feat(Tracing): return a buffer from tracing.stop (#2360)

Fixes #2148

docs/api.md

@@ -1602,15 +1602,15 @@ await page.tracing.stop();
 
 #### tracing.start(options)
 - `options` <[Object]>
-  - `path` <[string]> A path to write the trace file to. **required**
+  - `path` <[string]> A path to write the trace file to.
   - `screenshots` <[boolean]> captures screenshots in the trace.
   - `categories` <[Array]<[string]>> specify custom categories to use instead of default.
 - returns: <[Promise]>
 
 Only one trace can be active at a time per browser.
 
 #### tracing.stop()
-- returns: <[Promise]>
+- returns: <[Promise]<[Buffer]>> Promise which resolves to buffer with trace data.
 
 ### class: Dialog
 

lib/Tracing.js

@@ -35,7 +35,6 @@ class Tracing {
    */
   async start(options) {
     console.assert(!this._recording, 'Cannot start recording trace while already recording trace.');
-    console.assert(options.path, 'Must specify a path to write trace file to.');
 
     const defaultCategories = [
       '-*', 'devtools.timeline', 'v8.execute', 'disabled-by-default-devtools.timeline',
@@ -73,15 +72,26 @@ class Tracing {
    */
   async _readStream(handle, path) {
     let eof = false;
-    const file = await openAsync(path, 'w');
+    let file;
+    if (path)
+      file = await openAsync(path, 'w');
+    const bufs = [];
     while (!eof) {
       const response = await this._client.send('IO.read', {handle});
       eof = response.eof;
+      bufs.push(new Buffer(response.data));
       if (path)
         await writeAsync(file, response.data);
     }
-    await closeAsync(file);
+    if (path)
+      await closeAsync(file);
     await this._client.send('IO.close', {handle});
+    let resultBuffer = null;
+    try {
+      resultBuffer = Buffer.concat(bufs);
+    } finally {
+      return resultBuffer;
+    }
   }
 }
 helper.tracePublicAPI(Tracing);

test/tracing.spec.js

@@ -27,8 +27,10 @@ module.exports.addTests = function({testRunner, expect}) {
       state.outputFile = path.join(__dirname, 'assets', `trace-${state.parallelIndex}.json`);
     });
     afterEach(function(state) {
-      fs.unlinkSync(state.outputFile);
-      state.outputFile = null;
+      if (fs.existsSync(state.outputFile)) {
+        fs.unlinkSync(state.outputFile);
+        state.outputFile = null;
+      }
     });
     it('should output a trace', async({page, server, outputFile}) => {
       await page.tracing.start({screenshots: true, path: outputFile});
@@ -52,5 +54,29 @@ module.exports.addTests = function({testRunner, expect}) {
       expect(error).toBeTruthy();
       await page.tracing.stop();
     });
+    it('should return a buffer', async({page, server, outputFile}) => {
+      await page.tracing.start({screenshots: true, path: outputFile});
+      await page.goto(server.PREFIX + '/grid.html');
+      const trace = await page.tracing.stop();
+      const buf = fs.readFileSync(outputFile);
+      expect(trace.toString()).toEqual(buf.toString());
+    });
+    it('should return null in case of Buffer error', async({page, server}) => {
+      await page.tracing.start({screenshots: true});
+      await page.goto(server.PREFIX + '/grid.html');
+      const oldBufferConcat = Buffer.concat;
+      Buffer.concat = bufs => {
+        throw 'error';
+      };
+      const trace = await page.tracing.stop();
+      expect(trace).toEqual(null);
+      Buffer.concat = oldBufferConcat;
+    });
+    it('should support a buffer without a path', async({page, server}) => {
+      await page.tracing.start({screenshots: true});
+      await page.goto(server.PREFIX + '/grid.html');
+      const trace = await page.tracing.stop();
+      expect(trace.toString()).toContain('screenshot');
+    });
   });
 };