一步步实现对API的访问限制(节流)

一步步实现对API的访问限制(节流)

如果客户端很频繁的请求服务器，会给给服务器造成很大的压力，需要对客户端对API的请求，做一些限制，如Python 爬虫对服务器API的请求，对API的请求限制也是反爬虫的一个手段之一，那如何实现对API的访问的限制呢？

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实现API接口

一个基本的API接口实现，没有任何的限制，客户端可以随意访问，也没有访问限制

[HttpGet]
[Route("~/api/helloworld")]
public HttpResponseMessage HelloWorld()
{
        return Request.CreateResponse(HttpStatusCode.OK, "Hello World");
}

添加基本的限制

如果要做限制，首先想到的是在访问这个接口时，做一个计数器，记录访问的数量，达到一定的数量之后就不能访问，使用cache来实现计数

[HttpGet]
[Route("~/api/helloworld")]
public HttpResponseMessage HelloWorld()
{
    int? requestCount = (int?)System.Web.HttpRuntime.Cache["throttle"];

    if (!requestCount.HasValue) requestCount = 0;

    requestCount++;

    HttpRuntime.Cache["throttle"] = requestCount;

    if (requestCount > 10) return Request.CreateResponse((HttpStatusCode)429, "Too many requests");

    return Request.CreateResponse(HttpStatusCode.OK, "Hello World");
}

这样如果访问 /api/helloworld 这个接口超过10次，就返回 429错误，但是这个实现是不能用于生产环境的，只能演示使用，虽然实现了访问限制，但是超过了次数之后，就无法访问这个接口了，这不是我们想要的，期望的是限制一段时间之后，用户可以重新访问这个API

添加过期时间

改造一下上面的代码，对访问的限制添加一个过期时间，如果超过了限制了，会在一段时间之后，就可以继续访问了

[HttpGet]
[Route("~/api/helloworld")]
public HttpResponseMessage HelloWorld()
{
    ThrottleInfo throttleInfo = (ThrottleInfo)HttpRuntime.Cache["throttle"];

    if (throttleInfo == null)
        throttleInfo = new ThrottleInfo {
                    ExpiresAt = DateTime.Now.AddSeconds(10), RequestCount = 0 };

    throttleInfo.RequestCount++;

    HttpRuntime.Cache.Add("throttle", throttleInfo, null,
        throttleInfo.ExpiresAt, Cache.NoSlidingExpiration,
                CacheItemPriority.Normal, null);

    if (throttleInfo.RequestCount > 10)
            return Request.CreateResponse((HttpStatusCode)429, "Too many requests");

    return Request.CreateResponse(HttpStatusCode.OK, "Hello World");
}

private class ThrottleInfo
{
    public DateTime ExpiresAt { get; set; }
    public int RequestCount { get; set; }
}

这样访问超过了限制，等一段时间，就可以继续访问了

封装一下代码,将访问限制的代码提取出来

public HttpResponseMessage HelloWorld()
{
    var throttler = new Throttler("helloworld");

    if (throttler.RequestShouldBeThrottled())
                return Request.CreateResponse(
                    (HttpStatusCode)429, "Too many requests");

    return Request.CreateResponse(HttpStatusCode.OK, "Hello World");
}

public class Throttler
{
    private int _requestLimit;
    private int _timeoutInSeconds;
    private string _key;

    public Throttler(string key, int requestLimit = 5, int timeoutInSeconds = 10)
    {
        _requestLimit = requestLimit;
        _timeoutInSeconds = timeoutInSeconds;
        _key = key;
    }

    public bool RequestShouldBeThrottled()
    {
        ThrottleInfo throttleInfo = (ThrottleInfo)HttpRuntime.Cache[_key];

        if (throttleInfo == null) throttleInfo = new ThrottleInfo {
                ExpiresAt = DateTime.Now.AddSeconds(_timeoutInSeconds),
                RequestCount = 0
        };

        throttleInfo.RequestCount++;

        HttpRuntime.Cache.Add(_key,
      throttleInfo,
      null,
      throttleInfo.ExpiresAt,
      Cache.NoSlidingExpiration,
      CacheItemPriority.Normal,
      null);

        return (throttleInfo.RequestCount > _requestLimit);
    }

    private class ThrottleInfo
    {
        public DateTime ExpiresAt { get; set; }
        public int RequestCount { get; set; }
    }
}

