88 lines
2.9 KiB
C#
88 lines
2.9 KiB
C#
using DNS.Client.RequestResolver;
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using DNS.Protocol;
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using DNS.Protocol.ResourceRecords;
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using FastGithub.Scanner;
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using Microsoft.Extensions.Caching.Memory;
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using Microsoft.Extensions.DependencyInjection;
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using Microsoft.Extensions.Logging;
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using System;
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using System.Linq;
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using System.Net;
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using System.Threading;
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using System.Threading.Tasks;
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namespace FastGithub.Dns
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{
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[Service(ServiceLifetime.Singleton)]
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sealed class GithubRequestResolver : IRequestResolver
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{
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private readonly IGithubScanService githubScanService;
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private readonly IMemoryCache memoryCache;
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private readonly ILogger<GithubRequestResolver> logger;
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private readonly TimeSpan TTL = TimeSpan.FromMinutes(10d);
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public GithubRequestResolver(
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IGithubScanService githubScanService,
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IMemoryCache memoryCache,
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ILogger<GithubRequestResolver> logger)
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{
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this.githubScanService = githubScanService;
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this.memoryCache = memoryCache;
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this.logger = logger;
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}
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public Task<IResponse> Resolve(IRequest request, CancellationToken cancellationToken = default)
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{
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var response = Response.FromRequest(request);
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var question = request.Questions.FirstOrDefault();
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if (question != null && question.Type == RecordType.A)
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{
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var domain = question.Name.ToString();
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var address = this.GetGithubAddress(domain, TTL);
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if (address != null)
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{
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var record = new IPAddressResourceRecord(question.Name, address);
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response.AnswerRecords.Add(record);
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this.logger.LogInformation(record.ToString());
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}
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}
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return Task.FromResult<IResponse>(response);
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}
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/// <summary>
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/// 模拟TTL
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/// 如果ip可用，则10分钟内返回缓存的ip，防止客户端ip频繁切换
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/// </summary>
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/// <param name="domain"></param>
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/// <param name="ttl"></param>
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/// <returns></returns>
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private IPAddress? GetGithubAddress(string domain, TimeSpan ttl)
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{
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if (domain.Contains("github", StringComparison.OrdinalIgnoreCase) == false)
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{
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return default;
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}
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var key = $"ttl:{domain}";
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if (this.memoryCache.TryGetValue<IPAddress>(key, out var address))
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{
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if (this.githubScanService.IsAvailable(domain, address))
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{
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return address;
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}
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this.memoryCache.Remove(key);
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}
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address = this.githubScanService.FindBestAddress(domain);
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if (address != null)
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{
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this.memoryCache.Set(key, address, ttl);
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}
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return address;
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}
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}
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}
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