Mime Part Headers for multipart/mixed payload when using arrays

[jrihtarsic]

I would like to add body content with multipart/mixed payload, like this

"requestBody": {
          "content": {
            "multipart/mixed": {
              "schema": {
                "type": "object",
                  "properties": {
                    "payloads": {
                      "type": "array",
                      "items": {
                        "type": "string",
                        "format": "binary"
                      }
                    }
                  }
              }
            },

And I would also like define header "Part-Signature-Header" for each part in array
so that request body looks like this

-----------------------------37993639233119846881484177537
Content-Disposition: form-data; name="payloads"; filename="text-example1.txt"
Content-Type: text/plain
Part-Signature-Header: asdfsdf3223fsdfw...

Hello world text example 1. 

-----------------------------37993639233119846881484177537
Content-Disposition: form-data; name="payloads"; filename="text-example2.txt"
Content-Type: text/plain
Part-Signature-Header: asdfsd3345343fsdfw...
 
Hello world text example2. 

-----------------------------37993639233119846881484177537--

Is the correct encoding for this

"multipart/mixed": {
              "schema": {
                               "type": "object",
                  "properties": {
                    "**payloads**": {
                      "type": "array",
                      "items": {
                        "type": "string",
                        "format": "binary"
                      }
                    }
                  }
              },
              "encoding": {
                "**payloads**": {
                  "headers": {
                    "Part-Signature-Header": {
                      "$ref": "#/components/headers/Part-Signature-Header",
                      "required": true,
                      "style": "simple"
                    }
                  }
                }
              }
            },

or should i use asterix or some other char to mark that this header must be on every part of Multipart/mixed
as example:

"multipart/mixed": {
              "schema": {
                               "type": "object",
                  "properties": {
                    "payloads": {
                      "type": "array",
                      "items": {
                        "type": "string",
                        "format": "binary"
                      }
                    }
                  }
              },
              "encoding": {
                "*": {
                  "headers": {
                    "Part-Signature-Header": {
                      "$ref": "#/components/headers/Part-Signature-Header",
                      "required": true,
                      "style": "simple"
                    }
                  }
                }
              }
            },

[handrews]

The OpenAPI Specification does not explicitly support multipart/mixed, nor does JSON Schema define a mapping for it. So the answer is that if what you're doing works for you, with your tools, then it's as correct as it's going to get.

I've filed issue #3721 for adding multipart/mixed support because it comes up periodically and I thought we already had an issue for it. Closing this discussion in favor of the issue.