Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

I want to define api for 'Multiple File Upload' which refer the part in swagger document File Upload.
But the generated script deals with binaries as simple string.

localVarFormParams.append('files', files.join(COLLECTION_FORMATS.csv));

openapi-generator version

v4.3.1

OpenAPI declaration file content or url

I added encoding parameter to force form style but not works well.

openapi: 3.0.3
info:
  title: test
  version: '0.1'
tags:
  - name: test
    description: test
servers:
  - url: 'http://localhost:3000'
paths:
  /api/upload:
    post:
      tags: []
      operationId: upload files
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                message:
                  type: string
                files:
                  type: array
                  items:
                    type: string
                    format: binary
              required:
                - message
            encoding:
              files:
                style: form
                explode: true
      responses:
        '200':
          description: ok

Generation Details

use this command.

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:v4.3.1 generate \
    -p supportsES6=true \
    -p modelPropertyNaming=camelCase \
    -i /local/doc/test.yaml \
    -g typescript-axios \
    -o /local/app/javascript --verbose

Steps to reproduce

just run by above command, then it generate following script.

                if (files) {
                       localVarFormParams.append('files', files.join(COLLECTION_FORMATS.csv));
            }

here is verbose output https://gist.github.com/shrkw/5002c71e33177b99c0529f1506d6ff22

and api.ts https://gist.github.com/shrkw/5002c71e33177b99c0529f1506d6ff22#file-api-ts-L77

Related issues/PRs

Not sure but may be same issue.

BUG multi file upload not implemented fully · Issue #6752 · OpenAPITools/openapi-generator · GitHub

Same issue is facing to this guy.
BUGJavaSpring multiple files upload · Issue #4803 · OpenAPITools/openapi-generator · GitHub

Suggest a fix

I want to set isCollectionFormatMulti attribute, but not sure how to do it.

openapi-generator/apiInner.mustache at f752f29af202885e6b817e5ec002facee1ef0c33 · OpenAPITools/openapi-generator · GitHub

            {{#isCollectionFormatMulti}}
                {{paramName}}.forEach((element) => {
                    localVarFormParams.append('{{baseName}}', element as any);
                })
            {{/isCollectionFormatMulti}}