Change to when 'Content-Length: 0' is automatically added to a request

[alzimmermsft]

As part of an upgrade from Reactor Netty 1.0.48 to 1.2.1 we found a slight behavioral change to when Reactor Netty adds Content-Length: 0.

Using this simple reproduction:

public class ReactorNettyContentLength {
    public static void main(String[] args) {
        DisposableServer server = HttpServer.create().host("localhost").handle((request, response) -> {
            request.requestHeaders().forEach(header -> System.out.println(header.getKey() + ": " + header.getValue()));
            return response.status(200).send();
        }).bindNow();

        HttpClient httpClient = HttpClient.create();
        httpClient.request(HttpMethod.GET)
            .uri(server.host() + ":" + server.port())
            .send((request, outbound) -> {
                request.requestHeaders().set("Accept", "application/json");
                return outbound;
            })
            .response()
            .block();
    }
}

We found the headers logged by the HTTP server changed slightly.

1.0.48

user-agent: ReactorNetty/1.0.48
host: 127.0.0.1:58149
Accept: application/json

1.2.1

user-agent: ReactorNetty/1.2.1
host: 127.0.0.1:58062
Accept: application/json
content-length: 0

I don't hold a strong opinion on the correct behavior here and more so wanted to share this information in case this causes a problem for anyone else.

[violetagg]

@alzimmermsft Thanks for the details and the reproducible example. This is a regression caused by #3526

[joaodias14]

We are indeed facing problems while performing GET requests to external services that do not allow Content-Length in such requests. Thanks for checking this!

[violetagg]

@joaodias14 This is a regression of how we started to handle the use case where the send function does not change the NettyOutbound i.e.

            .send((request, outbound) -> {
                request.requestHeaders().set("Accept", "application/json");
                return outbound;
            })

We are not going to change the Reactor Netty behaviour about sending GET requests.

What is your use case?

[joaodias14]

@violetagg We are using the Netty HttpClient via Spring WebClient and with Spring Boot 3.4.1 we started to face GET requests failing when calling external services we don't own because of the inclusion of "Content-Length: 0" as a header.

Checking the HTTP Semantics, it seems that "A user agent SHOULD NOT send a Content-Length header field when the request message does not contain content and the method semantics do not anticipate such data." (in https://httpwg.org/specs/rfc9110.html#field.content-length). It is "SHOULD NOT" and not "MUST NOT", but maybe it is safer not to include the header by default in GET requests with no body.

We would be happy if we could avoid the Content-Length header being added, but so far we found no way of doing that.