4 files changed, 149 insertions, 0 deletions
diff --git a/internal/lfsutil/oid.go b/internal/lfsutil/oid.go
new file mode 100644
index 00000000..899c7332
--- /dev/null
+++ b/internal/lfsutil/oid.go
@@ -0,0 +1,30 @@
+// Copyright 2020 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package lfsutil
+
+import (
+	"strings"
+)
+
+// OID is an LFS object ID.
+type OID string
+
+// ValidOID returns true if given oid is valid according to spec:
+// https://github.com/git-lfs/git-lfs/blob/master/docs/spec.md
+func ValidOID(oid OID) bool {
+	fields := strings.SplitN(string(oid), ":", 2)
+	if len(fields) != 2 {
+		return false
+	}
+	method := fields[0]
+	hash := fields[1]
+
+	switch method {
+	case "sha256":
+		// SHA256 produces 64-char lower case hexadecimal hash
+		return len(hash) == 64 && strings.ToLower(hash) == hash
+	}
+	return false
+}
diff --git a/internal/lfsutil/oid_test.go b/internal/lfsutil/oid_test.go
new file mode 100644
index 00000000..1e3b020a
--- /dev/null
+++ b/internal/lfsutil/oid_test.go
@@ -0,0 +1,47 @@
+// Copyright 2020 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package lfsutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestValidOID(t *testing.T) {
+	tests := []struct {
+		name   string
+		oid    OID
+		expVal bool
+	}{
+		{
+			name: "malformed",
+			oid:  OID("12345678"),
+		},
+		{
+			name: "unknown method",
+			oid:  OID("sha1:7c222fb2927d828af22f592134e8932480637c0d"),
+		},
+
+		{
+			name: "sha256: malformed",
+			oid:  OID("sha256:7c222fb2927d828af22f592134e8932480637c0d"),
+		},
+		{
+			name: "sha256: not all lower cased",
+			oid:  OID("sha256:EF797c8118f02dfb649607dd5d3f8c7623048c9c063d532cc95c5ed7a898a64f"),
+		},
+		{
+			name:   "sha256: valid",
+			oid:    OID("sha256:ef797c8118f02dfb649607dd5d3f8c7623048c9c063d532cc95c5ed7a898a64f"),
+			expVal: true,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			assert.Equal(t, test.expVal, ValidOID(test.oid))
+		})
+	}
+}
diff --git a/internal/lfsutil/storage.go b/internal/lfsutil/storage.go
new file mode 100644
index 00000000..fa10ee03
--- /dev/null
+++ b/internal/lfsutil/storage.go
@@ -0,0 +1,29 @@
+// Copyright 2020 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package lfsutil
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// Storage is the storage type of an LFS object.
+type Storage string
+
+const (
+	StorageLocal Storage = "local"
+)
+
+// StorageLocalPath returns computed file path for storing object on local file system.
+// It returns empty string if given "oid" isn't valid.
+func StorageLocalPath(root string, oid OID) string {
+	if !ValidOID(oid) {
+		return ""
+	}
+
+	// Valid OID is guaranteed to have second element as hash.
+	hash := strings.SplitN(string(oid), ":", 2)[1]
+	return filepath.Join(root, string(hash[0]), string(hash[1]), hash)
+}
diff --git a/internal/lfsutil/storage_test.go b/internal/lfsutil/storage_test.go
new file mode 100644
index 00000000..4f64b92b
--- /dev/null
+++ b/internal/lfsutil/storage_test.go
@@ -0,0 +1,43 @@
+// Copyright 2020 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package lfsutil
+
+import (
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestStorageLocalPath(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Skipping testing on Windows")
+		return
+	}
+
+	tests := []struct {
+		name    string
+		root    string
+		oid     OID
+		expPath string
+	}{
+		{
+			name: "invalid oid",
+			oid:  OID("bad_oid"),
+		},
+
+		{
+			name:    "valid oid",
+			root:    "/lfs-objects",
+			oid:     OID("sha256:ef797c8118f02dfb649607dd5d3f8c7623048c9c063d532cc95c5ed7a898a64f"),
+			expPath: "/lfs-objects/e/f/ef797c8118f02dfb649607dd5d3f8c7623048c9c063d532cc95c5ed7a898a64f",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			assert.Equal(t, test.expPath, StorageLocalPath(test.root, test.oid))
+		})
+	}
+}