formats/packfile: type Hash instead of strings

1 files changed, 237 insertions, 0 deletions

diff --git a/formats/packfile/objects.go b/formats/packfile/objects.go
new file mode 100644
index 0000000..4c7ee75
--- /dev/null
+++ b/formats/packfile/objects.go
@@ -0,0 +1,237 @@
+package packfile
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"encoding/hex"
+	"fmt"
+	"strconv"
+	"time"
+)
+
+type ObjectType string
+
+const (
+	CommitObject ObjectType = "commit"
+	TreeObject   ObjectType = "tree"
+	BlobObject   ObjectType = "blob"
+)
+
+// Object generic object interface
+type Object interface {
+	Type() ObjectType
+	Hash() Hash
+}
+
+// Hash SHA1 hased content
+type Hash [20]byte
+
+// ComputeHash compute the hash for a given objType and content
+func ComputeHash(t ObjectType, content []byte) Hash {
+	h := []byte(t)
+	h = append(h, ' ')
+	h = strconv.AppendInt(h, int64(len(content)), 10)
+	h = append(h, 0)
+	h = append(h, content...)
+
+	return Hash(sha1.Sum(h))
+}
+
+func (h Hash) String() string {
+	return hex.EncodeToString(h[:])
+}
+
+// Commit points to a single tree, marking it as what the project looked like
+// at a certain point in time. It contains meta-information about that point
+// in time, such as a timestamp, the author of the changes since the last
+// commit, a pointer to the previous commit(s), etc.
+// http://schacon.github.io/gitbook/1_the_git_object_model.html
+type Commit struct {
+	Tree      Hash
+	Parents   []Hash
+	Author    Signature
+	Committer Signature
+	Message   string
+	hash      Hash
+}
+
+// ParseCommit transform a byte slice into a Commit struct
+func ParseCommit(b []byte) (*Commit, error) {
+	//	b64 := base64.StdEncoding.EncodeToString(b)
+	//fmt.Printf("%q\n", b64)
+
+	o := &Commit{hash: ComputeHash(CommitObject, b)}
+
+	lines := bytes.Split(b, []byte{'\n'})
+	for i := range lines {
+		if len(lines[i]) > 0 {
+			var err error
+
+			split := bytes.SplitN(lines[i], []byte{' '}, 2)
+			switch string(split[0]) {
+			case "tree":
+				_, err = hex.Decode(o.Tree[:], split[1])
+			case "parent":
+				var h Hash
+				_, err = hex.Decode(h[:], split[1])
+				if err == nil {
+					o.Parents = append(o.Parents, h)
+				}
+			case "author":
+				o.Author = ParseSignature(split[1])
+			case "committer":
+				o.Committer = ParseSignature(split[1])
+			}
+
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			o.Message = string(bytes.Join(append(lines[i+1:]), []byte{'\n'}))
+			break
+		}
+
+	}
+
+	return o, nil
+}
+
+// Type returns the object type
+func (o *Commit) Type() ObjectType {
+	return CommitObject
+}
+
+// Hash returns the computed hash of the commit
+func (o *Commit) Hash() Hash {
+	return o.hash
+}
+
+type Tree struct {
+	Entries []TreeEntry
+	hash    Hash
+}
+
+type TreeEntry struct {
+	Name string
+	Hash Hash
+}
+
+func NewTree(body []byte) (*Tree, error) {
+	o := &Tree{hash: ComputeHash(TreeObject, body)}
+
+	if len(body) == 0 {
+		return o, nil
+	}
+
+	for {
+		split := bytes.SplitN(body, []byte{0}, 2)
+		split1 := bytes.SplitN(split[0], []byte{' '}, 2)
+
+		entry := TreeEntry{}
+		entry.Name = string(split1[1])
+		copy(entry.Hash[:], split[1][0:20])
+
+		o.Entries = append(o.Entries, entry)
+
+		body = split[1][20:]
+		if len(split[1]) == 20 {
+			break
+		}
+	}
+
+	return o, nil
+}
+
+func (o *Tree) Type() ObjectType {
+	return TreeObject
+}
+
+func (o *Tree) Hash() Hash {
+	return o.hash
+}
+
+type Blob struct {
+	Len  int
+	hash Hash
+}
+
+func NewBlob(b []byte) (*Blob, error) {
+	return &Blob{
+		Len:  len(b),
+		hash: ComputeHash(BlobObject, b),
+	}, nil
+}
+
+func (o *Blob) Type() ObjectType {
+	return BlobObject
+}
+
+func (o *Blob) Hash() Hash {
+	return o.hash
+}
+
+type ContentCallback func(hash Hash, content []byte)
+
+// Signature represents an action signed by a person
+type Signature struct {
+	Name  string
+	Email string
+	When  time.Time
+}
+
+// ParseSignature parse a byte slice returning a new action signature.
+func ParseSignature(signature []byte) Signature {
+	ret := Signature{}
+	if len(signature) == 0 {
+		return ret
+	}
+
+	from := 0
+	state := 'n' // n: name, e: email, t: timestamp, z: timezone
+	for i := 0; ; i++ {
+		var c byte
+		var end bool
+		if i < len(signature) {
+			c = signature[i]
+		} else {
+			end = true
+		}
+
+		switch state {
+		case 'n':
+			if c == '<' || end {
+				if i == 0 {
+					break
+				}
+				ret.Name = string(signature[from : i-1])
+				state = 'e'
+				from = i + 1
+			}
+		case 'e':
+			if c == '>' || end {
+				ret.Email = string(signature[from:i])
+				i++
+				state = 't'
+				from = i + 1
+			}
+		case 't':
+			if c == ' ' || end {
+				t, err := strconv.ParseInt(string(signature[from:i]), 10, 64)
+				if err == nil {
+					ret.When = time.Unix(t, 0)
+				}
+				end = true
+			}
+		}
+
+		if end {
+			break
+		}
+	}
+
+	return ret
+}
+
+func (s *Signature) String() string {
+	return fmt.Sprintf("%q <%s> @ %s", s.Name, s.Email, s.When)
+}