Support "application/*+x-ndjson" mime type in Jackson codecs

[nlescure-pictet]

Hi there,

Following on #26817, a webclient call will crash with a org.springframework.web.reactive.function.UnsupportedMediaTypeException when deserializing a response with a content-type header such as application/my.company.v1+x-ndjson.

Constant org.springframework.http.codec.json.Jackson2CodecSupport#defaultMimeTypes already supports generic json mime type application/*+json. Shouldn't it contain the ndjson generic one application/*+x-ndjson as well.

Thanks !

[nlescure-pictet]

After further analysis, I realize that within a simple WebFluxTest the test crashes on two sides:

• on the server part with a org.springframework.http.converter.HttpMessageNotWritableException
• on the client part with a org.springframework.web.reactive.function.UnsupportedMediaTypeException - which is expected

In order to fix the test I need to register such as component:

`
class NDJSONWebFluxTestFixer(private val objectMapper: ObjectMapper): WebTestClientBuilderCustomizer, WebFluxConfigurer {

override fun customize(builder: WebTestClient.Builder) {
    builder.codecs { it.customCodecs().register(
            Jackson2JsonDecoder(
                objectMapper,
                MimeType.valueOf("application/*+x-ndjson")
            )
    ) }
}

override fun configureHttpMessageCodecs(configurer: ServerCodecConfigurer) {
    configurer.customCodecs().register(Jackson2JsonEncoder(
        objectMapper,
        MimeType.valueOf("application/*+x-ndjson")
    ))
}

}`

I tend to think that once the org.springframework.http.codec.json.Jackson2CodecSupport#defaultMimeTypes has the generic ndjson part, the test will work out of the box.

Cheers

[catturtle123]

Hi @bclozel ,

I noticed the recent title update. After looking into the issue, I think adding support for application/*+x-ndjson in Jackson2CodecSupport, consistent with how application/*+json is handled, is the right approach.

This would let vendor-suffixed NDJSON types be recognized naturally. If the team agrees, I can submit a small PR.