6 files changed, 236 insertions, 10 deletions

diff --git a/plumbing/storer/object.go b/plumbing/storer/object.go
index e793211..5d043cb 100644
--- a/plumbing/storer/object.go
+++ b/plumbing/storer/object.go
@@ -3,6 +3,7 @@ package storer
 import (
 	"errors"
 	"io"
+	"time"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 )
@@ -36,6 +37,19 @@ type EncodedObjectStorer interface {
 	//
 	// Valid plumbing.ObjectType values are CommitObject, BlobObject, TagObject,
 	IterEncodedObjects(plumbing.ObjectType) (EncodedObjectIter, error)
+	// HasEncodedObject returns ErrObjNotFound if the object doesn't
+	// exist.  If the object does exist, it returns nil.
+	HasEncodedObject(plumbing.Hash) error
+	// ForEachObjectHash iterates over all the (loose) object hashes
+	// in the repository without necessarily having to read those objects.
+	// Objects only inside pack files may be omitted.
+	ForEachObjectHash(func(plumbing.Hash) error) error
+	// LooseObjectTime looks up the (m)time associated with the
+	// loose object (that is not in a pack file). Implementations
+	// may
+	LooseObjectTime(plumbing.Hash) (time.Time, error)
+	// DeleteLooseObject deletes a loose object if it exists.
+	DeleteLooseObject(plumbing.Hash) error
 }
 
 // DeltaObjectStorer is an EncodedObjectStorer that can return delta
diff --git a/plumbing/storer/object_test.go b/plumbing/storer/object_test.go
index 6bdd25c..f8b1f73 100644
--- a/plumbing/storer/object_test.go
+++ b/plumbing/storer/object_test.go
@@ -3,6 +3,7 @@ package storer
 import (
 	"fmt"
 	"testing"
+	"time"
 
 	. "gopkg.in/check.v1"
 	"gopkg.in/src-d/go-git.v4/plumbing"
@@ -148,3 +149,15 @@ func (o *MockObjectStorage) IterEncodedObjects(t plumbing.ObjectType) (EncodedOb
 func (o *MockObjectStorage) Begin() Transaction {
 	return nil
 }
+
+func (o *MockObjectStorage) ForEachObjectHash(fun func(plumbing.Hash) error) error {
+	return nil
+}
+
+func (o *MockObjectStorage) LooseObjectTime(plumbing.Hash) (time.Time, error) {
+	return time.Time{}, plumbing.ErrObjectNotFound
+}
+
+func (o *MockObjectStorage) DeleteLooseObject(plumbing.Hash) error {
+	return plumbing.ErrObjectNotFound
+}
diff --git a/repository.go b/repository.go
index b159ff0..7079fd1 100644
--- a/repository.go
+++ b/repository.go
@@ -8,10 +8,12 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	"gopkg.in/src-d/go-git.v4/config"
 	"gopkg.in/src-d/go-git.v4/internal/revision"
 	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/filemode"
 	"gopkg.in/src-d/go-git.v4/plumbing/object"
 	"gopkg.in/src-d/go-git.v4/plumbing/storer"
 	"gopkg.in/src-d/go-git.v4/storage"
@@ -1011,3 +1013,125 @@ func (r *Repository) ResolveRevision(rev plumbing.Revision) (*plumbing.Hash, err
 
