LogDog: Use luci_config/server packages for config

logdog/server/service/config/opts.go

Index: logdog/server/service/config/opts.go
diff --git a/logdog/server/service/config/opts.go b/logdog/server/service/config/opts.go
new file mode 100644
index 0000000000000000000000000000000000000000..d26518b02a089326698795498fb683e1da2b8184
--- /dev/null
+++ b/logdog/server/service/config/opts.go
@@ -0,0 +1,39 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package config
+
+import (
+	"time"
+
+	"github.com/luci/luci-go/luci_config/server/cfgclient/backend"
+	"github.com/luci/luci-go/luci_config/server/cfgclient/backend/caching"
+
+	"golang.org/x/net/context"
+)
+
+// CacheOptions is the set of configuration options.
+type CacheOptions struct {
+	// CacheExpiration is the amount of time that a config entry should be cached.
+	//
+	// If this value is <= 0, no configuration caching will be enabled. This
+	// should not be set for production systems.
+	CacheExpiration time.Duration
+}
+
+// WrapBackend wraps the supplied base backend in caching layers and returns a
+// Conext with the resulting backend installed.
+func (o *CacheOptions) WrapBackend(c context.Context, base backend.B) context.Context {
+	return backend.WithFactory(c, func(c context.Context) backend.B {
+		// Start with our base Backend.
+		be := base
+
+		// Add a proccache-based config cache.
+		if o.CacheExpiration > 0 {
+			be = caching.ProcCache(be, o.CacheExpiration)
+		}
+
+		return be
+	})
+}