Public Access
Add the SSH session layer and the terminal data plane
The throughput harness the plan requires before any UI, plus the SSH plumbing under it. 94 new tests, no WebView involved. Credit-based flow control is what makes `yes` survivable. A terminal renders at 60 Hz at best while a remote produces output as fast as the network allows, and the difference has to accumulate somewhere or be refused. Credit is reserved *before* reading, never after: because the pump cannot read more than the renderer has room for, the coalescing buffer is bounded by the window rather than by how fast the remote can talk. When credit runs out the pump stops reading, SSH's own receive window closes, and the remote sshd blocks -- backpressure to the source with no custom protocol. Verified by falsification, not just by passing: with the credit gate removed three tests fail, including the throughput harness's bounded-memory assertion. Acknowledgements are clamped because they cross into JavaScript, where a buggy or hostile page could otherwise claim to have rendered a gigabyte and talk the host into an unbounded read. Host key trust is enforced by *failing* the connection rather than prompting inside the handshake. SSH.NET raises verification synchronously, so consulting the user there would block the handshake on a UI round trip and deadlock the first time the prompt needed the UI thread. Unknown host and changed key become distinct exceptions the caller resolves asynchronously. A mismatch has no retry path at all: a dialog offering to continue is how users are trained to click through the one warning that actually indicates interception. A legitimately rebuilt server is handled by removing the pin in settings, away from the moment of connecting. The data plane serves the renderer page from the same loopback listener as the socket, which makes Origin predictable -- always http://127.0.0.1:{port} -- where a WebView virtual-host mapping would give a different origin per backend and nothing to validate. The token is substituted at serve time, so it never touches disk and never appears in a URL. Being clear about what that buys: not protection from a process running as this user, which can read our memory anyway, but from a page in the user's browser attempting WebSocket connections to loopback ports, which is a real and routine thing. Two bugs the tests caught. The accept loop handled connections serially, so an upgraded WebSocket parked it inside the receive loop and every later request went unanswered -- the page's own script among them. The suite hung rather than failed, which is how I found it. And SHA-1 is unavoidable here: RFC 6455 mandates it for Sec-WebSocket-Accept, where it authenticates nothing. Suppressed narrowly with that reasoning; the alternative, HttpListener.AcceptWebSocketAsync, throws PlatformNotSupportedException off Windows.
This commit is contained in:
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using System.Diagnostics;
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using System.Globalization;
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using DodoSSH.Client.Ssh;
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namespace DodoSSH.Client.Terminal.Tests;
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/// <summary>
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/// The output path under load: coalescing, backpressure, and shutdown.
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/// </summary>
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/// <remarks>
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/// The plan calls for a throughput harness built before any UI, and this is it. Terminal throughput is
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/// where a client like this usually fails — <c>cat</c> on a large file either freezes the UI or grows
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/// memory until the process dies — and neither symptom is diagnosable once a WebView is in the picture.
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/// </remarks>
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public sealed class TerminalSessionPumpTests
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{
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private const uint SessionId = 7;
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[Fact]
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public async Task Output_ReachesTheTransportTaggedWithItsSession()
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{
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await using var session = new FakeShellSession(bytesToProduce: 64);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(session, transport);
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transport.AutoAcknowledge = pump;
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await pump.RunAsync(TestContext.Current.CancellationToken);
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transport.OutputBytes().Length.ShouldBe(64);
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foreach (var frame in transport.Frames)
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{
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TerminalFrame.TryRead(frame, out _, out var sessionId, out _).ShouldBeTrue();
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sessionId.ShouldBe(SessionId);
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}
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}
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[Fact]
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public async Task ASessionOpenedFrame_PrecedesAnyOutput()
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{
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// The renderer has to attach a terminal before bytes arrive for it, or the first screenful is
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// written into nothing.
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await using var session = new FakeShellSession(bytesToProduce: 16);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(session, transport);
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transport.AutoAcknowledge = pump;
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await pump.RunAsync(TestContext.Current.CancellationToken);
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TerminalFrame.TryRead(transport.Frames[0], out var opcode, out _, out _).ShouldBeTrue();
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opcode.ShouldBe((byte)TerminalServerOpcode.SessionOpened);
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}
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[Fact]
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public async Task SeveralReadsWithinOneInterval_BecomeASingleFrame()
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{
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// A terminal cannot render faster than the display refreshes, so sending each read separately
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// is work whose result is overwritten before anyone sees it.
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await using var session = new FakeShellSession(bytesToProduce: 8 * 1024);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(
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session,
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transport,
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new TerminalPumpOptions
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{
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ReadBufferBytes = 512,
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FlushInterval = TimeSpan.FromMilliseconds(400),
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});
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transport.AutoAcknowledge = pump;
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var run = pump.RunAsync(TestContext.Current.CancellationToken);
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// Long enough for one flush, short enough that a second cannot have happened.
