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

server/auth/openid/cookie.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 openid
 
 import (
         "net/http"
         "time"
 
         "github.com/luci/luci-go/common/clock"
-        "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/tokens"
         "golang.org/x/net/context"
 )
 
 // sessionCookieName is actual cookie name to set.
 const sessionCookieName = "oid_session"
 
 // sessionCookieToken is used to generate signed cookies that hold session ID.
 var sessionCookieToken = tokens.TokenKind{
         Algo:       tokens.TokenAlgoHmacSHA256,
@@ skipping 26 matching lines @@
 // decodeSessionCookie takes an incoming request and returns a session ID stored
 // in a session cookie, or "" if not there, invalid or expired. Returns errors
 // on transient errors only.
 func decodeSessionCookie(c context.Context, r *http.Request) (string, error) {
         cookie, err := r.Cookie(sessionCookieName)
         if err != nil {
                 return "", nil // no such cookie
         }
         payload, err := sessionCookieToken.Validate(c, cookie.Value, nil)
         switch {
-        case errors.IsTransient(err):
+        case transient.Tag.In(err):
                 return "", err
         case err != nil:
                 logging.Warningf(c, "Failed to decode session cookie %q: %s", cookie.Value, err)
                 return "", nil
         case payload["sid"] == "":
                 logging.Warningf(c, "No 'sid' key in cookie payload %v", payload)
                 return "", nil
         }
         return payload["sid"], nil
 }