From 338b222007ebe8610f1c4f029b7d919dd7e05a9d Mon Sep 17 00:00:00 2001
From: Cameron Murdoch <cameronm@uio.no>
Date: Wed, 18 Dec 2024 11:40:51 +0100
Subject: [PATCH] Proof of concept fix for `barman backup --wait` on pg17

pg_walfile_name_offset() has been changed in pg17 to return the current
segment if on a segment boundary.

Implement previous_segment_name() to calulate the previous segment
and use this to restore the pre pg17 behaviour.

Tested with pg16 and pg17.
---
 barman/postgres.py | 10 +++++++++-
 barman/xlog.py     | 20 ++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/barman/postgres.py b/barman/postgres.py
index 9fb1e0049..36a47880e 100644
--- a/barman/postgres.py
+++ b/barman/postgres.py
@@ -55,6 +55,7 @@
 from barman.postgres_plumbing import function_name_map
 from barman.remote_status import RemoteStatusMixin
 from barman.utils import force_str, simplify_version, with_metaclass
+from barman.xlog import previous_segment_name
 
 try:
     from queue import Empty
@@ -739,7 +740,14 @@ def current_xlog_info(self):
                     "CURRENT_TIMESTAMP AS timestamp "
                     "FROM {pg_current_wal_lsn}() AS location".format(**self.name_map)
                 )
-                return cur.fetchone()
+                result = cur.fetchone()
+                # pg_walfile_name_offset() in Postgres 17 returns the current segment
+                # if on a segment boundary so return the previous segment name in that case.
+                if self.server_version >= 170000 and result["file_offset"] == 00000000:
+                    result["file_name"] = previous_segment_name(
+                        result["file_name"], self.xlog_segment_size
+                    )
+                return result
             else:
                 cur.execute(
                     "SELECT location, "
diff --git a/barman/xlog.py b/barman/xlog.py
index 8415d5ec1..28c7faac8 100644
--- a/barman/xlog.py
+++ b/barman/xlog.py
@@ -302,6 +302,26 @@ def generate_segment_names(begin, end=None, version=None, xlog_segment_size=None
             cur_log += 1
 
 
+def previous_segment_name(segment, xlog_segment_size):
+    """
+    Get the previous XLOG segment name
+
+    :param str segment: segment name
+    :param int xlog_segment_size: the size of a XLOG segment
+    :rtype: str
+    :raise: BadXlogSegmentName
+    """
+    tli, log, seg = decode_segment_name(segment)
+    xlog_seg_per_file = xlog_segments_per_file(xlog_segment_size)
+    prev_log, prev_seg = log, seg
+    if prev_seg == 0:
+        prev_seg = xlog_seg_per_file
+        prev_log -= 1
+    else:
+        prev_seg -= 1
+    return encode_segment_name(tli, prev_log, prev_seg)
+
+
 def hash_dir(path):
     """
     Get the directory where the xlog segment will be stored