Malformed (base64 encoded) api-docs JSON when MappingJackson2HttpMessageConverter is active

[lbenedetto]

To Reproduce
Steps to reproduce the behavior:

• Spring Boot 3.0.4 or 2.7.8
• springdoc-openapi-starter-webmvc-ui:2.0.4 or 1.6.15

@Configuration
public class ApiWebMvcConfiguration extends DelegatingWebMvcConfiguration {

  @Autowired
  Jackson2ObjectMapperBuilder jacksonBuilder;

  @Override
  protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    var applicationContext = this.getApplicationContext();
    if (applicationContext != null) {
      jacksonBuilder.applicationContext(applicationContext);
    }
    converters.add(new MappingJackson2HttpMessageConverter(jacksonBuilder.build()));
  }
}

Expected behavior

Expected:

{
    "openapi": "3.0.1",
    "info": {
        "title": "OpenAPI definition",
        "version": "v0"
    },
    "servers": [
        {
            "url": "http://localhost:8080",
            "description": "Generated server url"
        }
    ],
    "paths": {
        ...
    },
    "components": {}
}

Actual:

"eyJvcGVuYXBpIjoiMy4wLjEiLCJpbmZvIjp7InRpdGxlIjoiT3BlbkFQSSBkZWZpbml0aW9uIiwidmVyc2lvbiI6InYwIn0sInNlcnZlcnMiOlt7InVybCI6Imh0dHA6Ly9sb2NhbGhvc3Q6ODA4MCIsImRlc2NyaXB0aW9uIjoiR2VuZXJhdGVkIHNlcnZlciB1cmwifV0sInBhdGhzIjp7Ii9pZC92MS8iOnsiZ2V0Ijp7InRhZ3MiOlsiZGVtby1jb250cm9sbGVyIl0sInN1bW1hcnkiOiJPSyIsIm9wZXJhdGlvbklkIjoiaW5zdGFuY2VDb25maWciLCJyZXNwb25zZXMiOnsiMjAwIjp7ImRlc2NyaXB0aW9uIjoiT0siLCJjb250ZW50Ijp7IiovKiI6eyJzY2hlbWEiOnsidHlwZSI6InN0cmluZyJ9fX19fX19fSwiY29tcG9uZW50cyI6e319"

This causes swagger-ui to be unable to parse the response

Additional context
I believe this is caused by the changes required for fixing #2051. I tried both adding and removing StringHttpMessageConverter, but the only thing that helps is not registering MappingJackson2HttpMessageConverter

[ctruzzi]

We are facing the same issue, not sure if this was an expected regression or not but seems like more than a patch version change.

[bnasslahsen]

@lbenedetto,

As you are overriding the default spring registered HttpMessageConverter, you should have ByteArrayHttpMessageConverter registered as well!

		converters.add(new ByteArrayHttpMessageConverter());
		converters.add(new MappingJackson2HttpMessageConverter(jacksonBuilder.build()));

Please note that order is very important, when registering HttpMessageConverters.

[lbenedetto]

Ah, I had addDefaultHttpMessageConverters(converters) (which adds a ByteArrayHttpMessageConverter) but it was registered after the Jackson converter. Thanks