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await Task.Delay(TimeSpan.FromMilliseconds(600), TestContext.Current.CancellationToken);
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// 8 KiB arrived as sixteen 512-byte reads and left as one frame.
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transport.CountOf(TerminalServerOpcode.Output).ShouldBe(1);
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transport.OutputBytes().Length.ShouldBe(8 * 1024);
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await run;
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}
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[Fact]
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public async Task WhenCreditRunsOut_ThePumpStopsReading()
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{
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// The property the whole design rests on. With no acknowledgement the pump must read exactly
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// the window and then stop, so nothing accumulates between the socket and the screen. Left
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// unbounded, a remote running `yes` grows the client's memory until it dies.
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const int Window = 4 * 1024;
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await using var session = new FakeShellSession(bytesToProduce: long.MaxValue);
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var transport = new RecordingTransport();
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// Deliberately no AutoAcknowledge: this models a renderer that has stopped keeping up.
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await using var pump = CreatePump(
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session,
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transport,
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new TerminalPumpOptions
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{
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ReadBufferBytes = 1024,
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FlushInterval = TimeSpan.FromMilliseconds(5),
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WindowBytes = Window,
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});
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var run = pump.RunAsync(TestContext.Current.CancellationToken);
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await Task.Delay(TimeSpan.FromMilliseconds(300), TestContext.Current.CancellationToken);
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pump.BytesRead.ShouldBe(
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Window,
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"The pump read past its credit window, so output accumulates without bound.");
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// Still stalled a moment later, rather than merely slow.
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await Task.Delay(TimeSpan.FromMilliseconds(200), TestContext.Current.CancellationToken);
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pump.BytesRead.ShouldBe(Window);
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pump.Credits.Available.ShouldBe(0);
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await pump.DisposeAsync();
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await run;
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}
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[Fact]
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public async Task AcknowledgingCredit_LetsThePumpResume()
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{
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const int Window = 4 * 1024;
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await using var session = new FakeShellSession(bytesToProduce: long.MaxValue);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(
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session,
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transport,
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new TerminalPumpOptions
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{
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ReadBufferBytes = 1024,
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FlushInterval = TimeSpan.FromMilliseconds(5),
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WindowBytes = Window,
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});
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var run = pump.RunAsync(TestContext.Current.CancellationToken);
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await Task.Delay(TimeSpan.FromMilliseconds(200), TestContext.Current.CancellationToken);
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pump.BytesRead.ShouldBe(Window);
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pump.Acknowledge(2048);
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await Task.Delay(TimeSpan.FromMilliseconds(200), TestContext.Current.CancellationToken);
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pump.BytesRead.ShouldBe(Window + 2048);
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await pump.DisposeAsync();
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await run;
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}
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[Fact]
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public async Task AnOverLargeAcknowledgement_DoesNotWidenTheWindow()
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{
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// The acknowledgement comes from JavaScript. A page claiming to have rendered a gigabyte must
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// not be able to talk the host into an unbounded read.
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const int Window = 4 * 1024;
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await using var session = new FakeShellSession(bytesToProduce: long.MaxValue);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(
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session,
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transport,
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new TerminalPumpOptions
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{
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ReadBufferBytes = 1024,
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FlushInterval = TimeSpan.FromMilliseconds(5),
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WindowBytes = Window,
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});
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var run = pump.RunAsync(TestContext.Current.CancellationToken);
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await Task.Delay(TimeSpan.FromMilliseconds(200), TestContext.Current.CancellationToken);
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pump.Acknowledge(uint.MaxValue);
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await Task.Delay(TimeSpan.FromMilliseconds(200), TestContext.Current.CancellationToken);
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// One further window's worth at most, never everything the endless producer could offer.
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pump.BytesRead.ShouldBeLessThanOrEqualTo(Window * 2);
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await pump.DisposeAsync();
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await run;
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}
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[Fact]
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public async Task WhenTheRemoteCloses_ASessionClosedFrameFollowsTheLastOutput()
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{
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// The last thing a remote writes is often the most important — an error, an exit code — and
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// dropping it makes a clean exit look like a crash.
