Fallback to the hostname for TLS if a hostname override isn't provided

Sources/GRPC/ClientConnection.swift

@@ -142,7 +142,8 @@ public class ClientConnection {
     // Configure the channel with the correct handlers and connect to our target.
     let configuredChannel = ClientConnection.initializeChannel(
       channel,
-      tls: configuration.tls,
+      tls: configuration.tls?.configuration,
+      serverHostname: configuration.tls?.hostnameOverride ?? configuration.target.host,
       errorDelegate: configuration.errorDelegate
     ).flatMap {
       channel.connect(to: socketAddress)
@@ -325,21 +326,34 @@ extension ClientConnection {
   ///
   /// - Parameter configuration: The configuration to prepare the bootstrap with.
   /// - Parameter group: The `EventLoopGroup` to use for the bootstrap.
-  /// - Parameter timeout: The connection timeout in seconds. 
+  /// - Parameter timeout: The connection timeout in seconds.
   private class func makeBootstrap(
     configuration: Configuration,
     group: EventLoopGroup,
     timeout: TimeInterval?,
     logger: Logger
   ) -> ClientBootstrapProtocol {
+    // Provide a server hostname if we're using TLS. Prefer the override.
+    let serverHostname: String? = configuration.tls.map {
+      if let hostnameOverride = $0.hostnameOverride {
+        logger.debug("using hostname override for TLS", metadata: ["hostname-override": "\(hostnameOverride)"])
+        return hostnameOverride
+      } else {
+        let host = configuration.target.host
+        logger.debug("using host connection target for TLS", metadata: ["hostname-override": "\(host)"])
+        return host
+      }
+    }
+
     let bootstrap = PlatformSupport.makeClientBootstrap(group: group)
       // Enable SO_REUSEADDR and TCP_NODELAY.
       .channelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEADDR), value: 1)
       .channelOption(ChannelOptions.socket(IPPROTO_TCP, TCP_NODELAY), value: 1)
       .channelInitializer { channel in
         initializeChannel(
           channel,
-          tls: configuration.tls,
+          tls: configuration.tls?.configuration,
+          serverHostname: serverHostname,
           errorDelegate: configuration.errorDelegate
         )
       }
@@ -356,14 +370,16 @@ extension ClientConnection {
   ///
   /// - Parameter channel: The channel to initialize.
   /// - Parameter tls: The optional TLS configuration for the channel.
+  /// - Parameter serverHostname: The hostname of the server to use for TLS.
   /// - Parameter errorDelegate: Optional client error delegate.
   private class func initializeChannel(
     _ channel: Channel,
-    tls: Configuration.TLS?,
+    tls: TLSConfiguration?,
+    serverHostname: String?,
     errorDelegate: ClientErrorDelegate?
   ) -> EventLoopFuture<Void> {
-    let tlsConfigured = tls.map { tlsConfiguration in
-      channel.configureTLS(tlsConfiguration, errorDelegate: errorDelegate)
+    let tlsConfigured = tls.map {
+      channel.configureTLS($0, serverHostname: serverHostname, errorDelegate: errorDelegate)
     }
 
     return (tlsConfigured ?? channel.eventLoop.makeSucceededFuture(())).flatMap {
@@ -484,15 +500,18 @@ fileprivate extension Channel {
   /// the `TLSVerificationHandler` which verifies that a successful handshake was completed.
   ///
   /// - Parameter configuration: The configuration to configure the channel with.
+  /// - Parameter serverHostname: The server hostname to use if the hostname should be verified.
   /// - Parameter errorDelegate: The error delegate to use for the TLS verification handler.
   func configureTLS(
-    _ configuration: ClientConnection.Configuration.TLS,
+    _ configuration: TLSConfiguration,
+    serverHostname: String?,
     errorDelegate: ClientErrorDelegate?
   ) -> EventLoopFuture<Void> {
     do {
       let sslClientHandler = try NIOSSLClientHandler(
-        context: try NIOSSLContext(configuration: configuration.configuration),
-        serverHostname: configuration.hostnameOverride)
+        context: try NIOSSLContext(configuration: configuration),
+        serverHostname: serverHostname
+      )
 
       return self.pipeline.addHandlers(sslClientHandler, TLSVerificationHandler())
     } catch {

Tests/GRPCTests/BasicEchoTestCase.swift

@@ -78,16 +78,14 @@ extension TransportSecurity {
       return nil
 
     case .anonymousClient:
-      return .init(
-        trustRoots: .certificates([self.caCert]),
-        certificateVerification: .noHostnameVerification)
+      return .init(trustRoots: .certificates([self.caCert]))
 
     case .mutualAuthentication:
       return .init(
         certificateChain: [.certificate(self.clientCert)],
         privateKey: .privateKey(SamplePrivateKey.client),
-        trustRoots: .certificates([self.caCert]),
-        certificateVerification: .noHostnameVerification)
+        trustRoots: .certificates([self.caCert])
+      )
     }
   }
 }

