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PORenaming concurrent uploaded files in ASP.NET
 

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  1. PORenaming concurrent uploaded files in ASP.NET
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    <p>I use the following code to receive uploaded files and store them in the uploadedFiles folder on the server.</p> <pre><code>public class CustomMultipartFormDataStreamProvider : MultipartFormDataStreamProvider { public CustomMultipartFormDataStreamProvider(string path) : base(path) { } public override string GetLocalFileName(HttpContentHeaders headers) { return headers.ContentDisposition.FileName.Replace("\"", string.Empty); } } [HttpPost] public async Task&lt;HttpResponseMessage&gt; ReceiveFileupload() { if (!Request.Content.IsMimeMultipartContent("form-data")) throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType); // Prepare CustomMultipartFormDataStreamProver in which our multipart form data will be loaded string fileSaveLocation = HttpContext.Current.Server.MapPath("~/UploadedFiles"); CustomMultipartFormDataStreamProvider provider = new CustomMultipartFormDataStreamProvider(fileSaveLocation); List&lt;string&gt; files = new List&lt;string&gt;(); Duck duck = null; try { // Read all contents of multipart message into CustomMultipartFormDataStreamProvider await Request.Content.ReadAsMultipartAsync(provider); // Parse an ID which is passed in the form data long id; if (!long.TryParse(provider.FormData["id"], out id)) { return Request.CreateResponse(HttpStatusCode.ExpectationFailed, "Couldn't determine id."); } duck = db.Ducks.Find(id); if (null == duck) return Request.CreateResponse(HttpStatusCode.NotAcceptable, "Duck with ID " + id + " could not be found."); // Loop through uploaded files foreach (MultipartFileData file in provider.FileData) { // File ending needs to be xml DoSomething(); // On success, add uploaded file to list which is returned to the client files.Add(file.LocalFileName); } // Send OK Response along with saved file names to the client. return Request.CreateResponse(HttpStatusCode.OK, files); } catch (System.Exception e) { return Request.CreateResponse(HttpStatusCode.InternalServerError, e); } } </code></pre> <p>Now I want to rename the uploaded files. As I understand, storing and renaming must be done in a critical section because when another user uploads a file with the same name at the same time, the first will be overwritten.</p> <p>That's how I imagine a solution, but <code>await</code> is not allowed in a lock statement.</p> <pre><code>lock(typeof(UploadController)) { await Request.Content.ReadAsMultipartAsync(provider); //That's the line after which the uploaded files are stored in the folder. foreach (MultipartFileData file in provider.FileData) { RenameFile(file); // Rename according to file's contents } } </code></pre> <p>How can I guarantee that the files will be stored and renamed atomically?</p>
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    1. USPeter Mortensen
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    1. COWhy not create files as a Tuple<string, string> have the first string the original filename (file.LocalFileName), the second string the desired (renamed) filename
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