Files uploaded to ftp server, corrupted why?

Question

Files are uploading successfully but with corrupted files. Kindly check my code and fix my problem. I think my problem in this line:

 byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());;

string ftpurl = "ftp://IP";
            string ftpusername = "u09z0fyuu"; // e.g. username
            string ftppassword = "Yamankatita1@"; // e.g. password

            string PureFileName = new FileInfo(file_name).Name;
            String uploadUrl = String.Format("{0}/{1}/{2}", ftpurl, "PDPix", file_name);
            FtpWebRequest request = (FtpWebRequest)FtpWebRequest.Create(uploadUrl);
            request.Method = WebRequestMethods.Ftp.UploadFile;
            // This example assumes the FTP site uses anonymous logon.  
            request.Credentials = new NetworkCredential(ftpusername, ftppassword);
            request.Proxy = null;
            request.KeepAlive = true;
            request.UseBinary = true;
            request.UsePassive = true;
            request.Method = WebRequestMethods.Ftp.UploadFile;

            // Copy the contents of the file to the request stream.  
            StreamReader sourceStream = new StreamReader(_mediaFile.Path);
            byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());;
            sourceStream.Close();
            request.ContentLength = fileContents.Length;
            Stream requestStream = request.GetRequestStream();
            requestStream.Write(fileContents, 0, fileContents.Length);
            requestStream.Close();
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();
            _ = DisplayAlert("Upload File Complete, status {0}", response.StatusDescription,"OK");

Are you uploading UTF8-encoded _text file_? If not, that seems likely to be your problem. — ProgrammingLlama, Nov 23 '21 at 13:52
No, I need to upload only image files. Kindly help me thanks! — Zikria Rasul, Nov 23 '21 at 13:54

ProgrammingLlama · Accepted Answer · 2021-11-23T14:03:47.530

You've said you're trying to upload image files. You can't treat these as UTF8 because they are binary data and they are not encoded with UTF8. You need to treat binary data as binary data.

You can read the bytes directly:

byte[] fileContents = File.ReadAllBytes(_mediaFile.Path);

Explanation

UTF8 can't represent all possible values of a byte (0x00 - 0xFF) as characters and roundtrip them back to a binary format again. We can observe this with the following code:

byte[] input = new byte[8];
RNGCryptoServiceProvider.Create().GetBytes(input);

Console.WriteLine(string.Join(", ", input.Select(i => i)));

string tmp = System.Text.Encoding.UTF8.GetString(input); // interpret arbitrary bianry data as text
// the data is corrupted by this point
byte[] result = System.Text.Encoding.UTF8.GetBytes(tmp); // convert the text back to a binary form (utf8-encoded)
Console.WriteLine(string.Join(", ", result.Select(i => i)));

Try it online

Here we generate 8 random bytes, print their values, try to interpret them as a string, convert that string back to bytes, and print their new values.

For the following 8 bytes:

16, 211, 7, 253, 207, 91, 24, 137

We got the following bytes as a result:

16, 239, 191, 189, 7, 239, 191, 189, 239, 191, 189, 91, 24, 239, 191, 189

And just like that, our data is corrupted! Long story short: don't use text encoding for binary data.

Files uploaded to ftp server, corrupted why?

1 Answers1