Phoenix - Send bytes in POST response

Question

I have an application that generates a PDF in memory. I need to return that PDF back to the browser. The request is of type POST but I am having problems using send_download. Currently, I am only able to get it working with a GET request.

Here is what I have tried:

In the controller, this works if the request is a get: (note pdf is bytes (<<37, 56, 66 ...>> etc)

send_download(conn, {:binary, pdf}, [filename: "doc.pdf"]

This however does not work if I turn the request into a POST. I get no errors on the server when I do.

I have also tried:

  conn
    |> put_resp_content_type("application/pdf")
    |> put_resp_header("content-disposition", "attachment; filename=html.pdf")
    |> send_file(200, pdf)

But I get the following error when I try:

cannot send_file/5 with null byte

pdf var which holds the bytes is not null. I have an inspect right before this and its not nil.

I have searched and can't seem to find an answer to something that seems so simple. send_file does not seem to be the correct function since the docs say it takes a full path and not the file in bytes...

I am trying to avoid writing the file to disk.

Thanks in advance.

The error you are getting has nothing to do with the pdf var being nil. It is saying that one of the bytes in your binary is a null byte. I do not know enough about PDF's to know whether or not it is normal to have a null byte, I also do not know why the send_file function would care. — Justin Wood

Botonomous Botonomous · Accepted Answer · 2019-07-23T13:19:13

I found the solution: send_file expects a full path and not binary data of the file. Use send_resp instead.

 conn
    |> put_resp_content_type("application/pdf")
    |> put_resp_header("content-disposition", "attachment; filename=html.pdf")
    |> Plug.Conn.send_resp(:ok, pdf)

Phoenix - Send bytes in POST response

1 Answers