Make HTTP middleware easier to use

appengine/cmd/cron/ui/invocation.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package ui
 
 import (
         "fmt"
         "net/http"
         "strconv"
 
         "github.com/julienschmidt/httprouter"
         "golang.org/x/net/context"
 
         "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),
         })
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // 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)
         })
 }
 
 func handleInvAction(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params, cb func(string, int64) error) {
         projectID := p.ByName("ProjectID")
         jobID := p.ByName("JobID")
         invID := p.ByName("InvID")
         if !isJobOwner(c, projectID, jobID) {
                 http.Error(w, "Forbidden", 403)
                 return
         }
         invIDAsInt, err := strconv.ParseInt(invID, 10, 64)
         if err != nil {
                 http.Error(w, "Bad invocation ID", 400)
                 return
         }
         if err := cb(projectID+"/"+jobID, invIDAsInt); err != nil {
                 panic(err)
         }
         http.Redirect(w, r, fmt.Sprintf("/jobs/%s/%s/%s", projectID, jobID, invID), http.StatusFound)
 }