[WIP] fswatch: add cross-platform filesystem watcher

fswatch/doc.go

@@ -0,0 +1,21 @@
+/*
+Copyright The Kubernetes Authors.
+
+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 fswatch is a small cross-platform filesystem watcher used by
+// Kubernetes to remove direct fsnotify dependencies from the Linux
+// build closure. The Linux implementation uses raw inotify; non-Linux
+// platforms wrap fsnotify.
+package fswatch

fswatch/fswatch.go

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+/*
+Copyright The Kubernetes Authors.
+
+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 fswatch
+
+import (
+	"errors"
+)
+
+// Sentinel errors.
+var (
+	ErrClosed           = errors.New("fswatch: watcher is closed")
+	ErrNonExistentWatch = errors.New("fswatch: path is not being watched")
+	// ErrEventOverflow is delivered on the errors channel when the
+	// kernel queue overflowed and events were dropped.
+	ErrEventOverflow = errors.New("fswatch: event queue overflow")
+)
+
+// Op is the cross-platform event class. Bits match fsnotify v1's
+// default set so direct callers can migrate by import-path swap.
+type Op uint32
+
+const (
+	Create Op = 1 << iota
+	Write
+	Remove
+	Rename
+	Chmod
+)
+
+// String returns a pipe-separated list of bits set in op.
+func (op Op) String() string {
+	if op == 0 {
+		return ""
+	}
+	var s string
+	add := func(name string) {
+		if s != "" {
+			s += "|"
+		}
+		s += name
+	}
+	if op&Create != 0 {
+		add("Create")
+	}
+	if op&Write != 0 {
+		add("Write")
+	}
+	if op&Remove != 0 {
+		add("Remove")
+	}
+	if op&Rename != 0 {
+		add("Rename")
+	}
+	if op&Chmod != 0 {
+		add("Chmod")
+	}
+	return s
+}
+
+// Event is a filesystem event.
+type Event struct {
+	Name string
+	Op   Op
+}
+
+// Has reports whether op is set in e.Op.
+func (e Event) Has(op Op) bool { return e.Op&op != 0 }
+
+// Watcher delivers filesystem events. Add, Remove, and Close are safe
+// to call from any goroutine; Close is idempotent. Reading Events and
+// Errors is the caller's responsibility.
+type Watcher struct {
+	impl watcherImpl
+}
+
+// watcherImpl is the platform-specific backing for Watcher.
+type watcherImpl interface {
+	Add(path string) error
+	Remove(path string) error
+	Events() <-chan Event
+	Errors() <-chan error
+	Close() error
+}
+
+// NewWatcher constructs a Watcher.
+func NewWatcher() (*Watcher, error) {
+	impl, err := newWatcherImpl()
+	if err != nil {
+		return nil, err
+	}
+	return &Watcher{impl: impl}, nil
+}
+
+// Add starts watching path. Returns ErrClosed if the watcher has been
+// closed.
+func (w *Watcher) Add(path string) error { return w.impl.Add(path) }
+
+// Remove stops watching path.
+func (w *Watcher) Remove(path string) error { return w.impl.Remove(path) }
+
+// Events returns the channel of filesystem events. Closed after Close.
+func (w *Watcher) Events() <-chan Event { return w.impl.Events() }
+
+// Errors returns the channel of backend errors. Closed after Close.
+func (w *Watcher) Errors() <-chan error { return w.impl.Errors() }
+
+// Close stops the watcher. In-flight events are dropped. Subsequent
+// Add and Remove return ErrClosed. Close is idempotent.
+func (w *Watcher) Close() error { return w.impl.Close() }