Update common/route vendoring for contextFn errors

vendor/github.com/prometheus/common/route/route.go

@@ -1,6 +1,7 @@
 package route
 
 import (
+	"fmt"
 	"net/http"
 	"sync"
 
@@ -32,7 +33,7 @@ func WithParam(ctx context.Context, p, v string) context.Context {
 	return context.WithValue(ctx, param(p), v)
 }
 
-type contextFn func(r *http.Request) context.Context
+type contextFn func(r *http.Request) (context.Context, error)
 
 // Router wraps httprouter.Router and adds support for prefixed sub-routers
 // and per-request context injections.
@@ -45,8 +46,8 @@ type Router struct {
 // New returns a new Router.
 func New(ctxFn contextFn) *Router {
 	if ctxFn == nil {
-		ctxFn = func(r *http.Request) context.Context {
-			return context.Background()
+		ctxFn = func(r *http.Request) (context.Context, error) {
+			return context.Background(), nil
 		}
 	}
 	return &Router{
@@ -63,7 +64,12 @@ func (r *Router) WithPrefix(prefix string) *Router {
 // handle turns a HandlerFunc into an httprouter.Handle.
 func (r *Router) handle(h http.HandlerFunc) httprouter.Handle {
 	return func(w http.ResponseWriter, req *http.Request, params httprouter.Params) {
-		ctx, cancel := context.WithCancel(r.ctxFn(req))
+		reqCtx, err := r.ctxFn(req)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("Error creating request context: %v", err), http.StatusBadRequest)
+			return
+		}
+		ctx, cancel := context.WithCancel(reqCtx)
 		defer cancel()
 
 		for _, p := range params {

vendor/vendor.json

@@ -211,8 +211,8 @@
 		{
 			"checksumSHA1": "CKVJRc1NREmfoAWQLHxqWQlvxo0=",
 			"path": "github.com/prometheus/common/route",
-			"revision": "ee21c31a8cbad2a29cce94a8c53855e1dab92bf7",
-			"revisionTime": "2016-09-21T02:27:24+02:00"
+			"revision": "a85e6c850a142b95b63f9dd0ffd9645e5e437da7",
+			"revisionTime": "2016-10-02T22:56:21+02:00"
 		},
 		{
 			"checksumSHA1": "91KYK0SpvkaMJJA2+BcxbVnyRO0=",

web/web.go

@@ -120,8 +120,8 @@ type Options struct {
 
 // New initializes a new web Handler.
 func New(o *Options) *Handler {
-	router := route.New(func(r *http.Request) context.Context {
-		return o.Context
+	router := route.New(func(r *http.Request) (context.Context, error) {
+		return o.Context, nil
 	})
 
 	h := &Handler{