = .http1_1(ssl: false, compress: false),
         proxy: Proxy = .none,
         bindTarget: BindTarget = .localhostIPv4RandomPort,
+        reusePort: Bool = false,
         handlerFactory: @escaping (Int) -> (RequestHandler)
     ) {
         self.mode = mode
@@ -460,6 +461,7 @@ internal final class HTTPBin<RequestHandler: ChannelInboundHandler> where
 
         self.serverChannel = try! ServerBootstrap(group: self.group)
             .serverChannelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEADDR), value: 1)
+            .serverChannelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEPORT), value: reusePort ? 1 : 0)
             .serverChannelInitializer { channel in
                 channel.pipeline.addHandler(self.activeConnCounterHandler)
             }.childChannelInitializer { channel in
@@ -642,9 +644,10 @@ extension HTTPBin where RequestHandler == HTTPBinHandler {
     convenience init(
         _ mode: Mode = .http1_1(ssl: false, compress: false),
         proxy: Proxy = .none,
-        bindTarget: BindTarget = .localhostIPv4RandomPort
+        bindTarget: BindTarget = .localhostIPv4RandomPort,
+        reusePort: Bool = false
     ) {
-        self.init(mode, proxy: proxy, bindTarget: bindTarget) { HTTPBinHandler(connectionID: $0) }
+        self.init(mode, proxy: proxy, bindTarget: bindTarget, reusePort: reusePort) { HTTPBinHandler(connectionID: $0) }
     }
 }