Spring The RestClient is configured without content-length attribute in the request header by default

Description: I'm using springboot3.2.5 and using RestClient.create() I'm getting an instance request header without content-length, which might be an error on some api service requests. But I'll change it to RestClient.builder() .requestInterceptor((request, body, execution) -> execution.execute(request, body)) After.build() gets the instance, there is content-length in the request header.Is this a bug?

Demo：

RestClient.create()
        .post()
        .uri("http://127.0.0.1:1930/api/test/haha")
        .body(map)
        .exchange((clientRequest, clientResponse) -> {
            System.out.println(clientRequest.getHeaders());
            return "";
        });

fix demo

            RestClient.builder()
                    requestInterceptor((request, body, execution) -> execution.execute(request, body))
                    .build()
                    .post()
                    .uri("http://127.0.0.1:1930/api/test/haha")
                    .body(map)
                    .exchange((clientRequest, clientResponse) -> {
                        System.out.println(clientRequest.getHeaders());
                        return "";
                    });

Comment From: bclozel

See our upgrading guide:

To reduce memory usage in RestClient and RestTemplate, most ClientHttpRequestFactory implementations no longer buffer request bodies before sending them to the server. As a result, for certain content types such as JSON, the contents size is no longer known, and a Content-Length header is no longer set. If you would like to buffer request bodies like before, simply wrap the ClientHttpRequestFactory you are using in a BufferingClientHttpRequestFactory.