Add 'user friendly' datastore API.

service/datastore/context.go

Index: service/datastore/context.go
diff --git a/service/datastore/context.go b/service/datastore/context.go
new file mode 100644
index 0000000000000000000000000000000000000000..c81f3c98fb143839c6e82603ea10b5cf52d37cc8
--- /dev/null
+++ b/service/datastore/context.go
@@ -0,0 +1,84 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package datastore
+
+import (
+	"golang.org/x/net/context"
+)
+
+type key int
+
+var (
+	rawDatastoreKey       key
+	rawDatastoreFilterKey key = 1
+)
+
+// RawFactory is the function signature for factory methods compatible with
+// SetRawFactory.
+type RawFactory func(context.Context) RawInterface
+
+// RawFilter is the function signature for a filter RDS implementation. It
+// gets the current RDS implementation, and returns a new RDS implementation
+// backed by the one passed in.
+type RawFilter func(context.Context, RawInterface) RawInterface
+
+// getUnfiltered gets gets the RawInterface implementation from context without
+// any of the filters applied.
+func getUnfiltered(c context.Context) RawInterface {
+	if f, ok := c.Value(rawDatastoreKey).(RawFactory); ok && f != nil {
+		return f(c)
+	}
+	return nil
+}
+
+// GetRaw gets the RawInterface implementation from context.
+func GetRaw(c context.Context) RawInterface {
+	ret := getUnfiltered(c)
+	if ret == nil {
+		return nil
+	}
+	for _, f := range getCurFilters(c) {
+		ret = f(c, ret)
+	}
+	return applyCheckFilter(c, ret)
+}
+
+// Get gets the Interface implementation from context.
+func Get(c context.Context) Interface {
+	return &datastoreImpl{GetRaw(c)}
+}
+
+// SetRawFactory sets the function to produce Datastore instances, as returned by
+// the GetRaw method.
+func SetRawFactory(c context.Context, rdsf RawFactory) context.Context {
+	return context.WithValue(c, rawDatastoreKey, rdsf)
+}
+
+// SetRaw sets the current Datastore object in the context. Useful for testing with
+// a quick mock. This is just a shorthand SetRawFactory invocation to set a factory
+// which always returns the same object.
+func SetRaw(c context.Context, rds RawInterface) context.Context {
+	return SetRawFactory(c, func(context.Context) RawInterface { return rds })
+}
+
+func getCurFilters(c context.Context) []RawFilter {
+	curFiltsI := c.Value(rawDatastoreFilterKey)
+	if curFiltsI != nil {
+		return curFiltsI.([]RawFilter)
+	}
+	return nil
+}
+
+// AddRawFilters adds RawInterface filters to the context.
+func AddRawFilters(c context.Context, filts ...RawFilter) context.Context {
+	if len(filts) == 0 {
+		return c
+	}
+	cur := getCurFilters(c)
+	newFilts := make([]RawFilter, 0, len(cur)+len(filts))
+	newFilts = append(newFilts, getCurFilters(c)...)
+	newFilts = append(newFilts, filts...)
+	return context.WithValue(c, rawDatastoreFilterKey, newFilts)
+}