backup: track errors/warnings from borg; add prefix to them

This also ignores the "file changed while we backed it up" error, because
that isn't important enough to warrant sending an email.

backup.py

@@ -251,11 +251,12 @@ def main(argv: list[str]):
 
     args = parser.parse_args()
     config = Config(args.config)
+    backup = Backup(config, args.dry_run)
 
     # Parse variables from vars.sh
     hostname = os.uname().nodename
-    borg = str(base / "borg.sh")
-    notify = str(base / "notify.sh")
+    borg_sh = str(base / "borg.sh")
+    notify_sh = str(base / "notify.sh")
     try:
         with open(args.vars) as f:
             for line in f:
@@ -267,14 +268,13 @@ def main(argv: list[str]):
                 if var == "HOSTNAME":
                     hostname = value
                 if var == "BORG":
-                    borg = value
+                    borg_sh = value
                 if var == "BORG_DIR":
-                    notify = pathlib.Path(value) / "notify.sh"
+                    notify_sh = str(pathlib.Path(value) / "notify.sh")
     except Exception as e:
-        self.log('W', f"failed to parse variables from {args.vars}: {str(e)}")
+        backup.log('W', f"failed to parse variables from {args.vars}: {str(e)}")
 
     # Run backup
-    backup = Backup(config, args.dry_run)
     captured_output: list[bytes] = []
 
     if args.dry_run:
@@ -285,7 +285,7 @@ def main(argv: list[str]):
                 backup.run(out)
         sys.stdout.flush()
     else:
-        borg = subprocess.Popen([borg,
+        borg = subprocess.Popen([borg_sh,
                                  "create",
                                  "--verbose",
                                  "--progress",
@@ -304,6 +304,9 @@ def main(argv: list[str]):
         if borg.stdin is None:
             raise Exception("no pipe")
 
+        borg_saw_warnings = 0
+        borg_saw_errors = 0
+
         # Use a thread to capture output
         def reader_thread(fh):
             last_progress = 0
@@ -313,7 +316,20 @@ def main(argv: list[str]):
                     if ((data['type'] == 'log_message' or
                          data['type'] == 'progress_message')
                         and 'message' in data):
-                        line = (data['message'] + '\n').encode()
+
+                        # Count warnings and errors, but ignore some.
+                        changed_msg = "file changed while we backed it up"
+                        if data['levelname'] == 'WARNING':
+                            prefix = "warning: "
+                            if changed_msg not in data['message']:
+                                borg_saw_warnings += 1
+                        elif data['levelname'] not in ('DEBUG', 'INFO'):
+                            prefix = "error: "
+                            borg_saw_errors += 1
+                        else:
+                            prefix = ""
+
+                        line = (prefix + data['message'] + '\n').encode()
                     elif data['type'] == 'archive_progress':
                         now = time.time()
                         if now - last_progress > 10:
@@ -359,8 +375,12 @@ def main(argv: list[str]):
         ret = borg.returncode
         if ret < 0:
             backup.log('E', f"borg exited with signal {-ret}")
-        elif ret != 0:
-            backup.log('E', f"borg exited with return code {ret}")
+        elif ret == 2 or borg_saw_errors:
+            backup.log('E', f"borg exited with errors (ret={ret})")
+        elif ret == 1 or borg_saw_warnings:
+            backup.log('W', f"borg exited with warnings (ret={ret})")
+        else:
+            backup.log('E', f"borg exited with unknown error code {ret}")
 
     # See if we had any errors
     warnings = sum(1 for (letter, msg) in backup.logs if letter == 'W')
@@ -405,12 +425,12 @@ def main(argv: list[str]):
             if errmsg and warnmsg:
                 summary = f"{errmsg}, {warnmsg}"
             elif errors:
-                summary = errmsg
+                summary = errmsg or ""
             else:
-                summary = warnmsg
+                summary = warnmsg or ""
 
             # Call notify.sh
-            res = subprocess.run([notify, summary, email], input=body_text)
+            res = subprocess.run([notify_sh, summary, email], input=body_text)
             if res.returncode != 0:
                 backup.log('E', f"failed to send notification")
                 errors += 1