Simplify RateLimitExceeded with no retry-duration

- Avoid passing negative durations in error cases
- Drop unused message
- Return a duration for a bad forwarded-for

service/src/main/java/org/whispersystems/textsecuregcm/mappers/RateLimitExceededExceptionMapper.java

@@ -4,6 +4,8 @@
  */
 package org.whispersystems.textsecuregcm.mappers;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
 
 import javax.ws.rs.core.Response;
@@ -12,17 +14,25 @@ import javax.ws.rs.ext.Provider;
 
 @Provider
 public class RateLimitExceededExceptionMapper implements ExceptionMapper<RateLimitExceededException> {
+  private static final Logger logger = LoggerFactory.getLogger(RateLimitExceededExceptionMapper.class);
 
   /**
    * Convert a RateLimitExceededException to a 413 response with a
    * Retry-After header.
    *
-   * @param e A RateLimitExceededException potentially containing a reccomended retry duration
+   * @param e A RateLimitExceededException potentially containing a recommended retry duration
    * @return the response
    */
   @Override
   public Response toResponse(RateLimitExceededException e) {
     return e.getRetryDuration()
+        .filter(d -> {
+          if (d.isNegative()) {
+            logger.warn("Encountered a negative retry duration: {}, will not include a Retry-After header in response", d);
+          }
+          // only include non-negative durations in retry headers
+          return !d.isNegative();
+        })
         .map(d -> Response.status(413).header("Retry-After", d.toSeconds()))
         .orElseGet(() -> Response.status(413)).build();
   }