 	return &commit.Hash, nil
 }
+
+type PruneHandler func(unreferencedObjectHash plumbing.Hash) error
+type PruneOptions struct {
+	// OnlyObjectsOlderThan if set to non-zero value
+	// selects only objects older than the time provided.
+	OnlyObjectsOlderThan time.Time
+	// Handler is called on matching objects
+	Handler PruneHandler
+}
+
+// DeleteObject deletes an object from a repository.
+// The type conveniently matches PruneHandler.
+func (r *Repository) DeleteObject(hash plumbing.Hash) error {
+	return r.Storer.DeleteLooseObject(hash)
+}
+
+func (r *Repository) Prune(opt PruneOptions) error {
+	pw := &pruneWalker{
+		r:    r,
+		seen: map[plumbing.Hash]struct{}{},
+	}
+	// Walk over all the references in the repo.
+	it, err := r.Storer.IterReferences()
+	if err != nil {
+		return nil
+	}
+	defer it.Close()
+	err = it.ForEach(func(ref *plumbing.Reference) error {
+		// Exit this iteration early for non-hash references.
+		if ref.Type() != plumbing.HashReference {
+			return nil
+		}
+		return pw.walkObjectTree(ref.Hash())
+	})
+	if err != nil {
+		return err
+	}
+	// Now walk all (loose) objects in storage.
+	err = r.Storer.ForEachObjectHash(func(hash plumbing.Hash) error {
+		// Get out if we have seen this object.
+		if pw.isSeen(hash) {
+			return nil
+		}
+		// Otherwise it is a candidate for pruning.
+		// Check out for too new objects next.
+		if opt.OnlyObjectsOlderThan != (time.Time{}) {
+			// Errors here are non-fatal. The object may be e.g. packed.
+			// Or concurrently deleted. Skip such objects.
+			t, err := r.Storer.LooseObjectTime(hash)
+			if err != nil {
+				return nil
+			}
+			// Skip too new objects.
+			if !t.Before(opt.OnlyObjectsOlderThan) {
+				return nil
+			}
+		}
+		return opt.Handler(hash)
+	})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+type pruneWalker struct {
+	r    *Repository
+	seen map[plumbing.Hash]struct{}
+}
+
+func (p *pruneWalker) isSeen(hash plumbing.Hash) bool {
+	_, seen := p.seen[hash]
+	return seen
+}
+
+func (p *pruneWalker) add(hash plumbing.Hash) {
+	p.seen[hash] = struct{}{}
+}
+
+func (p *pruneWalker) walkObjectTree(hash plumbing.Hash) error {
+	// Check if we have already seen, and mark this object
+	if p.isSeen(hash) {
+		return nil
+	}
+	p.add(hash)
+	// Fetch the object.
+	obj, err := object.GetObject(p.r.Storer, hash)
+	if err != nil {
+		return fmt.Errorf("Getting object %s failed: %v", hash, err)
+	}
+	// Walk all children depending on object type.
+	switch obj := obj.(type) {
+	case *object.Commit:
+		err = p.walkObjectTree(obj.TreeHash)
+		if err != nil {
+			return err
+		}
+		for _, h := range obj.ParentHashes {
+			err = p.walkObjectTree(h)
+			if err != nil {
+				return err
+			}
+		}
+	case *object.Tree:
+		for i := range obj.Entries {
+			// Shortcut for blob objects:
+			if obj.Entries[i].Mode|0755 == filemode.Executable {
+				p.add(obj.Entries[i].Hash)
+				continue
+			}
+			// Normal walk for sub-trees (and symlinks etc).
+			err = p.walkObjectTree(obj.Entries[i].Hash)
+			if err != nil {
+				return err
+			}
+		}
+	default:
+		// Error out on unhandled object types.
+		return fmt.Errorf("Unknown object %X %s %T\n", obj.ID(), obj.Type(), obj)
+	}
+	return nil
+}
diff --git a/storage/filesystem/internal/dotgit/dotgit.go b/storage/filesystem/internal/dotgit/dotgit.go
index 9d49945..83fe159 100644
--- a/storage/filesystem/internal/dotgit/dotgit.go
+++ b/storage/filesystem/internal/dotgit/dotgit.go
@@ -205,39 +205,67 @@ func (d *DotGit) NewObject() (*ObjectWriter, error) {
 // Objects returns a slice with the hashes of objects found under the
 // .git/objects/ directory.
 func (d *DotGit) Objects() ([]plumbing.Hash, error) {
+	var objects []plumbing.Hash
+	err := d.ForEachObjectHash(func(hash plumbing.Hash) error {
+		objects = append(objects, hash)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return objects, nil
+}
+
+// Objects returns a slice with the hashes of objects found under the
+// .git/objects/ directory.
+func (d *DotGit) ForEachObjectHash(fun func(plumbing.Hash) error) error {
 	files, err := d.fs.ReadDir(objectsPath)
 	if err != nil {
 		if os.IsNotExist(err) {
-			return nil, nil
+			return nil
 		}
 
