JdkClientHttpRequest does not support Content-Length 0

[dciarniello]

Affects: Spring Framework 6.1.0-M5 (via Spring Boot 3.2.0-M3)

With an @HttpExchange interface that only has @RequestParam parameters similar to

public interface MyClient {
  @PostExchange("/path")
  ResponseEntity<String> someCall(@RequestParam("param") String param);
}

and a RestClient configured with a BufferingClientHttpRequestFactory:

var restClient = RestClient.builder()
  .url("url")
  .requestFactory(new BufferingClientHttpRequestFactory(new JdkClientHttpRequestFactory()))
  .build();

calls to the service result error out with the message non-positive contentLength: 0.

The call can be made to work by either removing the requestFactory call to the RestClient builder or by adding a dummy @RequestBody parameter to the interface

public interface MyClient {
  @PostExchange("/path")
  ResponseEntity<String> someCall(@RequestParam("param") String param,
      @RequestBody String dummy);
}

The problem, I believe, is in the content length check in org.springframework.http.client.JdkClientHttpRequest#bodyPublisher:

private HttpRequest.BodyPublisher bodyPublisher(HttpHeaders headers, @Nullable Body body) {
  if (body != null) {
    Flow.Publisher<ByteBuffer> outputStreamPublisher = OutputStreamPublisher.create(
        outputStream -> body.writeTo(StreamUtils.nonClosing(outputStream)),
        BYTE_MAPPER, this.executor);

    long contentLength = headers.getContentLength();
    if (contentLength != -1) {
      return HttpRequest.BodyPublishers.fromPublisher(outputStreamPublisher, contentLength);
    }
    else {
      return HttpRequest.BodyPublishers.fromPublisher(outputStreamPublisher);
    }
  }
  else {
    return HttpRequest.BodyPublishers.noBody();
  }
}

If, with a debugger, I change the value of contentLength to -1, the call also succeeds which suggests that the check should be if(contentLength <= 0)