Openapi-generator: [BUG] [JavaScript] java.lang.OutOfMemoryError on simple OpenAPI file

[advance512]

Description

Using the following OpenAPI file below, the following error occurs:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at java.util.Arrays.copyOfRange(Arrays.java:3664)
    at java.lang.String.<init>(String.java:207)
    at java.lang.StringBuilder.toString(StringBuilder.java:407)
    at com.fasterxml.jackson.core.util.TextBuffer.contentsAsString(TextBuffer.java:404)
    at com.fasterxml.jackson.core.io.SegmentedStringWriter.getAndClear(SegmentedStringWriter.java:83)
    at com.fasterxml.jackson.databind.ObjectWriter.writeValueAsString(ObjectWriter.java:999)
    at io.swagger.v3.core.util.Json.pretty(Json.java:24)
    at org.openapitools.codegen.DefaultCodegen.fromModel(DefaultCodegen.java:1627)
    at org.openapitools.codegen.languages.JavascriptClientCodegen.fromModel(JavascriptClientCodegen.java:842)
    at org.openapitools.codegen.DefaultCodegen.fromOperation(DefaultCodegen.java:2437)
    at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:1021)
    at org.openapitools.codegen.DefaultGenerator.processPaths(DefaultGenerator.java:944)
    at org.openapitools.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:516)
    at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:902)
    at org.openapitools.codegen.cmd.Generate.run(Generate.java:368)
    at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:60)

openapi-generator version

This happens both in openapi-generator-cli-4.0.0-20190325.151629-451.jar and openapi-generator-cli-3.3.4.jar.

OpenAPI declaration file content or url

swagger: '2.0'
info:
  version: "1.0"
  title: DEV-2369

# ===============================================================================
# Paths
# ===============================================================================

paths:

  /users/responders:

    get:
      operationId: getUserResponderList
      summary: Gets a list of Responder objects
      responses:
        '200':
          description: A list of Responder objects
          schema:
            $ref: '#/definitions/ResponderList'
        '500':
          $ref: '#/responses/InternalServerError'
        default:
          $ref: '#/responses/TotallyUnexpectedResponse'

  /responders:

    post:
      operationId: createResponder
      parameters:
        - name: responder
          in: body
          required: true
          schema:
            $ref: '#/definitions/ResponderCreate'
      responses:
        '201':
          description: A Responder object
          schema:
            $ref: '#/definitions/Responder'
        '400':
          $ref: '#/responses/BadRequest'
        '500':
          $ref: '#/responses/InternalServerError'
        default:
          $ref: '#/responses/TotallyUnexpectedResponse'


# ===============================================================================
# Definitions
# ===============================================================================

definitions:

  ID:
    type: integer
    format: int64
    readOnly: true

  Reviewer:
    type: object
    properties:
      name:
        type: string
        maxLength: 100

  SuccessfulBugFix:
    type: object
    properties:
      reviewers:
        type: array
        minItems: 0
        maxItems: 100
        uniqueItems: true
        items:
          $ref: '#/definitions/Reviewer'

  ResponderProfileCreate:
    type: object
    properties:
      successfulBugFixes:
        type: array
        minItems: 0
        maxItems: 100
        uniqueItems: true
        items:
          $ref: '#/definitions/SuccessfulBugFix'

  ResponderProfile:
    type: object
    properties:
      successfulBugFixes:
        type: array
        minItems: 0
        maxItems: 100
        uniqueItems: true
        items:
          $ref: '#/definitions/SuccessfulBugFix'

  Error:
    type: object
    required:
      - message
    properties:
      message:
        type: string


  User:
    type: object
    properties:
      id:
        $ref: '#/definitions/ID'

  Responder:
    type: object
    properties:
      id:
        $ref: '#/definitions/ID'
      responderProfile:
        $ref: '#/definitions/ResponderProfile'

  # Used only for the creation of a new Responder
  ResponderCreate:
    type: object
    properties:
      responderProfile:
        $ref: '#/definitions/ResponderProfileCreate'

  ResponderList:
    type: object
    required:
      - items
    properties:
      items:
        type: array
        minItems: 0
        maxItems: 1000
        uniqueItems: true
        items:
          $ref: '#/definitions/Responder'



