add CQLSH command SHOW REPLICAS

patch by Brad Schoening; reviewed by Stefan Miklosovic and Brandon Williams for CASSANDRA-17577

CHANGES.txt

@@ -1,4 +1,5 @@
 4.2
+ * Add CQLSH command SHOW REPLICAS (CASSANDRA-17577)
  * Add guardrail to allow disabling of SimpleStrategy (CASSANDRA-17647)
  * Change default directory permission to 750 in packaging (CASSANDRA-17470)
  * Adding support for TLS client authentication for internode communication (CASSANDRA-17513)

bin/cqlsh.py

@@ -600,6 +600,13 @@ class Shell(cmd.Cmd):
     def show_session(self, sessionid, partial_session=False):
         print_trace_session(self, self.session, sessionid, partial_session)
 
+    def show_replicas(self, token_value, keyspace=None):
+        ks = self.current_keyspace if keyspace is None else keyspace
+        token_map = self.conn.metadata.token_map
+        nodes = token_map.get_replicas(ks, token_map.token_class(token_value))
+        addresses = [x.address for x in nodes]
+        print(f"{addresses}")
+
     def get_connection_versions(self):
         result, = self.session.execute("select * from system.local where key = 'local'")
         vers = {
@@ -979,7 +986,7 @@ class Shell(cmd.Cmd):
         if parsed:
             self.printerr('Improper %s command (problem at %r).' % (cmdword, parsed.remainder[0]))
         else:
-            self.printerr('Improper %s command.' % cmdword)
+            self.printerr(f'Improper {cmdword} command.')
 
     def do_use(self, parsed):
         ksname = parsed.get_binding('ksname')
@@ -1578,6 +1585,11 @@ class Shell(cmd.Cmd):
         SHOW SESSION <sessionid>
 
           Pretty-prints the requested tracing session.
+
+        SHOW REPLICAS <token> (<keyspace>)
+
+          Lists the replica nodes by IP address for the given token. The current
+          keyspace is used if one is not specified.
         """
         showwhat = parsed.get_binding('what').lower()
         if showwhat == 'version':
@@ -1588,6 +1600,10 @@ class Shell(cmd.Cmd):
         elif showwhat.startswith('session'):
             session_id = parsed.get_binding('sessionid').lower()
             self.show_session(UUID(session_id))
+        elif showwhat.startswith('replicas'):
+            token_id = parsed.get_binding('token')
+            keyspace = parsed.get_binding('keyspace')
+            self.show_replicas(token_id, keyspace)
         else:
             self.printerr('Wait, how do I show %r?' % (showwhat,))
 

doc/modules/cassandra/pages/tools/cqlsh.adoc

@@ -181,6 +181,21 @@ cqlsh> SHOW HOST
 Connected to Prod_Cluster at 192.0.0.1:9042.
 ----
 
+=== `SHOW REPLICAS`
+
+Prints the IP addresses of the Cassandra nodes which are replicas for the
+listed given token and keyspace. This command is available from Cassandra 4.2.
+
+`Usage`: `SHOW REPLICAS <token> (<keyspace>)`
+
+Example usage:
+
+[source,none]
+----
+cqlsh> SHOW REPLICAS 95
+['192.0.0.1', '192.0.0.2']
+----
+
 === `SHOW SESSION`
 
 Pretty prints a specific tracing session.

pylib/cqlshlib/cqlshhandling.py

@@ -131,7 +131,7 @@ cqlsh_serial_consistency_level_syntax_rules = r'''
 '''
 
 cqlsh_show_cmd_syntax_rules = r'''
-<showCommand> ::= "SHOW" what=( "VERSION" | "HOST" | "SESSION" sessionid=<uuid> )
+<showCommand> ::= "SHOW" what=( "VERSION" | "HOST" | "SESSION" sessionid=<uuid> | "REPLICAS" token=<integer> (keyspace=<keyspaceName>)? )
                 ;
 '''