A sink for PowerShell `Write-Debug`, `Write-Verbose`, etc.?

A few questions before you begin:

Does this issue relate to a new feature or an existing bug?

• Bug
• [x ] New Feature

What version of Serilog is affected? Please list the related NuGet package.

All

**What is the target framework and operating system? See [target frameworks]

• [x ] netCore 3.1
• netCore 2.0
• netCore 1.0
• 4.7
• 4.6.x
• 4.5.x

Please describe the current behavior?

I can’t find a Serilog sink that I can use from a PowerShell CmdLet that I’m building in C#. The CmdLet utilizes a library I’ve built that makes extensive use of Serilog for Debug and Information.

I currently setup Serilog like this:

            // Setup logging
            Log.Logger = new LoggerConfiguration()
                .MinimumLevel.ControlledBy(MasterLevelSwitch)
                .WriteTo.Console(levelSwitch: ConsoleLevelSwitch)
                .WriteTo.Debug(levelSwitch: DebugLevelSwitch)
                .WriteTo.File(LogPath, shared: true, levelSwitch: FileLevelSwitch)
                .CreateLogger();

I want to be able to add to my configuration, when my library is used from PowerShell:

            // Setup logging
            Log.Logger = new LoggerConfiguration()
                .MinimumLevel.ControlledBy(MasterLevelSwitch)
                .WriteTo.PowerShellWriteVerbose(levelSwitch: ConsoleLevelSwitch)
                .WriteTo.PowerShellWriteDebug(levelSwitch: DebugLevelSwitch)
                .WriteTo.File(LogPath, shared: true, levelSwitch: FileLevelSwitch)
                .CreateLogger();

(roughly).

I’ve searched for a Serilog sink for PowerShell’s Write-Output, Write-Verbose, Write-Debug, etc… to no avail. I suppose it wouldn’t be hard to write one, but I can’t believe I’m the first person to think of this…

[sandscap-sc]

@tig Would it be safer to instantiate the StringWriter strWriter = new StringWriter(); inside the _syncRoot lock? Otherwise, other threads might change the strWriter variable before the writer gets a chance to write out the message.

public void Emit(LogEvent logEvent) {
            if (logEvent == null) throw new ArgumentNullException(nameof(logEvent));

            lock (_syncRoot) {

                StringWriter strWriter = new StringWriter();
                TextFormatter.Format(logEvent, strWriter);

                switch (logEvent.Level) {
                    // -Verbose
                    case LogEventLevel.Verbose:
                    case LogEventLevel.Information:
                        _cmdlet.WriteVerbose(strWriter.ToString());
                        break;
...

[rstutton]

@tig thanks for your PowershellSink example. I found that the (text) output capability of Cmdlet was limiting - especially when you want to simply write to stderr - but AsyncCmdlet derives from a PSCmdlet which has a Host property, which in turn has a UI property of type PSHostUserInterface and this is much more useful:

namespace System.Management.Automation.Host
{
    public abstract class PSHostUserInterface
    {
        protected PSHostUserInterface();

        public abstract PSHostRawUserInterface RawUI { get; }
        public virtual bool SupportsVirtualTerminal { get; }

        public abstract Dictionary<string, PSObject> Prompt(string caption, string message, Collection<FieldDescription> descriptions);
        public abstract int PromptForChoice(string caption, string message, Collection<ChoiceDescription> choices, int defaultChoice);
        public abstract PSCredential PromptForCredential(string caption, string message, string userName, string targetName);
        public abstract PSCredential PromptForCredential(string caption, string message, string userName, string targetName, PSCredentialTypes allowedCredentialTypes, PSCredentialUIOptions options);
        public abstract string ReadLine();
        public abstract SecureString ReadLineAsSecureString();
        public abstract void Write(ConsoleColor foregroundColor, ConsoleColor backgroundColor, string value);
        public abstract void Write(string value);
        public abstract void WriteDebugLine(string message);
        public abstract void WriteErrorLine(string value);
        public virtual void WriteInformation(InformationRecord record);
        public virtual void WriteLine();
        public virtual void WriteLine(ConsoleColor foregroundColor, ConsoleColor backgroundColor, string value);
        public abstract void WriteLine(string value);
        public abstract void WriteProgress(long sourceId, ProgressRecord record);
        public abstract void WriteVerboseLine(string message);
        public abstract void WriteWarningLine(string message);
    }
}