Additional flexibility for http request parameters in adapter config

[parkin]

Hello - thank you for the amazing plugin!

I'm working with an LLM that expects a different post request format than what codecompanion currently provides by default.
This LLM expects the post content passed as a form instead of body, and it expects the content to be base64 encoded.

With the existing http.lua implementation, it assumes the content is requested in the body and encoded as a json string, which is great and makes sense for most LLMs.

  -- the body is encoded as a json string here, and there is no way currently to override this default
  local body = self.opts.encode(
    vim.tbl_extend(
      "keep",
      handlers.form_parameters
          and handlers.form_parameters(adapter, adapter:set_env_vars(adapter.parameters), payload.messages)
        or {},
      handlers.form_messages and handlers.form_messages(adapter, payload.messages) or {},
      handlers.form_tools and handlers.form_tools(adapter, payload.tools) or {},
      adapter.body and adapter.body or {},
      handlers.set_body and handlers.set_body(adapter, payload) or {}
    )
  )

  local body_file = Path.new(vim.fn.tempname() .. ".json")
  body_file:write(vim.split(body, "\n"), "w")

  log:info("Request body file: %s", body_file.filename)
  
  -- .....

  -- content is passed to the body parameter here, and there is no way to override this behavior or pass data to the form parameter instead
  local request_opts = {
    url = adapter:set_env_vars(adapter.url),
    headers = adapter:set_env_vars(adapter.headers),
    insecure = config.adapters.opts.allow_insecure,
    proxy = config.adapters.opts.proxy,
    raw = raw,
    body = body_file.filename or "",
    -- This is called when the request is finished. It will only ever be called
    -- once, even if the endpoint is streaming.
    callback = function(data)
      vim.schedule(function()
        if (not adapter.opts.stream) and data and data ~= "" then
          log:trace("Output data:\n%s", data)
          cb(nil, data, adapter)
        end
        if handlers and handlers.on_exit then
          handlers.on_exit(adapter, data)
        end
        if handlers and handlers.teardown then
          handlers.teardown(adapter)
        end
        if actions.done and type(actions.done) == "function" then
          actions.done()
        end

        opts.status = "success"
        if data.status >= 400 then
          opts.status = "error"
        end

        if not opts.silent then
          util.fire("RequestFinished", opts)
        end
        cleanup(opts.status)
        if self.user_args.event then
          if not opts.silent then
            util.fire("RequestFinished" .. (self.user_args.event or ""), opts)
          end
        end
      end)
    end,
    on_error = function(err)
      vim.schedule(function()
        actions.callback(err, nil)
        if not opts.silent then
          util.fire("RequestFinished", opts)
        end
      end)
    end,
  }

But, it seems there's no way override this default behavior to pass content to the form property instead of body, and it seems there's no way to override the json string encoding, which would be helpful in my case.

It would be very helpful in my case to provide some mechanism in adapters to override these request defaults.
I will try to draft an example, but I also expect that you will have a much better idea than me for how to implement this, so I would be very happy to hear any suggestions you might have.

[parkin]

Here is an example implementation, which adds

• set_form handler to allow the user to set the form data
• modify_request_opts handler to allow the adapter to modify the request before it is sent
  • The LLM I'm using actually won't respond if I include a body in the request, so I use this to set the request_opts.body = nil

[olimorris]

This looks entirely reasonable, I'd recommend you test this out with a large prompt. Issue #427 highlighted some potential limitations with curl which you may run into as you're using the form parameter in plenary.nvim.

But happy to accept a PR and test this out.

[parkin]

Thanks! I was wondering why the temporary files were being used.

I did indeed have the same issue with a large prompt (on WSL).

So, I made this implementation to also use temporary files for form content, which then fixes the issue.

Interestingly, my implementation uses "-F name=<filename", where "<" asks curl to not attach the file contents as an upload, but instead to make a text field with the file contents.
I think this suggests that the large prompt issue is with plenary and not curl.
(maybe you already figured this out, I haven't followed all of the discussion)