TD-5348 azure file download service

Author: OluwatobiAwe

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

@@ -74,17 +74,10 @@ public async Task<IActionResult> DownloadResource(string filePath, string fileNa
             }
 
             var file = await this.fileService.DownloadFileAsync(filePath, fileName);
+
             if (file != null)
             {
-                // 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();
+                return !string.IsNullOrEmpty(file.DownloadUrl) ? this.Redirect(file.DownloadUrl) : this.File(file.Content, file.ContentType, fileName);
             }
             else
             {
@@ -120,15 +113,7 @@ public async Task<IActionResult> DownloadResourceAndRecordActivity(int resourceV
                 };
                 await this.activityService.CreateResourceActivityAsync(activity);
 
-                // 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();
+                return !string.IsNullOrEmpty(file.DownloadUrl) ? this.Redirect(file.DownloadUrl) : this.File(file.Content, file.ContentType, fileName);
             }
             else
             {
@@ -607,20 +592,5 @@ 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/Models/FileDownloadResponse.cs

@@ -21,5 +21,10 @@ public class FileDownloadResponse
         /// Gets or sets the ContentType.
         /// </summary>
         public long ContentLength { get; set; }
+
+        /// <summary>
+        /// Gets or sets when downloading large files, a SAS URL is returned so the client can download directly from Azure Files.
+        /// </summary>
+        public string DownloadUrl { get; set; }
     }
 }

LearningHub.Nhs.WebUI/Services/FileService.cs

@@ -1,17 +1,13 @@
 namespace LearningHub.Nhs.WebUI.Services
 {
     using System;
-    using System.Buffers;
     using System.Collections.Generic;
     using System.IO;
     using System.Linq;
-    using System.Threading;
     using System.Threading.Tasks;
-    using System.Threading.Tasks.Dataflow;
-    using Azure;
-    using Azure.Storage;
     using Azure.Storage.Files.Shares;
     using Azure.Storage.Files.Shares.Models;
+    using Azure.Storage.Sas;
     using LearningHub.Nhs.Models.Resource;
     using LearningHub.Nhs.WebUI.Configuration;
     using LearningHub.Nhs.WebUI.Interfaces;
@@ -145,27 +141,19 @@ public async Task<FileDownloadResponse> DownloadFileAsync(string filePath, strin
 
             try
             {
-                if (fileSize <= 900 * 1024 * 1024)
+                var response = new FileDownloadResponse
                 {
-                    // For smaller files, download the entire file as a stream.
-                    var response = await file.DownloadAsync();
-                    return new FileDownloadResponse
-                    {
-                        Content = response.Value.Content,
-                        ContentType = properties.Value.ContentType,
-                        ContentLength = fileSize,
-                    };
-                }
-                else
+                    ContentType = properties.Value.ContentType,
+                    ContentLength = fileSize,
+                    Content = await file.OpenReadAsync(),
+                };
+
+                if (fileSize >= 999 * 1024 * 1024)
                 {
-                    // For large files, open a read stream
-                    return new FileDownloadResponse
-                    {
-                        Content = await file.OpenReadAsync(),
-                        ContentType = properties.Value.ContentType,
-                        ContentLength = fileSize,
-                    };
+                    response.DownloadUrl = this.GenerateSasUriForFile(file);
                 }
+
+                return response;
             }
             catch (Exception ex)
             {
@@ -461,5 +449,23 @@ private async Task<ShareFileClient> FindFileAsync(string filePath, string fileNa
 
             return null;
         }
+
+        private string GenerateSasUriForFile(ShareFileClient fileClient)
+        {
+            if (fileClient.CanGenerateSasUri)
+            {
+                ShareSasBuilder sasBuilder = new ShareSasBuilder(ShareFileSasPermissions.Read, DateTimeOffset.UtcNow.AddMinutes(20))
+                {
+                    Protocol = SasProtocol.Https,
+                };
+
+                Uri sasUri = fileClient.GenerateSasUri(sasBuilder);
+                return sasUri.ToString();
+            }
+            else
+            {
+                throw new InvalidOperationException("Unable to generate SAS URI for the file.");
+            }
+        }
     }
 }