git/odb: add implementation of annotated Tag object

tag.go

@@ -0,0 +1,116 @@
+package gitobj
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"strings"
+)
+
+type Tag struct {
+	Object     []byte
+	ObjectType ObjectType
+	Name       string
+	Tagger     string
+
+	Message string
+}
+
+// Decode implements Object.Decode and decodes the uncompressed tag being
+// read. It returns the number of uncompressed bytes being consumed off of the
+// stream, which should be strictly equal to the size given.
+//
+// If any error was encountered along the way it will be returned, and the
+// receiving *Tag is considered invalid.
+func (t *Tag) Decode(r io.Reader, size int64) (int, error) {
+	scanner := bufio.NewScanner(io.LimitReader(r, size))
+
+	var (
+		finishedHeaders bool
+		message         []string
+	)
+
+	for scanner.Scan() {
+		if finishedHeaders {
+			message = append(message, scanner.Text())
+		} else {
+			if len(scanner.Bytes()) == 0 {
+				finishedHeaders = true
+				continue
+			}
+
+			parts := strings.SplitN(scanner.Text(), " ", 2)
+			if len(parts) < 2 {
+				return 0, fmt.Errorf("git/odb: invalid tag header: %s", scanner.Text())
+			}
+
+			switch parts[0] {
+			case "object":
+				sha, err := hex.DecodeString(parts[1])
+				if err != nil {
+					return 0, fmt.Errorf("git/odb: unable to decode SHA-1: %s", err)
+				}
+
+				t.Object = sha
+			case "type":
+				t.ObjectType = ObjectTypeFromString(parts[1])
+			case "tag":
+				t.Name = parts[1]
+			case "tagger":
+				t.Tagger = parts[1]
+			default:
+				return 0, fmt.Errorf("git/odb: unknown tag header: %s", parts[0])
+			}
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return 0, err
+	}
+
+	t.Message = strings.Join(message, "\n")
+
+	return int(size), nil
+}
+
+// Encode encodes the Tag's contents to the given io.Writer, "w". If there was
+// any error copying the Tag's contents, that error will be returned.
+//
+// Otherwise, the number of bytes written will be returned.
+func (t *Tag) Encode(w io.Writer) (int, error) {
+	headers := []string{
+		fmt.Sprintf("object %s", hex.EncodeToString(t.Object)),
+		fmt.Sprintf("type %s", t.ObjectType),
+		fmt.Sprintf("tag %s", t.Name),
+		fmt.Sprintf("tagger %s", t.Tagger),
+	}
+
+	return fmt.Fprintf(w, "%s\n\n%s\n", strings.Join(headers, "\n"), t.Message)
+}
+
+// Equal returns whether the receiving and given Tags are equal, or in other
+// words, whether they are represented by the same SHA-1 when saved to the
+// object database.
+func (t *Tag) Equal(other *Tag) bool {
+	if (t == nil) != (other == nil) {
+		return false
+	}
+
+	if t != nil {
+		return bytes.Equal(t.Object, other.Object) &&
+			t.ObjectType == other.ObjectType &&
+			t.Name == other.Name &&
+			t.Tagger == other.Tagger &&
+			t.Message == other.Message
+	}
+
+	return true
+}
+
+// Type implements Object.ObjectType by returning the correct object type for
+// Tags, TagObjectType.
+func (t *Tag) Type() ObjectType {
+	return TagObjectType
+}

tag_test.go

@@ -0,0 +1,65 @@
+package gitobj
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTagTypeReturnsCorrectObjectType(t *testing.T) {
+	assert.Equal(t, TagObjectType, new(Tag).Type())
+}
+
+func TestTagEncode(t *testing.T) {
+	tag := &Tag{
+		Object:     []byte("aaaaaaaaaaaaaaaaaaaa"),
+		ObjectType: CommitObjectType,
+		Name:       "v2.4.0",
+		Tagger:     "A U Thor <author@example.com>",
+
+		Message: "The quick brown fox jumps over the lazy dog.",
+	}
+
+	buf := new(bytes.Buffer)
+
+	n, err := tag.Encode(buf)
+
+	assert.Nil(t, err)
+	assert.EqualValues(t, buf.Len(), n)
+
+	assertLine(t, buf, "object 6161616161616161616161616161616161616161")
+	assertLine(t, buf, "type commit")
+	assertLine(t, buf, "tag v2.4.0")
+	assertLine(t, buf, "tagger A U Thor <author@example.com>")
+	assertLine(t, buf, "")
+	assertLine(t, buf, "The quick brown fox jumps over the lazy dog.")
+
+	assert.Equal(t, 0, buf.Len())
+}
+
+func TestTagDecode(t *testing.T) {
+	from := new(bytes.Buffer)
+
+	fmt.Fprintf(from, "object 6161616161616161616161616161616161616161\n")
+	fmt.Fprintf(from, "type commit\n")
+	fmt.Fprintf(from, "tag v2.4.0\n")
+	fmt.Fprintf(from, "tagger A U Thor <author@example.com>\n")
+	fmt.Fprintf(from, "\n")
+	fmt.Fprintf(from, "The quick brown fox jumps over the lazy dog.\n")
+
+	flen := from.Len()
+
+	tag := new(Tag)
+	n, err := tag.Decode(from, int64(flen))
+
+	assert.Nil(t, err)
+	assert.Equal(t, n, flen)
+
+	assert.Equal(t, []byte("aaaaaaaaaaaaaaaaaaaa"), tag.Object)
+	assert.Equal(t, CommitObjectType, tag.ObjectType)
+	assert.Equal(t, "v2.4.0", tag.Name)
+	assert.Equal(t, "A U Thor <author@example.com>", tag.Tagger)
+	assert.Equal(t, "The quick brown fox jumps over the lazy dog.", tag.Message)
+}