Fix missing colored output in dcat serverless mode

- In serverless mode, output was written directly to stdout bypassing color processing
- Created ColorWriter wrapper that applies colors before writing to stdout
- Updated brush.Colorfy to also color severity levels (ERROR, WARN, FATAL) in plain text
- Ensured --plain flag still disables colors as expected
- Updated integration tests to use --noColor flag to get predictable output

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

5 files changed, 62 insertions, 14 deletions

diff --git a/integrationtests/dcat_line_endings_test.go b/integrationtests/dcat_line_endings_test.go
index 5484929..cdf99b0 100644
--- a/integrationtests/dcat_line_endings_test.go
+++ b/integrationtests/dcat_line_endings_test.go
@@ -26,8 +26,8 @@ func TestDCatLineEndings(t *testing.T) {
 	defer os.Remove(testFile)
 
 	t.Run("Serverless", func(t *testing.T) {
-		// Run dcat in serverless mode
-		cmd := exec.Command("../dcat", "--cfg", "none", testFile)
+		// Run dcat in serverless mode with colors disabled for testing
+		cmd := exec.Command("../dcat", "--cfg", "none", "--noColor", testFile)
 		output, err := cmd.Output()
 		if err != nil {
 			t.Fatalf("dcat command failed: %v", err)
@@ -74,7 +74,7 @@ func TestDCatLineEndings(t *testing.T) {
 		defer os.Remove(testFile3)
 
 		// Run dcat with multiple files
-		cmd := exec.Command("../dcat", "--cfg", "none", testFile, testFile2, testFile3)
+		cmd := exec.Command("../dcat", "--cfg", "none", "--noColor", testFile, testFile2, testFile3)
 		output, err := cmd.Output()
 		if err != nil {
 			t.Fatalf("dcat command failed: %v", err)
@@ -96,7 +96,7 @@ func TestDCatLineEndings(t *testing.T) {
 		}
 		defer os.Remove(emptyFile)
 
-		cmd := exec.Command("../dcat", "--cfg", "none", emptyFile)
+		cmd := exec.Command("../dcat", "--cfg", "none", "--noColor", emptyFile)
 		output, err := cmd.Output()
 		if err != nil {
 			t.Fatalf("dcat command failed: %v", err)
@@ -119,7 +119,7 @@ func TestDCatLineEndings(t *testing.T) {
 		defer os.Remove(crlfFile)
 
 		// Run dcat in regular mode
-		cmd := exec.Command("../dcat", "--cfg", "none", crlfFile)
+		cmd := exec.Command("../dcat", "--cfg", "none", "--noColor", crlfFile)
 		output, err := cmd.Output()
 		if err != nil {
 			t.Fatalf("dcat command failed: %v", err)
diff --git a/internal/color/brush/brush.go b/internal/color/brush/brush.go
index 63d63d8..2c89436 100644
--- a/internal/color/brush/brush.go
+++ b/internal/color/brush/brush.go
@@ -185,10 +185,14 @@ func Colorfy(line string) string {
 		paintServer(sb, line)
 
 	default:
-		color.PaintWithAttr(sb, line,
-			color.FgDefault,
-			color.BgDefault,
-			color.AttrNone)
+		// For lines that don't have protocol prefixes, check for severity levels
+		if !paintSeverity(sb, line) {
+			// No severity prefix found, paint with default colors
+			color.PaintWithAttr(sb, line,
+				color.FgDefault,
+				color.BgDefault,
+				color.AttrNone)
+		}
 	}
 	return sb.String()
 }
diff --git a/internal/io/dlog/dlog.go b/internal/io/dlog/dlog.go
index 044624e..6403f77 100644
--- a/internal/io/dlog/dlog.go
+++ b/internal/io/dlog/dlog.go
@@ -248,7 +248,8 @@ func (d *DLog) Raw(message string) string {
 		d.logger.Raw(time.Now(), message)
 		return message
 	}
-	d.logger.RawWithColors(time.Now(), message, brush.Colorfy(message))
+	coloredMessage := brush.Colorfy(message)
+	d.logger.RawWithColors(time.Now(), message, coloredMessage)
 	return message
 }
 
diff --git a/internal/server/handlers/colorwriter.go b/internal/server/handlers/colorwriter.go
new file mode 100644
index 0000000..6e0f1af
--- /dev/null
+++ b/internal/server/handlers/colorwriter.go
@@ -0,0 +1,43 @@
+package handlers
+
+import (
+	"io"
+	"github.com/mimecast/dtail/internal/color/brush"
+	"github.com/mimecast/dtail/internal/config"
+)
+
+// ColorWriter wraps an io.Writer and applies colors to output
+type ColorWriter struct {
+	writer io.Writer
+	noColor bool
+}
+
+// NewColorWriter creates a new ColorWriter
+func NewColorWriter(writer io.Writer, noColor bool) *ColorWriter {
+	return &ColorWriter{
+		writer: writer,
+		noColor: noColor,
+	}
+}
+
+// Write implements io.Writer, applying colors if enabled
+func (cw *ColorWriter) Write(p []byte) (n int, err error) {
+	if cw.noColor || !config.Client.TermColorsEnable {
+		// No colors, write as-is
+		return cw.writer.Write(p)
+	}
+
+	// Apply colors
+	coloredStr := brush.Colorfy(string(p))
+	coloredBytes := []byte(coloredStr)
+	
+	// Write the colored output
+	_, err = cw.writer.Write(coloredBytes)
+	if err != nil {
+		return 0, err
+	}
+	
+	// Return the original byte count to maintain compatibility
+	// (the caller expects n to match len(p))
+	return len(p), nil
+}
\ No newline at end of file
diff --git a/internal/server/handlers/readcommand.go b/internal/server/handlers/readcommand.go
index 616bf31..0a99aaa 100644
--- a/internal/server/handlers/readcommand.go
+++ b/internal/server/handlers/readcommand.go
@@ -146,8 +146,8 @@ func (r *readCommand) readFiles(ctx context.Context, ltx lcontext.LContext,
 	// Choose output writer based on server mode
 	var output io.Writer
 	if r.server.serverless {
-		// In serverless mode, write directly to stdout
-		output = os.Stdout
+		// In serverless mode, write to stdout with color support
+		output = NewColorWriter(os.Stdout, r.server.plain)
 	} else {
 		// In client-server mode, write to server handler lines channel
 		output = NewServerHandlerWriter(r.server, r.server.serverMessages, r.server.user)
@@ -216,8 +216,8 @@ func (r *readCommand) readStdin(ctx context.Context, ltx lcontext.LContext, re r
 	// Choose output writer based on server mode
 	var output io.Writer
 	if r.server.serverless {
-		// In serverless mode, write directly to stdout
-		output = os.Stdout
+		// In serverless mode, write to stdout with color support
+		output = NewColorWriter(os.Stdout, r.server.plain)
 	} else {
 		// In client-server mode, write to server handler lines channel
 		output = NewServerHandlerWriter(r.server, r.server.serverMessages, r.server.user)