How To Read (GET) from File if Extension is Unknown - .NET Core 6 API

Question

I have a controller, which I will include the methods for at the end. I allow users to upload either.DOC, .DOCX or.PDF files via my POST method.

I then have a GET method which I can currently return a file from, but it is hardcoded to.PDF. I want to know how I would enable my GET method read from any of the file types above? Or how would I get the file extension of a file, before I have read it into a stream?

If you have any feedback on my approach to either method, feedback is welcome!

    [HttpGet("Download/{requestId}/{lineNumber}")]
    public IActionResult Download([FromRoute] long requestId, [FromRoute] int lineNumber)
    {
        string fileName = requestId.ToString() + lineNumber.ToString();
        string fileDownloadName = fileName + DateTime.Now.ToString("ddMMyyyy");
        try
        {
            FileStream stream = new(GetFilePath() + fileName + ".pdf", FileMode.Open);
            return File(stream, "application/pdf", fileDownloadName + ".pdf");
        }

        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }
    }

    [HttpPost("Upload/{requestId}/{lineNumber}")]
    public async Task<IActionResult> OnPostUploadAsync(IFormFile formFile, [FromRoute] long requestId, [FromRoute] int lineNumber)
    {
        try
        {
            if (formFile.Length > 0)
            {
                string filename = formFile.FileName;
                string filepath = GetFilePath();
                string docId = requestId.ToString() + lineNumber.ToString();

                var supportedTypes = new[] { "doc", "docx", "pdf" };
                var fileExt = System.IO.Path.GetExtension(formFile.FileName).Substring(1);

                string concessionDocumentPath = filepath + "\\" + docId + "." + fileExt;

                if (!supportedTypes.Contains(fileExt))
                {
                    string ErrorMessage = "File Extension Is Invalid - Only Upload WORD/PDF File";
                    return BadRequest(ErrorMessage);
                }

                if (!System.IO.Directory.Exists(filepath))
                {
                    System.IO.Directory.CreateDirectory(filepath);
                }

                if (System.IO.File.Exists(concessionDocumentPath))
                {
                    System.IO.File.Delete(concessionDocumentPath);
                }
                using (FileStream stream = System.IO.File.Create(concessionDocumentPath))
                {
                    await formFile.CopyToAsync(stream);
                }
            }
        }
        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }

        return Ok(formFile.FileName.ToString() + " was uploaded successfully");
    }

    [NonAction]
    private string GetFilePath()
    {
        return this._environment.WebRootPath + "\\Uploads\\ConcessionDocuments\\";
    }

Answer 1

One way I could think of for getting the file extension is

DirectoryInfo di = new DirectoryInfo(GetFilePath());
FileInfo fileInfo = di.GetFiles().FirstOrDefault();

string fileExtension = System.IO.Path.GetExtension(fileInfo.FullName);

and you could use this extension in the hardcoded part.

Here I assumed you have only one file in the directory. Now if you have multiple files in the directory, try to identify the file using searchPattern overload of GetFiles .

Hope this helps.

Answer 2

With thanks to @WisdomSeeker for his help, I was able to get a solution in place. Instead of using GetFiles, I used EnumerateFiles

I'm doubtful it's the most effective, or best way to do this, but it works for what I need.

    [HttpGet("Download/{requestId}/{lineNumber}")]
    public IActionResult Download([FromRoute] long requestId, [FromRoute] int lineNumber)
    {
        string fileName = requestId.ToString() + lineNumber.ToString();
        string fileDownloadName = fileName + DateTime.Now.ToString("ddMMyyyy");
        string extension = null!;
        string mimeType = null!;
        string filePath;

        try
        {
            IEnumerable<string> directory = Directory.EnumerateFiles(GetFilePath(), fileName + "*");

            if (directory.Any())
            {
                filePath = directory.FirstOrDefault()!;

                if (filePath.EndsWith(".pdf"))
                {
                    extension = ".pdf";
                    mimeType = "application/pdf";
                }
                else if (filePath.EndsWith(".doc"))
                {
                    extension = ".doc";
                    mimeType = "application/msword";
                }
                else if (filePath.EndsWith(".docx"))
                {
                    extension = ".docx";
                    mimeType = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
                }

                FileStream stream = new(GetFilePath() + fileName + extension, FileMode.Open);

                return File(stream, mimeType, fileDownloadName + extension);
            }
            else
            {
                return BadRequest();
            }

        }
        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }
    }