安全规则中的 Firebase 速率限制？

Question

我启动了我的第一个开放存储库项目EphChat，人们立即开始向它发出大量请求。

Firebase 是否有办法在安全规则中对请求进行速率限制？我认为有一种方法可以使用请求的时间和先前写入的数据的时间来完成，但在文档中找不到任何关于我将如何执行此操作的内容。

目前的安全规则如下。

{
    "rules": {
      "rooms": {
        "$RoomId": {
          "connections": {
              ".read": true,
              ".write": "auth.username == newData.child('FBUserId').val()"
          },
          "messages": {
            "$any": {
            ".write": "!newData.exists() || root.child('rooms').child(newData.child('RoomId').val()).child('connections').hasChild(newData.child('FBUserId').val())",
            ".validate": "newData.hasChildren(['RoomId','FBUserId','userName','userId','message']) && newData.child('message').val().length >= 1",
            ".read": "root.child('rooms').child(data.child('RoomId').val()).child('connections').hasChild(data.child('FBUserId').val())"
            }
          },
          "poll": {
            ".write": "auth.username == newData.child('FBUserId').val()",
            ".read": true
          }
        }
      }
    }
}

我想对整个 Rooms 对象对数据库的写入（和读取？）进行速率限制，因此每秒只能发出 1 个请求（例如）。

Answer 1

诀窍是对用户上次发布消息的时间进行审核。然后您可以根据审核值强制发布每条消息的时间：

{
  "rules": {
          // this stores the last message I sent so I can throttle them by timestamp
      "last_message": {
        "$user": {
          // timestamp can't be deleted or I could just recreate it to bypass our throttle
          ".write": "newData.exists() && auth.uid === $user",
          // the new value must be at least 5000 milliseconds after the last (no more than one message every five seconds)
          // the new value must be before now (it will be since `now` is when it reaches the server unless I try to cheat)
          ".validate": "newData.isNumber() && newData.val() === now && (!data.exists() || newData.val() > data.val()+5000)"
        }
      },

      "messages": {
        "$message_id": {
          // message must have a timestamp attribute and a sender attribute
          ".write": "newData.hasChildren(['timestamp', 'sender', 'message'])",
          "sender": {
            ".validate": "newData.val() === auth.uid"
          },
          "timestamp": {
            // in order to write a message, I must first make an entry in timestamp_index
            // additionally, that message must be within 500ms of now, which means I can't
            // just re-use the same one over and over, thus, we've effectively required messages
            // to be 5 seconds apart
            ".validate": "newData.val() >= now - 500 && newData.val() === data.parent().parent().parent().child('last_message/'+auth.uid).val()"
          },
          "message": {
            ".validate": "newData.isString() && newData.val().length < 500" 
          },
          "$other": {
            ".validate": false 
          }
        }
      } 
  }
}

看到它在行动in this fiddle。这是小提琴的要点：

var fb = new Firebase(URL);
var userId; // log in and store user.uid here

// run our create routine
createRecord(data, function (recordId, timestamp) {
   console.log('created record ' + recordId + ' at time ' + new Date(timestamp));
});

// updates the last_message/ path and returns the current timestamp
function getTimestamp(next) {
    var ref = fb.child('last_message/' + userId);
    ref.set(Firebase.ServerValue.TIMESTAMP, function (err) {
        if (err) { console.error(err); }
        else {
            ref.once('value', function (snap) {
                next(snap.val());
            });
        }
    });
}

function createRecord(data, next) {
    getTimestamp(function (timestamp) {
        // add the new timestamp to the record data
        var data = {
          sender: userId,
          timestamp: timestamp,
          message: 'hello world'
        };

        var ref = fb.child('messages').push(data, function (err) {
            if (err) { console.error(err); }
            else {
               next(ref.name(), timestamp);
            }
        });
    })
}

Answer 2

我没有足够的声誉来写评论，但我同意 Victor 的评论。如果您将 fb.child('messages').push(...) 插入循环（即 for (let i = 0; i < 100; i++) {...} ），那么它将成功推送 60-80 条消息（在 500 毫秒的窗口框架中。

受加藤解决方案的启发，我建议对规则进行如下修改：

rules: {
  users: {
    "$uid": {
      "timestamp": { // similar to Kato's answer
        ".write": "auth.uid === $uid && newData.exists()"
        ,".read": "auth.uid === $uid"
        ,".validate": "newData.hasChildren(['time', 'key'])"
        ,"time": {
          ".validate": "newData.isNumber() && newData.val() === now && (!data.exists() || newData.val() > data.val() + 1000)"
        }
        ,"key": {

        }
      }
      ,"messages": {
        "$key": { /// this key has to be the same is the key in timestamp (checked by .validate)
           ".write": "auth.uid === $uid && !data.exists()" ///only 'create' allow
           ,".validate": "newData.hasChildren(['message']) && $key === root.child('/users/' + $uid + '/timestamp/key').val()"
           ,"message": { ".validate": "newData.isString()" }
           /// ...and any other datas such as 'time', 'to'....
        }
      }
    }
  }
}

.js 代码与 Kato 的解决方案非常相似，只是 getTimestamp 将返回 {time: number, key: string} 到下一个回调。然后我们只需要ref.update({[key]: data})

这个方案避免了 500ms 的时间窗口，我们不必担心客户端必须足够快才能在 500ms 内推送消息。如果发送多个写入请求（垃圾邮件），它们只能写入messages 中的 1 个单个键。或者，messages 中的仅创建规则可以防止这种情况发生。