# ===============================================================================
# Responses
# ===============================================================================

responses:

  InternalServerError:
    description: An unexpected error occured.
    schema:
      $ref: '#/definitions/Error'
  BadRequest:
    description: Bad request; could not perform requested operation.
  EntityDoesNotExist:
    description: Entity does not exist.
  TotallyUnexpectedResponse:
    description: A totally unexpected response

Command line used for generation

java -jar ./openapi-generator-cli-3.3.4.jar generate -i ../openapi.yaml -l javascript --additional-properties usePromises=true --additional-properties useES6=false -o ./javascript/

also:
java -jar ./openapi-generator-cli-4.0.0-20190325.151629-451.jar generate -i ../openapi.yaml -g javascript -o ./javascript/

also:
java -jar ./openapi-generator-cli-4.0.0-20190325.151629-451.jar generate -i ../openapi.yaml -g javascript --additional-properties usePromises=true --additional-properties useES6=false -o ./javascript/

Steps to reproduce

1. Save the OpenAPI spec into a file called openapi.yaml.
2. Run either of the commands above.

Related issues/PRs

None that I am aware of.

Suggest a fix

Not sure.

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[macjohnny]

by changing

definitions:
  Reviewer:
    type: string

the issue does not occur.
somehow the memory issue occurs due to the deep-nesting of objects

[advance512]

Super strange, ain't it? :)

[macjohnny]

It is. Maybe you could investigate the problem using the stacktrace?

[advance512]

We side-stepped the problem for now.
Unfortunately, I am not a Java developer and don't have time to go deep into this, as I am terribly busy with my own startup... but we will offer a bounty for fixing this, as soon as BountySource wake up and pay our previous bounties to those claiming them.

[macjohnny]

it seems that DefaultCodegen::fromModel is called twice for name = "ResponderList"
the first call works and schema in https://github.com/OpenAPITools/openapi-generator/blob/46e8ccbd1ec7482f665e63eaf036f16e1af432e3/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java#L1627 contains the following object:

schema

class ObjectSchema {
    class Schema {
        title: null
        multipleOf: null
        maximum: null
        exclusiveMaximum: null
        minimum: null
        exclusiveMinimum: null
        maxLength: null
        minLength: null
        pattern: null
        maxItems: null
        minItems: null
        uniqueItems: null
        maxProperties: null
        minProperties: null
        required: [items]
        type: null
        not: null
        properties: {items=class ArraySchema {
            class Schema {
                title: null
                multipleOf: null
                maximum: null
                exclusiveMaximum: null
                minimum: null
                exclusiveMinimum: null
                maxLength: null
                minLength: null
                pattern: null
                maxItems: 1000
                minItems: 0
                uniqueItems: true
                maxProperties: null
                minProperties: null
                required: null
                type: null
                not: null
                properties: null
                additionalProperties: null
                description: null
                format: null
                $ref: null
                nullable: null
                readOnly: null
                writeOnly: null
                example: null
                externalDocs: null
                deprecated: null
                discriminator: null
                xml: null
            }
            type: array
            items: class Schema {
                title: null
                multipleOf: null
                maximum: null
                exclusiveMaximum: null
                minimum: null
                exclusiveMinimum: null
                maxLength: null
                minLength: null
                pattern: null
                maxItems: null
                minItems: null
                uniqueItems: null
                maxProperties: null
                minProperties: null
                required: null
                type: null
                not: null
                properties: null
                additionalProperties: null
                description: null
                format: null
                $ref: #/components/schemas/Responder
                nullable: null
                readOnly: null
                writeOnly: null
                example: null
                externalDocs: null
                deprecated: null
                discriminator: null
                xml: null
            }
        }}
        additionalProperties: null
        description: null
        format: null
        $ref: null
        nullable: null
        readOnly: null
        writeOnly: null
        example: null
        externalDocs: null
        deprecated: null
        discriminator: null
        xml: null
    }
    type: object
    defaultObject: null
}

but in the second call, schema contains the following object:

