Add pushover notifications, this should be a super basic MVP

vendor/github.com/dgraph-io/badger/dir_unix.go

@@ -0,0 +1,118 @@
+// +build !windows,!plan9
+
+/*
+ * Copyright 2017 Dgraph Labs, Inc. and Contributors
+ *
+ * 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 badger
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/dgraph-io/badger/y"
+	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
+)
+
+// directoryLockGuard holds a lock on a directory and a pid file inside.  The pid file isn't part
+// of the locking mechanism, it's just advisory.
+type directoryLockGuard struct {
+	// File handle on the directory, which we've flocked.
+	f *os.File
+	// The absolute path to our pid file.
+	path string
+	// Was this a shared lock for a read-only database?
+	readOnly bool
+}
+
+// acquireDirectoryLock gets a lock on the directory (using flock). If
+// this is not read-only, it will also write our pid to
+// dirPath/pidFileName for convenience.
+func acquireDirectoryLock(dirPath string, pidFileName string, readOnly bool) (
+	*directoryLockGuard, error) {
+	// Convert to absolute path so that Release still works even if we do an unbalanced
+	// chdir in the meantime.
+	absPidFilePath, err := filepath.Abs(filepath.Join(dirPath, pidFileName))
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot get absolute path for pid lock file")
+	}
+	f, err := os.Open(dirPath)
+	if err != nil {
+		return nil, errors.Wrapf(err, "cannot open directory %q", dirPath)
+	}
+	opts := unix.LOCK_EX | unix.LOCK_NB
+	if readOnly {
+		opts = unix.LOCK_SH | unix.LOCK_NB
+	}
+
+	err = unix.Flock(int(f.Fd()), opts)
+	if err != nil {
+		f.Close()
+		return nil, errors.Wrapf(err,
+			"Cannot acquire directory lock on %q.  Another process is using this Badger database.",
+			dirPath)
+	}
+
+	if !readOnly {
+		// Yes, we happily overwrite a pre-existing pid file.  We're the
+		// only read-write badger process using this directory.
+		err = ioutil.WriteFile(absPidFilePath, []byte(fmt.Sprintf("%d\n", os.Getpid())), 0666)
+		if err != nil {
+			f.Close()
+			return nil, errors.Wrapf(err,
+				"Cannot write pid file %q", absPidFilePath)
+		}
+	}
+	return &directoryLockGuard{f, absPidFilePath, readOnly}, nil
+}
+
+// Release deletes the pid file and releases our lock on the directory.
+func (guard *directoryLockGuard) release() error {
+	var err error
+	if !guard.readOnly {
+		// It's important that we remove the pid file first.
+		err = os.Remove(guard.path)
+	}
+
+	if closeErr := guard.f.Close(); err == nil {
+		err = closeErr
+	}
+	guard.path = ""
+	guard.f = nil
+
+	return err
+}
+
+// openDir opens a directory for syncing.
+func openDir(path string) (*os.File, error) { return os.Open(path) }
+
+// When you create or delete a file, you have to ensure the directory entry for the file is synced
+// in order to guarantee the file is visible (if the system crashes). (See the man page for fsync,
+// or see https://github.com/coreos/etcd/issues/6368 for an example.)
+func syncDir(dir string) error {
+	f, err := openDir(dir)
+	if err != nil {
+		return errors.Wrapf(err, "While opening directory: %s.", dir)
+	}
+	err = y.FileSync(f)
+	closeErr := f.Close()
+	if err != nil {
+		return errors.Wrapf(err, "While syncing directory: %s.", dir)
+	}
+	return errors.Wrapf(closeErr, "While closing directory: %s.", dir)
+}