Make HTTP middleware easier to use

server/middleware/paniccatcher.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 middleware
 
 import (
         "net/http"
 
-        "github.com/julienschmidt/httprouter"
-        "golang.org/x/net/context"
-
         log "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/common/paniccatcher"
+        "github.com/luci/luci-go/server/router"
 )
 
 // WithPanicCatcher is a middleware that catches panics, dumps stack trace to
 // logging and returns HTTP 500.
-func WithPanicCatcher(h Handler) Handler {
-        return func(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params) {
-                defer paniccatcher.Catch(func(p *paniccatcher.Panic) {
-                        log.Fields{
-                                "panic.error": p.Reason,
-                        }.Errorf(c, "Caught panic during handling of %q:\n%s", r.RequestURI, p.Stack)
+func WithPanicCatcher(c *router.Context, next router.Handler) {
+        defer paniccatcher.Catch(func(p *paniccatcher.Panic) {
+                log.Fields{
+                        "panic.error": p.Reason,
+                }.Errorf(c.Context, "Caught panic during handling of %q:\n%s", c.Request.RequestURI, p.Stack)

[Vadim Sh., 2016/06/18 16:57:20]

same as in tsmon middleware: better to preserve the current state before calling
next(), since c is mutable now.

ctx := *c
defer .... {
  // use ctx, not c
}
next(c)

[nishanths, 2016/06/19 02:47:02]

Done. Now matches behavior at origin/master.

 
-                        // Note: it may be too late to send HTTP 500 if `h` already sent
-                        // headers. But there's nothing else we can do at this point anyway.
-                        http.Error(w, "Internal Server Error. See logs.", http.StatusInternalServerError)
-                })
-                h(c, w, r, p)
-        }
+                // Note: it may be too late to send HTTP 500 if `h` already sent
+                // headers. But there's nothing else we can do at this point anyway.
+                http.Error(c.Writer, "Internal Server Error. See logs.", http.StatusInternalServerError)
+        })
+        next(c)
 }