Custom Connector: binary body

[ben11]

I have the exact same problem described here. The endpoint I'm working with expects a content type such as 'application/pdf'. It does not expect a form, json, etc. - just the raw binary as the body.

For example, in Curl, the data can be sent using  --data-binary and --header 'Content-Type: application/pdf'.

Unfortunately, OpenAPI 2.0 (Swagger) only supports file upload as part of multipart/form-data. I can't figure out whether there's any extension or workaround in Power Automate to allow for other content types.

I tried to use OpenAPI 3.0, but it's not supported AFAICT. I tried to use a script to transform the incoming request from multipart to a simple binary body, but I haven't figured out how to do that in C#. I thought maybe there would be an existing Policy to transform the request, but I can't find any.

Is there any way to do this?

[ben11 · Accepted solution]

Okay, I figured this out. You can use the Swagger editor and add a body parameter like this:

      parameters:
      - name: body
        in: body
        schema: {type: string, format: binary}

It appears as a string parameter in the swagger editor and on the custom connector testing tab, but then when you're in the actual flow editor you can put the "File content" from a previous step in there and it gets sent as plain binary. I absolutely did not expect that to work, but it does.

Edit: I later noticed that the paconn validate tool gives a warning that  "the MIME type 'application/octet-stream' is not supported" when I try to set the content-type. So maybe what I discovered was a dirty hack, and not the intended behaviour after all.