From bb56586c4cab9a79dce6ec4738baddb5802c5de7 Mon Sep 17 00:00:00 2001
From: Cory Benfield <lukasa@apple.com>
Date: Tue, 11 Aug 2020 10:10:17 +0100
Subject: [PATCH] Avoid crashing when connecting to empty host. (#103)

Motivation:

Network.framework will crash when we attempt to connect to the host
string "". That's not ideal, so we should detect that case and avoid it.

Modifications:

- Add code to detect the empty host string.

Result:

No crashes when accidentally connecting to "".
---
 .../NIOTransportServices/NIOTSConnectionChannel.swift  | 10 ++++++++++
 Sources/NIOTransportServices/NIOTSErrors.swift         |  5 +++++
 .../NIOTSConnectionChannelTests.swift                  |  7 +++++++
 3 files changed, 22 insertions(+)

diff --git a/Sources/NIOTransportServices/NIOTSConnectionChannel.swift b/Sources/NIOTransportServices/NIOTSConnectionChannel.swift
index 9b80ba4..53836d8 100644
--- a/Sources/NIOTransportServices/NIOTSConnectionChannel.swift
+++ b/Sources/NIOTransportServices/NIOTSConnectionChannel.swift
@@ -500,6 +500,16 @@ extension NIOTSConnectionChannel: StateManagedChannel {
     internal func beginActivating0(to target: NWEndpoint, promise: EventLoopPromise<Void>?) {
         assert(self.nwConnection == nil)
         assert(self.connectPromise == nil)
+
+        // Before we start, we validate that the target won't cause a crash: see
+        // https://github.com/apple/swift-nio/issues/1617.
+        if case .hostPort(host: let host, port: _) = target, host == "" {
+            // We don't pass the promise in here because we'll actually not complete it. We complete it manually ourselves.
+            self.close0(error: NIOTSErrors.InvalidHostname(), mode: .all, promise: nil)
+            promise?.fail(NIOTSErrors.InvalidHostname())
+            return
+        }
+
         self.connectPromise = promise
 
         let parameters = NWParameters(tls: self.tlsOptions, tcp: self.tcpOptions)
diff --git a/Sources/NIOTransportServices/NIOTSErrors.swift b/Sources/NIOTransportServices/NIOTSErrors.swift
index bc55a41..e35a4d1 100644
--- a/Sources/NIOTransportServices/NIOTSErrors.swift
+++ b/Sources/NIOTransportServices/NIOTSErrors.swift
@@ -69,5 +69,10 @@ public enum NIOTSErrors {
             self.timeout = timeout
         }
     }
+
+    /// `InvalidHostname` is thrown when attempting to connect to an invalid host.
+    public struct InvalidHostname: NIOTSError {
+        public init() { }
+    }
 }
 #endif
diff --git a/Tests/NIOTransportServicesTests/NIOTSConnectionChannelTests.swift b/Tests/NIOTransportServicesTests/NIOTSConnectionChannelTests.swift
index 1476e02..3f896d7 100644
--- a/Tests/NIOTransportServicesTests/NIOTSConnectionChannelTests.swift
+++ b/Tests/NIOTransportServicesTests/NIOTSConnectionChannelTests.swift
@@ -778,5 +778,12 @@ class NIOTSConnectionChannelTests: XCTestCase {
         // throw
         XCTAssertNoThrow(try eventPromise.futureResult.wait())
     }
+
+    func testConnectingToEmptyStringErrors() throws {
+        let connectBootstrap = NIOTSConnectionBootstrap(group: self.group)
+        XCTAssertThrowsError(try connectBootstrap.connect(host: "", port: 80).wait()) { error in
+            XCTAssertTrue(error is NIOTSErrors.InvalidHostname)
+        }
+    }
 }
 #endif