Fix/empty hostname cluster slots (valkey-io#5373)

Fix: treat empty hostname in CLUSTER SLOTS metadata as absent

AWS ElastiCache (plaintext, cluster mode, Redis 7.2.4) returns
`hostname: ""` (empty string) in the CLUSTER SLOTS metadata for
every node. The parser was wrapping this in `Some("")`, which
caused `unwrap_or_else` at line 252 to use the empty string
instead of falling back to the IP address from the primary
identifier.

This resulted in connection addresses like `:6379` (no host),
which fail immediately. Because `refresh_slots_inner()` silently
drops connection errors, `createClient` resolves successfully but
the client has zero usable connections. Every subsequent command
fails with `AllConnectionsUnavailable`.

The fix filters out empty hostname strings at parse time, so they
are treated the same as absent hostnames, and the IP from the
primary identifier is used instead.

Signed-off-by: Daniel Rinehart <danielr@philo.com>

Author: NeoPhi

CHANGELOG.md

@@ -23,6 +23,7 @@
 * CORE: Track HELLO and AUTH state for reconnection ([#5145](https://github.com/valkey-io/valkey-glide/issues/5145))
 
 #### Fixes
+* CORE: Fix empty hostname in CLUSTER SLOTS metadata causing AllConnectionsUnavailable ([#5367](https://github.com/valkey-io/valkey-glide/issues/5367)). AWS ElastiCache (plaintext, cluster mode) returns `hostname: ""` in node metadata, which was used as the connection address instead of falling back to the IP.
 * Node: Fix to handle non-string types in toBuffersArray ([#4842](https://github.com/valkey-io/valkey-glide/issues/4842))
 * CORE: Enforce connection_timeout for initial standalone connection failures  ([#4991](https://github.com/valkey-io/valkey-glide/issues/4991))
 * Node: Fixed `Failed to convert napi value Undefined into rust type u32` error  ([#5128](https://github.com/valkey-io/valkey-glide/pull/5128))

glide-core/redis-rs/redis/src/cluster_topology.rs

@@ -200,8 +200,10 @@ pub(crate) fn parse_and_count_slots(
                                     metadata_ip =
                                         String::from_utf8_lossy(value_bytes).parse::<IpAddr>().ok();
                                 } else if key_str == "hostname" {
-                                    metadata_hostname =
-                                        Some(String::from_utf8_lossy(value_bytes).into_owned());
+                                    let h = String::from_utf8_lossy(value_bytes);
+                                    if !h.is_empty() {
+                                        metadata_hostname = Some(h.into_owned());
+                                    }
                                 }
                                 // Other keys are ignored - we only need ip and hostname
                             };
@@ -946,6 +948,46 @@ mod tests {
         });
     }
 
+    #[test]
+    fn parse_slots_empty_hostname_in_metadata_falls_back_to_ip() {
+        // ElastiCache (plaintext, cluster mode) returns hostname: "" (empty string)
+        // in CLUSTER SLOTS metadata. The parser should treat this as absent and
+        // fall back to the IP address from the primary identifier.
+        run_with_both_formats(|format| {
+            let view = Value::Array(vec![slot_value_with_metadata(
+                0,
+                16383,
+                vec![
+                    ("172.20.43.71", 6379, Some(vec![("hostname", "")])),
+                    ("172.20.78.117", 6379, Some(vec![("hostname", "")])),
+                ],
+                format,
+            )]);
+
+            let ParsedSlotsResult {
+                slots_count,
+                slots,
+                address_to_ip_map,
+            } = parse_and_count_slots(&view, None, "fallback").unwrap();
+
+            assert_eq!(slots_count, 16384);
+            assert_eq!(slots.len(), 1);
+            // Should use the IP as the address, not the empty hostname
+            assert_eq!(slots[0].master(), "172.20.43.71:6379");
+            assert_eq!(slots[0].replicas(), vec!["172.20.78.117:6379".to_string()]);
+
+            assert_eq!(address_to_ip_map.len(), 2);
+            assert_eq!(
+                address_to_ip_map.get("172.20.43.71:6379"),
+                Some(&"172.20.43.71".parse().unwrap())
+            );
+            assert_eq!(
+                address_to_ip_map.get("172.20.78.117:6379"),
+                Some(&"172.20.78.117".parse().unwrap())
+            );
+        });
+    }
+
     enum ViewType {
         SingleNodeViewFullCoverage,
         SingleNodeViewMissingSlots,