-		return nil, err
+		return err
 	}
 
-	var objects []plumbing.Hash
 	for _, f := range files {
 		if f.IsDir() && len(f.Name()) == 2 && isHex(f.Name()) {
 			base := f.Name()
 			d, err := d.fs.ReadDir(d.fs.Join(objectsPath, base))
 			if err != nil {
-				return nil, err
+				return err
 			}
 
 			for _, o := range d {
-				objects = append(objects, plumbing.NewHash(base+o.Name()))
+				err = fun(plumbing.NewHash(base + o.Name()))
+				if err != nil {
+					return err
+				}
 			}
 		}
 	}
 
-	return objects, nil
+	return nil
 }
 
-// Object return a fs.File pointing the object file, if exists
-func (d *DotGit) Object(h plumbing.Hash) (billy.File, error) {
+func (d *DotGit) objectPath(h plumbing.Hash) string {
 	hash := h.String()
-	file := d.fs.Join(objectsPath, hash[0:2], hash[2:40])
+	return d.fs.Join(objectsPath, hash[0:2], hash[2:40])
+}
+
+// Object returns a fs.File pointing the object file, if exists
+func (d *DotGit) Object(h plumbing.Hash) (billy.File, error) {
+	return d.fs.Open(d.objectPath(h))
+}
+
+// ObjectStat returns a os.FileInfo pointing the object file, if exists
+func (d *DotGit) ObjectStat(h plumbing.Hash) (os.FileInfo, error) {
+	return d.fs.Stat(d.objectPath(h))
+}
 
-	return d.fs.Open(file)
+// ObjectDelete removes the object file, if exists
+func (d *DotGit) ObjectDelete(h plumbing.Hash) error {
+	return d.fs.Remove(d.objectPath(h))
 }
 
 func (d *DotGit) readReferenceFrom(rd io.Reader, name string) (ref *plumbing.Reference, err error) {
diff --git a/storage/filesystem/object.go b/storage/filesystem/object.go
index 9690c0e..9b2790f 100644
--- a/storage/filesystem/object.go
+++ b/storage/filesystem/object.go
@@ -3,6 +3,7 @@ package filesystem
 import (
 	"io"
 	"os"
+	"time"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/cache"
@@ -479,3 +480,26 @@ func hashListAsMap(l []plumbing.Hash) map[plumbing.Hash]bool {
 
 	return m
 }
+
+func (s *ObjectStorage) ForEachObjectHash(fun func(plumbing.Hash) error) error {
+	err := s.dir.ForEachObjectHash(fun)
+	if err != nil {
+		if err == storer.ErrStop {
+			return nil
+		}
+		return err
+	}
+	return nil
+}
+
+func (s *ObjectStorage) LooseObjectTime(hash plumbing.Hash) (time.Time, error) {
+	fi, err := s.dir.ObjectStat(hash)
+	if err != nil {
+		return time.Time{}, err
+	}
+	return fi.ModTime(), nil
+}
+
+func (s *ObjectStorage) DeleteLooseObject(hash plumbing.Hash) error {
+	return s.dir.ObjectDelete(hash)
+}
diff --git a/storage/memory/storage.go b/storage/memory/storage.go
index 3d4e84a..bfcad34 100644
--- a/storage/memory/storage.go
+++ b/storage/memory/storage.go
@@ -3,6 +3,7 @@ package memory
 
 import (
 	"fmt"
+	"time"
 
 	"gopkg.in/src-d/go-git.v4/config"
 	"gopkg.in/src-d/go-git.v4/plumbing"
@@ -156,6 +157,28 @@ func (o *ObjectStorage) Begin() storer.Transaction {
 	}
 }
 
+func (o *ObjectStorage) ForEachObjectHash(fun func(plumbing.Hash) error) error {
+	for h, _ := range o.Objects {
+		err := fun(h)
+		if err != nil {
+			if err == storer.ErrStop {
+				return nil
+			}
+			return err
+		}
+	}
+	return nil
+}
+
+var errNotSupported = fmt.Errorf("Not supported")
+
+func (s *ObjectStorage) LooseObjectTime(hash plumbing.Hash) (time.Time, error) {
+	return time.Time{}, errNotSupported
+}
+func (s *ObjectStorage) DeleteLooseObject(plumbing.Hash) error {
+	return errNotSupported
+}
+
 type TxObjectStorage struct {
 	Storage *ObjectStorage
 	Objects map[plumbing.Hash]plumbing.EncodedObject