TD-5348 stream files with keep alive.

LearningHub.Nhs.WebUI/Controllers/Api/ResourceController.cs

@@ -2,14 +2,18 @@ namespace LearningHub.Nhs.WebUI.Controllers.Api
 {
     using System;
     using System.Collections.Generic;
+    using System.IO;
     using System.Linq;
+    using System.Net.Http.Headers;
+    using System.Threading;
     using System.Threading.Tasks;
     using LearningHub.Nhs.Models.Enums;
     using LearningHub.Nhs.Models.Resource;
     using LearningHub.Nhs.Models.Resource.Activity;
     using LearningHub.Nhs.Models.Resource.Contribute;
     using LearningHub.Nhs.WebUI.Interfaces;
     using Microsoft.AspNetCore.Authorization;
+    using Microsoft.AspNetCore.Http;
     using Microsoft.AspNetCore.Mvc;
     using Microsoft.Extensions.Configuration;
 
@@ -71,7 +75,15 @@ public async Task<IActionResult> DownloadResource(string filePath, string fileNa
             var file = await this.fileService.DownloadFileAsync(filePath, fileName);
             if (file != null)
             {
-                return this.File(file.Content, file.ContentType, fileName);
+                // Set response headers.
+                this.Response.ContentType = file.ContentType;
+                this.Response.ContentLength = file.ContentLength;
+                var contentDisposition = new ContentDispositionHeaderValue("attachment") { FileNameStar = fileName };
+                this.Response.Headers["Content-Disposition"] = contentDisposition.ToString();
+
+                // Stream the file in chunks with periodic flushes to keep the connection active.
+                await this.StreamFileWithKeepAliveAsync(file.Content, this.Response.Body, this.HttpContext.RequestAborted);
+                return this.Ok();
             }
             else
             {
@@ -106,7 +118,16 @@ public async Task<IActionResult> DownloadResourceAndRecordActivity(int resourceV
                     ActivityStatus = ActivityStatusEnum.Completed,
                 };
                 await this.activityService.CreateResourceActivityAsync(activity);
-                return this.File(file.Content, file.ContentType, fileName);
+
+                // Set response headers.
+                this.Response.ContentType = file.ContentType;
+                this.Response.ContentLength = file.ContentLength;
+                var contentDisposition = new ContentDispositionHeaderValue("attachment") { FileNameStar = fileName };
+                this.Response.Headers["Content-Disposition"] = contentDisposition.ToString();
+
+                // Stream the file in chunks with periodic flushes to keep the connection active.
+                await this.StreamFileWithKeepAliveAsync(file.Content, this.Response.Body, this.HttpContext.RequestAborted);
+                return this.Ok();
             }
             else
             {
@@ -585,5 +606,20 @@ public async Task<List<string>> GetObsoleteResourceFile(int resourceVersionId, b
             var result = await this.resourceService.GetObsoleteResourceFile(resourceVersionId, deletedResource);
             return result;
         }
+
+        /// <summary>
+        /// Reads from the source stream in chunks and writes to the destination stream,
+        /// flushing after each chunk to help keep the connection active.
+        /// </summary>
+        private async Task StreamFileWithKeepAliveAsync(Stream source, Stream destination, CancellationToken cancellationToken)
+        {
+            byte[] buffer = new byte[8192];
+            int bytesRead;
+            while ((bytesRead = await source.ReadAsync(buffer, 0, buffer.Length, cancellationToken)) > 0)
+            {
+                await destination.WriteAsync(buffer, 0, bytesRead, cancellationToken);
+                await destination.FlushAsync(cancellationToken);
+            }
+        }
     }
 }

LearningHub.Nhs.WebUI/Services/FileService.cs

@@ -147,7 +147,7 @@ public async Task<FileDownloadResponse> DownloadFileAsync(string filePath, strin
             {
                 if (fileSize <= 900 * 1024 * 1024)
                 {
-                    // Directly download the entire file as a stream
+                    // For smaller files, download the entire file as a stream.
                     var response = await file.DownloadAsync();
                     return new FileDownloadResponse
                     {
@@ -158,6 +158,7 @@ public async Task<FileDownloadResponse> DownloadFileAsync(string filePath, strin
                 }
                 else
                 {
+                    // For large files, open a read stream
                     return new FileDownloadResponse
                     {
                         Content = await file.OpenReadAsync(),