# web.send_file

## Function

Send local files directly as HTTP responses, suitable for downloading large files or exporting files, to avoid reading the file content into the BT dynamic response string at once.

## Syntax

```bt
web.send_file(path)
send_file(path)
```

## Parameters

| Parameters | Type | Required | Default value | Description |
| ------ | ------ | ------ | ------ | ------ |
| path | String/Fs | Yes | None | The local file path to send. The relative path is resolved based on the current source code file directory, and `@/` is resolved based on the project root. |

## Return value

| Type | Description |
| ------ | ------ |
| Bool | Returns true if set successfully; the file is sent by the web layer at the end of the request. |

## Example

```bt
web.header('Cache-Control', 'public, max-age=3600')
web.send_file('@/downloads/report.csv')
```

## Notes

- Can only be called in a web request.
- This ability will read local files and is subject to `BT_PERMISSION_DENY=fs` / `BT_PERMISSION_ALLOW` permission configuration.
- File responses are sent in chunks by the web framework, supporting ETag, Last-Modified, conditional requests and HTTP Range.
- After `web.send_file()` is set, this request will not write back the last expression or the dynamic response body generated by `print`.
- `Content-Type` is inferred by file extension by default; you can call `web.header('Content-Type', value)` in advance when overwriting is required.