[BUG] multipart/form-data Content-Disposition missing

[spacether]

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?
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Description

When uploading a file with content type multipart/form-data the Content-Disposition part is missing.

Expected:

-----------------------------31264598498482450412031672804
Content-Disposition: form-data; name="file"; filename="test.txt"
Content-Type: text/plain

Hello World
-----------------------------31264598498482450412031672804--

Actual:

--3332f21c28498ce486e94b8ec5a48291
Content-Type: application/octet-stream

Hello World
--3332f21c28498ce486e94b8ec5a48291--

openapi-generator version

6.2.1

OpenAPI declaration file content or url

{
    "openapi": "3.0.1",
    "info": {},
    "servers": [],
    "security": [],
    "paths": {
        ...,
        "/files/{fileContainerId}/payload": {
            "post": {
                "tags": [
                    "file"
                ],
                "description": "Upload a new file",
                "operationId": "createFile",
                "parameters": [
                    {
                        "name": "fileContainerId",
                        "in": "path",
                        "required": true,
                        "schema": {
                            "type": "integer",
                            "format": "int64"
                        }
                    }
                ],
                "requestBody": {
                    "content": {
                        "multipart/form-data": {
                            "schema": {
                                "required": [
                                    "file"
                                ],
                                "type": "object",
                                "properties": {
                                    "file": {
                                        "type": "string",
                                        "description": "File which you want to upload",
                                        "format": "binary"
                                    }
                                }
                            }
                        }
                    }
                },
                "responses": {
                    "201": {
                        "description": "created"
                    },
                    "404": {
                        "description": "not found"
                    }
                }
            }
        },
        ...
    },
    "components": {...}
}

Generation Details

... generate -i target/openapi/openapi.json -g python -o clients/python

Steps to reproduce

Related issues/PRs

Suggest a fix

Note: duplicated from OpenAPITools/openapi-generator#13887