From 49d30a7189f3ce0a2dc7594a1a01ef2e0d63942d Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Wed, 21 Aug 2019 09:19:26 -0700
Subject: [PATCH] feat: make delete idempotent

fixes #104
---
 autobatch/autobatch.go | 4 ----
 basic_ds.go            | 3 ---
 batch.go               | 5 -----
 datastore.go           | 7 ++++---
 examples/fs.go         | 8 ++++++--
 mount/mount.go         | 2 +-
 mount/mount_test.go    | 4 ++--
 7 files changed, 13 insertions(+), 20 deletions(-)

diff --git a/autobatch/autobatch.go b/autobatch/autobatch.go
index aeca9a4..66d701e 100644
--- a/autobatch/autobatch.go
+++ b/autobatch/autobatch.go
@@ -75,10 +75,6 @@ func (d *Datastore) Flush() error {
 		var err error
 		if o.delete {
 			err = b.Delete(k)
-			if err == ds.ErrNotFound {
-				// Ignore these, let delete be idempotent.
-				err = nil
-			}
 		} else {
 			err = b.Put(k, o.value)
 		}
diff --git a/basic_ds.go b/basic_ds.go
index 19b74e2..08ae2af 100644
--- a/basic_ds.go
+++ b/basic_ds.go
@@ -53,9 +53,6 @@ func (d *MapDatastore) GetSize(key Key) (size int, err error) {
 
 // Delete implements Datastore.Delete
 func (d *MapDatastore) Delete(key Key) (err error) {
-	if _, found := d.values[key]; !found {
-		return ErrNotFound
-	}
 	delete(d.values, key)
 	return nil
 }
diff --git a/batch.go b/batch.go
index 57880dd..41e23ff 100644
--- a/batch.go
+++ b/batch.go
@@ -35,11 +35,6 @@ func (bt *basicBatch) Commit() error {
 	for k, op := range bt.ops {
 		if op.delete {
 			err = bt.target.Delete(k)
-			// We could try to do something smarter but I really
-			// don't care. Delete should be idempotent anyways.
-			if err == ErrNotFound {
-				err = nil
-			}
 		} else {
 			err = bt.target.Put(k, op.value)
 		}
diff --git a/datastore.go b/datastore.go
index eec1932..604ff71 100644
--- a/datastore.go
+++ b/datastore.go
@@ -50,7 +50,8 @@ type Write interface {
 	// type-safe interface to your application, and do the checking up-front.
 	Put(key Key, value []byte) error
 
-	// Delete removes the value for given `key`.
+	// Delete removes the value for given `key`. If the key is not in the
+	// datastore, this method returns no error.
 	Delete(key Key) error
 }
 
@@ -191,8 +192,8 @@ type TxnDatastore interface {
 
 // Errors
 
-// ErrNotFound is returned by Get, Has, and Delete when a datastore does not
-// map the given key to a value.
+// ErrNotFound is returned by Get and GetSize when a datastore does not map the
+// given key to a value.
 var ErrNotFound = errors.New("datastore: key not found")
 
 // ErrInvalidType is returned by Put when a given value is incopatible with
diff --git a/examples/fs.go b/examples/fs.go
index 94cefab..87369e8 100644
--- a/examples/fs.go
+++ b/examples/fs.go
@@ -86,10 +86,14 @@ func (d *Datastore) GetSize(key ds.Key) (size int, err error) {
 func (d *Datastore) Delete(key ds.Key) (err error) {
 	fn := d.KeyFilename(key)
 	if !isFile(fn) {
-		return ds.ErrNotFound
+		return nil
 	}
 
-	return os.Remove(fn)
+	err = os.Remove(fn)
+	if os.IsNotExist(err) {
+		err = nil // idempotent
+	}
+	return err
 }
 
 // Query implements Datastore.Query
diff --git a/mount/mount.go b/mount/mount.go
index 326277a..71ed8e8 100644
--- a/mount/mount.go
+++ b/mount/mount.go
@@ -216,7 +216,7 @@ func (d *Datastore) GetSize(key ds.Key) (size int, err error) {
 func (d *Datastore) Delete(key ds.Key) error {
 	cds, _, k := d.lookup(key)
 	if cds == nil {
-		return ds.ErrNotFound
+		return nil
 	}
 	return cds.Delete(k)
 }
diff --git a/mount/mount_test.go b/mount/mount_test.go
index 5a32772..3613536 100644
--- a/mount/mount_test.go
+++ b/mount/mount_test.go
@@ -171,8 +171,8 @@ func TestDeleteNotFound(t *testing.T) {
 	})
 
 	err := m.Delete(datastore.NewKey("/quux/thud"))
-	if g, e := err, datastore.ErrNotFound; g != e {
-		t.Fatalf("expected ErrNotFound, got: %v\n", g)
+	if err != nil {
+		t.Fatalf("expected nil, got: %v\n", err)
 	}
 }