# Introducing plugins for loading any file to Rerun

Written by Nikolaus West 2 years ago

Developers in robotics and AI use the Rerun SDK to log and visualize multimodal data that changes over time, and that would otherwise be stuck inside their running code.

Rerun also opens many common file types (`.jpg`, `.obj`, `.md` etc) directly. Still, developers should be able to open any file containing data they want to see, whether it's highly complex, rare, or proprietary to their team. With the new [plugin system for loading arbitrary files](/content/docs/reference/data-loaders/overview/index.html) in Rerun's [0.12 release](https://github.com/rerun-io/rerun/releases/tag/0.12.0) that's now starting to become possible.

Here are a couple examples for inspiration and potential starting points for your own plugins.

### Example: Open a Tensorboard log file (TFRecord of Events) [Link to this heading](/content/blog/data-loaders#example-open-a-tensorboard-log-file-tfrecord-of-events/index.html)

This example uses an external plugin, written in Python, to open [Tensorboard](https://www.tensorflow.org/tensorboard) log files (TFRecord containing Events) directly in Rerun. Check out [the code here](https://github.com/rerun-io/rerun-loader-python-example-tfrecord).

rerun_opens_tfevents from Nikolaus West on Vimeo

### Example: Open a docx file [Link to this heading](/content/blog/data-loaders#example-open-a-docx-file/index.html)

This example also uses an external Python plugin to open docx files directly in Rerun. Check out [the code here](https://github.com/rerun-io/rerun-loader-python-example-docx)

rerun_opens_docx from Nikolaus West on Vimeo

## Unified file loading with `DataLoader`s [Link to this heading](/content/blog/data-loaders#unified-file-loading-with-dataloaders/index.html)

The Rerun Viewer can load files in 3 different ways:

- via CLI arguments (e.g. `rerun myfile.jpeg`),
- using drag-and-drop,
- using the open dialog in the Rerun Viewer.

All these file loading methods support loading a single file, many files at once (e.g. `rerun myfiles/*`), or even folders.

### How does it work? [Link to this heading](/content/blog/data-loaders#how-does-it-work/index.html)

All internal data-loaders implement the [`DataLoader`](https://docs.rs/re_data_source/latest/re_data_source/trait.DataLoader.html) trait and are registered dynamically at runtime. This means you can [easily add your own custom data-loaders](/content/docs/reference/data-loaders/overview#custom-rust-dataloaders/index.html) if you are extending the viewer in Rust.

When a user attempts to open a file in the Viewer, all known `DataLoader`s are notified of the path to be opened, unconditionally. This gives `DataLoader`s maximum flexibility to decide what files they are interested in, as opposed to e.g. only being able to look at a file's extension.

Once notified, a `DataLoader` can return a [`DataLoaderError::Incompatible`](https://docs.rs/re_data_source/latest/re_data_source/enum.DataLoaderError.html#variant.Incompatible) error to indicate that it doesn't support a given file type. If all loaders known to the Viewer return an `Incompatible` error code, then an error message is shown to the user indicating that this file type is not ( _yet_) supported. Multiple `DataLoader`s may send data from the same file to the Data Store.

## User defined external data-loaders [Link to this heading](/content/blog/data-loaders#user-defined-external-dataloaders/index.html)

The easiest way to create your own `DataLoader` is by implementing what we call an _external data-loader_; a stand alone executable written in any language that the Rerun SDK ships for. Any executable on your `$PATH` with a name that starts with `rerun-loader-` will be treated as an external data-loader.

This executable takes a file path as a command line argument and outputs Rerun logs on `stdout`. It will be called by the Rerun Viewer when the user opens a file, and be passed the path to that file. From there, it can log data as usual, using the [`stdout` logging sink](/content/docs/reference/sdk-operating-modes#standard-inputoutput/index.html).

The Rerun Viewer will then automatically load the data streamed to the external loader's standard output.

### How do they get called? [Link to this heading](/content/blog/data-loaders#how-do-they-get-called/index.html)

Under the hood, the system for finding and calling external data-loaders is implemented as just another built-in `DataLoader` called `ExternalLoader`. It keeps track of all executables with names that start with `rerun-loader-` and passes on the file path and `recording_id` (if present) when a user tries to open a file. If all external loaders respond with the error code `rr.EXTERNAL_DATA_LOADER_INCOMPATIBLE_EXIT_CODE`, the `ExternalLoader` will itself return the `DataLoaderError::Incompatible` error. If one or more external data-loaders respond with streams of data it will route those streams to the correct place.

## We're looking forward to see what you build [Link to this heading](/content/blog/data-loaders#were-looking-forward-to-see-what-you-build/index.html)

We hope this new plugin system for loading arbitrary files will help make Rerun even more useful for you and your team. We'd love to share any useful data-loaders you build with the broader community so if you have anything you'd like to share please let us know. As usual, we'd also love to hear any thoughts you might have on how to improve this feature further!