Merge pull request #51 from versity/posix-windows

Posix windows

backend/posix/posix_windows.go

@@ -0,0 +1,89 @@
+// Copyright 2023 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package posix
+
+import (
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+)
+
+type tmpfile struct {
+	f       *os.File
+	bucket  string
+	objname string
+	size    int64
+}
+
+func openTmpFile(dir, bucket, obj string, size int64) (*tmpfile, error) {
+	// Create a temp file for upload while in progress (see link comments below).
+	err := os.MkdirAll(dir, 0700)
+	if err != nil {
+		return nil, fmt.Errorf("make temp dir: %w", err)
+	}
+	f, err := os.CreateTemp(dir,
+		fmt.Sprintf("%x.", sha256.Sum256([]byte(obj))))
+	if err != nil {
+		return nil, err
+	}
+	return &tmpfile{f: f, bucket: bucket, objname: obj, size: size}, nil
+}
+
+func (tmp *tmpfile) link() error {
+	tempname := tmp.f.Name()
+	// cleanup in case anything goes wrong, if rename succeeds then
+	// this will no longer exist
+	defer os.Remove(tempname)
+
+	// We use Rename as the atomic operation for object puts. The upload is
+	// written to a temp file to not conflict with any other simultaneous
+	// uploads. The final operation is to move the temp file into place for
+	// the object. This ensures the object semantics of last upload completed
+	// wins and is not some combination of writes from simultaneous uploads.
+	objPath := filepath.Join(tmp.bucket, tmp.objname)
+	err := os.Remove(objPath)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return fmt.Errorf("remove stale path: %w", err)
+	}
+
+	err = tmp.f.Close()
+	if err != nil {
+		return fmt.Errorf("close tmpfile: %w", err)
+	}
+
+	err = os.Rename(tempname, objPath)
+	if err != nil {
+		return fmt.Errorf("rename tmpfile: %w", err)
+	}
+
+	return nil
+}
+
+func (tmp *tmpfile) Write(b []byte) (int, error) {
+	if int64(len(b)) > tmp.size {
+		return 0, fmt.Errorf("write exceeds content length")
+	}
+
+	n, err := tmp.f.Write(b)
+	tmp.size -= int64(n)
+	return n, err
+}
+
+func (tmp *tmpfile) cleanup() {
+	tmp.f.Close()
+}