add a post-processing option for the update script

Setups that process expiry data need to do that after
each run of osm2pgsql. The new option provides the means
to insert additional operations via a script when osm2pgsql
is run multiple times.

Author: lonvia

scripts/osm2pgsql-replication

@@ -184,6 +184,18 @@ def update(conn, args):
     Any additional arguments to osm2pgsql need to be given after '--'. Database
     and the prefix parameter are handed through to osm2pgsql. They do not need
     to be repeated. '--append' and '--slim' will always be added as well.
+
+    Use the '--post-processing' parameter to execute a script after osm2pgsql has
+    run successfully. If the updates consists of multiple runs because the
+    maximum size of downloaded data was reached, then the script is executed
+    each time that osm2pgsql has run. When the post-processing fails, then
+    the entire update run is considered a failure and the replication information
+    is not updated. That means that when 'update' is run the next time it will
+    recommence with downloading the diffs again and reapplying them to the
+    database. This is usually safe. The script receives two parameters:
+    the sequence ID and timestamp of the last successful run. The timestamp
+    may be missing in the rare case that the replication service stops responding
+    after the updates have been downloaded.
     """
     with conn.cursor() as cur:
         cur.execute('SELECT * FROM pg_tables where tablename = %s', (args.table, ))
@@ -244,6 +256,13 @@ def update(conn, args):
         seq = endseq
 
         nextstate = repl.get_state_info(seq)
+        timestamp = nextstate.timestamp if nextstate else None
+
+        if args.post_processing:
+            cmd = [args.post_processing, str(endseq), str(timestamp or '')]
+            LOG.debug('Calling post-processing script: %s', ' '.join(cmd))
+            subprocess.run(cmd, check=True)
+
         update_replication_state(conn, args.table, seq,
                                  nextstate.timestamp if nextstate else None)
 
@@ -318,6 +337,8 @@ def get_parser():
                      help='Path to osm2pgsql command (default: osm2pgsql)')
     cmd.add_argument('--once', action='store_true',
                      help='Run updates only once, even when more data is available.')
+    cmd.add_argument('--post-processing', metavar='SCRIPT',
+                     help='Post-processing script to run after each execution of osm2pgsql.')
 
     return parser