[BUG][Swift5] binary upload (application/octet-stream) are not working

[Stormshield-robinc]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• [-] Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

The swift5 generator is broken for API endpoint that should upload binary data (request body with a "application/octet-stream" content).

Currently, the generated code ask for a swift Url.
I would expect this to read the request body's data from the file at Url, but instead, it send the Url as is in the request body.
(Note: I find surprising to ask for a file Url instead of a Data, since we could want to generate the binary blob on the fly without using any file.)

I saw that there is an option named mapFileBinaryToData which replace the Url type with a Data one (but it is marked as deprecated).
With this option I am able to give the binary blob directly to the function, but instead of being send as is, it get base64 encoded.

Looking into the code I can see that this is a bug, as there is no piece of code to read a file, and as we never add the "application/octet-stream" content-type (which explain the base64 encoding since we default to json)

openapi-generator version

master

OpenAPI declaration file content or url

Here is a minimalist file for reproduction

{
  "openapi": "3.0.0",
  "info": {
    "title": "Test",
    "description": "Test",
    "version": "6.2.1"
  },
  "paths": {
    "/send_binary_blob": {
      "post": {
        "tags": [
          "Test"
        ],
        "description": "Test the upload of a file (or binary blob)",
        "operationId": "test",
        "parameters": [],
        "requestBody": {
          "description": "Byte stream",
          "content": {
            "application/octet-stream": {
              "schema": {
                "type": "string",
                "format": "binary"
              },
              "example": ""
            }
          },
          "required": true
        },
        "responses": {
          "200": {
            "description": "Return some message",
            "content": {
              "text/plain; charset=utf-8": {
                "example": "upload successful"
              }
            }
          },
          "403": {
            "description": "Access forbidden.",
            "content": {
              "text/plain; charset=utf-8": {
                "example": "access denied"
              }
            }
          },
          "422": {
            "description": "Unprocessable entity.",
            "content": {
              "text/plain; charset=utf-8": {
                "example": "unprocessable entity"
              }
            }
          },
          "500": {
            "description": "Internal server error.",
            "content": {
              "text/plain; charset=utf-8": {
                "example": "internal server error"
              }
            }
          }
	}
      }
    }
  }
}

Generation Details

No special option, just generate the API with -g swift5

Steps to reproduce

Generate the swift code from the above json and try to use the endpoint with a Url.
See that it is not sending the binary data

Related issues/PRs

Very similar problem
#14268

PR that introduced file upload
#16299
With its issue
#16300

Suggest a fix

PR incoming