fix(gen): set Explode:false for multipart arrays

[Liooo]

problem

• currently the gen code from the schema below raises invalid length uuid error, when receiving multiple array items

  requestBody:
    content:
      multipart/form-data:
        schema:
        	type: object
             properties:
               ids:
                 type: array
                 items:
                   type: string
                   format: uuid

• here, there seems to be multiple possible ways to describe array in multipart/form-data as I looked shallowly on the internet (no canonical information like RFC kind), for example:

  • 1. single key comma separated

    ------WebKitFormBoundaryBrahBrah
    Content-Disposition: form-data; name="ids"
    <uuid1>,<uuid2>
    

  • 2. multiple keys

    ------WebKitFormBoundaryBrahBrah
    Content-Disposition: form-data; name="ids"
    <uuid1>
    
    ------WebKitFormBoundaryBrahBrah
    Content-Disposition: form-data; name="ids"
    <uuid2>
    

  • 3. multiple bracketed keys

    ------WebKitFormBoundaryBrahBrah
    Content-Disposition: form-data; name="ids[]"
    <uuid1>
    
    ------WebKitFormBoundaryBrahBrah
    Content-Disposition: form-data; name="ids[]"
    <uuid2>
    

• the error above occurs when format 1. is specified, because ogen uses hardcoded Explode:true for the array decoding, and then parse comma separated values as a single uuid

solution

set Explode to false for multipart array

others

• seems like there's encoding field that can be used to specify the style and explode of multipart data, which was introduced from OpenAPI3.1 , ideally we might wanna see this field someday
  • though ogen generated code uses ParseMultipartForm() from standard http package before its own parsing logic, and seems like this one accepts the format 1. only (for format 2. and 3. only first item is picked and the rest is ignored this might not be true), and might need more investigation to thoroughly support things

[Liooo]

this part might have been my misunderstanding, seems like ParseMultipartForm does render format 2.

though ogen generated code uses ParseMultipartForm() from standard http package before its own parsing logic, and seems like this one accepts the format 1. only

The solution may be just about supporting encoding field and allowing explode: false.