Some character are not encoded in UriComponentsBuilder

I'm currently experimenting some weird behaviour when migrate from Zuul (with spring 5) to spring gateway mvc (with spring 6). During this migration, I see that the parameter are not alway correctly encoded to the downstream services.

Issue are linked to issue1 and issue2.

I reduce the scope of the issue, and observe that some parameters are not encoded in the parameter, and I really don't understand why it's the current behaviour.

Can someone explain me why this is a wanted behaviour, if not a bug?

        String uri = UriComponentsBuilder.fromPath("/user@[%&+{?")
                .scheme("http")
                .host("localhost")
                .port("9099")
                .replaceQueryParams(new LinkedMultiValueMap<>(
                        Map.of(
                                "at", List.of("@"),
                                "squareBracket", List.of("["),
                                "percent", List.of("%"),
                                "and", List.of("&"),
                                "plus", List.of("+"),
                                "bracket", List.of("{"),
                                "point", List.of("?")
                        )
                ))
                .build(false)
                .toUri()
                .toString();

// uri = http://localhost:9099/user@%5B%25&+%7B%3F?at=@&and=&&squareBracket=[&point=?&percent=%25&bracket=%7B&plus=+

Note: I voluntary keep the code close to org.springframework.cloud.gateway.server.mvc.handler.ProxyExchangeHandlerFunction#handle in spring gateway 4.1.6:

	@Override
	public ServerResponse handle(ServerRequest serverRequest) {
		URI uri = uriResolver.apply(serverRequest);
		boolean encoded = containsEncodedQuery(serverRequest.uri(), serverRequest.params());
		// @formatter:off
		URI url = UriComponentsBuilder.fromUri(serverRequest.uri())
				.scheme(uri.getScheme())
				.host(uri.getHost())
				.port(uri.getPort())
				.replaceQueryParams(serverRequest.params())
				.build(encoded)
				.toUri();
		// @formatter:on

		HttpHeaders filteredRequestHeaders = filterHeaders(this.requestHttpHeadersFilters,
				serverRequest.headers().asHttpHeaders(), serverRequest);

		boolean preserveHost = (boolean) serverRequest.attributes()
			.getOrDefault(MvcUtils.PRESERVE_HOST_HEADER_ATTRIBUTE, false);
		if (preserveHost) {
			filteredRequestHeaders.set(HttpHeaders.HOST, serverRequest.headers().firstHeader(HttpHeaders.HOST));
		}
		else {
			filteredRequestHeaders.remove(HttpHeaders.HOST);
		}

		// @formatter:off
		ProxyExchange.Request proxyRequest = proxyExchange.request(serverRequest).uri(url)
				.headers(filteredRequestHeaders)
				// TODO: allow injection of ResponseConsumer
				.responseConsumer((response, serverResponse) -> {
					HttpHeaders httpHeaders = filterHeaders(this.responseHttpHeadersFilters, response.getHeaders(), serverResponse);
					serverResponse.headers().putAll(httpHeaders);
				})
				.build();
		// @formatter:on
		return proxyExchange.exchange(proxyRequest);
	}
```

Start by reproducing the URI and query-parameter output in the issue, then read UriComponentsBuilder and ProxyExchangeHandlerFunction#handle in Spring Cloud Gateway 4.1.6. Compare the encoding behavior for each listed character and determine the expected result. Done should include an agreed behavior and regression coverage for the affected parameters.