backup: If a database exists write an intial snapshot

backup/backup-cli

@@ -1,8 +1,10 @@
 #!/usr/bin/env python3
-from backup import FileBackend, get_backend
+from backup import FileBackend, get_backend, Change
 import os
 import click
 import json
+import sqlite3
+import sys
 
 
 @click.command()
@@ -17,6 +19,7 @@ def init(lightning_dir, backend_url):
     backend.write_metadata()
 
     lock_file = os.path.join(lightning_dir, "backup.lock")
+    db_file = os.path.join(lightning_dir, "lightningd.sqlite3")
 
     with open(lock_file, "w") as f:
         f.write(json.dumps({
@@ -25,6 +28,28 @@ def init(lightning_dir, backend_url):
 
     # TODO Take a snapshot
 
+    data_version = 0
+    if os.path.exists(db_file):
+        print("Found an existing database at {db_file}, initializing the backup with a snapshot".format(db_file=db_file))
+        # Peek into the DB to see if we have
+        db = sqlite3.connect(db_file)
+        cur = db.cursor()
+        rows = cur.execute("SELECT intval FROM vars WHERE name = 'data_version'")
+        data_version = rows.fetchone()[0]
+
+        snapshot = Change(
+            version=data_version,
+            snapshot=open(db_file, 'rb').read(),
+            transaction=None
+        )
+        if not backend.add_change(snapshot):
+            print("Could not write snapshot to backend")
+            sys.exit(1)
+        else:
+            print("Successfully written initial snapshot to {destination}".format(destination=destination))
+    else:
+        print("Database does not exist yet, created an empty backup file")
+
     print("Initialized backup backend {destination}, you can now start c-lightning".format(
         destination=destination,
     ))

backup/test_backup.py

@@ -54,6 +54,26 @@ def test_start_no_init(node_factory, directory):
     ))
 
 
+def test_init_not_empty(node_factory, directory):
+    """We want to add backups to an existing lightning node.
+
+    backup-cli init should start the backup with an initial snapshot.
+    """
+    bpath = os.path.join(directory, 'lightning-1', 'regtest')
+    bdest = 'file://' + os.path.join(bpath, 'backup.dbak')
+    l1 = node_factory.get_node()
+    l1.stop()
+
+    out = subprocess.check_output([cli_path, "init", bpath, bdest])
+    assert(b'Found an existing database' in out)
+    assert(b'Successfully written initial snapshot' in out)
+
+    # Now restart and add the plugin
+    l1.daemon.opts['plugin'] = plugin_path
+    l1.start()
+    l1.daemon.wait_for_log(r'plugin-backup.py: Versions match up')
+
+
 def test_tx_abort(node_factory, directory):
     """Simulate a crash between hook call and DB commit.