dnsfilter -- add trace()

dnsfilter/helpers.go

@@ -1,6 +1,10 @@
 package dnsfilter
 
 import (
+	"fmt"
+	"os"
+	"path"
+	"runtime"
 	"strings"
 	"sync/atomic"
 )
@@ -58,3 +62,17 @@ func updateMax(valuePtr *int64, maxPtr *int64) {
 		// swapping failed because value has changed after reading, try again
 	}
 }
+
+func trace(format string, args ...interface{}) {
+	pc := make([]uintptr, 10) // at least 1 entry needed
+	runtime.Callers(2, pc)
+	f := runtime.FuncForPC(pc[0])
+	var buf strings.Builder
+	buf.WriteString(fmt.Sprintf("%s(): ", path.Base(f.Name())))
+	text := fmt.Sprintf(format, args...)
+	buf.WriteString(text)
+	if len(text) == 0 || text[len(text)-1] != '\n' {
+		buf.WriteRune('\n')
+	}
+	fmt.Fprint(os.Stderr, buf.String())
+}