ConPTY adds extra newlines symbols at soft-wrapped rows

[Mervap]

Windows Terminal version

Not installed

Windows build number

10.0.19045.2788

Other Software

.NET 7.0 x64

Steps to reproduce

1. Create ConPTY from dotnet (minimized version below, full working code here, based on samples/GUIConsole.ConPTY)
2. Run powershell.exe
3. Send 500 'a' charachters to PTY input (as a single row)
4. Read 500 charachters from PTY output

SafeFileHandle inputRead, inputWrite, outputRead, outputWrite;

CreatePseudoConsole(new COORD { X = 40, Y = 20 }, inputRead, outputWrite, 0, out IntPtr hPC);
ProcessFactory.Start("powershell.exe -nologo", 0x00020016, hPC);

var writer = new StreamWriter(new FileStream(inputWrite, FileAccess.Write)) { AutoFlush = true };
var reader = new StreamReader(new FileStream(outputRead, FileAccess.Read));


// Write long row
writer.Write(new string('a', 500));

// Read output
char[] buf = new char[500];
var bytesRead = reader.ReadBlock(buf, 0, 500);
var output = new string(buf.Take(bytesRead).ToArray());

// Check output
// Expected: zero '\n' characters
// Actual: a lot of '\n' characters
Console.Out.Write(output.Split('\n').Length);

Expected Behavior

Pty output contains zero newlines symbols since only one line was sent

Actual Behavior

PTY adds extra \n to output turning soft-wrapping to hard-wrapping

[zadjii-msft]

Thanks for the report! I suspect this is fixed in main, but I'm gonna leave this open to validate that either there's already a test for it, or if not, to add one.

If it is fixed in main, then I'm betting it's only fixed in >22000 builds of Windows.

If it's not fixed, well, it should be ☺️

[Mervap]

Ok, thanks!
Any chance that it would be fixed in win10?

[zadjii-msft]

Probably not, though, our recommendation is going to be using a nuget package to ingest ConPTY. This nuget package doesn't exist yet¹, but when it does, that'll let you use the latest version of ConPTY regardless of what OS version you're on. That's effectively what the Terminal does today (so that we can use ConPTY fixes even on Windows 10). I think there's other folks that have copied what we've done, but that's firmly in the "not yet officially supported" territory.

Footnotes

1. Originally, this was tracked in conpty: produce a NuGet package (for internal consumption, for now) #3577, but apparently we have no thread for "productize the conpty nuget" and we should. I'll take a todo item to create one. ↩

[zadjii-msft]

addenda: now tracking that in #15065

[zadjii-msft]

Yep, we definitely already had a test for this one:

terminal/src/cascadia/UnitTests_TerminalCore/ConptyRoundtripTests.cpp

Lines 451 to 500 in 10c6206

	void ConptyRoundtripTests::TestWrappingALongString()
	{
	auto& g = ServiceLocator::LocateGlobals();
	auto& renderer = *g.pRender;
	auto& gci = g.getConsoleInformation();
	auto& si = gci.GetActiveOutputBuffer();
	auto& hostSm = si.GetStateMachine();
	auto& hostTb = si.GetTextBuffer();
	auto& termTb = *term->_mainBuffer;
	_flushFirstFrame();
	_checkConptyOutput = false;
	const auto initialTermView = term->GetViewport();
	const auto charsToWrite = gsl::narrow_cast<til::CoordType>(TestUtils::Test100CharsString.size());
	VERIFY_ARE_EQUAL(100, charsToWrite);
	VERIFY_ARE_EQUAL(0, initialTermView.Top());
	VERIFY_ARE_EQUAL(32, initialTermView.BottomExclusive());
	hostSm.ProcessString(TestUtils::Test100CharsString);
	const auto secondView = term->GetViewport();
	VERIFY_ARE_EQUAL(0, secondView.Top());
	VERIFY_ARE_EQUAL(32, secondView.BottomExclusive());
	auto verifyBuffer = [&](const TextBuffer& tb) {
	auto& cursor = tb.GetCursor();
	// Verify the cursor wrapped to the second line
	VERIFY_ARE_EQUAL(charsToWrite % initialTermView.Width(), cursor.GetPosition().x);
	VERIFY_ARE_EQUAL(1, cursor.GetPosition().y);
	// Verify that we marked the 0th row as _wrapped_
	const auto& row0 = tb.GetRowByOffset(0);
	VERIFY_IS_TRUE(row0.WasWrapForced());
	const auto& row1 = tb.GetRowByOffset(1);
	VERIFY_IS_FALSE(row1.WasWrapForced());
	TestUtils::VerifyExpectedString(tb, TestUtils::Test100CharsString, { 0, 0 });
	};
	verifyBuffer(hostTb);
	VERIFY_SUCCEEDED(renderer.PaintFrame());
	verifyBuffer(termTb);
	}

So, I'll just say "fixed in the latest conpty, but that's probably not on Windows 10, so we'll need to start shipping a conpty nuget that folks can consume externally"