84 lines
2.8 KiB
C#
84 lines
2.8 KiB
C#
using DNS.Client;
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using Microsoft.Extensions.Caching.Memory;
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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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/// 受信任的域名解析器
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/// </summary>
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sealed class DomainResolver
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{
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private readonly IMemoryCache memoryCache;
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private readonly TimeSpan cacheTimeSpan = TimeSpan.FromSeconds(10d);
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private readonly IOptionsMonitor<FastGithubOptions> options;
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/// <summary>
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/// 受信任的域名解析器
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/// </summary>
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/// <param name="options"></param>
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public DomainResolver(
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IMemoryCache memoryCache,
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IOptionsMonitor<FastGithubOptions> options)
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{
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this.memoryCache = memoryCache;
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this.options = options;
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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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public async 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 = $"domain:{domain}";
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var address = await 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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return address;
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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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private async Task<IPAddress> LookupAsync(string domain, CancellationToken cancellationToken)
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{
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var endpoint = this.options.CurrentValue.TrustedDns.ToIPEndPoint();
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try
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{
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var dnsClient = new DnsClient(endpoint);
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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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// 如果解析到的ip为本机ip，会产生反向代理请求死循环
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if (address.Equals(IPAddress.Loopback))
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{
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throw new Exception($"dns受干扰，解析{domain}的ip为{address}");
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}
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return address;
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}
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catch (Exception ex)
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{
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throw new ReverseProxyException($"dns({endpoint})：{ex.Message}", ex);
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}
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}
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}
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}
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