FileContentResult encoding issue with Sharepoint file by Azure Function - azure

Question

I am facing en enconding issue when downloading a file from Sharepoint Online by an Azure function. So I have an Azure HTTP triggered function that calls Sharepoint Online to retrieve a file and download it. Here is how I call Sharepoint:
public dynamic DownloadFile(Guid fileUniqueId)
{
const string apiUrl = "{0}/_api/web/GetFileById('{1}')/$value";
try
{
var fileInfo = GetFileInfo(fileUniqueId);
if (string.IsNullOrEmpty(_sharepointSiteUrl)) return null;
string api = string.Format(apiUrl, _sharepointSiteUrl, fileUniqueId.ToString());
string response = new TokenHelper().GetAPIResponse(api);
if (string.IsNullOrEmpty(response)) return null;
return new {
fileInfo.FileName,
Bytes = Encoding.UTF8.GetBytes(response)
};
}
catch (Exception ex)
{
throw ex;
}
}
And Here is the Azure App function that is called:
string guidString = req.Query["id"];
if (!Guid.TryParse(guidString, out var fileId))
return new BadRequestResult();
var fileManager = new FileManager();
dynamic fileData = fileManager.DownloadFile(fileId);
if (null == fileData) return new NotFoundResult();
var contentType = (((string)fileData.FileName).ToUpper().EndsWith(".PNG") || ((string)fileData.FileName).ToUpper().EndsWith(".JPEG") || ((string)fileData.FileName).ToUpper().EndsWith(".JPG")) ? "image/jpeg" : "application/octet-stream";
return new FileContentResult(fileData.Bytes, contentType)
{
FileDownloadName = fileData.FileName
};
The file is succesfully downloaded but it seems corrupted as it says that the file type is not recognised. I think that it's an issue related to encoding. Does somebody sees what I'm doing wrong ?

Answer 1

Your code is using UTF8.GetBytes() to try and get the file content from SharePoint Online. You should instead use the CSOM method OpenBinaryDirect() like this:
var fileRef = file.ServerRelativeUrl;
var fileInfo = Microsoft.SharePoint.Client.File.OpenBinaryDirect(clientContext, fileRef);
using (var fileStream = System.IO.File.Create(fileName))
{
fileInfo.Stream.CopyTo(fileStream);
}