Make HTTP middleware easier to use

common/testing/prpctest/server.go

Index: common/testing/prpctest/server.go
diff --git a/common/testing/prpctest/server.go b/common/testing/prpctest/server.go
index 670482440596f82ba99e157f6af35790aee079a5..298f5f3459bb80ff30504dc1ad1e98dab6c4c79d 100644
--- a/common/testing/prpctest/server.go
+++ b/common/testing/prpctest/server.go
@@ -5,55 +5,63 @@
 // Package prpctest is a package to facilitate pRPC testing by wrapping
 // httptest with a pRPC Server.
 package prpctest
 
 import (
 	"errors"
 	"fmt"
 	"net/http/httptest"
 	"net/url"
 
-	"github.com/julienschmidt/httprouter"
 	prpcCommon "github.com/luci/luci-go/common/prpc"
 	"github.com/luci/luci-go/server/auth"
-	"github.com/luci/luci-go/server/middleware"
 	"github.com/luci/luci-go/server/prpc"
+	"github.com/luci/luci-go/server/router"
 	"golang.org/x/net/context"
 )
 
 // Server is a pRPC test server.
 type Server struct {
 	prpc.Server
 
-	// Base is the base middleware generator factory. It is handed the Context
-	// passed to Start. If nil, middleware.TestingBase will be used.
-	Base func(context.Context) middleware.Base
+	// Base returns a middleware chain. It is handed the Context passed to
+	// Start. If Base is nil, setContext will be used.
+	Base func(context.Context) router.MiddlewareChain
 
 	// HTTP is the active HTTP test server. It will be valid when the Server is
 	// running.
 	HTTP *httptest.Server
 }
 
+func setContext(c context.Context) router.MiddlewareChain {
+	return router.MiddlewareChain{
+		func(ctx *router.Context, next router.Handler) {
+			ctx.Context = c
+			next(ctx)
+		},
+	}
+}
+
 // Start starts the server. Any currently-registered services will be installed
 // into the pRPC Server.
 func (s *Server) Start(c context.Context) {
 	// Clean up any active server.
 	s.Close()
 
 	s.Authenticator = auth.Authenticator{}
-	mwb := s.Base
-	if mwb == nil {
-		mwb = middleware.TestingBase
+	base := s.Base
+	if base == nil {
+		base = setContext
 	}
 
-	r := httprouter.New()
-	s.InstallHandlers(r, mwb(c))
+	r := router.New()
+	s.InstallHandlers(r, base(c))
 	s.HTTP = httptest.NewServer(r)
 }
 
 // NewClient returns a prpc.Client configured to use the Server.
 func (s *Server) NewClient() (*prpcCommon.Client, error) {
 	if s.HTTP == nil {
 		return nil, errors.New("not running")
 	}
 
 	u, err := url.Parse(s.HTTP.URL)