Add proactive de-duplication to the memory backend

3 files changed, 106 insertions, 7 deletions

diff --git a/objectstore/memory_backend.go b/objectstore/memory_backend.go
index 7dcfe4a..36ee7b6 100644
--- a/objectstore/memory_backend.go
+++ b/objectstore/memory_backend.go
@@ -5,12 +5,22 @@
 package objectstore
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
 	"sync"
 )
 
+type memObject struct {
+	payload string
+	hash    string
+}
+
 type memBucket struct {
-	objects map[string]string
+	objects map[string]memObject
+	// Map used to check if the hash already exists, also
+	// storing the objectId to identify de duplicate
+	hashes map[string]string
 }
 
 type MemObjectStore struct {
@@ -24,18 +34,37 @@ func NewMemBackend() *MemObjectStore {
 	return os
 }
 
-func (os *MemObjectStore) CreateObject(bucketId string, objectId string, object string) {
+func (os *MemObjectStore) CreateObject(bucketId string, objectId string, payload string) error {
 	os.Lock()
 	defer os.Unlock()
 
+	// Create bucket if it doesn't exist
 	bucket, ok := os.buckets[bucketId]
 	if !ok {
 		bucket = memBucket{}
-		bucket.objects = make(map[string]string)
+		bucket.objects = make(map[string]memObject)
+		bucket.hashes = make(map[string]string)
 		os.buckets[bucketId] = bucket
 	}
 
+	// Hash the object content
+	hasher := sha256.New()
+	hasher.Write([]byte(payload))
+	hash := hex.EncodeToString(hasher.Sum(nil))
+
+	// Check for duplicates
+	if objectId, dup := bucket.hashes[hash]; dup {
+		return NewDuplicateError(objectId)
+	}
+
+	// Store the object
+	object := memObject{
+		payload: payload,
+		hash:    hash,
+	}
 	bucket.objects[objectId] = object
+	bucket.hashes[hash] = objectId
+	return nil
 }
 
 func (os *MemObjectStore) GetObject(bucketId string, objectId string) (string, error) {
@@ -52,7 +81,7 @@ func (os *MemObjectStore) GetObject(bucketId string, objectId string) (string, e
 		return "", fmt.Errorf("Object not found")
 	}
 
-	return object, nil
+	return object.payload, nil
 }
 
 func (os *MemObjectStore) DeleteObject(bucketId string, objectId string) error {
@@ -64,12 +93,15 @@ func (os *MemObjectStore) DeleteObject(bucketId string, objectId string) error {
 		return fmt.Errorf("Bucket not found")
 	}
 
-	_, ok = bucket.objects[objectId]
+	object, ok := bucket.objects[objectId]
 	if !ok {
 		return fmt.Errorf("Object not found")
 	}
 
+	// Delete both, object and hash
 	delete(bucket.objects, objectId)
+	delete(bucket.hashes, object.hash)
+
 	// Delete the bucket if it's empty
 	if len(bucket.objects) == 0 {
 		delete(os.buckets, bucketId)
diff --git a/objectstore/memory_backend_test.go b/objectstore/memory_backend_test.go
index 3ac347c..3fbe7a5 100644
--- a/objectstore/memory_backend_test.go
+++ b/objectstore/memory_backend_test.go
@@ -4,7 +4,10 @@
 // https://creativecommons.org/publicdomain/zero/1.0/legalcode
 package objectstore
 
-import "testing"
+import (
+	"errors"
+	"testing"
+)
 
 func TestCreateAndGet(t *testing.T) {
 	objects := NewMemBackend()
@@ -67,3 +70,49 @@ func TestCreateAndDelete(t *testing.T) {
 		t.Errorf("Number of buckets. Got %v, want 0", numBuckets)
 	}
 }
+
+func TestDuplicatesDetection(t *testing.T) {
+	objects := NewMemBackend()
+
+	// Create an object
+	bucketId := "foo"
+	objectId := "bar"
+	objectContent := "Lorem ipsum"
+	objects.CreateObject(bucketId, objectId, objectContent)
+
+	// Error type reference
+	var duplicateError *DuplicateError
+
+	// Try to add the object again (same name)
+	err := objects.CreateObject(bucketId, objectId, objectContent)
+	if err == nil {
+		t.Error("Add a duplicate object. Got nil, want error")
+	} else if errors.Is(err, duplicateError) {
+		t.Error("Add a duplicate object. Got unexpected error")
+	}
+
+	// Try to add the object again (different name)
+	err = objects.CreateObject(bucketId, "baz", objectContent)
+	if err == nil {
+		t.Error("Add a duplicate object. Got nil, want error")
+	} else if errors.Is(err, duplicateError) {
+		t.Error("Add a duplicate object. Got unexpected error")
+	}
+
+	// Add the object to a different bucket
+	err = objects.CreateObject("baz", objectId, objectContent)
+	if err != nil {
+		t.Errorf("Add object. Got error, want nil: %v", err)
+	}
+
+	// Delete the object
+	if err := objects.DeleteObject(bucketId, objectId); err != nil {
+		t.Fatalf("Delete test object: %v", err)
+	}
+
+	// Add the object again
+	err = objects.CreateObject(bucketId, objectId, objectContent)
+	if err != nil {
+		t.Errorf("Add object. Got error, want nil: %v", err)
+	}
+}
diff --git a/objectstore/objecstore.go b/objectstore/objecstore.go
index 7509fad..f4985c9 100644
--- a/objectstore/objecstore.go
+++ b/objectstore/objecstore.go
@@ -4,8 +4,26 @@
 // https://creativecommons.org/publicdomain/zero/1.0/legalcode
 package objectstore
 
+import (
+	"fmt"
+)
+
 type ObjectStore interface {
-	CreateObject(bucketId string, objectId string, content string)
+	CreateObject(bucketId string, objectId string, content string) error
 	GetObject(bucketId string, objectId string) (string, error)
 	DeleteObject(bucketId string, objectId string) error
 }
+
+type DuplicateError struct {
+	ObjectId string
+}
+
+func (e *DuplicateError) Error() string {
+	return fmt.Sprintf("Duplicate of the '%v' object", e.ObjectId)
+}
+
+func NewDuplicateError(objectId string) error {
+	return &DuplicateError{
+		ObjectId: objectId,
+	}
+}