Add filters for RawDatastore

go/src/infra/gae/libs/gae/globalinfo.go

Index: go/src/infra/gae/libs/gae/globalinfo.go
diff --git a/go/src/infra/gae/libs/gae/globalinfo.go b/go/src/infra/gae/libs/gae/globalinfo.go
index afeaac492baf92da423b775dde503ad97dde7691..e3ed5199e472e7ba40413e444f2af8509e7db3d4 100644
--- a/go/src/infra/gae/libs/gae/globalinfo.go
+++ b/go/src/infra/gae/libs/gae/globalinfo.go
@@ -38,14 +38,32 @@ type GlobalInfo interface {
 // SetGIFactory.
 type GIFactory func(context.Context) GlobalInfo
 
-// GetGI gets gets the GlobalInfo implementation from context.
-func GetGI(c context.Context) GlobalInfo {
+// GIFilter is the function signature for a filter GI implementation. It
+// gets the current GI implementation, and returns a new GI implementation
+// backed by the one passed in.
+type GIFilter func(context.Context, GlobalInfo) GlobalInfo
+
+// GetGIUnfiltered gets gets the GlobalInfo implementation from context without
+// any of the filters applied.
+func GetGIUnfiltered(c context.Context) GlobalInfo {
 	if f, ok := c.Value(globalInfoKey).(GIFactory); ok && f != nil {
 		return f(c)
 	}
 	return nil
 }
 
+// GetGI gets gets the GlobalInfo implementation from context.
+func GetGI(c context.Context) GlobalInfo {
+	ret := GetGIUnfiltered(c)
+	if ret == nil {
+		return nil
+	}
+	for _, f := range getCurGIFilters(c) {
+		ret = f(c, ret)
+	}
+	return ret

[Vadim Sh., 2015/07/16 23:39:51]

it would have been nice to cache it somehow

[iannucci, 2015/07/16 23:46:19]

yeah, though I think that would make things more complex (and I don't expect
this method to be anything close to a hot spot in the code). We can definitely
add that later if it's an issue.

Really, the big win here would be simplifying the way that transactions work to
make them part of the gae package (interfaces) instead of part of the
implementation... I'm not sure if that's possible.

+}
+
 // SetGIFactory sets the function to produce GlobalInfo instances, as returned
 // by the GetGI method.
 func SetGIFactory(c context.Context, gif GIFactory) context.Context {
@@ -58,3 +76,23 @@ func SetGIFactory(c context.Context, gif GIFactory) context.Context {
 func SetGI(c context.Context, gi GlobalInfo) context.Context {
 	return SetGIFactory(c, func(context.Context) GlobalInfo { return gi })
 }
+
+func getCurGIFilters(c context.Context) []GIFilter {
+	curFiltsI := c.Value(globalInfoFilterKey)
+	if curFiltsI != nil {
+		return curFiltsI.([]GIFilter)
+	}
+	return nil
+}
+
+// AddGIFilters adds GlobalInfo filters to the context.
+func AddGIFilters(c context.Context, filts ...GIFilter) context.Context {
+	if len(filts) == 0 {
+		return c
+	}
+	cur := getCurGIFilters(c)
+	newFilts := make([]GIFilter, 0, len(cur)+len(filts))
+	newFilts = append(newFilts, getCurGIFilters(c)...)
+	newFilts = append(newFilts, filts...)
+	return context.WithValue(c, globalInfoFilterKey, newFilts)
+}