bevyengine/bevy · error · WorldAssetLoaderError

Error while trying to read the world file: {0}

Error message

Error while trying to read the world file: {0}

What it means

The WorldAssetLoader (bevy_world_serialization) deserializes a saved Bevy World from RON. Any std::io::Error raised while reading the asset's bytes is wrapped into WorldAssetLoaderError::Io with the message "Error while trying to read the world file: {0}". This is the IO-layer failure of a .world asset load; note that a missing file usually surfaces earlier as an asset-reader error, so this variant typically means the file was found but reading it failed.

Source

Thrown at crates/bevy_world_serialization/src/world_asset_loader.rs:42

    type_registry: TypeRegistryArc,
}

impl FromWorld for WorldAssetLoader {
    fn from_world(world: &mut World) -> Self {
        let type_registry = world.resource::<AppTypeRegistry>();
        WorldAssetLoader {
            type_registry: type_registry.0.clone(),
        }
    }
}

/// Possible errors that can be produced by [`WorldAssetLoader`]
#[cfg(feature = "serialize")]
#[non_exhaustive]
#[derive(Debug, Error)]
pub enum WorldAssetLoaderError {
    /// An [IO Error](std::io::Error)
    #[error("Error while trying to read the world file: {0}")]
    Io(#[from] std::io::Error),
    /// A [RON Error](ron::error::SpannedError)
    #[error("Could not parse RON: {0}")]
    RonSpannedError(#[from] ron::error::SpannedError),
}

#[cfg(feature = "serialize")]
impl AssetLoader for WorldAssetLoader {
    type Asset = DynamicWorld;
    type Settings = ();
    type Error = WorldAssetLoaderError;

    async fn load(
        &self,
        reader: &mut dyn Reader,
        _settings: &(),
        load_context: &mut LoadContext<'_>,
    ) -> Result<Self::Asset, Self::Error> {

View on GitHub (pinned to 396ca72708)

Solutions

1. Check the file exists, is non-empty, and is readable by the process (permissions, size on disk).
2. If the save was interrupted, regenerate or restore the .world file from a backup or re-export from the editor.
3. Handle load failure gracefully: watch the asset's LoadState and show recovery UI instead of assuming success.
4. For network sources, retry the load once after an Io error — transient reader failures are common.
5. Write saves atomically (temp file + rename) so interrupted saves never leave truncated files.

Example fix

// before
let world: Handle<WorldAsset> = asset_server.load("worlds/level1.world"); // truncated file -> Io error

// after: validate before relying on it, and regenerate broken saves
if std::fs::metadata("assets/worlds/level1.world").map(|m| m.len() < 16).unwrap_or(true) {
    warn!("level1.world missing or truncated — restoring default");
    std::fs::copy("assets/worlds/default.world", "assets/worlds/level1.world");
}

// cheap pre-flight before requesting the asset
fn world_file_readable(path: &std::path::Path) -> bool {
    std::fs::metadata(path).map(|m| m.len() > 0).unwrap_or(false)
}

use bevy_asset::LoadState;

match asset_server.get_load_state(&world_handle) {
    Some(LoadState::Failed(err)) => {
        if let bevy_asset::AssetLoadError::AssetLoaderError(loader_err) = &*err {
            if let Some(io_err) = loader_err.error.downcast_ref::<WorldAssetLoaderError>() {
                error!("world asset failed: {io_err}"); // Io(e) or RonSpannedError(e)
            }
        }
        // recover: restore a backup, show an error screen, etc.
    }
    _ => {}
}

When it happens

Trigger: Loading a truncated or zero-byte .world file; a file that becomes unreadable mid-load (permissions, disk, network filesystem hiccup with an async file source); custom AssetSource readers returning io::Error during read.

Common situations: World save files corrupted by interrupted writes or crashes; deploy pipelines truncating assets; cloud/streamed asset sources with flaky IO; partial downloads when serving worlds over HTTP.

Related errors

• Could not parse RON: {0}
• world contains the unregistered component `{type_path}`. con
• Failed to load image bytes: {0}
• missing texture atlas layout for the font
• missing texture for the font atlas

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/19da023c48471477. Report an issue: GitHub.