Add support for the DECREQTPARM report (#7939)

This PR adds support for the `DECREQTPARM` (Request Terminal Parameters)
escape sequence, which was originally used on the VT100 terminal to
report the serial communication parameters. Modern terminal emulators
simply hardcode the reported values for backward compatibility.

The `DECREQTPARM` sequence has one parameter, which was originally used
to tell the terminal whether it was permitted to send unsolicited
reports or not. However, since we have no reason to send an unsolicited
report, we don't need to keep track of that state, but the permission
parameter does still determine the value of the first parameter in the
response.

The response parameters are as follows:

| Parameter        | Value  | Meaning                  |
| ---------------- | ------ | ------------------------ |
| response type    | 2 or 3 | unsolicited or solicited |
| parity           | 1      | no parity                |
| data bits        | 1      | 8 bits per character     |
| transmit speed   | 128    | 38400 baud               |
| receive speed    | 128    | 38400 baud               |
| clock multiplier | 1      |                          |
| flags            | 0      |                          |

There is some variation in the baud rate reported by modern terminal
emulators, and 9600 baud seems to be a little more common than 38400
baud, but I thought the higher speed was probably more appropriate,
especially since that's also the value reported by XTerm.

## Validation Steps Performed

I've added a couple of adapter and output engine tests to verify that
the sequence is dispatched correctly, and the expected responses are
generated. I've also manually tested in Vttest and confirmed that we now
pass the `DECREQTPARM` test in the _Test of terminal reports_.

Closes #7852

.github/actions/spell-check/expect/expect.txt

@@ -537,6 +537,7 @@ DECOM
 deconstructed
 DECPCTERM
 DECRC
+DECREQTPARM
 DECRLM
 DECRQM
 DECRST

src/terminal/adapter/DispatchTypes.hpp

@@ -325,6 +325,12 @@ namespace Microsoft::Console::VirtualTerminal::DispatchTypes
         SteadyBar = 6
     };
 
+    enum class ReportingPermission : size_t
+    {
+        Unsolicited = 0,
+        Solicited = 1
+    };
+
     enum class LineFeedType : unsigned int
     {
         WithReturn,

src/terminal/adapter/ITermDispatch.hpp

@@ -97,6 +97,7 @@ class Microsoft::Console::VirtualTerminal::ITermDispatch
     virtual bool SecondaryDeviceAttributes() = 0; // DA2
     virtual bool TertiaryDeviceAttributes() = 0; // DA3
     virtual bool Vt52DeviceAttributes() = 0; // VT52 Identify
+    virtual bool RequestTerminalParameters(const DispatchTypes::ReportingPermission permission) = 0; // DECREQTPARM
 
     virtual bool DesignateCodingSystem(const VTID codingSystem) = 0; // DOCS
     virtual bool Designate94Charset(const size_t gsetNumber, const VTID charset) = 0; // SCS

src/terminal/adapter/adaptDispatch.cpp

@@ -773,6 +773,40 @@ bool AdaptDispatch::Vt52DeviceAttributes()
     return _WriteResponse(L"\x1b/Z");
 }
 
+// Routine Description:
+// - DECREQTPARM - This sequence was originally used on the VT100 terminal to
+//   report the serial communication parameters (baud rate, data bits, parity,
+//   etc.). On modern terminal emulators, the response is simply hardcoded.
+// Arguments:
+// - permission - This would originally have determined whether the terminal
+//   was allowed to send unsolicited reports or not.
+// Return Value:
+// - True if handled successfully. False otherwise.
+bool AdaptDispatch::RequestTerminalParameters(const DispatchTypes::ReportingPermission permission)
+{
+    // We don't care whether unsolicited reports are allowed or not, but the
+    // requested permission does determine the value of the first response
+    // parameter. The remaining parameters are just hardcoded to indicate a
+    // 38400 baud connection, which matches the XTerm response. The full
+    // parameter sequence is as follows:
+    // - response type:    2 or 3 (unsolicited or solicited)
+    // - parity:           1 (no parity)
+    // - data bits:        1 (8 bits per character)
+    // - transmit speed:   128 (38400 baud)
+    // - receive speed:    128 (38400 baud)
+    // - clock multiplier: 1
+    // - flags:            0
+    switch (permission)
+    {
+    case DispatchTypes::ReportingPermission::Unsolicited:
+        return _WriteResponse(L"\x1b[2;1;1;128;128;1;0x");
+    case DispatchTypes::ReportingPermission::Solicited:
+        return _WriteResponse(L"\x1b[3;1;1;128;128;1;0x");
+    default:
+        return false;
+    }
+}
+
 // Routine Description:
 // - DSR-OS - Reports the operating status back to the input channel
 // Arguments:

