server/config: Generic caching backend.

luci_config/server/cfgclient/backend/caching/proccache.go

Index: luci_config/server/cfgclient/backend/caching/proccache.go
diff --git a/luci_config/server/cfgclient/backend/caching/proccache.go b/luci_config/server/cfgclient/backend/caching/proccache.go
new file mode 100644
index 0000000000000000000000000000000000000000..1cd87973db8c1807c0c9b3e3802ed2729eefa8df
--- /dev/null
+++ b/luci_config/server/cfgclient/backend/caching/proccache.go
@@ -0,0 +1,56 @@
+// 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 caching
+
+import (
+	"strings"
+	"time"
+
+	"github.com/luci/luci-go/common/data/caching/proccache"
+	"github.com/luci/luci-go/luci_config/server/cfgclient/backend"
+
+	"golang.org/x/net/context"
+)
+
+// ProcCache returns a backend.B that caches configuration service results in an
+// in-memory proccache instance.
+//
+// This will only cache results for AsService calls; any other Authority will
+// pass through.
+func ProcCache(b backend.B, exp time.Duration) backend.B {
+	return &Backend{
+		B: b,
+		CacheGet: func(c context.Context, key Key, l Loader) (*Value, error) {
+			if key.Authority != backend.AsService {
+				return l(c, key, nil)
+			}
+
+			k := mkProcCacheKey(&key)
+			ret, err := proccache.GetOrMake(c, k, func() (interface{}, time.Duration, error) {
+				v, err := l(c, key, nil)
+				if err != nil {
+					return nil, 0, err
+				}
+				return v, exp, nil
+			})
+			if err != nil {
+				return nil, err
+			}
+			return ret.(*Value), nil
+		},
+	}
+}
+
+type procCacheKey string
+
+func mkProcCacheKey(key *Key) procCacheKey {
+	return procCacheKey(strings.Join([]string{
+		key.Schema,
+		string(key.Op),
+		key.ConfigSet,
+		key.Path,
+		string(key.GetAllTarget),
+	}, ":"))
+}