Unable to attach files to prompt

[YanCarlos]

Hello everyone! I'm unable to attach files to prompt using with: path or with: ActionDispatch::Http::UploadedFile :(

For

• Ruby 3.2.5
• Rails 7.0.8.7
• ruby_llm 1.3.0
• model gemini-2.0-flash

I'm currently trying to use the with: parameter to attach a PDF file to the prompt, but it seems the file is not being passed correctly to the model. No matter whether I use the @source object (which is an ActionDispatch::Http::UploadedFile) or the file path (@source.path), the response from the assistant is always the same: it asks me to attach the document, as if it wasn't received.

Here are the details:

@source 
=> #<ActionDispatch::Http::UploadedFile:0x00007125b6371818
  @content_type="application/pdf",
  @original_filename="CERTIFICACION LABORAL - YAN MARIN.pdf",
  @tempfile=#<File:/tmp/document20250725-896272-u0ubwd.pdf>
  >

@source.path
=> "/tmp/document20250725-896272-u0ubwd.pdf"

chat.ask("What is this document about?", with: @source.path)

or

chat.ask("What is this document about?", with: @source)

Both attempts result in the assistant replying:

"Please attach the document. I can't determine the topic without the text."

Debug output shows that @attachments=[], meaning no attachment is passed to the underlying model:

 #<RubyLLM::Message:0x00007125b63767c8
 @content=
  #<RubyLLM::Content:0x00007125b44936f8
   @attachments=[],
   @text="Please attach the document. I can't determine the topic without the text">,
 @input_tokens=500,
 @model_id="gemini-2.0-flash",
 @output_tokens=19,
 @role=:assistant,
 @tool_call_id=nil,
 @tool_calls=nil>

Expected behavior:
Passing a local file path (e.g. /tmp/file.pdf) or an ActionDispatch::Http::UploadedFile should correctly attach the document to the prompt.

Let me know if I should structure the file differently or if only specific object types are supported in the with: parameter.

Thanks in advance for your help!

[YanCarlos]

✅ Update: Solved by wrapping the file in a hash with file: key
Hi everyone! I just wanted to post an update for anyone facing the same issue.

After trying multiple ways to pass the file using the with: parameter in chat.ask, I discovered that you need to wrap the file in a hash with a file: key, like this:

response = chat.ask("What is this document about?", with: { file: @source })

This works for both ActionDispatch::Http::UploadedFile objects and file paths (strings), as long as the file is wrapped properly:

response = chat.ask("What is this document about?", with: { file: "/tmp/myfile.pdf" })

🚫 What didn't work for me:
Passing the file directly, like this:

chat.ask("What is this document about?", with: @source)

# or

chat.ask("What is this document about?", with: @source.path)

results in no attachment being passed to the assistant, and @attachments stays empty. The assistant then replies with a message like:

"Please attach the document. I can't determine the topic without the text."

✅ Final takeaway:
Make sure to always wrap the file (or file path) using{ file: ... } inside the with: option.

🧐 Additional note: If you're still running into issues, it's worth double-checking the behavior of the Marcel gem, which is used internally to detect file MIME types. In some environments, MIME type resolution might fail silently, causing attachments to be ignored.

Hope this helps!

[the-s-anton]

Hey, how do you process your responses? Do you do chat.ask directly in the controller or inside the worker/job?

Curious how you handle the async part