src/terminal/adapter/adaptDispatch.hpp

@@ -61,6 +61,7 @@ namespace Microsoft::Console::VirtualTerminal
         bool SecondaryDeviceAttributes() override; // DA2
         bool TertiaryDeviceAttributes() override; // DA3
         bool Vt52DeviceAttributes() override; // VT52 Identify
+        bool RequestTerminalParameters(const DispatchTypes::ReportingPermission permission) override; // DECREQTPARM
         bool ScrollUp(const size_t distance) override; // SU
         bool ScrollDown(const size_t distance) override; // SD
         bool InsertLine(const size_t distance) override; // IL

src/terminal/adapter/termDispatch.hpp

@@ -91,6 +91,7 @@ class Microsoft::Console::VirtualTerminal::TermDispatch : public Microsoft::Cons
     bool SecondaryDeviceAttributes() noexcept override { return false; } // DA2
     bool TertiaryDeviceAttributes() noexcept override { return false; } // DA3
     bool Vt52DeviceAttributes() noexcept override { return false; } // VT52 Identify
+    bool RequestTerminalParameters(const DispatchTypes::ReportingPermission /*permission*/) noexcept override { return false; } // DECREQTPARM
 
     bool DesignateCodingSystem(const VTID /*codingSystem*/) noexcept override { return false; } // DOCS
     bool Designate94Charset(const size_t /*gsetNumber*/, const VTID /*charset*/) noexcept override { return false; } // SCS

src/terminal/adapter/ut_adapter/adapterTest.cpp

@@ -1823,6 +1823,30 @@ class AdapterTest
         VERIFY_IS_FALSE(_pDispatch.get()->TertiaryDeviceAttributes());
     }
 
+    TEST_METHOD(RequestTerminalParametersTests)
+    {
+        Log::Comment(L"Starting test...");
+
+        Log::Comment(L"Test 1: Verify response for unsolicited permission.");
+        _testGetSet->PrepData();
+        VERIFY_IS_TRUE(_pDispatch.get()->RequestTerminalParameters(DispatchTypes::ReportingPermission::Unsolicited));
+        _testGetSet->ValidateInputEvent(L"\x1b[2;1;1;128;128;1;0x");
+
+        Log::Comment(L"Test 2: Verify response for solicited permission.");
+        _testGetSet->PrepData();
+        VERIFY_IS_TRUE(_pDispatch.get()->RequestTerminalParameters(DispatchTypes::ReportingPermission::Solicited));
+        _testGetSet->ValidateInputEvent(L"\x1b[3;1;1;128;128;1;0x");
+
+        Log::Comment(L"Test 3: Verify failure with invalid parameter.");
+        _testGetSet->PrepData();
+        VERIFY_IS_FALSE(_pDispatch.get()->RequestTerminalParameters((DispatchTypes::ReportingPermission)2));
+
+        Log::Comment(L"Test 4: Verify failure when WriteConsoleInput doesn't work.");
+        _testGetSet->PrepData();
+        _testGetSet->_privateWriteConsoleInputWResult = FALSE;
+        VERIFY_IS_FALSE(_pDispatch.get()->RequestTerminalParameters(DispatchTypes::ReportingPermission::Unsolicited));
+    }
+
     TEST_METHOD(CursorKeysModeTest)
     {
         Log::Comment(L"Starting test...");

src/terminal/parser/OutputStateMachineEngine.cpp

@@ -509,6 +509,10 @@ bool OutputStateMachineEngine::ActionCsiDispatch(const VTID id, const VTParamete
         success = parameters.at(0).value_or(0) == 0 && _dispatch->TertiaryDeviceAttributes();
         TermTelemetry::Instance().Log(TermTelemetry::Codes::DA3);
         break;
+    case CsiActionCodes::DECREQTPARM_RequestTerminalParameters:
+        success = _dispatch->RequestTerminalParameters(parameters.at(0));
+        TermTelemetry::Instance().Log(TermTelemetry::Codes::DECREQTPARM);
+        break;
     case CsiActionCodes::SU_ScrollUp:
         success = _dispatch->ScrollUp(parameters.at(0));
         TermTelemetry::Instance().Log(TermTelemetry::Codes::SU);

src/terminal/parser/OutputStateMachineEngine.hpp

@@ -127,6 +127,7 @@ namespace Microsoft::Console::VirtualTerminal
             ANSISYSSC_CursorSave = VTID("s"), // NOTE: Overlaps with DECLRMM/DECSLRM. Fix when/if implemented.
             DTTERM_WindowManipulation = VTID("t"), // NOTE: Overlaps with DECSLPP. Fix when/if implemented.
             ANSISYSRC_CursorRestore = VTID("u"),
+            DECREQTPARM_RequestTerminalParameters = VTID("x"),
             DECSCUSR_SetCursorStyle = VTID(" q"),
             DECSTR_SoftReset = VTID("!p"),
             DECSCPP_SetColumnsPerPage = VTID("$|")

