How to pass any number of headers to Feign client without knowing all the names?

Question

I've a use case where I need to pass all headers that start with a certain prefix to the feign client. I don't know the number or exact names of these headers. There doesn't seem to be a way to to do this easily as the Feign client expects all headers to be specified using @RequestHeader("name"). It doesn't seem to support something like @RequestHeader HttpHeaders, which would be very useful. Any suggestions?

Answer 1

As of this writing, Feign doesn't support dynamic headers or query parameters using a Map. The Spring Cloud Feign client relies on the Spring annotations instead of Feign annotations, and the implementations of AnnotatedParameterProcessor have a bug such that they don't do what the documentation states they should be doing.

RequestHeader doc:

If the method parameter is Map, MultiValueMap, or HttpHeaders then the map is populated with all header names and values.

RequestParam doc:

If the method parameter is Map or MultiValueMap and a parameter name is not specified, then the map parameter is populated with all request parameter names and values.

I submitted a pull request that will fix this. Until then, I'm using an extension of SpringMvcContract that uses my own AnnotatedParameterProcessor implementations. I set the custom SpringMvcContract using a Feign.Builder as follows:

@Autowired
FormattingConversionService feignConversionService;

@Bean
@Scope(SCOPE_PROTOTYPE)
public Feign.Builder feignBuilder() {
    return HystrixFeign.builder()
            .contract(feignContract());
}

@Bean
public Contract feignContract() {
    return new EnhancedSpringMvcContract(feignConversionService);
}