96 lines
3.4 KiB
C#
96 lines
3.4 KiB
C#
using DNS.Client;
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using Microsoft.Extensions.Caching.Memory;
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using Microsoft.Extensions.Logging;
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using Microsoft.Extensions.Options;
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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.ReverseProxy
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{
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/// <summary>
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/// 域名解析器
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/// </summary>
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sealed class DomainResolver
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{
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private DnsClient dnsClient;
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private readonly IMemoryCache memoryCache;
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private readonly IOptionsMonitor<FastGithubOptions> options;
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private readonly ILogger<DomainResolver> logger;
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private readonly TimeSpan cacheTimeSpan = TimeSpan.FromSeconds(10d);
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/// <summary>
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/// 域名解析器
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/// </summary>
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/// <param name="memoryCache"></param>
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/// <param name="options"></param>
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/// <param name="logger"></param>
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public DomainResolver(
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IMemoryCache memoryCache,
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IOptionsMonitor<FastGithubOptions> options,
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ILogger<DomainResolver> logger)
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{
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this.memoryCache = memoryCache;
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this.options = options;
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this.logger = logger;
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this.dnsClient = new DnsClient(options.CurrentValue.PureDns.ToIPEndPoint());
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options.OnChange(opt => this.dnsClient = new DnsClient(opt.PureDns.ToIPEndPoint()));
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}
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/// <summary>
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/// 解析指定的域名
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/// </summary>
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/// <param name="domain"></param>
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/// <returns></returns>
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/// <exception cref="FastGithubException"></exception>
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public Task<IPAddress> ResolveAsync(string domain, CancellationToken cancellationToken)
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{
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// 缓存以避免做不必要的并发查询
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var key = $"{nameof(DomainResolver)}:{domain}";
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return this.memoryCache.GetOrCreateAsync(key, e =>
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{
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e.SetAbsoluteExpiration(this.cacheTimeSpan);
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return this.LookupAsync(domain, cancellationToken);
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});
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}
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/// <summary>
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/// 查找ip
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/// </summary>
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/// <param name="domain"></param>
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/// <param name="cancellationToken"></param>
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/// <returns></returns>
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/// <exception cref="FastGithubException">
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private async Task<IPAddress> LookupAsync(string domain, CancellationToken cancellationToken)
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{
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try
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{
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var addresses = await dnsClient.Lookup(domain, DNS.Protocol.RecordType.A, cancellationToken);
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var address = addresses?.FirstOrDefault();
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if (address == null)
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{
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throw new Exception($"解析不到{domain}的ip");
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}
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// 受干扰的dns，常常返回127.0.0.1来阻断请求
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// 虽然DnscryptProxy的抗干扰能力，但它仍然可能降级到不安全的普通dns上游
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if (address.Equals(IPAddress.Loopback))
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{
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throw new Exception($"dns被污染，解析{domain}为{address}");
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}
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this.logger.LogInformation($"[{domain}->{address}]");
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return address;
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}
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catch (Exception ex)
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{
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var dns = this.options.CurrentValue.PureDns;
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throw new FastGithubException($"dns({dns})服务器异常：{ex.Message}", ex);
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}
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}
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}
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}
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