Make HTTP middleware easier to use

appengine/cmd/cron/ui/invocation.go

Index: appengine/cmd/cron/ui/invocation.go
diff --git a/appengine/cmd/cron/ui/invocation.go b/appengine/cmd/cron/ui/invocation.go
index ff9fe101df40ec2018f08d05325014f74bc406e5..076f1336b441b9b61e4c64a561c6a380485f3233 100644
--- a/appengine/cmd/cron/ui/invocation.go
+++ b/appengine/cmd/cron/ui/invocation.go
@@ -14,29 +14,32 @@ import (
 
 	"github.com/luci/luci-go/common/clock"
 	"github.com/luci/luci-go/server/auth"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/templates"
 )
 
-func invocationPage(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params) {
-	projectID := p.ByName("ProjectID")
-	jobID := p.ByName("JobID")
-	invID, err := strconv.ParseInt(p.ByName("InvID"), 10, 64)
+func invocationPage(c *router.Context) {
+	projectID := c.Params.ByName("ProjectID")
+	jobID := c.Params.ByName("JobID")
+	invID, err := strconv.ParseInt(c.Params.ByName("InvID"), 10, 64)
 	if err != nil {
-		http.Error(w, "No such invocation", http.StatusNotFound)
+		http.Error(c.Writer, "No such invocation", http.StatusNotFound)
+		c.Abort()

[iannucci, 2016/06/13 19:23:28]

probably-unpopular-idea: instead of adding a new method to indicate that the
chain is aborted, why not have the Context's ResponseWriter be a tiny wrapper
that looks for calls to WriteHeader? That way this sort of code wouldn't need to
change, and all existing mechanisms for terminating the http request (e.g.
writing an status code) continue do the right thing?

That would also let us capture the actually-sent status code for e.g.
monitoring.

 		return
 	}
 
-	inv, err := config(c).Engine.GetInvocation(c, projectID+"/"+jobID, invID)
+	inv, err := config(c.Context).Engine.GetInvocation(c.Context, projectID+"/"+jobID, invID)
 	if err != nil {
 		panic(err)
 	}
 	if inv == nil {
-		http.Error(w, "No such invocation", http.StatusNotFound)
+		http.Error(c.Writer, "No such invocation", http.StatusNotFound)
+		c.Abort()
 		return
 	}
 
-	now := clock.Now(c).UTC()
-	templates.MustRender(c, w, "pages/invocation.html", map[string]interface{}{
+	now := clock.Now(c.Context).UTC()
+	templates.MustRender(c.Context, c.Writer, "pages/invocation.html", map[string]interface{}{
 		"ProjectID": projectID,
 		"JobID":     jobID,
 		"Inv":       makeInvocation(projectID, jobID, inv, now),
@@ -46,10 +49,10 @@ func invocationPage(c context.Context, w http.ResponseWriter, r *http.Request, p
 ////////////////////////////////////////////////////////////////////////////////
 // Actions.
 
-func abortInvocationAction(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params) {
-	handleInvAction(c, w, r, p, func(jobID string, invID int64) error {
-		who := auth.CurrentIdentity(c)
-		return config(c).Engine.AbortInvocation(c, jobID, invID, who)
+func abortInvocationAction(c *router.Context) {
+	handleInvAction(c.Context, c.Writer, c.Request, c.Params, func(jobID string, invID int64) error {
+		who := auth.CurrentIdentity(c.Context)
+		return config(c.Context).Engine.AbortInvocation(c.Context, jobID, invID, who)
 	})
 }