[BUG][Go] Invalid code for files array in multipart/form-data request

[aliakseiz]

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

Files array in multipart/form-data requestBody produces following code:

// AddCard - Add card
func (c *DefaultApiController) AddCard(w http.ResponseWriter, r *http.Request) { 
	err := r.ParseForm()
	if err != nil {
		w.WriteHeader(500)
		return
	}
	
	iD, err := parseIntParameter( r.FormValue("iD"))
	if err != nil {
		w.WriteHeader(500)
		return
	}
	
	file, err := ReadFormFileToTempFile(r, "file")
	if err != nil {
		w.WriteHeader(500)
		return
	}
	
	result, err := c.service.AddCard(iD, file)
	if err != nil {
		w.WriteHeader(500)
		return
	}
	
	EncodeJSONResponse(result, nil, w)
}

Where file is of type *os.File, but service.AddCard expects []*os.File.

openapi-generator version

Reproducible with 3.4.1 and 5.0.0-beta3.

OpenAPI declaration file content or url

openapi: "3.0.0"
info:
  version: 1.0.0
  title: "Custom API"
servers:
  - url: http://localhost:8080/api/v1
    description: development server
paths:
  /cards:
    post:
      summary: Add card
      operationId: addCard
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                ID:
                  type: integer
                  format: int64
                File:
                  type: array
                  items:
                    type: string
                    format: binary
      responses:
        '200':
          description: Successful operation

Generation Details

Generated with

npx openapi-generator-cli generate -i openapi.yaml -g go-server -o server

Non-info output:

[main] WARN  o.o.codegen.DefaultCodegen - Could not compute datatypeWithEnum from *os.File, null
[main] WARN  o.o.c.languages.AbstractGoCodegen - 4.3.0 has deprecated the use of vendor extensions which don't follow lower-kebab casing standards with x- prefix.

Steps to reproduce

Generate a go-server with the command provided above or a Docker-container.

Related issues/PRs

Suggest a fix

PR (#8103)

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