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Catch exception in SerialStream constructor if DTR or RTS is not available (Windows) #121468

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Catch exception in SerialStream constructor if DTR or RTS is not available (Windows) #121468

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bb4681b
fix: catch exception when setting dtrEnable and rtsEnable to their de…
jarnedemeulemeester Nov 8, 2025
cbed082
Fix styling issues
jarnedemeulemeester Nov 11, 2025
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40 changes: 30 additions & 10 deletions src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -634,17 +634,37 @@
// set constant properties of the DCB
InitializeDCB(baudRate, parity, dataBits, stopBits, discardNull);

DtrEnable = dtrEnable;

// query and cache the initial RtsEnable value
// so that set_RtsEnable can do the (value != rtsEnable) optimization
_rtsEnable = (GetDcbFlag(Interop.Kernel32.DCBFlags.FRTSCONTROL) == Interop.Kernel32.DCBRTSFlowControl.RTS_CONTROL_ENABLE);
try
{
DtrEnable = dtrEnable;
}
catch (IOException) when (dtrEnable == false)

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src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L641 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(641,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

Check failure on line 641 in src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs

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Azure Pipelines / runtime-dev-innerloop (Build linux-x64 debug Libraries_WithPackages)

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L641 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(641,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

Check failure on line 641 in src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs

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Azure Pipelines / runtime-dev-innerloop (Build linux-x64 debug Libraries_WithPackages)

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L641 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(641,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

Check failure on line 641 in src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs

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src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L641 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(641,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

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src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L641 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(641,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)
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@huoyaoyuan huoyaoyuan Nov 8, 2025

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It is not a good approach to throw and immediately catch the exception.

Instead, the setter of DtrEnable/RtsEnable can be refactored into methods of TryEnable, then the callers here can call the TryEnable methods directly and ignores the failure.

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@jarnedemeulemeester jarnedemeulemeester Nov 9, 2025

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Alright, I will try to refactor the setters into methods.

I just took this approach from the unix implementation.
Do you want me to also refactor the unix implementation?

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@huoyaoyuan huoyaoyuan Nov 10, 2025

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It's up to the area owners for decision. Following existing pattern is also acceptable.

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@jarnedemeulemeester jarnedemeulemeester Nov 11, 2025

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I'll leave it up to the area owners then.

{
// An IOException can be thrown when using a port which doesn't implement
// the required termios command for setting DtrEnable, but it still works without setting the value
Comment on lines +643 to +644
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Copilot AI Nov 11, 2025

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The comment refers to 'termios command' which is Unix-specific terminology. On Windows, this should refer to Windows API calls like SetCommState or EscapeCommFunction instead. Consider updating to: 'the required Windows API calls for setting DtrEnable'.

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// so we ignore this error in the constructor only if being set to false (which is the default).
// When the property is set manually the exception is still thrown.
}

// now set this.RtsEnable to the specified value.
// Handshake takes precedence, this will be a nop if
// handshake is either RequestToSend or RequestToSendXOnXOff
if ((handshake != Handshake.RequestToSend && handshake != Handshake.RequestToSendXOnXOff))
RtsEnable = rtsEnable;
try
{
// query and cache the initial RtsEnable value
// so that set_RtsEnable can do the (value != rtsEnable) optimization
_rtsEnable = (GetDcbFlag(Interop.Kernel32.DCBFlags.FRTSCONTROL) == Interop.Kernel32.DCBRTSFlowControl.RTS_CONTROL_ENABLE);

// now set this.RtsEnable to the specified value.
// Handshake takes precedence, this will be a nop if
// handshake is either RequestToSend or RequestToSendXOnXOff
if ((handshake != Handshake.RequestToSend && handshake != Handshake.RequestToSendXOnXOff))
RtsEnable = rtsEnable;
}
catch (IOException) when (rtsEnable == false)

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src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L661 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(661,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

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Azure Pipelines / runtime-dev-innerloop (Build linux-x64 debug Libraries_WithPackages)

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L661 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(661,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

Check failure on line 661 in src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs

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Azure Pipelines / runtime-dev-innerloop

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L661 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(661,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)

Check failure on line 661 in src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs

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src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs#L661 

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs(661,53): error IDE0100: (NETCORE_ENGINEERING_TELEMETRY=Build) Remove redundant equality (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0100)
{
// An IOException can be thrown when using a port which doesn't implement
// the required termios command for setting RtsEnable, but it still works without setting the value
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The comment refers to 'termios command' which is Unix-specific terminology. On Windows, this should refer to Windows API calls like SetCommState or EscapeCommFunction instead. Consider updating to: 'the required Windows API calls for setting RtsEnable'.

Suggested change
// the required termios command for setting RtsEnable, but it still works without setting the value
// the required Windows API calls (such as SetCommState or EscapeCommFunction) for setting RtsEnable, but it still works without setting the value

Copilot uses AI. Check for mistakes.
// so we ignore this error in the constructor only if being set to false (which is the default).
// When the property is set manually the exception is still thrown.
}

// NOTE: this logic should match what is in the ReadTimeout property
if (readTimeout == 0)
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