125 lines
4.0 KiB
C#
125 lines
4.0 KiB
C#
using System;
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using System.Collections.Generic;
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using UnityEngine.Networking;
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namespace YooAsset
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{
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/// <summary>
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/// UnityWebRequest HEAD 请求下载器
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/// </summary>
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/// <remarks>
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/// 仅获取响应头信息，不下载实际内容。
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/// 用于检查资源是否存在、获取资源大小、检查缓存有效性等场景。
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/// </remarks>
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internal sealed class UnityWebRequestHeadDownloader : UnityWebRequestDownloaderBase, IDownloadHeadRequest
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{
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// 注意：缓存响应头（因为 WebRequest 释放后无法获取）
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private Dictionary<string, string> _cachedResponseHeaders;
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private readonly DownloadDataRequestArgs _args;
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/// <summary>
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/// 获取 ETag 响应头
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/// </summary>
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public string ETag
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{
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get { return GetResponseHeader("ETag"); }
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}
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/// <summary>
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/// 获取 Last-Modified 响应头
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/// </summary>
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public string LastModified
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{
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get { return GetResponseHeader("Last-Modified"); }
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}
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/// <summary>
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/// 获取 Content-Type 响应头
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/// </summary>
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public string ContentType
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{
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get { return GetResponseHeader("Content-Type"); }
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}
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/// <summary>
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/// 获取 Content-Length 响应头
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/// 预期下载的总字节数
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/// </summary>
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public long ContentLength
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{
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get
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{
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string contentLengthStr = GetResponseHeader("Content-Length");
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if (string.IsNullOrEmpty(contentLengthStr))
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return -1;
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if (long.TryParse(contentLengthStr, out long contentLength))
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{
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return contentLength;
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}
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else
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{
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return -1;
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}
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}
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}
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/// <summary>
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/// 构造 HEAD 请求下载器
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/// </summary>
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/// <param name="args">数据下载参数</param>
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/// <param name="webRequestCreator">UnityWebRequest 创建器（可选）</param>
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public UnityWebRequestHeadDownloader(DownloadDataRequestArgs args, UnityWebRequestCreator webRequestCreator)
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: base(args.URL, webRequestCreator)
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{
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_args = args;
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}
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/// <summary>
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/// 获取响应头信息
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/// </summary>
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/// <param name="name">响应头名称（不区分大小写）</param>
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/// <returns>响应头的值，如果不存在或请求未完成则返回 null</returns>
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public string GetResponseHeader(string name)
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{
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if (_cachedResponseHeaders == null)
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return null;
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// 注意：UnityWebRequest 的响应头 key 是小写的
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string lowerName = name.ToLowerInvariant();
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if (_cachedResponseHeaders.TryGetValue(lowerName, out string value))
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return value;
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return null;
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}
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/// <summary>
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/// 创建 UnityWebRequest
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/// </summary>
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protected override void CreateWebRequest()
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{
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_webRequest = CreateUnityWebRequestHead(URL);
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_webRequest.downloadHandler = null; // HEAD 请求不需要 DownloadHandler
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ApplyRequestOptions(_args.Timeout, _args.WatchdogTime, _args.Headers);
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}
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/// <summary>
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/// 请求成功时的回调
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/// </summary>
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protected override void OnRequestSucceed()
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{
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var headers = _webRequest.GetResponseHeaders();
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if (headers != null)
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{
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_cachedResponseHeaders = new Dictionary<string, string>(headers.Count, StringComparer.OrdinalIgnoreCase);
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foreach (var kvp in headers)
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{
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string name = kvp.Key.ToLowerInvariant();
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string value = kvp.Value;
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_cachedResponseHeaders[name] = value;
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}
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}
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}
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}
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}
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