Perf: speed up text line stream

Build/download-mock-assets.ts

@@ -19,13 +19,12 @@ export const downloadMockAssets = task(require.main === module, __filename)((spa
   ([filename, url]) => span
     .traceChildAsync(url, async () => {
       const res = await fetchWithRetry(url);
-
-      const src = path.join(OUTPUT_MOCK_DIR, filename);
       if (!res.body) {
         throw new Error(`Empty body from ${url}`);
       }
 
       await mkdirp(OUTPUT_MOCK_DIR);
+      const src = path.join(OUTPUT_MOCK_DIR, filename);
 
       return pipeline(
         Readable.fromWeb(res.body),

Build/lib/fetch-text-by-line.ts

@@ -10,6 +10,7 @@ import { processLine } from './process-line';
 
 const getReadableStream = (file: string | FileHandle): ReadableStream => {
   if (typeof file === 'string') {
+    // return fs.openAsBlob(file).then(blob => blob.stream())
     return Readable.toWeb(fs.createReadStream(file/* , { encoding: 'utf-8' } */));
   }
   return file.readableWebStream();

Build/lib/text-line-transform-stream.ts

@@ -25,23 +25,25 @@ export class TextLineStream extends TransformStream<string, string> {
     allowCR = false
   }: TextLineStreamOptions = {}) {
     let __buf = '';
+    let chunkIndex = 0;
 
     super({
       transform(chunk, controller) {
         chunk = __buf + chunk;
+        chunkIndex = 0;
 
         for (; ;) {
-          const lfIndex = chunk.indexOf('\n');
+          const lfIndex = chunk.indexOf('\n', chunkIndex);
 
           if (allowCR) {
-            const crIndex = chunk.indexOf('\r');
+            const crIndex = chunk.indexOf('\r', chunkIndex);
 
             if (
               crIndex !== -1 && crIndex !== (chunk.length - 1)
               && (lfIndex === -1 || (lfIndex - 1) > crIndex)
             ) {
-              controller.enqueue(chunk.slice(0, crIndex));
-              chunk = chunk.slice(crIndex + 1);
+              controller.enqueue(chunk.slice(chunkIndex, crIndex));
+              chunkIndex = crIndex + 1;
               continue;
             }
           }
@@ -51,15 +53,15 @@ export class TextLineStream extends TransformStream<string, string> {
             if (chunk[lfIndex - 1] === '\r') {
               crOrLfIndex--;
             }
-            controller.enqueue(chunk.slice(0, crOrLfIndex));
-            chunk = chunk.slice(lfIndex + 1);
+            controller.enqueue(chunk.slice(chunkIndex, crOrLfIndex));
+            chunkIndex = lfIndex + 1;
             continue;
           }
 
           break;
         }
 
-        __buf = chunk;
+        __buf = chunk.slice(chunkIndex);
       },
       flush(controller) {
         if (__buf.length > 0) {