Implement a server-side config service interface.

luci_config/server/cfgclient/format.go

+// Copyright 2016 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 cfgclient
+
+import (
+        "fmt"
+        "sync"
+)
+
+// Formatter applies a transformation to the data's cached representation.
+//
+// The Formatter is supplied with the content to format along with the
+// formatter-specific metadata, fd.
+//
+// Formatter operates on a backend.Item's Content via the "format" Backend.
+type Formatter interface {
+        FormatItem(c, fd string) (string, error)
+}
+
+// FormatterRegistry is a registry of Resolver key mapped to the Formatter to
+// use to format that key.
+type FormatterRegistry struct {
+        registryMu sync.RWMutex
+        registry   map[string]Formatter
+}
+
+// Register registers a Formatter with the FormatBackend.
+//
+// If the supplied key is already registered, Register will panic.
+func (r *FormatterRegistry) Register(rk string, f Formatter) {
+        if rk == "" {
+                panic("cannot register empty key")
+        }
+
+        r.registryMu.Lock()
+        defer r.registryMu.Unlock()
+
+        if _, ok := r.registry[rk]; ok {
+                panic(fmt.Errorf("key %q is already registered", rk))
+        }
+        if r.registry == nil {
+                r.registry = map[string]Formatter{}
+        }
+        r.registry[rk] = f
+}
+
+// Get returns the Formatter associated with the provided Format.
+func (r *FormatterRegistry) Get(f string) Formatter {
+        r.registryMu.RLock()
+        defer r.registryMu.RUnlock()
+        return r.registry[f]
+}