perf: bound runtime memory and storage usage

test/back/logReader.test.cjs

@@ -0,0 +1,72 @@
+const assert = require('node:assert/strict');
+const fs = require('node:fs/promises');
+const os = require('node:os');
+const path = require('node:path');
+const test = require('node:test');
+
+const {
+  DEFAULT_LOG_CHUNK_BYTES,
+  MAX_LOG_CHUNK_BYTES,
+  readLogChunk,
+} = require('../../back/shared/logReader');
+
+test('log reader defaults to a bounded tail and supports incremental reads', async (t) => {
+  const directory = await fs.mkdtemp(path.join(os.tmpdir(), 'ql-log-reader-'));
+  const file = path.join(directory, 'task.log');
+  t.after(() => fs.rm(directory, { recursive: true, force: true }));
+
+  const initial = 'a'.repeat(DEFAULT_LOG_CHUNK_BYTES * 2);
+  await fs.writeFile(file, initial);
+
+  const tail = await readLogChunk(file);
+  assert.equal(tail.content.length, DEFAULT_LOG_CHUNK_BYTES);
+  assert.equal(tail.offset, DEFAULT_LOG_CHUNK_BYTES);
+  assert.equal(tail.nextOffset, initial.length);
+  assert.equal(tail.truncated, true);
+
+  await fs.appendFile(file, 'next');
+  const incremental = await readLogChunk(file, { offset: tail.nextOffset });
+  assert.equal(incremental.content, 'next');
+  assert.equal(incremental.nextOffset, initial.length + 4);
+});
+
+test('log reader enforces the maximum chunk size', async (t) => {
+  const directory = await fs.mkdtemp(path.join(os.tmpdir(), 'ql-log-reader-'));
+  const file = path.join(directory, 'large.log');
+  t.after(() => fs.rm(directory, { recursive: true, force: true }));
+  await fs.writeFile(file, 'x'.repeat(MAX_LOG_CHUNK_BYTES + 1024));
+
+  const chunk = await readLogChunk(file, { limit: Number.MAX_SAFE_INTEGER });
+  assert.equal(Buffer.byteLength(chunk.content), MAX_LOG_CHUNK_BYTES);
+});
+
+test('log reader preserves UTF-8 characters across byte boundaries', async (t) => {
+  const directory = await fs.mkdtemp(path.join(os.tmpdir(), 'ql-log-reader-'));
+  const file = path.join(directory, 'utf8.log');
+  t.after(() => fs.rm(directory, { recursive: true, force: true }));
+  await fs.writeFile(file, 'a'.repeat(5) + '中文日志');
+
+  const first = await readLogChunk(file, { offset: 0, limit: 7 });
+  const second = await readLogChunk(file, {
+    offset: first.nextOffset,
+    limit: 7,
+  });
+  const third = await readLogChunk(file, {
+    offset: second.nextOffset,
+    limit: 7,
+  });
+
+  assert.equal(first.content + second.content + third.content, 'aaaaa中文日志');
+  assert.equal((first.content + second.content + third.content).includes('�'), false);
+});
+
+test('missing logs return an empty chunk', async () => {
+  const chunk = await readLogChunk('/path/that/does/not/exist.log');
+  assert.deepEqual(chunk, {
+    content: '',
+    offset: 0,
+    nextOffset: 0,
+    total: 0,
+    truncated: false,
+  });
+});