// Package xsrftoken provides methods for generating and validating secure XSRF tokens.
package xsrftoken // import "golang.org/x/net/xsrftoken"
import (
"crypto/hmac"
"crypto/sha1"
"crypto/subtle"
"encoding/base64"
"fmt"
"strconv"
"strings"
"time"
)
// 设置xsrf存活周期
// 也许会设置和cookie生命周期一样
const Timeout = 24 * time.Hour
// 清理字符串中：替换为_ 。替换所有
func clean(s string) string { return strings.Replace(s, ":", "_", -1)
}
// Generate returns a URL-safe secure XSRF token that expires in 24 hours.
//返回一个安全且加密的url 默认存活周期为24小时
// key 是应用程序的密钥.
// userID 唯一标识符.
// actionID 用户实际的动作(例如 ： 访问的资源的地址).
func Generate(key, userID, actionID string) string { return generateTokenAtTime(key, userID, actionID, time.Now())
}
// generateTokenAtTime is like Generate, but returns a token that expires 24 hours from now.
func generateTokenAtTime(key, userID, actionID string, now time.Time) string { // now转化为毫秒
milliTime := (now.UnixNano() + 1e6 - 1) / 1e6
h := hmac.New(sha1.New, []byte(key)) //使用hmac进行加密
fmt.Fprintf(h, "%s:%s:%d", clean(userID), clean(actionID), milliTime)
// Get the padded base64 string then removing the padding.
tok := string(h.Sum(nil))
tok = base64.URLEncoding.EncodeToString([]byte(tok))
tok = strings.TrimRight(tok, "=")
return fmt.Sprintf("%s:%d", tok, milliTime)}
// Valid reports whether a token is a valid, unexpired token returned by Generate.
//验证 token 对应的key userid actionID 是否正确 并且在存活周期中
func Valid(token, key, userID, actionID string) bool { return validTokenAtTime(token, key, userID, actionID, time.Now())
}
// validTokenAtTime reports whether a token is valid at the given time.
func validTokenAtTime(token, key, userID, actionID string, now time.Time) bool { // Extract the issue time of the token.
sep := strings.LastIndex(token, ":")
if sep < 0 { return false
}
millis, err := strconv.ParseInt(token[sep+1:], 10, 64)
if err != nil { return false
}
issueTime := time.Unix(0, millis*1e6)
// Check that the token is not expired.
if now.Sub(issueTime) >= Timeout { return false
}
// Check that the token is not from the future.
// Allow 1 minute grace period in case the token is being verified on a
// machine whose clock is behind the machine that issued the token.
if issueTime.After(now.Add(1 * time.Minute)) { return false
}
expected := generateTokenAtTime(key, userID, actionID, issueTime)
// Check that the token matches the expected value.
// Use constant time comparison to avoid timing attacks.
return subtle.ConstantTimeCompare([]byte(token), []byte(expected)) == 1
}