[errors] de-specialize Transient in favor of Tags.

server/auth/xsrf/xsrf.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 xsrf provides Cross Site Request Forgery prevention middleware.
 //
 // Usage:
 //   1. When serving GET request put hidden "xsrf_token" input field with
 //      the token value into the form. Use TokenField(...) to generate it.
 //   2. Wrap POST-handling route with WithTokenCheck(...) middleware.
 package xsrf
 
 import (
         "fmt"
         "html/template"
         "net/http"
         "time"
 
         "golang.org/x/net/context"
 
-        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
+        "github.com/luci/luci-go/common/retry/transient"
 
         "github.com/luci/luci-go/server/auth"
         "github.com/luci/luci-go/server/router"
         "github.com/luci/luci-go/server/tokens"
 )
 
 // xsrfToken described how to generate tokens.
 var xsrfToken = tokens.TokenKind{
         Algo:       tokens.TokenAlgoHmacSHA256,
         Expiration: 4 * time.Hour,
@@ skipping 36 matching lines @@
 // If searches for the token in "xsrf_token" POST form field (as generated by
 // TokenField). Aborts the request with HTTP 403 if XSRF token is missing or
 // invalid.
 func WithTokenCheck(c *router.Context, next router.Handler) {
         tok := c.Request.PostFormValue("xsrf_token")
         if tok == "" {
                 replyError(c.Context, c.Writer, http.StatusForbidden, "XSRF token is missing")
                 return
         }
         switch err := Check(c.Context, tok); {
-        case errors.IsTransient(err):
+        case transient.Tag.In(err):
                 replyError(c.Context, c.Writer, http.StatusInternalServerError, "Transient error when checking XSRF token - %s", err)
         case err != nil:
                 replyError(c.Context, c.Writer, http.StatusForbidden, "Bad XSRF token - %s", err)
         default:
                 next(c)
         }
 }
 
 ///
 
 // state must return exact same value when generating and verifying token for
 // the verification to succeed.
 func state(c context.Context) []byte {
         return []byte(auth.CurrentUser(c).Identity)
 }
 
 // replyError sends error response and logs it.
 func replyError(c context.Context, rw http.ResponseWriter, code int, msg string, args ...interface{}) {
         text := fmt.Sprintf(msg, args...)
         logging.Errorf(c, "xsrf: %s", text)
         http.Error(rw, text, code)
 }