vendor: update buildkit with typed errors support

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/gorilla/mux/README.md

@@ -1,10 +1,10 @@
 # gorilla/mux
 
 [![GoDoc](https://godoc.org/github.com/gorilla/mux?status.svg)](https://godoc.org/github.com/gorilla/mux)
-[![Build Status](https://travis-ci.org/gorilla/mux.svg?branch=master)](https://travis-ci.org/gorilla/mux)
+[![CircleCI](https://circleci.com/gh/gorilla/mux.svg?style=svg)](https://circleci.com/gh/gorilla/mux)
 [![Sourcegraph](https://sourcegraph.com/github.com/gorilla/mux/-/badge.svg)](https://sourcegraph.com/github.com/gorilla/mux?badge)
 
-![Gorilla Logo](http://www.gorillatoolkit.org/static/images/gorilla-icon-64.png)
+![Gorilla Logo](https://cloud-cdn.questionable.services/gorilla-icon-64.png)
 
 https://www.gorillatoolkit.org/pkg/mux
 
@@ -25,10 +25,12 @@ The name mux stands for "HTTP request multiplexer". Like the standard `http.Serv
 * [Examples](#examples)
 * [Matching Routes](#matching-routes)
 * [Static Files](#static-files)
+* [Serving Single Page Applications](#serving-single-page-applications) (e.g. React, Vue, Ember.js, etc.)
 * [Registered URLs](#registered-urls)
 * [Walking Routes](#walking-routes)
 * [Graceful Shutdown](#graceful-shutdown)
 * [Middleware](#middleware)
+* [Handling CORS Requests](#handling-cors-requests)
 * [Testing Handlers](#testing-handlers)
 * [Full Example](#full-example)
 
@@ -210,6 +212,93 @@ func main() {
 }
 ```
 
+### Serving Single Page Applications
+
+Most of the time it makes sense to serve your SPA on a separate web server from your API,
+but sometimes it's desirable to serve them both from one place. It's possible to write a simple
+handler for serving your SPA (for use with React Router's [BrowserRouter](https://reacttraining.com/react-router/web/api/BrowserRouter) for example), and leverage
+mux's powerful routing for your API endpoints.
+
+```go
+package main
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/gorilla/mux"
+)
+
+// spaHandler implements the http.Handler interface, so we can use it
+// to respond to HTTP requests. The path to the static directory and
+// path to the index file within that static directory are used to
+// serve the SPA in the given static directory.
+type spaHandler struct {
+	staticPath string
+	indexPath  string
+}
+
+// ServeHTTP inspects the URL path to locate a file within the static dir
+// on the SPA handler. If a file is found, it will be served. If not, the
+// file located at the index path on the SPA handler will be served. This
+// is suitable behavior for serving an SPA (single page application).
+func (h spaHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+    // get the absolute path to prevent directory traversal
+	path, err := filepath.Abs(r.URL.Path)
+	if err != nil {
+        // if we failed to get the absolute path respond with a 400 bad request
+        // and stop
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+    // prepend the path with the path to the static directory
+	path = filepath.Join(h.staticPath, path)
+
+    // check whether a file exists at the given path
+	_, err = os.Stat(path)
+	if os.IsNotExist(err) {
+		// file does not exist, serve index.html
+		http.ServeFile(w, r, filepath.Join(h.staticPath, h.indexPath))
+		return
+	} else if err != nil {
+        // if we got an error (that wasn't that the file doesn't exist) stating the
+        // file, return a 500 internal server error and stop
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+    // otherwise, use http.FileServer to serve the static dir
+	http.FileServer(http.Dir(h.staticPath)).ServeHTTP(w, r)
+}
+
+func main() {
+	router := mux.NewRouter()
+
+	router.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
+		// an example API handler
+		json.NewEncoder(w).Encode(map[string]bool{"ok": true})
+	})
+
+	spa := spaHandler{staticPath: "build", indexPath: "index.html"}
+	router.PathPrefix("/").Handler(spa)
+
+	srv := &http.Server{
+		Handler: router,
+		Addr:    "127.0.0.1:8000",
+		// Good practice: enforce timeouts for servers you create!
+		WriteTimeout: 15 * time.Second,
+		ReadTimeout:  15 * time.Second,
+	}
+
+	log.Fatal(srv.ListenAndServe())
+}
+```
+
 ### Registered URLs
 
 Now let's see how to build registered URLs.
@@ -491,6 +580,73 @@ r.Use(amw.Middleware)
 
 Note: The handler chain will be stopped if your middleware doesn't call `next.ServeHTTP()` with the corresponding parameters. This can be used to abort a request if the middleware writer wants to. Middlewares _should_ write to `ResponseWriter` if they _are_ going to terminate the request, and they _should not_ write to `ResponseWriter` if they _are not_ going to terminate it.
 
+### Handling CORS Requests
+
+[CORSMethodMiddleware](https://godoc.org/github.com/gorilla/mux#CORSMethodMiddleware) intends to make it easier to strictly set the `Access-Control-Allow-Methods` response header.
+
+* You will still need to use your own CORS handler to set the other CORS headers such as `Access-Control-Allow-Origin`
+* The middleware will set the `Access-Control-Allow-Methods` header to all the method matchers (e.g. `r.Methods(http.MethodGet, http.MethodPut, http.MethodOptions)` -> `Access-Control-Allow-Methods: GET,PUT,OPTIONS`) on a route
+* If you do not specify any methods, then:
+> _Important_: there must be an `OPTIONS` method matcher for the middleware to set the headers.
+
+Here is an example of using `CORSMethodMiddleware` along with a custom `OPTIONS` handler to set all the required CORS headers:
+
+```go
+package main
+
+import (
+	"net/http"
+	"github.com/gorilla/mux"
+)
+
+func main() {
+    r := mux.NewRouter()
+
+    // IMPORTANT: you must specify an OPTIONS method matcher for the middleware to set CORS headers
+    r.HandleFunc("/foo", fooHandler).Methods(http.MethodGet, http.MethodPut, http.MethodPatch, http.MethodOptions)
+    r.Use(mux.CORSMethodMiddleware(r))
+    
+    http.ListenAndServe(":8080", r)
+}
+
+func fooHandler(w http.ResponseWriter, r *http.Request) {
+    w.Header().Set("Access-Control-Allow-Origin", "*")
+    if r.Method == http.MethodOptions {
+        return
+    }
+
+    w.Write([]byte("foo"))
+}
+```
+
+And an request to `/foo` using something like:
+
+```bash
+curl localhost:8080/foo -v
+```
+
+Would look like:
+
+```bash
+*   Trying ::1...
+* TCP_NODELAY set
+* Connected to localhost (::1) port 8080 (#0)
+> GET /foo HTTP/1.1
+> Host: localhost:8080
+> User-Agent: curl/7.59.0
+> Accept: */*
+> 
+< HTTP/1.1 200 OK
+< Access-Control-Allow-Methods: GET,PUT,PATCH,OPTIONS
+< Access-Control-Allow-Origin: *
+< Date: Fri, 28 Jun 2019 20:13:30 GMT
+< Content-Length: 3
+< Content-Type: text/plain; charset=utf-8
+< 
+* Connection #0 to host localhost left intact
+foo
+```
+
 ### Testing Handlers
 
 Testing handlers in a Go web application is straightforward, and _mux_ doesn't complicate this any further. Given two files: `endpoints.go` and `endpoints_test.go`, here's how we'd test an application using _mux_.