goipgrep: refactor into module; pure-Go ping/resolve; cache+CI; drop binary

projects/go-tools/go/goipgrep/internal/normalize/mac.go

@@ -0,0 +1,43 @@
+package normalize
+
+import (
+	"strings"
+)
+
+// NormalizeMAC converts supported MAC forms to canonical lower-case colon-separated form.
+// Accepts: xx:xx:xx:xx:xx:xx, xx-xx-xx-xx-xx-xx, xxxx.xxxx.xxxx
+func NormalizeMAC(s string) (string, bool) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return "", false
+	}
+	s = strings.ToLower(s)
+
+	// remove common separators
+	s = strings.ReplaceAll(s, ":", "")
+	s = strings.ReplaceAll(s, "-", "")
+	s = strings.ReplaceAll(s, ".", "")
+
+	if len(s) != 12 {
+		return "", false
+	}
+	for i := 0; i < 12; i++ {
+		c := s[i]
+		if (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') {
+			continue
+		}
+		return "", false
+	}
+
+	// canonical form aa:bb:cc:dd:ee:ff
+	var b strings.Builder
+	b.Grow(17)
+	for i := 0; i < 12; i += 2 {
+		if i > 0 {
+			b.WriteByte(':')
+		}
+		b.WriteByte(s[i])
+		b.WriteByte(s[i+1])
+	}
+	return b.String(), true
+}