不一定需要依赖 HttpRuntime.Cache,使用 ConcurrentDictionary 实现cache

public class Throttler
{
    private int _requestLimit;
    private int _timeoutInSeconds;
    private string _key;
    private static ConcurrentDictionary _cache =
        new ConcurrentDictionary();

    public Throttler(string key, int requestLimit = 5, int timeoutInSeconds = 10)
    {
        _requestLimit = requestLimit;
        _timeoutInSeconds = timeoutInSeconds;
        _key = key;
    }

    public bool RequestShouldBeThrottled()
    {
        ThrottleInfo throttleInfo = _cache.ContainsKey(_key) ? _cache[_key] : null;

        if (throttleInfo == null || throttleInfo.ExpiresAt <= DateTime.Now)
        {
            throttleInfo = new ThrottleInfo {
                ExpiresAt = DateTime.Now.AddSeconds(_timeoutInSeconds),
                RequestCount = 0};
        };

        throttleInfo.RequestCount++;

        _cache[_key] = throttleInfo;

        return (throttleInfo.RequestCount > _requestLimit);
    }

    private class ThrottleInfo
    {
        public DateTime ExpiresAt { get; set; }
        public int RequestCount { get; set; }
    }
}

使用user id作为key，也可以使用IP地址作为key

• UserName作为key

[HttpGet]
[Route("~/api/helloworld")]
public HttpResponseMessage HelloWorld()
{
    var throttler = new Throttler(User.Identity.Name);
}

• 使用IP地址作为key

[HttpGet]
[Route("~/api/helloworld")]
public HttpResponseMessage HelloWorld()
{
    var ipAddress = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
    var throttler = new Throttler(ipAddress);
}

让客户端知道访问限制，已经过期时间等

封装一下返回结果

public HttpResponseMessage HelloWorld()
{
    var throttler = new Throttler(User.Identity.Name);

    HttpResponseMessage response = createResponse("Hello World", throttler);

    return response;
}

private HttpResponseMessage createResponse(object content, Throttler throttler)
{
    HttpResponseMessage response;

    if (throttler.RequestShouldBeThrottled())
        response = Request.CreateResponse((HttpStatusCode)429, "Too many requests");
    else
        response = Request.CreateResponse(HttpStatusCode.OK, content);

    response.Headers.Add("X-RateLimit-Limit", throttler.RequestLimit.ToString());
    response.Headers.Add("X-RateLimit-Remaining", throttler.RequestsRemaining.ToString());
    response.Headers.Add("X-RateLimit-Reset", toUnixTime(throttler.WindowResetDate).ToString());

    return response;
}

private long toUnixTime(DateTime date)
{
    var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
    return Convert.ToInt64((date.ToUniversalTime() - epoch).TotalSeconds);
}

在返回的结果中添加了三个 header ，重构一下 Throttler来支持这个三个属性

public class Throttler
{
    public int RequestLimit { get; private set; }
    public int RequestsRemaining { get; private set; }
    public DateTime WindowResetDate { get; private set; }
    private static ConcurrentDictionary _cache =
        new ConcurrentDictionary();

    private string _key;
    private int _timeoutInSeconds;

    public Throttler(string key, int requestLimit = 5, int timeoutInSeconds = 10)
    {
        RequestLimit = requestLimit;
        _timeoutInSeconds = timeoutInSeconds;
        _key = key;
    }

    public bool RequestShouldBeThrottled()
    {
        ThrottleInfo throttleInfo = _cache.ContainsKey(_key) ? _cache[_key] : null;

        if (throttleInfo == null || throttleInfo.ExpiresAt <= DateTime.Now)
        {
            throttleInfo = new ThrottleInfo {
                ExpiresAt = DateTime.Now.AddSeconds(_timeoutInSeconds),
                RequestCount = 0};
        };

        WindowResetDate = throttleInfo.ExpiresAt;

        throttleInfo.RequestCount++;

        _cache[ThrottleGroup] = throttleInfo;

        RequestsRemaining = Math.Max(RequestLimit - throttleInfo.RequestCount, 0);

        return (throttleInfo.RequestCount > RequestLimit);
    }

    private class ThrottleInfo
    {
        public DateTime ExpiresAt { get; set; }
        public int RequestCount { get; set; }
    }
}

创建一个属性

using System;
using System.Net;
using System.Net.Http;
using System.Runtime.CompilerServices;
using System.Web;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;

namespace Throttling
{
    public class ThrottleFilter : ActionFilterAttribute
    {
        private Throttler _throttler;
        private string _throttleGroup;

        public ThrottleFilter(
            int RequestLimit = 5,
            int TimeoutInSeconds = 10,
            [CallerMemberName] string ThrottleGroup = null)
        {
            _throttleGroup = ThrottleGroup;
            _throttler = new Throttler(ThrottleGroup, RequestLimit, TimeoutInSeconds);
        }

        public override void OnActionExecuting(HttpActionContext actionContext)
        {
            setIdentityAsThrottleGroup();

            if (_throttler.RequestShouldBeThrottled)
            {
                actionContext.Response = actionContext.Request.CreateResponse(
                    (HttpStatusCode)429, "Too many requests");

