Crash in `SSHChildChannel`

[gaetanzanella]

SwiftNIO SSH commit hash: c56ababb0e22e0cdf5ec8b31698e07f943ea92e7

Context

While writing Xcode tests in one of my project which uses swift-nio-ssh, I encountered a crash. I reproduced it using the NIOSSHClient target.

• I noticed the crash only appears when using a command which produces a long output such as yes \"long text\" | head -n 1000000\n
• I only reproduced it when exchanging to the linked docker container. I used it in my automate tests.

Steps to reproduce

1. Launch the ssh server: docker-compose -f ./docker/ssh-docker-compose.yaml up -d
2. Run the modified NIOSSHClient target.
3. Observe the crash in Xcode

   * thread #2, name = 'NIO-ELT-0-#0', stop reason = Fatal error: Sent channel window adjust on channel in invalid state
   frame #0: 0x0000000193fe4ae8 libswiftCore.dylib`_swift_runtime_on_report
   frame #1: 0x00000001940825d4 libswiftCore.dylib`_swift_stdlib_reportFatalErrorInFile + 208
   frame #2: 0x0000000193c614b4 libswiftCore.dylib`closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in Swift._assertionFailure(_: Swift.StaticString, _: Swift.String, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never + 196
   frame #3: 0x0000000193c60210 libswiftCore.dylib`Swift._assertionFailure(_: Swift.StaticString, _: Swift.String, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never + 308
   * frame #4: 0x00000001002cae7c NIOSSHClient`ChildChannelStateMachine.sendChannelWindowAdjust(message=(recipientChannel = 0, bytesToAdd = 8811376), self=NIOSSH.ChildChannelStateMachine @ 0x0000000101e040a8) at ChildChannelStateMachine.swift:432:13
   ...

   Configuration

   $ swift --version swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100) Target: arm64-apple-macosx13.0

Operating system: macOS Ventura 13.2

Xcode version: 14.2

$ uname -a Darwin MBP-de-Gaetan-Zanella 22.3.0 Darwin Kernel Version 22.3.0: Thu Jan 5 20:48:54 PST 2023; root:xnu-8792.81.2~2/RELEASE_ARM64_T6000 arm64