AR文件更新流程&AR网络延时问题

Assets/Scripts/Utils/Loom.cs

@@ -7,6 +7,7 @@ using System.Collections;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Net;
 using System.Threading;
 using System.Threading.Tasks;
 using UnityEngine;
@@ -171,7 +172,7 @@ public class Loom : MonoBehaviour
         }
     }
 
-    public static Dictionary<string, DownloadInfo> DownloadStack = new Dictionary<string, DownloadInfo>();
+    public static Dictionary<string, DownloadInfo> DownloadStack { get; set; } = new Dictionary<string, DownloadInfo>();
 
     public static async Task DownloadLoadARDataAndVideo(MapRoute route,IProgress<float> progress)
     {
@@ -184,7 +185,6 @@ public class Loom : MonoBehaviour
         var cancelToken = new CancellationTokenSource();
         var dataPath = $"{localPath}/{route.Id}";
 
-        Helper.CreateDirectoryIfNotExsit(dataPath);
         Helper.CreateDirectoryIfNotExsit(dataPath);
 
         await Loom.DownloadToFileAsync(arDataPath, $"{dataPath}/{route.Id}.json");
@@ -206,9 +206,45 @@ public class Loom : MonoBehaviour
         };
 
         var request = UnityWebRequest.Get(downloadUrl);
-        request.method = UnityWebRequest.kHttpVerbGET;
         request.downloadHandler = dh;
-
+        request.method = UnityWebRequest.kHttpVerbGET;
+        
         return await request.SendWebRequest().ToUniTask(progress, PlayerLoopTiming.Update, (cancellation?.Token ?? default(CancellationToken)));
     }
+    
+    /// <summary>
+    /// head request for file meta info such as etag.
+    /// </summary>
+    /// <param name="downloadUrl">download url</param>
+    /// <param name="fullPath">local path for storage</param>
+    /// <returns></returns>
+    public static async UniTask<UnityWebRequest> HeadFileAsync(string downloadUrl, string fullPath, IProgress<float> progress = null,CancellationTokenSource cancellation = default(CancellationTokenSource))
+    {
+        try
+        {   var etagFile = fullPath + ".etag";
+            var etag = string.Empty;
+            if (File.Exists(etagFile))
+            {
+                etag = File.ReadAllText(etagFile);
+            }
+
+            var request = UnityWebRequest.Head(downloadUrl);
+            if(!string.IsNullOrEmpty(etag))
+                request.SetRequestHeader("If-None-Match", etag);
+
+            var result = await request.SendWebRequest();//.ToUniTask(progress, PlayerLoopTiming.Update, (cancellation?.Token ?? default(CancellationToken)));
+        
+            if (result.responseCode != (long)HttpStatusCode.NotModified)
+            {
+                etag = result.GetResponseHeader("ETag");
+                File.WriteAllText(fullPath+".etag",etag);
+            }
+            return result;
+
+        }
+        catch (Exception e)
+        {
+            return null;
+        }
+    }
 }