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await using var session = new FakeShellSession(bytesToProduce: 4096);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(
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session,
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transport,
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new TerminalPumpOptions { FlushInterval = TimeSpan.FromMilliseconds(20) });
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transport.AutoAcknowledge = pump;
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await pump.RunAsync(TestContext.Current.CancellationToken);
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transport.OutputBytes().Length.ShouldBe(4096);
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TerminalFrame.TryRead(transport.Frames[^1], out var opcode, out _, out var payload)
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.ShouldBeTrue();
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opcode.ShouldBe((byte)TerminalServerOpcode.SessionClosed);
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System.Text.Encoding.UTF8.GetString(payload).ShouldNotBeNullOrWhiteSpace();
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}
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[Fact]
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public async Task Input_ReachesTheRemote()
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{
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await using var session = new FakeShellSession();
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var transport = new RecordingTransport();
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await using var pump = CreatePump(session, transport);
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await pump.WriteInputAsync("ls -la\r"u8.ToArray(), TestContext.Current.CancellationToken);
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System.Text.Encoding.UTF8.GetString(session.Written).ShouldBe("ls -la\r");
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}
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[Fact]
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public async Task AResize_ReachesTheRemote()
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{
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await using var session = new FakeShellSession();
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var transport = new RecordingTransport();
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await using var pump = CreatePump(session, transport);
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pump.Resize(new TerminalSize(132, 43, 1320, 1075));
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session.ResizeCount.ShouldBe(1);
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session.LastResize.ShouldBe(new TerminalSize(132, 43, 1320, 1075));
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}
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[Fact]
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public async Task AZeroSizedResize_IsDropped()
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{
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// Arrives naturally when a pane collapses or a window minimises. Forwarding it leaves the
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// remote's idea of the terminal nonsensical until the next resize.
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await using var session = new FakeShellSession();
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var transport = new RecordingTransport();
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await using var pump = CreatePump(session, transport);
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pump.Resize(new TerminalSize(0, 0));
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session.ResizeCount.ShouldBe(0);
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}
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[Fact]
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public async Task ThroughputHarness_SustainsTenMegabytesPerSecondWithBoundedMemory()
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{
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// The plan's target: `yes` at full tilt must hold a fixed memory ceiling. Throughput is
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// asserted well below what the machine manages, because a CI runner under load is slower than
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// a desktop and a flaky performance test gets deleted rather than fixed. The bounded-memory
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// assertion is the one that carries the real meaning.
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const long Target = 32L * 1024 * 1024;
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const int Window = CreditWindow.DefaultWindowBytes;
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await using var session = new FakeShellSession(bytesToProduce: Target);
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var transport = new RecordingTransport();
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await using var pump = CreatePump(
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session,
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transport,
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new TerminalPumpOptions
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{
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ReadBufferBytes = 32 * 1024,
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FlushInterval = TimeSpan.FromMilliseconds(1),
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WindowBytes = Window,
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});
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transport.AutoAcknowledge = pump;
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using var monitor = new CancellationTokenSource();
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var sampler = SamplePeakOutstandingAsync(pump, monitor.Token);
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var stopwatch = Stopwatch.StartNew();
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await pump.RunAsync(TestContext.Current.CancellationToken);
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stopwatch.Stop();
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await monitor.CancelAsync();
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var peakOutstanding = await sampler;
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pump.BytesRead.ShouldBe(Target);
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transport.OutputBytes().Length.ShouldBe((int)Target);
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var megabytesPerSecond = Target / 1024d / 1024d / stopwatch.Elapsed.TotalSeconds;
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megabytesPerSecond.ShouldBeGreaterThan(
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10,
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string.Create(
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CultureInfo.InvariantCulture,
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$"Sustained {megabytesPerSecond:F1} MB/s, below the 10 MB/s target."));
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// The real assertion: in-flight bytes never exceeded the window, however fast the producer ran.
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peakOutstanding.ShouldBeLessThanOrEqualTo(
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Window,
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string.Create(
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CultureInfo.InvariantCulture,
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$"Peak in-flight was {peakOutstanding} bytes against a {Window}-byte window."));
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}
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/// <summary>Watches in-flight bytes for the duration of a run, returning the highest seen.</summary>
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private static async Task<int> SamplePeakOutstandingAsync(
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TerminalSessionPump pump,
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CancellationToken cancellationToken)
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{
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var peak = 0;
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while (!cancellationToken.IsCancellationRequested)
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{
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peak = Math.Max(peak, pump.Credits.Outstanding);
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try
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{
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await Task.Delay(1, cancellationToken);
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}
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catch (OperationCanceledException)
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{
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break;
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}
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}
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return peak;
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}
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private static TerminalSessionPump CreatePump(
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FakeShellSession session,
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ITerminalTransport transport,
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TerminalPumpOptions? options = null) =>
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new(
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SessionId,
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session,
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transport,
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TimeProvider.System,
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options ?? new TerminalPumpOptions { FlushInterval = TimeSpan.FromMilliseconds(10) });
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}
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