schema

class ObjectSchema {
    class Schema {
        title: null
        multipleOf: null
        maximum: null
        exclusiveMaximum: null
        minimum: null
        exclusiveMinimum: null
        maxLength: null
        minLength: null
        pattern: null
        maxItems: null
        minItems: null
        uniqueItems: null
        maxProperties: null
        minProperties: null
        required: [items]
        type: null
        not: null
        properties: {items=class ArraySchema {
            class Schema {
                title: null
                multipleOf: null
                maximum: null
                exclusiveMaximum: null
                minimum: null
                exclusiveMinimum: null
                maxLength: null
                minLength: null
                pattern: null
                maxItems: 1000
                minItems: 0
                uniqueItems: true
                maxProperties: null
                minProperties: null
                required: null
                type: null
                not: null
                properties: null
                additionalProperties: null
                description: null
                format: null
                $ref: null
                nullable: null
                readOnly: null
                writeOnly: null
                example: null
                externalDocs: null
                deprecated: null
                discriminator: null
                xml: null
            }
            type: array
            items: class Schema {
                title: null
                multipleOf: null
                maximum: null
                exclusiveMaximum: null
                minimum: null
                exclusiveMinimum: null
                maxLength: null
                minLength: null
                pattern: null
                maxItems: null
                minItems: null
                uniqueItems: null
                maxProperties: null
                minProperties: null
                required: null
                type: null
                not: null
                properties: null
                additionalProperties: null
                description: null
                format: null
                $ref: #/components/schemas/Responder
                nullable: null
                readOnly: null
                writeOnly: null
                example: null
                externalDocs: null
                deprecated: null
                discriminator: null
                xml: null
            }
        }}
        additionalProperties: null
        description: null
        format: null
        $ref: null
        nullable: null
        readOnly: null
        writeOnly: null
        example: {items=[Ljava.lang.Object;@1cfd1875}
        externalDocs: null
        deprecated: null
        discriminator: null
        xml: null
    }
    type: object
    defaultObject: null
}

The only difference seems to be

example: {items=[Ljava.lang.Object;@1cfd1875}

where items is an object with 1000 entries similar to

{responderProfile={successfulBugFixes=[Ljava.lang.Object;@1af7f54a}, id=0}

it seems that the example-generation with 1000 entries is clearly an overkill and leads to a memory issue for many nested objects.

[macjohnny]

the relevant code that generates the examples is located here:
https://github.com/OpenAPITools/openapi-generator/blob/46e8ccbd1ec7482f665e63eaf036f16e1af432e3/modules/openapi-generator/src/main/java/org/openapitools/codegen/examples/ExampleGenerator.java#L234

it creates arrays of length maxItems.

@advance512 a simple workaround for you:
explicitly define an example in the models where you use type: array properties in combination with maxItems, e.g.:

definitions:
  ResponderList:
    type: object
    required:
      - items
    properties:
      items:
        type: array
        minItems: 0
        maxItems: 1000
        uniqueItems: true
        items:
          $ref: '#/definitions/Responder'
    example:
      items: []

so this is your adapted spec where the issue does not occur anymore:

adapted spec

swagger: '2.0'
info:
  version: "1.0"
  title: DEV-2369

# ===============================================================================
# Paths
# ===============================================================================

paths:

  /users/responders:

    get:
      operationId: getUserResponderList
      summary: Gets a list of Responder objects
      responses:
        '200':
          description: A list of Responder objects
          schema:
            $ref: '#/definitions/ResponderList'
        '500':
          $ref: '#/responses/InternalServerError'
        default:
          $ref: '#/responses/TotallyUnexpectedResponse'

  /responders:

    post:
      operationId: createResponder
      parameters:
        - name: responder
          in: body
          required: true
          schema:
            $ref: '#/definitions/ResponderCreate'
      responses:
        '201':
          description: A Responder object
          schema:
            $ref: '#/definitions/Responder'
        '400':
          $ref: '#/responses/BadRequest'
        '500':
          $ref: '#/responses/InternalServerError'
        default:
          $ref: '#/responses/TotallyUnexpectedResponse'


# ===============================================================================
# Definitions
# ===============================================================================

definitions:

  ID:
    type: integer
    format: int64
    readOnly: true

  Reviewer:
    type: object
    properties:
      name:
        type: string
        maxLength: 100

