fix(core): set correct mimetype for asset protocol streams, closes #5203 (#5210)

Co-authored-by: Lucas Nogueira <lucas@tauri.studio>

Author: amrbashir

Diff for: .changes/asset-protocol-streaming-mime-type.md

@@ -0,0 +1,5 @@
+---
+"tauri": "patch"
+---
+
+Set the correct mimetype when streaming files through `asset:` protocol

Diff for: core/tauri/src/manager.rs

@@ -507,7 +507,9 @@ impl<R: Runtime> WindowManager<R> {
       use crate::api::file::SafePathBuf;
       use tokio::io::{AsyncReadExt, AsyncSeekExt};
       use url::Position;
-      let asset_scope = self.state().get::<crate::Scopes>().asset_protocol.clone();
+      let state = self.state();
+      let asset_scope = state.get::<crate::Scopes>().asset_protocol.clone();
+      let mime_type_cache = MimeTypeCache::default();
       pending.register_uri_scheme_protocol("asset", move |request| {
         let parsed_path = Url::parse(request.uri())?;
         let filtered_path = &parsed_path[..Position::AfterPath];
@@ -626,7 +628,7 @@ impl<R: Runtime> WindowManager<R> {
             response = response.header(k, v);
           }
 
-          let mime_type = MimeType::parse(&data, &path);
+          let mime_type = mime_type_cache.get_or_insert(&data, &path);
           response.mimetype(&mime_type).status(status_code).body(data)
         } else {
           match crate::async_runtime::safe_block_on(async move { tokio::fs::read(path_).await }) {
@@ -1431,6 +1433,26 @@ fn request_to_path(request: &tauri_runtime::http::Request, base_url: &str) -> St
   }
 }
 
+// key is uri/path, value is the store mime type
+#[cfg(protocol_asset)]
+#[derive(Debug, Clone, Default)]
+struct MimeTypeCache(Arc<Mutex<HashMap<String, String>>>);
+
+#[cfg(protocol_asset)]
+impl MimeTypeCache {
+  pub fn get_or_insert(&self, content: &[u8], uri: &str) -> String {
+    let mut cache = self.0.lock().unwrap();
+    let uri = uri.to_string();
+    if let Some(mime_type) = cache.get(&uri) {
+      mime_type.clone()
+    } else {
+      let mime_type = MimeType::parse(content, &uri);
+      cache.insert(uri, mime_type.clone());
+      mime_type
+    }
+  }
+}
+
 #[cfg(test)]
 mod tests {
   use super::replace_with_callback;