Add bounded file logging rotation and retention #832

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

docs/Config_params/CONFIG_PARAMS.en.md

@@ -14,6 +14,7 @@ This document lists all configuration keys accepted by `config.toml`.
 
 # Table of contents
  - [Top-level keys](#top-level-keys)
+ - [logging](#logging)
  - [general](#general)
  - [general.modes](#generalmodes)
  - [general.links](#generallinks)
@@ -35,6 +36,7 @@ This document lists all configuration keys accepted by `config.toml`.
 | --- | ---- | ------- | ---------- |
 | [`include`](#include) | `String` (special directive) | — | `✔` |
 | [`show_link`](#show_link) | `"*"` or `String[]` | `[]` (`ShowLink::None`) | `✘` |
+| [`logging`](#logging) | Table | default values | `✘` |
 | [`dc_overrides`](#dc_overrides) | `Map<String, String or String[]>` | `{}` | `✘` |
 | [`default_dc`](#default_dc) | `u8` | — (effective fallback: `2` in ME routing) | `✘` |
 | [`beobachten`](#beobachten) | `bool` | `true` | `✘` |
@@ -83,6 +85,84 @@ This document lists all configuration keys accepted by `config.toml`.
     default_dc = 2
     ```
 
+# [logging]
+
+| Key | Type | Default | Hot-Reload |
+| --- | ---- | ------- | ---------- |
+| [`destination`](#loggingdestination) | `"stderr"` / `"syslog"` / `"file"` | `"stderr"` | `✘` |
+| [`path`](#loggingpath) | `String` | — | `✘` |
+| [`rotation`](#loggingrotation) | `"never"` / `"minutely"` / `"hourly"` / `"daily"` / `"weekly"` | `"never"` | `✘` |
+| [`max_size_bytes`](#loggingmax_size_bytes) | `u64` | `0` | `✘` |
+| [`max_files`](#loggingmax_files) | `usize` | `0` | `✘` |
+| [`max_age_secs`](#loggingmax_age_secs) | `u64` | `0` | `✘` |
+
+## logging.destination
+  - **Constraints / validation**: Must be `stderr`, `syslog`, or `file`. `syslog` is supported only on Unix platforms. `file` requires `logging.path`.
+  - **Description**: Selects the runtime log destination. CLI flags override this value.
+  - **Example**:
+
+    ```toml
+    [logging]
+    destination = "file"
+    path = "/var/log/telemt.log"
+    ```
+## logging.path
+  - **Constraints / validation**: Required when `logging.destination = "file"`; must not be empty.
+  - **Description**: File path used for file logging. With time rotation, the file name is used as the rolling prefix.
+  - **Example**:
+
+    ```toml
+    [logging]
+    destination = "file"
+    path = "/var/log/telemt.log"
+    ```
+## logging.rotation
+  - **Constraints / validation**: Must be `never`, `minutely`, `hourly`, `daily`, or `weekly`.
+  - **Description**: Time-based file rotation interval. `weekly` rotates at the Sunday UTC boundary. `never` writes to the exact `logging.path` unless size rotation is enabled.
+  - **Example**:
+
+    ```toml
+    [logging]
+    destination = "file"
+    path = "/var/log/telemt.log"
+    rotation = "daily"
+    ```
+## logging.max_size_bytes
+  - **Constraints / validation**: `0` disables size rotation.
+  - **Description**: Rotates file logs before writing the next record when the active file is non-empty and that record would exceed this byte limit. Records are written whole and are not split.
+  - **Example**:
+
+    ```toml
+    [logging]
+    destination = "file"
+    path = "/var/log/telemt.log"
+    max_size_bytes = 104857600
+    ```
+## logging.max_files
+  - **Constraints / validation**: `0` disables count-based retention.
+  - **Description**: Keeps at most this many matching file logs, counting the active file and rotated archives. The active file is never deleted by retention cleanup.
+  - **Example**:
+
+    ```toml
+    [logging]
+    destination = "file"
+    path = "/var/log/telemt.log"
+    rotation = "daily"
+    max_files = 14
+    ```
+## logging.max_age_secs
+  - **Constraints / validation**: `0` disables age-based retention.
+  - **Description**: Removes rotated file logs older than this many seconds based on file modification time. The active file is never deleted by retention cleanup.
+  - **Example**:
+
+    ```toml
+    [logging]
+    destination = "file"
+    path = "/var/log/telemt.log"
+    rotation = "daily"
+    max_age_secs = 1209600
+    ```
+
 # [general]