RPKI: ask a cache without data yet again soon

A validator that is still running its first validation answers a query
with No Data Available (error code 2). That ended the session, and the
next attempt came after the retry interval: 600 seconds when the cache
had not yet said otherwise, which it cannot have before it has data.
For those ten minutes after a validator started, nothing was validated.

No Data Available is now asked again after 30 seconds, or after
retry_seconds if that is shorter, and logged as information rather than
as a warning. Other failures wait as before, after trying the next
cache if there is one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/rpki/src/client.rs

@@ -54,6 +54,12 @@ const MAX_RECORDS: usize = 8_000_000;
 /// How long to wait before trying the next cache after one has failed.
 const NEXT_CACHE_DELAY: Duration = Duration::from_secs(1);
 
+/// How long to wait before asking a cache again that said it has no data
+/// yet, rather than the retry interval: it is up and validating, which
+/// takes minutes after it starts, and the retry interval is ten unless it
+/// has said otherwise, which it has not had the chance to.
+const NO_DATA_RETRY: Duration = Duration::from_secs(30);
+
 /// How long a cache that is being left is given to take the reason.
 const ERROR_REPORT_TIMEOUT: Duration = Duration::from_secs(1);
 
@@ -419,23 +425,29 @@ impl Client {
                 self.protocol_version = version;
                 continue;
             }
-            warn!(%cache, err = %ended, "RPKI cache session ended");
+            let no_data = matches!(
+                ended,
+                SessionError::Reported {
+                    code: error_code::NO_DATA_AVAILABLE,
+                    ..
+                }
+            );
+            if no_data {
+                info!(%cache, "RPKI cache has no data yet; asking again soon");
+            } else {
+                warn!(%cache, err = %ended, "RPKI cache session ended");
+            }
             self.status(|status| {
                 status.state = CacheState::Connecting;
                 status.last_error = Some(ended.to_string());
             });
 
-            // The next cache at once; when all have been tried, a rest.
             attempt += 1;
             // The next cache, or this one when it is back, may speak a
             // newer version.
             self.protocol_version = VERSION_2;
-            let wait = if attempt.is_multiple_of(self.config.caches.len()) {
-                self.retry()
-            } else {
-                NEXT_CACHE_DELAY
-            };
-            self.wait(wait).await;
+            let all_tried = attempt.is_multiple_of(self.config.caches.len());
+            self.wait(rest(all_tried, no_data, self.retry())).await;
         }
     }
 
@@ -889,3 +901,33 @@ enum Answer {
     /// With a request to ask for everything instead.
     Reset,
 }
+
+/// How long to rest after a session ended: the next cache at once; when
+/// all have been tried, the retry interval, or less if the last one is
+/// only still validating.
+fn rest(all_tried: bool, no_data: bool, retry: Duration) -> Duration {
+    match (all_tried, no_data) {
+        (false, _) => NEXT_CACHE_DELAY,
+        (true, true) => NO_DATA_RETRY.min(retry),
+        (true, false) => retry,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A cache that is still validating after it started is asked again
+    /// in half a minute, not the ten the retry interval is by default.
+    #[test]
+    fn a_cache_without_data_yet_is_asked_again_soon() {
+        let ten_minutes = Duration::from_secs(600);
+        assert_eq!(rest(true, true, ten_minutes), NO_DATA_RETRY);
+        assert_eq!(rest(true, false, ten_minutes), ten_minutes);
+        // Never later than the retry interval says.
+        let short = Duration::from_secs(5);
+        assert_eq!(rest(true, true, short), short);
+        // Another cache first, whatever this one said.
+        assert_eq!(rest(false, true, ten_minutes), NEXT_CACHE_DELAY);
+    }
+}