  SuccessfulBugFix:
    type: object
    properties:
      reviewers:
        type: array
        minItems: 0
        maxItems: 100
        uniqueItems: true
        items:
          $ref: '#/definitions/Reviewer'
    example:
      reviewers: []

  ResponderProfileCreate:
    type: object
    properties:
      successfulBugFixes:
        type: array
        minItems: 0
        maxItems: 100
        uniqueItems: true
        items:
          $ref: '#/definitions/SuccessfulBugFix'

  ResponderProfile:
    type: object
    properties:
      successfulBugFixes:
        type: array
        minItems: 0
        maxItems: 100
        uniqueItems: true
        items:
          $ref: '#/definitions/SuccessfulBugFix'
    example:
      successfulBugFixes: []

  Error:
    type: object
    required:
      - message
    properties:
      message:
        type: string


  User:
    type: object
    properties:
      id:
        $ref: '#/definitions/ID'

  Responder:
    type: object
    properties:
      id:
        $ref: '#/definitions/ID'
      responderProfile:
        $ref: '#/definitions/ResponderProfile'

  # Used only for the creation of a new Responder
  ResponderCreate:
    type: object
    properties:
      responderProfile:
        $ref: '#/definitions/ResponderProfileCreate'

  ResponderList:
    type: object
    required:
      - items
    properties:
      items:
        type: array
        minItems: 0
        maxItems: 1000
        uniqueItems: true
        items:
          $ref: '#/definitions/Responder'
    example:
      items: []



# ===============================================================================
# Responses
# ===============================================================================

responses:

  InternalServerError:
    description: An unexpected error occured.
    schema:
      $ref: '#/definitions/Error'
  BadRequest:
    description: Bad request; could not perform requested operation.
  EntityDoesNotExist:
    description: Entity does not exist.
  TotallyUnexpectedResponse:
    description: A totally unexpected response

your maxItems: 1000 is just a little below the value 1024 that would trigger a warning
https://github.com/OpenAPITools/openapi-generator/blob/46e8ccbd1ec7482f665e63eaf036f16e1af432e3/modules/openapi-generator/src/main/java/org/openapitools/codegen/examples/ExampleGenerator.java#L234-L244

Anyway, even the trigger value of 1024 is not useful if the spec contains many nested objects.

If you feel like this answer solves the problem for you, feel free to contribute a bounty here: https://github.com/bithost-gmbh/ngx-mat-select-search#support-development

I think this issue should be closed as it is not really a bug that can be prevented in every possible situation.

[advance512]

Thanks for your help, @macjohnny.

Say, why does the generator instantiate a thousand objects of responderProfile? What is the point?
If we're talking about an example object that is being generated - first of all, where is it used? Second, why create the maximum items in an array, and not just.. 3 items, for example? Or 5? Is it not much more confusing, having an example with 1000 objects?

I think this also makes the generator itself slower than it should be.

Letting the generator crash is definitely a bug that should be fixed. It doesn't communicate anything of value to the person using the generator - there is no clear route of "how to fix the problem". A proper fix would be to cap the amount of items created in the example, I think.

We will definitely contribute a bounty. Could you cap the items in the example to 3 or 5?

[macjohnny]

I think you are right, limiting the number of objects to 5 does make sense.
The generated example is used here
https://github.com/OpenAPITools/openapi-generator/blob/3a0d520c389ddff9300f15f4e47967c8ff8b12c0/modules/openapi-generator/src/main/resources/JavaSpring/methodBody.mustache#L10-L13
and results in some server api implementations in an example response, e.g.
https://github.com/OpenAPITools/openapi-generator/blob/3a0d520c389ddff9300f15f4e47967c8ff8b12c0/samples/server/petstore/springboot/src/main/java/org/openapitools/api/PetApi.java#L85-L89

I opened PR https://github.com/OpenAPITools/openapi-generator/pull/2536 to limit the number of example items in an array to max. 5, which fixes the issue (tested with your original spec).

[advance512]

Thanks for your help, @macjohnny.

[macjohnny]

@advance512 you are welcome. Thanks for your bounty!