src/terminal/parser/telemetry.cpp

@@ -227,6 +227,7 @@ void TermTelemetry::WriteFinalTraceLog() const
                                       TraceLoggingUInt32(_uiTimesUsed[DA], "DA"),
                                       TraceLoggingUInt32(_uiTimesUsed[DA2], "DA2"),
                                       TraceLoggingUInt32(_uiTimesUsed[DA3], "DA3"),
+                                      TraceLoggingUInt32(_uiTimesUsed[DECREQTPARM], "DECREQTPARM"),
                                       TraceLoggingUInt32(_uiTimesUsed[VPA], "VPA"),
                                       TraceLoggingUInt32(_uiTimesUsed[HPR], "HPR"),
                                       TraceLoggingUInt32(_uiTimesUsed[VPR], "VPR"),

src/terminal/parser/telemetry.hpp

@@ -54,6 +54,7 @@ namespace Microsoft::Console::VirtualTerminal
             DA,
             DA2,
             DA3,
+            DECREQTPARM,
             VPA,
             HPR,
             VPR,

src/terminal/parser/ut_parser/OutputEngineTest.cpp

@@ -1026,6 +1026,8 @@ class StatefulDispatch final : public TermDispatch
         _secondaryDeviceAttributes{ false },
         _tertiaryDeviceAttributes{ false },
         _vt52DeviceAttributes{ false },
+        _requestTerminalParameters{ false },
+        _reportingPermission{ (DispatchTypes::ReportingPermission)-1 },
         _isAltBuffer{ false },
         _cursorKeysMode{ false },
         _cursorBlinking{ true },
@@ -1237,6 +1239,14 @@ class StatefulDispatch final : public TermDispatch
         return true;
     }
 
+    bool RequestTerminalParameters(const DispatchTypes::ReportingPermission permission) noexcept override
+    {
+        _requestTerminalParameters = true;
+        _reportingPermission = permission;
+
+        return true;
+    }
+
     bool _PrivateModeParamsHelper(_In_ DispatchTypes::PrivateModeParams const param, const bool fEnable)
     {
         bool fSuccess = false;
@@ -1476,6 +1486,8 @@ class StatefulDispatch final : public TermDispatch
     bool _secondaryDeviceAttributes;
     bool _tertiaryDeviceAttributes;
     bool _vt52DeviceAttributes;
+    bool _requestTerminalParameters;
+    DispatchTypes::ReportingPermission _reportingPermission;
     bool _isAltBuffer;
     bool _cursorKeysMode;
     bool _cursorBlinking;
@@ -2434,6 +2446,44 @@ class StateMachineExternalTest final
         pDispatch->ClearState();
     }
 
+    TEST_METHOD(TestRequestTerminalParameters)
+    {
+        auto dispatch = std::make_unique<StatefulDispatch>();
+        auto pDispatch = dispatch.get();
+        auto engine = std::make_unique<OutputStateMachineEngine>(std::move(dispatch));
+        StateMachine mach(std::move(engine));
+
+        Log::Comment(L"Test 1: Check default case, no params.");
+        mach.ProcessCharacter(AsciiChars::ESC);
+        mach.ProcessCharacter(L'[');
+        mach.ProcessCharacter(L'x');
+
+        VERIFY_IS_TRUE(pDispatch->_requestTerminalParameters);
+        VERIFY_ARE_EQUAL(DispatchTypes::ReportingPermission::Unsolicited, pDispatch->_reportingPermission);
+
+        pDispatch->ClearState();
+
+        Log::Comment(L"Test 2: Check unsolicited permission, 0 param.");
+        mach.ProcessCharacter(AsciiChars::ESC);
+        mach.ProcessCharacter(L'[');
+        mach.ProcessCharacter(L'0');
+        mach.ProcessCharacter(L'x');
+
+        VERIFY_IS_TRUE(pDispatch->_requestTerminalParameters);
+        VERIFY_ARE_EQUAL(DispatchTypes::ReportingPermission::Unsolicited, pDispatch->_reportingPermission);
+
+        Log::Comment(L"Test 3: Check solicited permission, 1 param.");
+        mach.ProcessCharacter(AsciiChars::ESC);
+        mach.ProcessCharacter(L'[');
+        mach.ProcessCharacter(L'1');
+        mach.ProcessCharacter(L'x');
+
+        VERIFY_IS_TRUE(pDispatch->_requestTerminalParameters);
+        VERIFY_ARE_EQUAL(DispatchTypes::ReportingPermission::Solicited, pDispatch->_reportingPermission);
+
+        pDispatch->ClearState();
+    }
+
     TEST_METHOD(TestStrings)
     {
         auto dispatch = std::make_unique<StatefulDispatch>();