[BUG][PHP][PSR18] Invalid client generation when request body is json or xml

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 have generated PHP PSR-18 clients and models from an external API. The OpenAPI spec has a POST endpoint which supports json and xml format in the request body. In this case the generated code of the create*Request method looks weird. It produces this passage:

$headers = $this->headerSelector->selectHeaders(
    [],
    'application/jsonapplication/xml',
    $multipart
);

which leads to an error, because it uses application/jsonapplication/xml as Content-Type, which is obviously wrong, and it fails with the following

TypeError: GuzzleHttp\Psr7\Request::withBody(): Argument #1 ($body) must be of type Psr\Http\Message\StreamInterface, Test\Api\Models\CreateUserTaskRequest given, called in /srv/htdocs/tests/openapi-generator/generated/lib/Clients/DefaultClient.php on line 413

openapi-generator version

generator cli version: 7.11.0

OpenAPI declaration file content or url

The API is not public, so I have taken the specific endpoint and anonymized the spec. But the issue is reproducible with it.

openapi: 3.0.1
info: {title: Test API, description: test description, version: 1.8.8}
servers: [{url: https://example.com/api}]
paths:
    /usertasks:
        post:
            summary: Create a task
            description: "Create a new task for a user"
            operationId: createUserTask
            requestBody:
                content:
                    application/json:
                        schema:
                            $ref: '#/components/schemas/CreateUserTaskRequest'
                    application/xml:
                        schema:
                            $ref: '#/components/schemas/CreateUserTaskRequest'
                required: true
            responses:
                "204":
                    $ref: '#/components/responses/NoContent'
                "400":
                    $ref: '#/components/responses/BadRequest'
components:
    schemas:
        CreateUserTaskRequest:
            required:
                - channel
                - subject
                - text
                - type
            type: object
            properties:
                subject:
                    type: string
                    description: Title
                text:
                    type: string
                    description: Description
                channel:
                    description: Channel
                    $ref: '#/components/schemas/UserTaskChannel'
                type:
                    type: string
                    description: Task type
            description: Create task
            xml:
                name: userTaskRequest
        UserTaskChannel:
            type: string
            description: Channel
            enum: [BACKOFFICE, LOGISTICS, TRADING]
    responses:
        BadRequest:
            description: Invaid request, e.g. syntax error, exceeding limit
        NoContent:
            description: "Request successfull, but no response"

Generation Details

I have used this snippet for the generation:

npx @openapitools/openapi-generator-cli@2.15.3 generate \
        -o generated \
        -i openapi.yaml \
        --api-name-suffix Client \
        -g php \
        --additional-properties 'apiPackage=Clients' \
        --additional-properties 'modelPackage=Models' \
        --additional-properties 'invokerPackage=Test\\Api' \
        --additional-properties 'library=psr-18'

Steps to reproduce

1. Generate the code with the snippet above.
2. Open the file ./generated/test/Api/DefaultClientTest.php
3. Insert the following code into the prepared testCreateUserTask() method:

        $client = new DefaultClient();

        $data = new CreateUserTaskRequest([
            'subject' => 'test',
            'text' => 'test',
            'channel' => 'BACKOFFICE',
            'type' => 'test',
        ]);
        $client->createUserTask($data);

5. do a composer install
6. run vendor/bin/phpunit

Then you should get the error mentioned above.

Related issues/PRs

I did not found any

Suggest a fix

When I comment out these lines in the spec:

                    application/xml:
                        schema:
                            $ref: '#/components/schemas/CreateUserTaskRequest'

The correct code is generated. So my guess is that the generator cannot handle different media types in the request body. Maybe in such cases there should be a further parameter in the client method (in this case createUserTask()) to pass the desired content-type.

Reproduce the issue with the supplied OpenAPI YAML and the npx @openapitools/openapi-generator-cli@2.15.3 command, then inspect the generated DefaultClient.php and DefaultClientTest.php. Compare generation with both media types against JSON alone, and run composer install followed by vendor/bin/phpunit; done means the generated PSR-18 client handles the request body and content type correctly for JSON and XML.