Optional error-file logging

RustProxy can write an additional local file containing only ERROR events. This is an optional sink layered on the existing tracing/logging pipeline; journald/systemd and other configured sinks remain independent.

Configuration

The settings document contains:

{
  "error_log": {
    "enabled": true,
    "path": "/var/log/rustproxy/error.log",
    "format": "JSON"
  }
}

format is JSON or RAW. The feature is disabled by default. The administration Settings UI exposes the same enable/path/format controls and applies changes at runtime.

The sink accepts only ERROR events. JSON is one object per line; RAW is one human-readable line per event.

Runtime behavior

Events are handed to a bounded queue and written by one asynchronous worker. The request path does not perform the file write. When the queue is full, new error-file events are dropped and counted instead of allowing unbounded memory growth.

Filesystem errors do not stop RustProxy. The worker reports failures through the existing logger, rate-limits repeated diagnostics and retries opening the file. Changing the path or disabling the sink closes the current file; a format change takes effect without an application restart.

Created log files use mode 0600 on POSIX. Symlink/non-regular targets are refused.

Secret redaction

The common logging pipeline redacts sensitive keys and values before they reach the error-file sink. This includes authorization credentials, provider tokens/passwords, backup passwords, private-key PEM material and Secret Store/master-key related values. Structured secret fields are replaced with [REDACTED].

Error messages from dependencies should still be treated as untrusted diagnostic input; do not deliberately embed secrets in error text.

Rotation

RustProxy does not implement file rollover, retention or compression. Use the system logrotate. Debian packaging is maintained outside this source tree and ready packages are published at https://rustproxy.linuxiarz.pl; package-specific logrotate policy belongs to that packaging repository.

Stored-log explorer

The authenticated /logs workspace can read the configured error file alongside structured access/protocol files. It remains independent from Live Logs and can inspect an existing error file even while error_log.enabled is false. The browser API does not accept arbitrary paths; it resolves only the configured error-log path and applies the same bounded, read-only regular-file/symlink protections documented in FILE_LOGS.

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