From a3d7be4ded2af18dc92182aed41ceb38682dd75b Mon Sep 17 00:00:00 2001
From: Holger Frey <mail@holgerfrey.de>
Date: Wed, 7 Aug 2019 16:13:49 +0200
Subject: [PATCH] updated filename creation

---
 zfs-snapshot-backup.py | 39 ++++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/zfs-snapshot-backup.py b/zfs-snapshot-backup.py
index ce79a1f..c1bd014 100755
--- a/zfs-snapshot-backup.py
+++ b/zfs-snapshot-backup.py
@@ -16,7 +16,10 @@ TMP_BACKUP_FOLDER = "/mnt/Datenspeicher/snap-backup-dataset/temporary-backups"
 
 def call(arguments, as_text=False):
     result = subprocess.run(
-        arguments, check=True, stdout=subprocess.PIPE, universal_newlines=as_text
+        arguments,
+        check=True,
+        stdout=subprocess.PIPE,
+        universal_newlines=as_text,
     )
     return result.stdout
 
@@ -50,13 +53,27 @@ def list_elab_snapshots():
     return result
 
 
-def gzip_filename(snapshot_name):
-    pool, name = snapshot_name.split("/", 1)
-    return f"{name}.gz"
+def snapshot_short_name(full_snapshot_name):
+    pool, name = full_snapshot_name.split("/", 1)
+    return name
 
 
-def gzip_filepath(snapshot_name):
-    return pathlib.Path(TMP_BACKUP_FOLDER) / gzip_filename(snapshot_name)
+def gzip_filename(current, last=None):
+    current_name = snapshot_short_name(current)
+    if last is None:
+        return f"{current_name}.gz"
+    else:
+        last_name = snapshot_name(last)
+        return f"{last_name}.to.{current_name}.gz"
+
+
+def extract_snapshot_name(filename):
+    parts = filename.split(".")
+    if len(parts) in (2, 4):
+        # snapshot1.gz or snapshot1.to.snapshot2.gz
+        return parts[-2]
+    else:
+        raise ValueError(f"Unknown Filename Format: {filename}")
 
 
 def list_remote_backups(members):
@@ -65,7 +82,7 @@ def list_remote_backups(members):
         remote_sub_dir = f"{REMOTE_PATH}/{member}"
         try:
             backups = clean_split(remote_call(["ls", remote_sub_dir]))
-            result[member] = set(backups)
+            result[member] = set((extract_snapshot_name(i) for i in backups))
         except subprocess.CalledProcessError:
             remote_call(["mkdir", remote_sub_dir])
             result[member] = set()
@@ -78,7 +95,7 @@ def backup_latest_snapshot(member, elab_snapshots, existing_backups):
     current_snapshot = snapshots[0]
     latest_backup = None
     for snapshot in snapshots:
-        if gzip_filename(snapshot) in existing_backups:
+        if snapshot_short_name(snapshot) in existing_backups:
             latest_backup = snapshot
             break
     if current_snapshot == latest_backup:
@@ -88,16 +105,20 @@ def backup_latest_snapshot(member, elab_snapshots, existing_backups):
     elif latest_backup is None:
         # no snapshot was found in backups, make a full backup for consistency
         send_cmd = ["zfs", "send", current_snapshot]
+        gzip_tmp_filename = gzip_filename(current_snapshot)
         print(f" - full backup, latest snapshot: {current_snapshot}")
     else:
         # make an incremental backup
         print(
             f" - incremental backup, from: {latest_backup} to: {current_snapshot}"
         )
+        gzip_tmp_filename = gzip_filename(
+            current=current_snapshot, last=latest_backup
+        )
         send_cmd = ["zfs", "send", "-I", latest_backup, current_snapshot]
 
     # create the backup
-    tmp_gzip_filepath = gzip_filepath(current_snapshot)
+    tmp_gzip_filepath = pathlib.Path(TMP_BACKUP_FOLDER) / gzip_tmp_filename
     print(f" - generating temporary backup file {tmp_gzip_filepath.name}")
     with open(tmp_gzip_filepath, "wb") as file_handle:
         gzip_in = subprocess.Popen(