Answer 3

现有答案使用两个数据库更新：(1) 标记时间戳，(2) 将标记的时间戳附加到实际写入。 Kato's answer 需要 500 毫秒的时间窗口，而 ChiNhan 需要记住下一个键。

有一种更简单的方法可以在单个数据库更新中完成。这个想法是使用update() 方法一次将多个值写入数据库。安全规则验证写入的值，以便写入不会超过配额。配额定义为一对值：quotaTimestamp 和postCount。 postCount 是在 quotaTimestamp 的 1 分钟内写的帖子数。如果 postCount 超过某个值，安全规则会简单地拒绝下一次写入。当 quotaTimestamp 过时 1 分钟时， postCount 被重置。

这里是发布新消息的方法：

function postMessage(user, message) {
  const now = Date.now() + serverTimeOffset;
  if (!user.quotaTimestamp || user.quotaTimestamp + 60 * 1000 < now) {
    // Resets the quota when 1 minute has elapsed since the quotaTimestamp.
    user.quotaTimestamp = database.ServerValue.TIMESTAMP;
    user.postCount = 0;
  }
  user.postCount++;

  const values = {};
  const messageId = // generate unique id
  values[`users/${user.uid}/quotaTimestamp`] = user.quotaTimestamp;
  values[`users/${user.uid}/postCount`] = user.postCount;
  values[`messages/${messageId}`] = {
    sender: ...,
    message: ...,
    ...
  };
  return this.db.database.ref().update(values);
}

将速率限制为每分钟最多 5 个帖子的安全规则：

{
  "rules": {
    "users": {
      "$uid": {
        ".read": "$uid === auth.uid",
        ".write": "$uid === auth.uid && newData.child('postCount').val() <= 5",
        "quotaTimestamp": {
          // Only allow updating quotaTimestamp if it's staler than 1 minute.
          ".validate": "
            newData.isNumber()
            && (newData.val() === now
              ? (data.val() + 60 * 1000 < now)
              : (data.val() == newData.val()))"
        },
        "postCount": {
          // Only allow postCount to be incremented by 1
          // or reset to 1 when the quotaTimestamp is being refreshed.
          ".validate": "
            newData.isNumber()
            && (data.exists()
              ? (data.val() + 1 === newData.val()
                || (newData.val() === 1
                    && newData.parent().child('quotaTimestamp').val() === now))
              : (newData.val() === 1))"
        },
        "$other": { ".validate": false }
      }
    },

    "messages": {
      ...
    }
  }
}

注意：应保持serverTimeOffset 以避免时钟偏差。

Answer 4

我喜欢Kato's answer，但它没有考虑到恶意用户仅使用 for 循环就在 500 毫秒窗口之间充斥着聊天。 我提出了消除这种可能性的变体：

{
  "rules": {
    "users": {
      "$uid": {
        "rateLimit": {
          "lastMessage": {
            // newData.exists() ensures newData is not null and prevents deleting node
            // and $uid === auth.uid ensures the user writing this child node is the owner
            ".write": "newData.exists() && $uid === auth.uid",
            // newData.val() === now ensures the value written is the current timestamp
            // to avoid tricking the rules writting false values
            // and (!data.exists() || newData.val() > data.val() + 5000)
            // ensures no data exists currently in the node. Otherwise it checks if the
            // data that will overwrite the node is a value higher than the current timestamp
            // plus the value that will rate limit our messages expressed in milliseconds.
            // In this case a value of 5000 means that we can only send a message if
            // the last message we sent was more than 5 seconds ago
            ".validate": "newData.val() === now && (!data.exists() || newData.val() > data.val() + 5000)"
          }
        }
      }
    },
    "messages": {
      "$messageId": {
        // This rule ensures that we write lastMessage node avoiding just sending the message without
        // registering a new timestamp
        ".write": "newData.parent().parent().child('users').child(auth.uid).child('rateLimit').child('lastMessage').val() === now",
        // This rule ensures that we have all the required message fields
        ".validate": "newData.hasChildren(['timestamp', 'uid', 'message'])",
        "uid": {
          // This rule ensures that the value written is the id of the message sender
          ".validate": "newData.val() === auth.uid"
        },
        "timestamp": {
          // This rule ensures that the message timestamp can't be modified
          ".write": "!data.exists()",
          // This rule ensures that the value written is the current timestamp
          ".validate": "newData.val() === now"
        },
        "message": {
          // This rule ensures that the value written is a string
          ".validate": "newData.isString()"
        },
        "$other": {
          // This rule ensures that we cant write other fields in the message other than
         // the explicitly declared above
         ".validate": false
        }
      }
    }
  }
}

代码实现使用跨多个位置的原子写入。如果一次验证失败，则操作未完成，数据库中不进行任何操作

function sendMessage(message) {
    const database = firebase.database();

    const pushId = database.ref().child("messages").push().key;
    const userId = firebase.auth().currentUser.uid;
    const timestampPlaceholder = firebase.database.ServerValue.TIMESTAMP;

    let updates = {};
    updates["messages/" + pushId] = {
      uid: userId,
      timestamp: timestampPlaceholder,
      message: message,
    };
    updates[`users/${userId}/rateLimit/lastMessage`] = timestampPlaceholder;

    database.ref().update(updates);
  }