Make HTTP middleware easier to use

appengine/gaemiddleware/context.go

Index: appengine/gaemiddleware/context.go
diff --git a/appengine/gaemiddleware/context.go b/appengine/gaemiddleware/context.go
index 60a8bce83791c2a309cd777a9bd2c7ade7e19373..57b0d886685b9fdb264e0bf0ff8be48c866bb1df 100644
--- a/appengine/gaemiddleware/context.go
+++ b/appengine/gaemiddleware/context.go
@@ -5,13 +5,8 @@
 package gaemiddleware
 
 import (
-	"net/http"
-
 	"google.golang.org/appengine"
 
-	"github.com/julienschmidt/httprouter"
-	"golang.org/x/net/context"
-
 	"github.com/luci/gae/filter/dscache"
 	"github.com/luci/gae/impl/prod"
 	"github.com/luci/luci-go/appengine/gaeauth/client"
@@ -25,6 +20,7 @@ import (
 	"github.com/luci/luci-go/server/auth"
 	"github.com/luci/luci-go/server/middleware"
 	"github.com/luci/luci-go/server/proccache"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/settings"
 )
 
@@ -52,38 +48,35 @@ var (
 //   * github.com/luci/luci-go/appengine/gaesecrets (access to secret keys in datastore)
 //   * github.com/luci/luci-go/appengine/gaeauth/server/gaesigner (RSA signer)
 //   * github.com/luci/luci-go/appengine/gaeauth/server/auth (user groups database)
-func WithProd(c context.Context, req *http.Request) context.Context {
+func WithProd(c *router.Context, next router.Handler) {
 	// These are needed to use fetchCachedSettings.
-	c = logging.SetLevel(c, logging.Debug)
-	c = prod.Use(c, req)
-	c = settings.Use(c, globalSettings)
+	c.Context = logging.SetLevel(c.Context, logging.Debug)
+	c.Context = prod.Use(c.Context, c.Request)
+	c.Context = settings.Use(c.Context, globalSettings)
 
 	// Fetch and apply configuration stored in the datastore.
-	settings := fetchCachedSettings(c)
-	c = logging.SetLevel(c, settings.LoggingLevel)
+	settings := fetchCachedSettings(c.Context)
+	c.Context = logging.SetLevel(c.Context, settings.LoggingLevel)
 	if !settings.DisableDSCache {
-		c = dscache.AlwaysFilterRDS(c, nil)
+		c.Context = dscache.AlwaysFilterRDS(c.Context, nil)
 	}
 
 	// The rest of the service may use applied configuration.
-	c = proccache.Use(c, globalProcessCache)
-	c = client.UseAnonymousTransport(c)
-	c = gaesecrets.Use(c, nil)
-	c = gaesigner.Use(c)
-	c = auth.UseDB(c, globalAuthDBCache)
-	return cacheContext.Wrap(c)
+	c.Context = proccache.Use(c.Context, globalProcessCache)
+	c.Context = client.UseAnonymousTransport(c.Context)
+	c.Context = gaesecrets.Use(c.Context, nil)
+	c.Context = gaesigner.Use(c.Context)
+	c.Context = auth.UseDB(c.Context, globalAuthDBCache)
+	c.Context = cacheContext.Wrap(c.Context)
 }
 
-// BaseProd adapts a middleware-style handler to a httprouter.Handle.
-//
-// It installs services using WithProd, installs a panic catcher if this
-// is not a devserver, and injects the monitoring middleware.
-func BaseProd(h middleware.Handler) httprouter.Handle {
-	h = globalTsMonState.Middleware(h)
-	if !appengine.IsDevAppServer() {
-		h = middleware.WithPanicCatcher(h)
+// BaseProd returns a list of middleware: WithProd middleware, a panic catcher if this
+// is not a devserver, and the monitoring middleware.
+func BaseProd() router.MiddlewareChain {
+	if appengine.IsDevAppServer() {
+		return router.MiddlewareChain{WithProd, globalTsMonState.Middleware}
 	}
-	return func(rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
-		h(WithProd(context.Background(), r), rw, r, p)
+	return router.MiddlewareChain{
+		WithProd, middleware.WithPanicCatcher, globalTsMonState.Middleware,
 	}
 }