[docs] add config docs about logging

Author: zachmann

docs/config/logging.md

@@ -2,4 +2,105 @@
 icon: material/script-text
 ---
 
-TODO
+Under the `logging` config option the logging behavior and locations can be 
+configured.
+
+## `access`
+<span class="badge badge-purple" title="Value Type">object</span>
+<span class="badge badge-green" title="If this option is required or optional">recommended</span>
+
+Under the `access` option the http access log can be configured.
+
+??? file "config.yaml"
+
+    ```yaml
+    logging:
+        access:
+            dir: /var/log/offa
+            stderr: true
+    ```
+
+The following options are available:
+
+### `dir`
+<span class="badge badge-purple" title="Value Type">directory path</span>
+<span class="badge badge-green" title="If this option is required or optional">optional</span>
+
+The `dir` option is used to configure the directory where the log file 
+should be stored.
+If not set, OFFA will not log to file.
+
+### `stderr`
+<span class="badge badge-purple" title="Value Type">boolean</span>
+<span class="badge badge-blue" title="Default Value">`false`</span>
+<span class="badge badge-green" title="If this option is required or optional">optional</span>
+
+The `stderr` option indicates if OFFA logs to `stderr`.
+
+## `internal`
+The `internal` option is used to configure logging for OFFA's internal 
+logging, i.e. logging related to what OFFA does.
+
+??? file "config.yaml"
+
+    ```yaml
+    logging:
+        internal:
+            dir: /var/log/offa
+            stderr: true
+            level: info
+            smart:
+                enabled: true
+                dir: /var/log/offa/errors
+    ```
+
+All configuration options from [`access`](#access) also can be used with 
+`internal`.
+In additional the following options can be used:
+
+### `level`
+<span class="badge badge-purple" title="Value Type">enum</span>
+<span class="badge badge-blue" title="Default Value">info</span>
+<span class="badge badge-green" title="If this option is required or optional">optional</span>
+
+The `level` option sets the minimal log level that should be logged.
+
+Valid values are:
+
+- `trace`
+- `debug`
+- `info`
+- `warn` / `warning`
+- `error`
+- `fatal`
+- `panic`
+
+### `smart`
+
+Under the `smart` option 'smart' logging can be enabled and configured. 
+Smart logging allows to have a higher (less verbose) log level set for 
+general (internal) logging without loosing valuable debug information in 
+case errors occure.
+
+If smart logging is enabled, the general logs are still done with the level 
+set through the [`level`](#level) option, but if an error occurs a special 
+error log is created to a dedicated file. This dedicated error log contains 
+all log entries - including all log levels, also levels that normally woud 
+not be logged - for that particular request.
+
+#### `enabled`
+<span class="badge badge-purple" title="Value Type">boolean</span>
+<span class="badge badge-blue" title="Default Value">`false`</span>
+<span class="badge badge-green" title="If this option is required or optional">optional</span>
+
+The `enabled` option is used to enable smart logging.
+
+#### `dir`
+<span class="badge badge-purple" title="Value Type">directory path</span>
+<span class="badge badge-blue" title="Default Value">same as the internal logging dir</span>
+<span class="badge badge-green" title="If this option is required or optional">optional</span>
+
+The `dir` option is used to specify the directory where smart error log 
+files should be stored.
+If not set and smart logging is enabled, smart error logs are placed in the 
+same directory as the regular internal log file.

internal/config/config.go

@@ -178,14 +178,14 @@ type loggingConf struct {
 
 type internalLoggerConf struct {
 	LoggerConf `yaml:",inline"`
+	Level      string          `yaml:"level"`
 	Smart      smartLoggerConf `yaml:"smart"`
 }
 
 // LoggerConf holds configuration related to logging
 type LoggerConf struct {
 	Dir    string `yaml:"dir"`
 	StdErr bool   `yaml:"stderr"`
-	Level  string `yaml:"level"`
 }
 
 type smartLoggerConf struct {