package difftree
// A treenoder is a helper type that wraps git trees into merkletrie
// noders.
//
// As a merkletrie noder doesn't understand the concept of modes (e.g.
// file permissions), the treenoder includes the mode of the git tree in
// the hash, so changes in the modes will be detected as modifications
// to the file contents by the merkletrie difftree algorithm. This is
// consistent with how the "git diff-tree" command works.
import (
"encoding/binary"
"io"
"os"
"srcd.works/go-git.v4/plumbing"
"srcd.works/go-git.v4/plumbing/object"
"srcd.works/go-git.v4/utils/merkletrie/noder"
)
type treeNoder struct {
parent *object.Tree // the root node is its own parent
name string // empty string for the root node
mode os.FileMode
hash plumbing.Hash
children []noder.Noder // memoized
}
func newTreeNoder(t *object.Tree) *treeNoder {
if t == nil {
return &treeNoder{}
}
return &treeNoder{
parent: t,
name: "",
mode: os.ModeDir,
hash: t.Hash,
}
}
func (t *treeNoder) isRoot() bool {
return t.name == ""
}
func (t *treeNoder) String() string {
return "treeNoder <" + t.name + ">"
}
func (t *treeNoder) Hash() []byte {
return append(t.hash[:], modeToBytes(t.mode)...)
}
// mode in little endian (endianess is an arbitrary decission).
func modeToBytes(m os.FileMode) []byte {
ret := make([]byte, 4)
binary.LittleEndian.PutUint32(ret, uint32(m))
return ret
}
func (t *treeNoder) Name() string {
return t.name
}
func (t *treeNoder) IsDir() bool {
return t.mode.IsDir()
}
// Children will return the children of a treenoder as treenoders,
// building them from the children of the wrapped git tree.
func (t *treeNoder) Children() ([]noder.Noder, error) {
if !t.mode.IsDir() {
return noder.NoChildren, nil
}
// children are memoized for efficiency
if t.children != nil {
return t.children, nil
}
// the parent of the returned children will be ourself as a tree if
// we are a not the root treenoder. The root is special as it
// is is own parent.
parent := t.parent
if !t.isRoot() {
var err error
if parent, err = t.parent.Tree(t.name); err != nil {
return nil, err
}
}
return transformChildren(parent)
}
// Returns the children of a tree as treenoders.
// Efficiency is key here.
func transformChildren(t *object.Tree) ([]noder.Noder, error) {
var err error
var e object.TreeEntry
// there will be more tree entries than children in the tree,
// due to submodules and empty directories, but I think it is still
// worth it to pre-allocate the whole array now, even if sometimes
// is bigger than needed.
ret := make([]noder.Noder, 0, len(t.Entries))
walker := object.NewTreeWalker(t, false) // don't recurse
// don't defer walker.Close() for efficiency reasons.
for {
_, e, err = walker.Next()
if err == io.EOF {
break
}
if err != nil {
walker.Close()
return nil, err
}
ret = append(ret, &treeNoder{
parent: t,
name: e.Name,
mode: e.Mode,
hash: e.Hash,
})
}
walker.Close()
return ret, nil
}
// len(t.tree.Entries) != the number of elements walked by treewalker
// for some reason because of empty directories, submodules, etc, so we
// have to walk here.
func (t *treeNoder) NumChildren() (int, error) {
children, err := t.Children()
if err != nil {
return 0, err
}
return len(children), nil
}
