Find rsync in PATH and pass the SSH password only to rsync

A missing /usr/bin/rsync ended in a traceback, possibly after --remove-before-backup had removed old backups, and left SSHPASS in the environment.

simple_backup/simple_backup.py

@@ -229,7 +229,8 @@ class Backup:
         self._exclude_path = ''
         self._remote = False
         self._ssh: paramiko.client.SSHClient | None = None
-        self._password_auth = False
+        # Passed to sshpass through rsync's environment only
+        self._password: str | None = None
         self._removed_count = 0
 
     def check_params(self, homedir: str = '') -> int:
@@ -558,8 +559,7 @@ class Backup:
 
                 ssh.connect(**host, username=self.ssh_user, timeout=SSH_TIMEOUT, password=password)
 
-                self._password_auth = True
-                os.environ['SSHPASS'] = password
+                self._password = password
 
                 return ssh
             except GetPassWarning as e:
@@ -690,6 +690,16 @@ class Backup:
 
         _notify('Starting backup...')
 
+        # Check before anything is removed (--remove-before-backup)
+        rsync = which('rsync')
+
+        if rsync is None:
+            logger.critical('rsync not found. Install rsync to perform the backup')
+
+            _notify('Backup failed (check log for details)')
+
+            return 4
+
         self.define_backup_dir()
 
         fd, self._inputs_path = mkstemp(prefix='tmp_inputs', text=True)
@@ -729,7 +739,7 @@ class Backup:
         logger.info('Copying files. This may take a long time...')
 
         # Build the argument list directly, so paths with spaces or quotes are passed unchanged
-        args = ['/usr/bin/rsync', *self.options.split()]
+        args = [rsync, *self.options.split()]
 
         if self._last_backup != '':
             args.append(f'--link-dest={self._last_backup}')
@@ -737,11 +747,15 @@ class Backup:
         args.extend([f'--exclude-from={self._exclude_path}', f'--files-from={self._inputs_path}',
                      '/', f'{self._server}{self._output_dir}'])
 
+        # None inherits our environment
+        env: dict[str, str] | None = None
+
         # rsync splits the -e command itself, so quote the parts that may contain spaces
         if self.ssh_keyfile is not None:
             ssh = f'ssh -i {shlex.quote(self.ssh_keyfile)} -o StrictHostKeyChecking=accept-new'
-        elif self._password_auth and self.ssh_user is not None and which('sshpass'):
+        elif self._password is not None and self.ssh_user is not None and which('sshpass'):
             ssh = f'sshpass -e ssh -l {shlex.quote(self.ssh_user)} -o StrictHostKeyChecking=accept-new'
+            env = {**os.environ, 'SSHPASS': self._password}
         else:
             ssh = 'ssh -o StrictHostKeyChecking=accept-new'
 
@@ -756,7 +770,7 @@ class Backup:
             args.append('--info=progress2')
             bar = _ProgressBar()
 
-        with Popen(args, stdin=PIPE, stdout=PIPE, stderr=STDOUT, shell=False) as p:
+        with Popen(args, stdin=PIPE, stdout=PIPE, stderr=STDOUT, shell=False, env=env) as p:
             assert p.stdin is not None and isinstance(p.stdout, io.BufferedIOBase)
             p.stdin.close()
 
@@ -770,11 +784,6 @@ class Backup:
                 if bar is not None:
                     bar.clear()
 
-            try:
-                del os.environ['SSHPASS']
-            except KeyError:
-                pass
-
             returncode = p.wait()
 
         if returncode == 0: