Add debug printer.

dbg/dbg.go

@@ -0,0 +1,76 @@
+// Package dbg implements a debug printer.
+package dbg
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+// A DebugPrinter is a drop-in replacement for fmt.Print*, and also acts as
+// an io.WriteCloser when enabled.
+type DebugPrinter struct {
+	// If Enabled is false, the print statements won't do anything.
+	Enabled bool
+	out     io.WriteCloser
+}
+
+// Close satisfies the Closer interface.
+func (dbg *DebugPrinter) Close() error {
+	return dbg.out.Close()
+}
+
+// Write satisfies the Writer interface.
+func (dbg *DebugPrinter) Write(p []byte) (int, error) {
+	if dbg.Enabled {
+		return dbg.out.Write(p)
+	}
+	return 0, nil
+}
+
+// New returns a new DebugPrinter on os.Stdout.
+func New() *DebugPrinter {
+	return &DebugPrinter{
+		out: os.Stdout,
+	}
+}
+
+// ToFile sets up a new DebugPrinter to a file, truncating it if it exists.
+func ToFile(path string) (*DebugPrinter, error) {
+	file, err := os.Create(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return &DebugPrinter{
+		out: file,
+	}, nil
+}
+
+// To sets up a new DebugPrint to an io.WriteCloser.
+func To(w io.WriteCloser) *DebugPrinter {
+	return &DebugPrinter{
+		out: w,
+	}
+}
+
+// Print calls fmt.Print if Enabled is true.
+func (dbg DebugPrinter) Print(v ...interface{}) {
+	if dbg.Enabled {
+		fmt.Fprint(dbg.out, v...)
+	}
+}
+
+// Println calls fmt.Println if Enabled is true.
+func (dbg DebugPrinter) Println(v ...interface{}) {
+	if dbg.Enabled {
+		fmt.Fprintln(dbg.out, v...)
+	}
+}
+
+// Printf calls fmt.Printf if Enabled is true.
+func (dbg DebugPrinter) Printf(format string, v ...interface{}) {
+	if dbg.Enabled {
+		fmt.Fprintf(dbg.out, format, v...)
+	}
+}