[BUG][JAVA] Wrong request body created for array of files upload

Java code generated for request body for multi-part form data does not put the content of the files in request body, instead it places the file path and name in the request body.

WGET OpenAPI generator version 3.3.4 via instructions on Github README

OpenAPI yaml openapi-upload-files.yaml

openapi: 3.0.0
info:
  title: OpenApi file upload request body
  version: "1.0.0"
  contact:
    name: Walt Shands
    email: jshands@ucsc.edu
tags:
        - name: upload_test
          description: test multipart upload
paths:
  /runs:
    post:
      summary: Upload an array of files.
      description: >-
        This endpoint uploads an array of files.

      operationId: UploadFiles
      responses:
        '200':
          description: ''
        '400':
          description: The request is malformed.
        '401':
          description: The request is unauthorized.
        '403':
          description: The requester is not authorized to perform this action.
        '500':
          description: An unexpected error occurred.

      tags:
        - UploadFilesService
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                file_list:
                  type: array
                  items:
                    type: string
                    format: binary

Build client from OpenApi yaml with OpenAPI generator

java -jar <path>/openapi-generator-cli.jar generate -l java -i <path>/openapi-upload-files.yaml

Java class used for generation of POST request

package io.arrayoffiles;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import org.openapitools.client.ApiClient;
import org.openapitools.client.ApiException;
import org.openapitools.client.api.UploadFilesServiceApi;

public class PostArrayOfFiles {
    public static void main(String[] args) {
        UploadFilesServiceApi apiInstance = new UploadFilesServiceApi();
        try {
            ApiClient apiClient = apiInstance.getApiClient();
            //apiClient.setBasePath("http://0.0.0.0:8080");
            apiClient.setBasePath("http://swagger.io");

            List<File> uploadFileList = new ArrayList<File>();
            File testfile = new File("Users/waltershands/junk/test1.txt");
            uploadFileList.add(testfile);
            testfile = new File("Users/waltershands/junk/test2.txt");
            uploadFileList.add(testfile);

            apiInstance.uploadFiles(uploadFileList);
        } catch (ApiException var4) {
            System.err.println("Exception when calling uploadFileList");
            var4.printStackTrace();
        }
    }
}

Compile test program

javac -cp <path to openapi generated client>/target/openapi-java-client-1.0.0.jar <path>/src/main/java/io/arrayoffiles/PostArrayOfFiles.java 

Monitor POST requests in another terminal window

sudo tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'

Run test program

java -debug -cp <path to PostArrayOfFiles class>/target/classes:<path to openapi generated client>target/*:<path to other needed jars>/target/lib/*  io.arrayoffiles.PostArrayOfFiles

Produces this POST request body (seen in tcpdump window):

...
User-Agent: OpenAPI-Generator/1.0.0/java
Content-Type: multipart/form-data; boundary=616f0c35-868f-443c-b8f7-676d25a52c4b
Content-Length: 223
Host: swagger.io
Connection: Keep-Alive
Accept-Encoding: gzip

--616f0c35-868f-443c-b8f7-676d25a52c4b
Content-Disposition: form-data; name="file_list"
Content-Length: 67

Users/waltershands/junk/test1.txt,Users/waltershands/junk/test2.txt
--616f0c35-868f-443c-b8f7-676d25a52c4b--
...

There should have been two bodies with Content-Disposition that included a 'filename="test<#>.txt" and the contents of the file

ApiClient.java creates a correct body only if the instance of the formParams Object is a File, but in the test case it is a List of Files and so the correct body is not created.

Start with ApiClient.java multipart handling and reproduce the generated Java client from openapi-upload-files.yaml using the supplied generation command. Compare the existing File handling with the List case; done means the array upload emits separate file parts with filenames and file contents rather than comma-joined paths.