Perf: drop stream transform for certain cases

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

@@ -0,0 +1,57 @@
+import { describe, it } from 'mocha';
+import { expect } from 'earl';
+import { TextLineStream } from 'foxts/text-line-stream';
+
+import { splitTextIntoLines } from './fetch-text-by-line';
+import { ProcessLineStream } from './process-line';
+
+/** The streaming pipeline splitTextIntoLines replaces, for equivalence checks */
+async function viaStream(text: string, processLine: boolean, chunkSize: number): Promise<string[]> {
+  let stream = new ReadableStream<string>({
+    start(controller) {
+      for (let i = 0; i < text.length; i += chunkSize) {
+        controller.enqueue(text.slice(i, i + chunkSize));
+      }
+      controller.close();
+    }
+  }).pipeThrough(new TextLineStream({ skipEmptyLines: processLine }));
+  if (processLine) {
+    stream = stream.pipeThrough(new ProcessLineStream());
+  }
+  return Array.fromAsync(stream);
+}
+
+const SAMPLES = [
+  '',
+  'single line without newline',
+  'a\nb\nc\n',
+  'a\nb\nc',
+  'a\r\nb\r\n\r\nc\r\n',
+  '\n\n\n',
+  '\r\n',
+  '# comment\n  padded  \n\n! adguard comment\n0.0.0.0 example.com\n\n'
+];
+
+const CHUNK_SIZES = [1, 3, 1024];
+
+describe('splitTextIntoLines', () => {
+  [false, true].forEach((processLine) => {
+    it(`matches the TextLineStream pipeline (processLine=${processLine})`, async () => {
+      for (let i = 0, len = SAMPLES.length; i < len; i++) {
+        for (let j = 0, jlen = CHUNK_SIZES.length; j < jlen; j++) {
+          // eslint-disable-next-line no-await-in-loop -- sequential equivalence checks
+          expect(splitTextIntoLines(SAMPLES[i], processLine)).toEqual(await viaStream(SAMPLES[i], processLine, CHUNK_SIZES[j]));
+        }
+      }
+    });
+  });
+
+  it('drops a lone trailing CR on an unterminated last line (TextLineStream keeps it -- a flush quirk, not a feature)', () => {
+    expect(splitTextIntoLines('a\r\nb\r', false)).toEqual(['a', 'b']);
+  });
+
+  it('applies the filter before processLine and lets it rewrite lines', () => {
+    const lines = splitTextIntoLines('keep\n  drop me \nrewrite\n', true, line => (line.includes('drop') ? null : line.toUpperCase()));
+    expect(lines).toEqual(['KEEP', 'REWRITE']);
+  });
+});