[dsrouter] log redirected console output (#5524)

Context: #5494
Context: #5241
Fixes: #5435

We added `--dsrouter` switch to both `dotnet-trace` and `dotnet-gcdump`,
which runs `dotnet-dsrouter` as a child process.

Many of `dotnet-dsrouter`'s console messages are pretty useful for
developers, but we are simply ignoring them:

private static async Task ReadAndIgnoreAllStreamAsync(StreamReader
streamToIgnore, CancellationToken cancelToken)
    {
        Memory<char> memory = new char[4096];
while (await streamToIgnore.ReadAsync(memory,
cancelToken).ConfigureAwait(false) != 0)
        {
        }
    }

To make this a bit more useful, we now log the output to either
`Console.Out` or `Console.Error` where appropriate.

If we simply did:

    string line;
while ((line = await
streamToRead.ReadLineAsync(cancelToken).ConfigureAwait(false)) != null)
    {
        output.WriteLine(line);
    }

This would work fine, but we'd lose all coloring.

`dotnet-dsrouter` uses `SimpleConsoleFormatter` to colorize its output:


https://github.com/dotnet/runtime/blob/aadcceeb03ce0ecbc2ad645de0feb10189daa64c/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs#L163-L199

So, for now, a very simple solution is to check the known prefixes and
add coloring. This looks to have a pretty good result.

I also dropped the duplicate message:

WARNING: dotnet-dsrouter is a development tool not intended for
production environments.

Now that we print all of `dotnet-dsrouter`'s output, we can handle this
case and color it yellow.

<img width="2524" height="582" alt="image"
src="https://github.com/user-attachments/assets/4924ec93-c616-4511-83f8-f318f4ce4471"
/>

Author: jonathanpeppers

src/Tools/Common/Commands/Utils.cs

@@ -46,10 +46,6 @@ public static int FindProcessIdWithName(string name)
         // <returns>processId</returns>
         public static int LaunchDSRouterProcess(string dsrouterCommand)
         {
-            ConsoleColor currentColor = Console.ForegroundColor;
-            Console.ForegroundColor = ConsoleColor.Yellow;
-            Console.WriteLine("WARNING: dotnet-dsrouter is a development tool not intended for production environments.");
-            Console.ForegroundColor = currentColor;
             Console.WriteLine("For finer control over the dotnet-dsrouter options, run it separately and connect to it using -p" + Environment.NewLine);
 
             return DsRouterProcessLauncher.Launcher.Start(dsrouterCommand, default);

src/Tools/Common/DsRouterProcessLauncher.cs

@@ -24,11 +24,92 @@ internal sealed partial class DsRouterProcessLauncher
         internal static DsRouterProcessLauncher Launcher = new();
         private bool _processStarted;
 
-        private static async Task ReadAndIgnoreAllStreamAsync(StreamReader streamToIgnore, CancellationToken cancelToken)
+        private static async Task ReadAndLogAllLinesAsync(StreamReader streamToRead, TextWriter output, CancellationToken cancelToken)
         {
-            Memory<char> memory = new char[4096];
-            while (await streamToIgnore.ReadAsync(memory, cancelToken).ConfigureAwait(false) != 0)
+            string line;
+            while ((line = await streamToRead.ReadLineAsync(cancelToken).ConfigureAwait(false)) != null)
             {
+                // Just log with no colors if redirected
+                if (Console.IsOutputRedirected)
+                {
+                    output.WriteLine(line);
+                    continue;
+                }
+
+                // Console coloring is not preserved, so this is a naive approach based on SimpleConsoleFormatter's output:
+                // https://github.com/dotnet/runtime/blob/aadcceeb03ce0ecbc2ad645de0feb10189daa64c/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs#L163-L199
+
+                ConsoleColor foregroundColor = Console.ForegroundColor;
+                ConsoleColor backgroundColor = Console.BackgroundColor;
+                try
+                {
+                    // Specific dotnet-dsrouter warning message
+                    if (line.StartsWith("WARNING: dotnet-dsrouter", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.Yellow;
+                        output.WriteLine(line);
+                        continue;
+                    }
+
+                    // SimpleConsoleFormatter prefixes
+                    if (line.StartsWith("crit:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.White;
+                        Console.BackgroundColor = ConsoleColor.DarkRed;
+                        output.Write("crit");
+                    }
+                    else if (line.StartsWith("fail:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.Black;
+                        Console.BackgroundColor = ConsoleColor.DarkRed;
+                        output.Write("fail");
+                    }
+                    else if (line.StartsWith("warn:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.Yellow;
+                        Console.BackgroundColor = ConsoleColor.Black;
+                        output.Write("warn");
+                    }
+                    else if (line.StartsWith("info:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.DarkGreen;
+                        Console.BackgroundColor = ConsoleColor.Black;
+                        output.Write("info");
+                    }
+                    else if (line.StartsWith("dbug:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.Gray;
+                        Console.BackgroundColor = ConsoleColor.Black;
+                        output.Write("dbug");
+                    }
+                    else if (line.StartsWith("trce:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.ForegroundColor = ConsoleColor.Gray;
+                        Console.BackgroundColor = ConsoleColor.Black;
+                        output.Write("trce");
+                    }
+                    else
+                    {
+                        output.WriteLine(line);
+                        continue; // If it doesn't match any prefix, just write the line as is
+                    }
+                }
+                finally
+                {
+                    Console.ForegroundColor = foregroundColor;
+                    Console.BackgroundColor = backgroundColor;
+                }
+
+                // If we get here, we logged a prefix, so we can log the rest of the line
+                if (line.Length > 4)
+                {
+                    output.WriteLine(line.AsSpan().Slice(4));
+                }
+                else
+                {
+                    // If the line is just the prefix, we still need to write a new line
+                    output.WriteLine();
+                }
             }
         }
 
@@ -69,8 +150,8 @@ public int Start(string dsrouterCommand, CancellationToken ct)
                 return -1;
             }
 
-            _stdErrTask = ReadAndIgnoreAllStreamAsync(_childProc.StandardError, ct);
-            _stdOutTask = ReadAndIgnoreAllStreamAsync(_childProc.StandardOutput, ct);
+            _stdErrTask = ReadAndLogAllLinesAsync(_childProc.StandardError, Console.Error, ct);
+            _stdOutTask = ReadAndLogAllLinesAsync(_childProc.StandardOutput, Console.Out, ct);
             Task.Delay(1000, ct).Wait(ct);
             return !_childProc.HasExited ? _childProc.Id : -2;
         }