Don't put NUL in the buffer in VT mode (#3015)

* Potentially fixes #1825

  I haven't had a chance to test this fix on my machine with a CentOS VM quite yet, but this _should_ work

  Also adds a test

* add a comment

* woah hey this test was wrong

* Revert bx.ps1

src/host/ut_host/ScreenBufferTests.cpp

@@ -105,6 +105,8 @@ class ScreenBufferTests
 
  TEST_METHOD(EraseAllTests);
 
+ TEST_METHOD(OutputNULTest);
+
  TEST_METHOD(VtResize);
  TEST_METHOD(VtResizeComprehensive);
  TEST_METHOD(VtResizeDECCOLM);
@@ -373,14 +375,14 @@ void ScreenBufferTests::TestReverseLineFeed()
 
  cursor.SetPosition({ 0, 5 });
  VERIFY_SUCCEEDED(screenInfo.SetViewportOrigin(true, { 0, 5 }, true));
- stateMachine.ProcessString(L"ABCDEFGH", 9);
- VERIFY_ARE_EQUAL(cursor.GetPosition().X, 9);
+ stateMachine.ProcessString(L"ABCDEFGH");
+ VERIFY_ARE_EQUAL(cursor.GetPosition().X, 8);
  VERIFY_ARE_EQUAL(cursor.GetPosition().Y, 5);
  VERIFY_ARE_EQUAL(screenInfo.GetViewport().Top(), 5);
 
  LOG_IF_FAILED(DoSrvPrivateReverseLineFeed(screenInfo));
 
- VERIFY_ARE_EQUAL(cursor.GetPosition().X, 9);
+ VERIFY_ARE_EQUAL(cursor.GetPosition().X, 8);
  VERIFY_ARE_EQUAL(cursor.GetPosition().Y, 5);
  viewport = screenInfo.GetViewport();
  VERIFY_ARE_EQUAL(viewport.Top(), 5);
@@ -816,6 +818,45 @@ void ScreenBufferTests::EraseAllTests()
  viewport.BottomInclusive()));
 }
 
+void ScreenBufferTests::OutputNULTest()
+{
+ auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
+ auto& si = gci.GetActiveOutputBuffer();
+ auto& stateMachine = si.GetStateMachine();
+ auto& cursor = si._textBuffer->GetCursor();
+
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().X);
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().Y);
+
+ Log::Comment(NoThrowString().Format(
+ L"Writing a single NUL"));
+ stateMachine.ProcessString(L"\0", 1);
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().X);
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().Y);
+
+ Log::Comment(NoThrowString().Format(
+ L"Writing many NULs"));
+ stateMachine.ProcessString(L"\0\0\0\0\0\0\0\0", 8);
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().X);
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().Y);
+
+ Log::Comment(NoThrowString().Format(
+ L"Testing a single NUL followed by real text"));
+ stateMachine.ProcessString(L"\0foo", 4);
+ VERIFY_ARE_EQUAL(3, cursor.GetPosition().X);
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().Y);
+
+ stateMachine.ProcessString(L"\n");
+ VERIFY_ARE_EQUAL(0, cursor.GetPosition().X);
+ VERIFY_ARE_EQUAL(1, cursor.GetPosition().Y);
+
+ Log::Comment(NoThrowString().Format(
+ L"Writing NULs in between other strings"));
+ stateMachine.ProcessString(L"\0foo\0bar\0", 9);
+ VERIFY_ARE_EQUAL(6, cursor.GetPosition().X);
+ VERIFY_ARE_EQUAL(1, cursor.GetPosition().Y);
+}
+
 void ScreenBufferTests::VtResize()
 {
  // Run this test in isolation - for one reason or another, this breaks other tests.

src/terminal/parser/OutputStateMachineEngine.cpp

@@ -42,6 +42,14 @@ ITermDispatch& OutputStateMachineEngine::Dispatch() noexcept
 // - true iff we successfully dispatched the sequence.
 bool OutputStateMachineEngine::ActionExecute(const wchar_t wch)
 {
+ // microsoft/terminal#1825 - VT applications expect to be able to write NUL
+ // and have _nothing_ happen. Filter the NULs here, so they don't fill the
+ // buffer with empty spaces.
+ if (wch == AsciiChars::NUL)
+ {
+ return true;
+ }
+
  _dispatch->Execute(wch);
  _ClearLastChar();