feat: improve download engine performance and error handling with async stream closure

Author: ido-pluto

src/download/download-engine/download-file/download-engine-file.ts

@@ -234,6 +234,8 @@ export default class DownloadEngineFile extends EventEmitter<DownloadEngineFileE
         await this.options.onStartedAsync?.();
         this._sendProgressDownloadPart();
 
+        const streamPromises = new Set<Promise<void>>();
+
         for (let i = this._progress.part; i < this.file.parts.length && !this.options.skipExisting; i++) {
             if (this._closed) return;
             // If we are starting a new part, we need to reset the progress
@@ -275,7 +277,17 @@ export default class DownloadEngineFile extends EventEmitter<DownloadEngineFileE
                 await this._downloadSlice(0, chunksToRead);
             }
 
-            this._activePart.fetchStream.close();
+            const closePromise = this._activePart.fetchStream.close();
+            if (closePromise) {
+                streamPromises.add(closePromise);
+                closePromise.then(() => {
+                    streamPromises.delete(closePromise);
+                });
+            }
+        }
+
+        if (streamPromises.size > 0) {
+            await Promise.all(streamPromises);
         }
 
         // All parts are downloaded, we can clear the progress

src/download/download-engine/engine/base-download-engine.ts

@@ -224,7 +224,7 @@ export default class BaseDownloadEngine extends EventEmitter<BaseDownloadEngineE
         return downloadFile;
     }
 
-    protected static _validatePartRange(url: string, range: InputRange, remoteFileSize?: number) {
+    protected static _validatePartRange(url: string, range: InputRange, remoteFileSize: number = 0) {
         if (range.start < 0) {
             throw new InvalidOptionError(`Range start cannot be negative for URL: ${url}`);
         }
@@ -233,7 +233,7 @@ export default class BaseDownloadEngine extends EventEmitter<BaseDownloadEngineE
             throw new InvalidOptionError(`Range start (${range.start}) cannot be greater than range end (${range.end}) for URL: ${url}`);
         }
 
-        if (remoteFileSize != null && range.end >= remoteFileSize) {
+        if (remoteFileSize > 0 && range.end >= remoteFileSize) {
             throw new RangeOutOfPartLengthError(url, range.end, remoteFileSize);
         }
     }

src/download/download-engine/streams/download-engine-fetch-stream/download-engine-fetch-stream-local-file.ts

@@ -56,9 +56,9 @@ export default class DownloadEngineFetchStreamLocalFile extends BaseDownloadEngi
         };
     }
 
-    override close() {
+    override async close() {
         super.close();
-        this._fd?.close();
+        await this._fd?.close();
         this._fd = null;
     }
 }