[BUG] [JAVA] High memory consumption when uploading a file

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

I am uploading a 700 MB zip file with the generated client of the following api definition.
The memory, according to the taks manager, skyrockets to about 4 GB.
When i limit the memory via -Xmx, then i get an OutOfMemoryError.

Exception:
java.lang.OutOfMemoryError: Java heap space at java.base/java.lang.StringCoding.decodeUTF8_0(StringCoding.java:733) at java.base/java.lang.StringCoding.decodeUTF8(StringCoding.java:725) at java.base/java.lang.StringCoding.decode(StringCoding.java:257) at java.base/java.lang.String.<init>(String.java:507) at java.base/java.lang.String.<init>(String.java:561) at okio.Buffer.readString(Buffer.kt:313) at okio.Buffer.readUtf8(Buffer.kt:297) at client.communication.rest.gen.invoker.ApiClient.requestBodyToString(ApiClient.java:1569) at client.communication.rest.gen.invoker.ApiClient.buildRequest(ApiClient.java:1220) at client.communication.rest.gen.invoker.ApiClient.buildCall(ApiClient.java:1168) at client.communication.rest.gen.api.FileApi.postFileCall(FileApi.java:542) at client.communication.rest.gen.api.FileApi.postFileValidateBeforeCall(FileApi.java:557) at client.communication.rest.gen.api.FileApi.postFileAsync(FileApi.java:617)

openapi-generator version

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  description: Server REST API
  title: Server
  version: 1.0.1
servers:
  - description: Server url definition
    url: '{protocol}://{domain}:{port}/{path}'
    variables:
      protocol:
        default: https
        enum:
          - http
          - https
      domain:
        default: localhost
        description: Domain assigned by the service provider
      port:
        default: '33003'
        description: Port assigned by the service provider
      path:
        default: api
        description: The path for the API resources
security:
  - apiKeyAuth: []
tags:
  - name: File
paths:
  /file/{type}/{id}:
    delete:
      description: Deletes a File
      operationId: deleteFile
      parameters:
        - description: Id for the file path
          in: path
          name: id
          required: true
          schema:
            format: integer
            type: integer
        - description: File Type for the file path.
          in: path
          name: type
          required: true
          schema:
            $ref: '#/components/schemas/fileType'
      responses:
        '200':
          description: File successfully deleted
        '401':
          description: API key is missing or invalid
          headers:
            X-API-KEY:
              explode: false
              schema:
                type: string
              style: simple
      tags:
        - File
    get:
      description: Provides a file, if available
      operationId: getFile
      parameters:
        - description: Id for the file path.
          in: path
          name: id
          required: true
          schema:
            format: integer
            type: integer
        - description: File Type for the file path.
          in: path
          name: type
          required: true
          schema:
            $ref: '#/components/schemas/fileType'
      responses:
        '200':
          content:
            application/octet-stream:
              schema:
                format: binary
                type: string
          description: Success
        '401':
          description: API key is missing or invalid
          headers:
            X-API-KEY:
              explode: false
              schema:
                type: string
              style: simple
      tags:
        - File
    post:
      description: Uploads a File
      operationId: postFile
      parameters:
        - description: Id for the file path.
          in: path
          name: id
          required: true
          schema:
            format: integer
            type: integer
        - description: File Type for the file path.
          in: path
          name: type
          required: true
          schema:
            $ref: '#/components/schemas/fileType'
      requestBody:
        content:
          application/octet-stream:
            schema:
              format: binary
              type: string
      responses:
        '200':
          description: File successfully uploaded
        '401':
          description: API key is missing or invalid
          headers:
            X-API-KEY:
              explode: false
              schema:
                type: string
              style: simple
      tags:
        - File
components:
  parameters:
    filePathId:
      description: Id for the file path.
      in: path
      name: id
      required: true
      schema:
        format: integer
        type: integer
    filePathType:
      description: File Type for the file path.
      in: path
      name: type
      required: true
      schema:
        $ref: '#/components/schemas/fileType'
  responses:
    Unauthorized:
      description: API key is missing or invalid
      headers:
        X-API-KEY:
          explode: false
          schema:
            type: string
          style: simple
    fileAvailableResponse:
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/fileAvailableResponse'
      description: File Availability Response
  schemas:
    fileType:
      description: Type of a File
      enum:
        - TEXT
        - PDF
      title: File Type
      type: string
    fileAvailableResponse:
      properties:
        available:
          description: If the requested file is available or not
          type: boolean
      required:
        - available
      title: File Availability Response
      type: object
  securitySchemes:
    apiKeyAuth:
      in: header
      name: X-API-KEY
      type: apiKey

Generation Details

Gradle Plugin: id 'org.openapi.generator' version '6.6.0'
Task Config:
tasks.register('buildOpenApiClientSource', GenerateTask) { generatorName = "java" inputSpec = "$buildDir/generated/server_openapi.json".toString() outputDir = "$buildDir/generated".toString() apiPackage = "client.communication.rest.gen.api" modelPackage = "client.communication.rest.gen.model" invokerPackage = "client.communication.rest.gen.invoker" generateModelTests = false generateModelDocumentation = false generateApiTests = false generateApiDocumentation = false cleanupOutput = false configOptions.put("sourceFolder", "src/gen/java") configOptions.put("booleanGetterPrefix", "is") configOptions.put("enumUnknownDefaultCase", "true") configOptions.put("dateLibrary", "java8") configOptions.put("useGzipFeature", "false") configOptions.put("serializableModel", "true") configOptions.put("serializationLibrary", "gson") configOptions.put("hideGenerationTimestamp", "true") }

Steps to reproduce

Upload a file with the generated client.

Related issues/PRs

Suggest a fix

As a temporary fix i created a sub class, overrode the method, copied the code from the generated code and passed null as a payload for the method updateParamsForAuth.

The payload was added with https://github.com/OpenAPITools/openapi-generator/commit/c06a21e63806546562d82d9e5e15f0060d0d3c1c.

I found the Pull Request https://github.com/OpenAPITools/openapi-generator/pull/10858 for the library jersey.
In the library jersey the ApiClient.mustache the payload is only filled if a signature method is present:
{{#hasHttpSignatureMethods}} serializeToString(body, formParams, contentType, isBodyNullable), {{/hasHttpSignatureMethods}} {{^hasHttpSignatureMethods}} null, {{/hasHttpSignatureMethods}}

Maybe this can be added for the okhttp-gson.

Start with the generated ApiClient.java stack-trace locations, especially requestBodyToString and buildRequest, then inspect the okhttp-gson ApiClient.mustache template. Compare its payload handling with the jersey template shown from PR #10858 and reproduce through the Gradle buildOpenApiClientSource task using the supplied specification. Done means a large binary upload no longer creates the reported heap exhaustion.