[JAVA] Bug generating request body 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.

Git clone and build Swagger-codegen version 3.0.5 via instructions on Github README

Swagger 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 Swagger Codegen

java -jar <path>/swagger-codegen-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 io.swagger.client.ApiClient;
import io.swagger.client.ApiException;
import io.swagger.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 generated swagger client>/target/swagger-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 generated swagger client>target/*:<path to other needed swagger jars>/target/lib/*  io.arrayoffiles.PostArrayOfFiles

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

....    wU5POST /runs HTTP/1.1
User-Agent: Swagger-Codegen/1.0.0/java
Content-Type: multipart/form-data; boundary=e2b790d8-0149-47ac-8740-755c53c982c3
Content-Length: 223
Host: swagger.io
Connection: Keep-Alive
Accept-Encoding: gzip

--e2b790d8-0149-47ac-8740-755c53c982c3
Content-Disposition: form-data; name="file_list"
Content-Length: 67

Users/waltershands/junk/test1.txt,Users/waltershands/junk/test2.txt
--e2b790d8-0149-47ac-8740-755c53c982c3--
...

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.

...
1109     public RequestBody buildRequestBodyMultipart(Map<String, Object> formParams) {$
1110         MultipartBuilder mpBuilder = new MultipartBuilder().type(MultipartBuilder.FORM);$
1111         for (Entry<String, Object> param : formParams.entrySet()) {$
1112             if (param.getValue() instanceof File) {$
1113                 File file = (File) param.getValue();$
1114                 Headers partHeaders = Headers.of("Content-Disposition", "form-data; name=\"" + param.getKey() + "\"; filename=\"" + fi     le.getName() + "\"");$
1115                 MediaType mediaType = MediaType.parse(guessContentTypeFromFile(file));$
1116                 mpBuilder.addPart(partHeaders, RequestBody.create(mediaType, file));$

Reproduce the issue with openapi-upload-files.yaml and the generated Java client, then inspect ApiClient.java in buildRequestBodyMultipart around lines 1109-1116. Confirm the multipart handling for a List; done means the request contains separate file parts with filenames and file contents instead of comma-joined file paths.