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/limits/CardinalityRateLimiter.java

@@ -54,7 +54,8 @@ public class CardinalityRateLimiter {
     });
 
     if (rateLimitExceeded) {
-      throw new RateLimitExceededException(Duration.ofSeconds(getRemainingTtl(key)));
+      long remainingTtl = getRemainingTtl(key);
+      throw new RateLimitExceededException(remainingTtl >= 0 ? Duration.ofSeconds(remainingTtl) : null);
     }
   }
 
@@ -66,7 +67,14 @@ public class CardinalityRateLimiter {
     return ttl;
   }
 
+  /**
+   * Get the remaining ttl for the specified key
+   *
+   * @param key with timeout to check
+   * @return the ttl, or negative in the case of error
+   */
   public long getRemainingTtl(final String key) {
+    // ttl() returns -2 if key does not exist, -1 if key has no expiration
     return cacheCluster.withCluster(connection -> connection.sync().ttl(getHllKey(key)));
   }
 

service/src/main/java/org/whispersystems/textsecuregcm/limits/LockingRateLimiter.java

@@ -31,7 +31,7 @@ public class LockingRateLimiter extends RateLimiter {
   public void validate(String key, int amount) throws RateLimitExceededException {
     if (!acquireLock(key)) {
       meter.mark();
-      throw new RateLimitExceededException("Locked", Duration.ZERO);
+      throw new RateLimitExceededException(Duration.ZERO);
     }
 
     try {

service/src/main/java/org/whispersystems/textsecuregcm/limits/RateLimiter.java

@@ -57,7 +57,7 @@ public class RateLimiter {
         setBucket(key, bucket);
       } else {
         meter.mark();
-        throw new RateLimitExceededException(key + " , " + amount, bucket.getTimeUntilSpaceAvailable(amount));
+        throw new RateLimitExceededException(bucket.getTimeUntilSpaceAvailable(amount));
       }
     }
   }