Wrong Forwarded header when original X-Forwarded-For is an IPv6

[ZIRAKrezovic]

When X-Forwarded-For contains an IPv6 and server.forward-headers-strategy is set to framework, Gateway will pass an incorrect Forwarded header to downstream, as shown in the picture - resulting in an exception being thrown in services that also set server.forward-headers-strategy=framework

I have narrowed down issue to spring-cloud-gateway, as nothing else seems to add Forwarded header. I have prepared a reproducer that demonstrates this using IPv6 only haproxy and docker

https://github.com/ZIRAKrezovic/gateway-reproducer.git

There is a single test that starts 3 containers and uses ipv6 only to communicate, up to returning back to host (gateway) on 8080. Make sure to adjust the port in haproxy.cfg and application.properties if they should be changed.

The test contains a commented out direct entry to its own "/test" REST resource, and a call that causes the issue to "/testgateway", that simply routes back to itself and rewrites the path to "/test"

[ZIRAKrezovic]

I can also reproduce this by using WebClient. Example has been updated.

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.DEFINED_PORT)
class DemoApplicationSimpleTests {
    @Autowired
    private WebTestClient webClient;

    @Test
    void contextLoads() {
        webClient.get()
                // working url, bypasses gateway
                //.uri("/test")
                .uri("/testgateway")
                .header("X-Forwarded-For", "fd00:fefe:1::4")
                .exchange()
                .expectStatus()
                .isOk();
    }
}