Question

Title sais it all really.

private bool addToBinary(byte[] msg, string filepath)
{
    bool succ = false;

    do
    {
        try
        {
            using (Stream fileStream = new FileStream(filepath, FileMode.Append, FileAccess.Write, FileShare.None))
            {
                using (BinaryWriter bw = new BinaryWriter(fileStream))
                {
                    bw.Write(msg);

                    bw.Flush();
                    fileStream.Flush();
                    bw.Close();
                }
            }
            succ = true;
        }
        catch (IOException ex) { Console.WriteLine("Write Exception (addToBinary) : " + ex.Message); }
        catch (Exception ex) { Console.WriteLine("Some Exception occured (addToBinary) : " + ex.Message); return false; }
    } while (!succ);
    return true;
}

(bw.close also closes the underlying stream)

Using this in any loop causes an output such as;

A first chance exception of type 'System.IO.IOException' occurred in mscorlib.dll
Write Exception (addToBinary) : The process cannot access the file 'C:\test\test.png' because it is being used by another process.

The bigger the file gets, the more of these errors pop up. It does get through eventually but it significantly reduces file writing speed. It’s the Stream fileStream = bit that causes the exception.

What did I do wrong?

Example usage;

do
{
    serverStream = clientSocket.GetStream();
    bytesRead = serverStream.Read(inStream, 0, buffSize); //How many bytes did we just read from the stream?

    recstrbytes = new byte[bytesRead]; //Final byte array
    Array.Copy(inStream, recstrbytes, bytesRead); //Copy from inStream to the final byte array
    addToBinary(recstrbytes, @"C:\test\test.png"); //Append final byte array to binary
    received += recstrbytes.Length; //Increment bytes received
}while (received < filesize);

Answer 1

You need to first check if you can access the file before using Stream to read the file.

You can have a look at this link :

Best way to handle errors when opening file

Have a look at the answers
Although I posted my answer

https://stackoverflow.com/a/9503939/448407 but you can look at the post marked as answer.

Only read the file contents if you can access the file and I think it will then work.