Add an optional request URL mapping function to WASM asset io

Author: eero-lehtinen

crates/bevy_asset/src/io/wasm.rs

@@ -3,7 +3,10 @@ use crate::io::{
 };
 use alloc::{borrow::ToOwned, boxed::Box, format};
 use js_sys::{Uint8Array, JSON};
-use std::path::{Path, PathBuf};
+use std::{
+    borrow::Cow,
+    path::{Path, PathBuf},
+};
 use tracing::error;
 use wasm_bindgen::{prelude::wasm_bindgen, JsCast, JsValue};
 use wasm_bindgen_futures::JsFuture;
@@ -27,15 +30,27 @@ extern "C" {
 /// Reader implementation for loading assets via HTTP in Wasm.
 pub struct HttpWasmAssetReader {
     root_path: PathBuf,
+    request_mapper: Option<Box<dyn Fn(&str) -> Cow<str> + Send + Sync + 'static>>,
 }
 
 impl HttpWasmAssetReader {
     /// Creates a new `WasmAssetReader`. The path provided will be used to build URLs to query for assets.
     pub fn new<P: AsRef<Path>>(path: P) -> Self {
         Self {
             root_path: path.as_ref().to_owned(),
+            request_mapper: None,
         }
     }
+
+    /// Sets a mapper function to modify the request URL for each asset fetch. This can be used to
+    /// add query parameters or modify the path in any way.
+    pub fn with_request_mapper<F>(mut self, mapper: F) -> Self
+    where
+        F: Fn(&str) -> Cow<str> + Send + Sync + 'static,
+    {
+        self.request_mapper = Some(Box::new(mapper));
+        self
+    }
 }
 
 fn js_value_to_err(context: &str) -> impl FnOnce(JsValue) -> std::io::Error + '_ {
@@ -57,14 +72,20 @@ impl HttpWasmAssetReader {
         &self,
         path: PathBuf,
     ) -> Result<impl Reader + use<>, AssetReaderError> {
+        let path = path.to_str().unwrap();
+        let fetch_path = self
+            .request_mapper
+            .as_ref()
+            .map_or_else(|| Cow::Borrowed(path), |mapper| mapper(path));
+
         // The JS global scope includes a self-reference via a specializing name, which can be used to determine the type of global context available.
         let global: Global = js_sys::global().unchecked_into();
         let promise = if !global.window().is_undefined() {
             let window: web_sys::Window = global.unchecked_into();
-            window.fetch_with_str(path.to_str().unwrap())
+            window.fetch_with_str(&fetch_path)
         } else if !global.worker().is_undefined() {
             let worker: web_sys::WorkerGlobalScope = global.unchecked_into();
-            worker.fetch_with_str(path.to_str().unwrap())
+            worker.fetch_with_str(&fetch_path)
         } else {
             let error = std::io::Error::other("Unsupported JavaScript global context");
             return Err(AssetReaderError::Io(error.into()));
@@ -85,7 +106,7 @@ impl HttpWasmAssetReader {
             // Some web servers, including itch.io's CDN, return 403 when a requested file isn't present.
             // TODO: remove handling of 403 as not found when it's easier to configure
             // see https://github.com/bevyengine/bevy/pull/19268#pullrequestreview-2882410105
-            403 | 404 => Err(AssetReaderError::NotFound(path)),
+            403 | 404 => Err(AssetReaderError::NotFound(path.into())),
             status => Err(AssetReaderError::HttpError(status)),
         }
     }