                addThrottleHeaders(actionContext.Response);
            }

            base.OnActionExecuting(actionContext);
        }

        public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
        {
            setIdentityAsThrottleGroup();
            if (actionExecutedContext.Exception == null) _throttler.IncrementRequestCount();
            addThrottleHeaders(actionExecutedContext.Response);
            base.OnActionExecuted(actionExecutedContext);
        }

        private void setIdentityAsThrottleGroup()
        {
            if (_throttleGroup == "identity")
                _throttler.ThrottleGroup = HttpContext.Current.User.Identity.Name;

            if (_throttleGroup == "ipaddress")
                _throttler.ThrottleGroup = HttpContext.Current.Request.UserHostAddress;
        }

        private void addThrottleHeaders(HttpResponseMessage response)
        {
            if (response == null) return;

            foreach (var header in _throttler.GetRateLimitHeaders())
                response.Headers.Add(header.Key, header.Value);
        }
    }
}

对应的 Throttler代码

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;

namespace Throttling
{
    public class Throttler
    {
        public int RequestLimit { get; private set; }
        public int RequestsRemaining { get; private set; }
        public DateTime WindowResetDate { get; private set; }
        private static ConcurrentDictionary _cache =
            new ConcurrentDictionary();

        public string ThrottleGroup { get; set; }
        private int _timeoutInSeconds;

        public Throttler(string key, int requestLimit = 5, int timeoutInSeconds = 10)
        {
            RequestLimit = requestLimit;
            _timeoutInSeconds = timeoutInSeconds;
            ThrottleGroup = key;
        }

        private ThrottleInfo getThrottleInfoFromCache()
        {
            ThrottleInfo throttleInfo =
                _cache.ContainsKey(ThrottleGroup) ? _cache[ThrottleGroup] : null;

            if (throttleInfo == null || throttleInfo.ExpiresAt <= DateTime.Now)
            {
                throttleInfo = new ThrottleInfo
                {
                    ExpiresAt = DateTime.Now.AddSeconds(_timeoutInSeconds),
                    RequestCount = 0
                };
            };

            return throttleInfo;
        }

        public bool RequestShouldBeThrottled
        {
            get
            {
                ThrottleInfo throttleInfo = getThrottleInfoFromCache();
                WindowResetDate = throttleInfo.ExpiresAt;
                RequestsRemaining = Math.Max(RequestLimit - throttleInfo.RequestCount, 0);
                return (throttleInfo.RequestCount > RequestLimit);
            }
        }

        public void IncrementRequestCount()
        {
            ThrottleInfo throttleInfo = getThrottleInfoFromCache();
            throttleInfo.RequestCount++;
            _cache[ThrottleGroup] = throttleInfo;
        }

        private class ThrottleInfo
        {
            public DateTime ExpiresAt { get; set; }
            public int RequestCount { get; set; }
        }

        public Dictionary GetRateLimitHeaders()
        {
            ThrottleInfo throttleInfo = getThrottleInfoFromCache();

            int requestsRemaining = Math.Max(RequestLimit - throttleInfo.RequestCount, 0);

            var headers = new Dictionary();
            headers.Add("X-RateLimit-Limit", RequestLimit.ToString());
            headers.Add("X-RateLimit-Remaining", RequestsRemaining.ToString());
            headers.Add("X-RateLimit-Reset", toUnixTime(throttleInfo.ExpiresAt).ToString());
            return headers;
        }

        private long toUnixTime(DateTime date)
        {
            var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
            return Convert.ToInt64((date.ToUniversalTime() - epoch).TotalSeconds);
        }

    }
}

如何使用

• 基本使用

[ThrottleFilter()]
[HttpGet]
[Route("~/api/helloworld")]
public HttpResponseMessage HelloWorld()
{
  return Request.CreateResponse(HttpStatusCode.OK, "Hello World");
}

• 添加限制

[ThrottleFilter(RequestLimit: 50, TimeoutInSeconds: 5)]
[HttpGet]
[Route("~/api/allow-more")]
public HttpResponseMessage HelloWorld2()
{
    return Request.CreateResponse(HttpStatusCode.OK, "Hello World2");
}

• 使用IP地址

[ThrottleFilter(ThrottleGroup: "ipaddress")]
[HttpGet]
[Route("~/api/name")]
public HttpResponseMessage GetName(int id)
{
    return Request.CreateResponse(HttpStatusCode.OK, "John Smith");
}

• 使用user Id

[ThrottleFilter(ThrottleGroup: "identity")]
[HttpGet]
[Route("~/api/name")]
public HttpResponseMessage GetName(int id)
{
    return Request.CreateResponse(HttpStatusCode.OK, "Jane Doe");
}

也可以使用第三方库实现节流 WebApiThrottle Github

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