# File transport (main process only)

The file transport writes log messages to a file 

## Options

#### `archiveLogFn` {(oldLogFile: LogFile) => void}

Default:

```js
function archiveLog(file) {
  file = file.toString();
  const info = path.parse(file);

  try {
    fs.renameSync(file, path.join(info.dir, info.name + '.old' + info.ext));
  } catch (e) {
    console.warn('Could not rotate log', e);
  }
}
```

Callback which is called on log rotation. You can override it if you need
custom log rotation behavior. This function should remove old file
synchronously.

#### `fileName` {string}

Default: `'main.log'`

The actual file name without path.

#### `format` {string | (params: FormatParams) => any[]}

Default: `'[{y}-{m}-{d} {h}:{i}:{s}.{ms}] [{level}] {text}'`

Determines how to serialize log message while writing to a file.
[Read more](format.md).

#### `inspectOptions` {InspectOptions}

Default: `{ depth: 5 }`

How to serialize objects passed to log function
https://nodejs.org/api/util.html#util_util_inspect_object_options

#### `level` {LogLevel | false}
  
Default: `'silly'`

Filter log messages which can be sent via the transport.

#### `maxSize` {number}

Default: `1048576` (1mb)

Maximum size of a log file in bytes. When a log file exceeds this limit,
it will be moved to {file name}.old.log file. You can set it to 0 to disable
log rotation.
  
#### `resolvePathFn` {(variables: PathVariables, message?: LogMessage) => string}

Default:
```js
function resolvePath(variables) {
  return path.join(variables.libraryDefaultDir, variables.fileName);
}
```

Allows to set a custom path for a log file. Directory hierarchy will be created
automatically if necessary.

That's just an option, so it's not recommended calling it directly.

The variables argument is just an object of 
[PathVariables type](../../src/index.d.ts#L93), which contains several
predefined values. Feel free to choose the most suitable for your application.
  
Electron has built-in method to get logs path `app.getPath('logs')`. But it
seems not stable in the current version. There is a chance that default path on
some platforms might be changed later. However, if you would like to use default
Electron path, just use the following resolver:

```js
log.transports.file.resolvePathFn = (variables) => {
  return path.join(variables.electronDefaultDir, variables.fileName);
}
```
  
#### `sync` {boolean}
 
Default: `true` 
 
Whether to write a log file synchronously.

#### `writeOptions` {WriteOptions}

Default:

```
{
  encoding: 'utf8',
  flag: 'a',
  mode: 0o666,
}
```

Options for 
[fs.writeFile]https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback

## Methods

#### `getFile(message?: Partial<LogMessage>) => LogFile`

Return the current file instance used for the transport.

The `message` argument is optional and only required if you define log path
inside `resolvePath` callback depending on a message.

#### `readAllLogs() => Array<{ path: string, lines: string[] }>`

Reads content of all log files.

Be careful, if you use multiple log directories through overriding resolvePath,
it won't return all the files.

#### `setAppName(appName: string)`

Overrides appName used for resolving the log path

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