Don't omit commit id when marshal commit to json (#491)

fileserver/commitmgr/null.go

@@ -0,0 +1,114 @@
+package commitmgr
+
+import (
+	"bytes"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+)
+
+// nullBytes is a JSON null literal
+var nullBytes = []byte("null")
+
+// String is a nullable string. It supports SQL and JSON serialization.
+// It will marshal to null if null. Blank string input will be considered null.
+type String struct {
+	sql.NullString
+}
+
+// StringFrom creates a new String that will never be blank.
+func StringFrom(s string) String {
+	return NewString(s, true)
+}
+
+// StringFromPtr creates a new String that be null if s is nil.
+func StringFromPtr(s *string) String {
+	if s == nil {
+		return NewString("", false)
+	}
+	return NewString(*s, true)
+}
+
+// ValueOrZero returns the inner value if valid, otherwise zero.
+func (s String) ValueOrZero() string {
+	if !s.Valid {
+		return ""
+	}
+	return s.String
+}
+
+// NewString creates a new String
+func NewString(s string, valid bool) String {
+	return String{
+		NullString: sql.NullString{
+			String: s,
+			Valid:  valid,
+		},
+	}
+}
+
+// UnmarshalJSON implements json.Unmarshaler.
+// It supports string and null input. Blank string input does not produce a null String.
+func (s *String) UnmarshalJSON(data []byte) error {
+	if bytes.Equal(data, nullBytes) {
+		s.Valid = false
+		return nil
+	}
+
+	if err := json.Unmarshal(data, &s.String); err != nil {
+		return fmt.Errorf("null: couldn't unmarshal JSON: %w", err)
+	}
+
+	s.Valid = true
+	return nil
+}
+
+// MarshalJSON implements json.Marshaler.
+// It will encode null if this String is null.
+func (s String) MarshalJSON() ([]byte, error) {
+	if !s.Valid {
+		return []byte("null"), nil
+	}
+	return json.Marshal(s.String)
+}
+
+// MarshalText implements encoding.TextMarshaler.
+// It will encode a blank string when this String is null.
+func (s String) MarshalText() ([]byte, error) {
+	if !s.Valid {
+		return []byte{}, nil
+	}
+	return []byte(s.String), nil
+}
+
+// UnmarshalText implements encoding.TextUnmarshaler.
+// It will unmarshal to a null String if the input is a blank string.
+func (s *String) UnmarshalText(text []byte) error {
+	s.String = string(text)
+	s.Valid = s.String != ""
+	return nil
+}
+
+// SetValid changes this String's value and also sets it to be non-null.
+func (s *String) SetValid(v string) {
+	s.String = v
+	s.Valid = true
+}
+
+// Ptr returns a pointer to this String's value, or a nil pointer if this String is null.
+func (s String) Ptr() *string {
+	if !s.Valid {
+		return nil
+	}
+	return &s.String
+}
+
+// IsZero returns true for null strings, for potential future omitempty support.
+func (s String) IsZero() bool {
+	return !s.Valid
+}
+
+// Equal returns true if both strings have the same value or are both null.
+func (s String) Equal(other String) bool {
+	return s.Valid == other.Valid && (!s.Valid || s.String == other.String)
+}