Tests/GRPCTests/ClientTLSTests.swift

@@ -0,0 +1,101 @@
+import Foundation
+import GRPC
+import GRPCSampleData
+import NIO
+import NIOSSL
+import XCTest
+
+class ClientTLSHostnameOverrideTests: GRPCTestCase {
+  var eventLoopGroup: EventLoopGroup!
+  var server: Server!
+  var connection: ClientConnection!
+
+  override func setUp() {
+    super.setUp()
+    self.eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
+  }
+
+  override func tearDown() {
+    super.tearDown()
+    XCTAssertNoThrow(try self.server.close().wait())
+    XCTAssertNoThrow(try connection.close().wait())
+    XCTAssertNoThrow(try self.eventLoopGroup.syncShutdownGracefully())
+  }
+
+  func makeEchoServer(tls: Server.Configuration.TLS) throws -> Server {
+    let configuration: Server.Configuration = .init(
+      target: .hostAndPort("localhost", 0),
+      eventLoopGroup: self.eventLoopGroup,
+      serviceProviders: [EchoProvider()],
+      tls: tls
+    )
+
+    return try Server.start(configuration: configuration).wait()
+  }
+
+  func makeConnection(port: Int, tls: ClientConnection.Configuration.TLS) -> ClientConnection {
+    let configuration: ClientConnection.Configuration = .init(
+      target: .hostAndPort("localhost", port),
+      eventLoopGroup: self.eventLoopGroup,
+      tls: tls
+    )
+
+    return ClientConnection(configuration: configuration)
+  }
+
+  func doTestUnary() throws {
+    let client = Echo_EchoServiceClient(connection: self.connection)
+    let get = client.get(.with { $0.text = "foo" })
+
+    let response = try get.response.wait()
+    XCTAssertEqual(response.text, "Swift echo get: foo")
+
+    let status = try get.status.wait()
+    XCTAssertEqual(status.code, .ok)
+  }
+
+  func testTLSWithHostnameOverride() throws {
+    // Run a server presenting a certificate for example.com on localhost.
+    let serverTLS: Server.Configuration.TLS = .init(
+      certificateChain: [.certificate(SampleCertificate.exampleServer.certificate)],
+      privateKey: .privateKey(SamplePrivateKey.exampleServer),
+      trustRoots: .certificates([SampleCertificate.ca.certificate])
+    )
+
+    self.server = try makeEchoServer(tls: serverTLS)
+    guard let port = self.server.channel.localAddress?.port else {
+      XCTFail("could not get server port")
+      return
+    }
+
+    let clientTLS: ClientConnection.Configuration.TLS = .init(
+      trustRoots: .certificates([SampleCertificate.ca.certificate]),
+      hostnameOverride: "example.com"
+    )
+
+    self.connection = self.makeConnection(port: port, tls: clientTLS)
+    try self.doTestUnary()
+  }
+
+  func testTLSWithoutHostnameOverride() throws {
+    // Run a server presenting a certificate for localhost on localhost.
+    let serverTLS: Server.Configuration.TLS = .init(
+      certificateChain: [.certificate(SampleCertificate.server.certificate)],
+      privateKey: .privateKey(SamplePrivateKey.server),
+      trustRoots: .certificates([SampleCertificate.ca.certificate])
+    )
+
+    self.server = try makeEchoServer(tls: serverTLS)
+    guard let port = self.server.channel.localAddress?.port else {
+      XCTFail("could not get server port")
+      return
+    }
+
+    let clientTLS: ClientConnection.Configuration.TLS = .init(
+      trustRoots: .certificates([SampleCertificate.ca.certificate])
+    )
+
+    self.connection = self.makeConnection(port: port, tls: clientTLS)
+    try self.doTestUnary()
+  }
+}

Tests/GRPCTests/XCTestManifests.swift

@@ -63,6 +63,16 @@ extension ClientTLSFailureTests {
     ]
 }
 
+extension ClientTLSHostnameOverrideTests {
+    // DO NOT MODIFY: This is autogenerated, use:
+    //   `swift test --generate-linuxmain`
+    // to regenerate.
+    static let __allTests__ClientTLSHostnameOverrideTests = [
+        ("testTLSWithHostnameOverride", testTLSWithHostnameOverride),
+        ("testTLSWithoutHostnameOverride", testTLSWithoutHostnameOverride),
+    ]
+}
+
 extension ClientThrowingWhenServerReturningErrorTests {
     // DO NOT MODIFY: This is autogenerated, use:
     //   `swift test --generate-linuxmain`
@@ -418,6 +428,7 @@ public func __allTests() -> [XCTestCaseEntry] {
         testCase(ClientClosedChannelTests.__allTests__ClientClosedChannelTests),
         testCase(ClientConnectionBackoffTests.__allTests__ClientConnectionBackoffTests),
         testCase(ClientTLSFailureTests.__allTests__ClientTLSFailureTests),
+        testCase(ClientTLSHostnameOverrideTests.__allTests__ClientTLSHostnameOverrideTests),
         testCase(ClientThrowingWhenServerReturningErrorTests.__allTests__ClientThrowingWhenServerReturningErrorTests),
         testCase(ClientTimeoutTests.__allTests__ClientTimeoutTests),
         testCase(ConnectionBackoffTests.__allTests__ConnectionBackoffTests),