Bring back the sensitive data filtering feature (#280)

* Bring back the sensitive data filtering feature

* Add `// global` comment

tap/api/serializable_regexp.go

@@ -0,0 +1,30 @@
+package api
+
+import "regexp"
+
+type SerializableRegexp struct {
+	regexp.Regexp
+}
+
+func CompileRegexToSerializableRegexp(expr string) (*SerializableRegexp, error) {
+	re, err := regexp.Compile(expr)
+	if err != nil {
+		return nil, err
+	}
+	return &SerializableRegexp{*re}, nil
+}
+
+// UnmarshalText is by json.Unmarshal.
+func (r *SerializableRegexp) UnmarshalText(text []byte) error {
+	rr, err := CompileRegexToSerializableRegexp(string(text))
+	if err != nil {
+		return err
+	}
+	*r = *rr
+	return nil
+}
+
+// MarshalText is used by json.Marshal.
+func (r *SerializableRegexp) MarshalText() ([]byte, error) {
+	return []byte(r.String()), nil
+}