ui/build.js

// Copyright (C) 2021 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

'use strict';


// This script takes care of:
// - The build process for the whole UI and the chrome extension.
// - The HTTP dev-server with live-reload capabilities.
// The reason why this is a hand-rolled script rather than a conventional build
// system is keeping incremental build fast and maintaining the set of
// dependencies contained.
// The only way to keep incremental build fast (i.e. O(seconds) for the
// edit-one-line -> reload html cycles) is to run both the TypeScript compiler
// and the rollup bundler in --watch mode. Any other attempt, leads to O(10s)
// incremental-build times.
// This script allows mixing build tools that support --watch mode (tsc and
// rollup) and auto-triggering-on-file-change rules via node-watch.
// When invoked without any argument (e.g., for production builds), this script
// just runs all the build tasks serially. It doesn't to do any mtime-based
// check, it always re-runs all the tasks.
// When invoked with --watch, it mounts a pipeline of tasks based on node-watch
// and runs them together with tsc --watch and rollup --watch.
// The output directory structure is carefully crafted so that any change to UI
// sources causes cascading triggers of the next steps.
// The overall build graph looks as follows:
// +----------------+      +-----------------------------+
// | protos/*.proto |----->| pbjs out/tsc/gen/protos.js  |--+
// +----------------+      +-----------------------------+  |
//                         +-----------------------------+  |
//                         | pbts out/tsc/gen/protos.d.ts|<-+
//                         +-----------------------------+
//                             |
//                             V      +-------------------------+
// +---------+              +-----+   |  out/tsc/frontend/*.js  |
// | ui/*.ts |------------->| tsc |-> +-------------------------+   +--------+
// +---------+              +-----+   | out/tsc/controller/*.js |-->| rollup |
//                            ^       +-------------------------+   +--------+
//                +------------+      |   out/tsc/engine/*.js   |       |
// +-----------+  |*.wasm.js   |      +-------------------------+       |
// |ninja *.cc |->|*.wasm.d.ts |                                        |
// +-----------+  |*.wasm      |-----------------+                      |
//                +------------+                 |                      |
//                                               V                      V
// +-----------+  +------+    +------------------------------------------------+
// | ui/*.scss |->| scss |--->|              Final out/dist/ dir               |
// +-----------+  +------+    +------------------------------------------------+
// +----------------------+   | +----------+ +---------+ +--------------------+|
// | src/assets/*.png     |   | | assets/  | |*.wasm.js| | frontend_bundle.js ||
// +----------------------+   | |  *.css   | |*.wasm   | +--------------------+|
// | buildtools/typefaces |-->| |  *.png   | +---------+ |  engine_bundle.js  ||
// +----------------------+   | |  *.woff2 |             +--------------------+|
// | buildtools/legacy_tv |   | |  tv.html |             |traceconv_bundle.js ||
// +----------------------+   | +----------+             +--------------------+|
//                            +------------------------------------------------+

const argparse = require('argparse');
const childProcess = require('child_process');
const crypto = require('crypto');
const fs = require('fs');
const http = require('http');
const path = require('path');
const fswatch = require('node-watch');  // Like fs.watch(), but works on Linux.
const pjoin = path.join;

const ROOT_DIR = path.dirname(__dirname);  // The repo root.
const VERSION_SCRIPT = pjoin(ROOT_DIR, 'tools/write_version_header.py');
const GEN_IMPORTS_SCRIPT = pjoin(ROOT_DIR, 'tools/gen_ui_imports');

const cfg = {
  watch: false,
  verbose: false,
  debug: false,
  bigtrace: false,
  startHttpServer: false,
  httpServerListenHost: '127.0.0.1',
  httpServerListenPort: 10000,
  wasmModules: ['trace_processor', 'traceconv'],
  crossOriginIsolation: false,
  testFilter: '',
  noOverrideGnArgs: false,

  // The fields below will be changed by main() after cmdline parsing.
  // Directory structure:
  // out/xxx/    -> outDir         : Root build dir, for both ninja/wasm and UI.
  //   ui/       -> outUiDir       : UI dir. All outputs from this script.
  //    tsc/     -> outTscDir      : Transpiled .ts -> .js.
  //      gen/   -> outGenDir      : Auto-generated .ts/.js (e.g. protos).
  //    dist/    -> outDistRootDir : Only index.html and service_worker.js
  //      v1.2/  -> outDistDir     : JS bundles and assets
  //    chrome_extension/          : Chrome extension.
  outDir: pjoin(ROOT_DIR, 'out/ui'),
  version: '',  // v1.2.3, derived from the CHANGELOG + git.
  outUiDir: '',
  outUiTestArtifactsDir: '',
  outDistRootDir: '',
  outTscDir: '',
  outGenDir: '',
  outDistDir: '',
  outExtDir: '',
  outBigtraceDistDir: '',
};

const RULES = [
  {r: /ui\/src\/assets\/index.html/, f: copyIndexHtml},
  {r: /ui\/src\/assets\/bigtrace.html/, f: copyBigtraceHtml},
  {r: /ui\/src\/assets\/((.*)[.]png)/, f: copyAssets},
  {r: /buildtools\/typefaces\/(.+[.]woff2)/, f: copyAssets},
  {r: /buildtools\/catapult_trace_viewer\/(.+(js|html))/, f: copyAssets},
  {r: /ui\/src\/assets\/.+[.]scss/, f: compileScss},
  {r: /ui\/src\/chrome_extension\/.*/, f: copyExtensionAssets},
  {
    r: /ui\/src\/test\/diff_viewer\/(.+[.](?:html|js))/,
    f: copyUiTestArtifactsAssets,
  },
  {r: /.*\/dist\/.+\/(?!manifest\.json).*/, f: genServiceWorkerManifestJson},
  {r: /.*\/dist\/.*/, f: notifyLiveServer},
];

const tasks = [];
let tasksTot = 0;
let tasksRan = 0;
const httpWatches = [];
const tStart = Date.now();
const subprocesses = [];

async function main() {
  const parser = new argparse.ArgumentParser();
  parser.add_argument('--out', {help: 'Output directory'});
  parser.add_argument('--watch', '-w', {action: 'store_true'});
  parser.add_argument('--serve', '-s', {action: 'store_true'});
  parser.add_argument('--serve-host', {help: '--serve bind host'});
  parser.add_argument('--serve-port', {help: '--serve bind port', type: 'int'});
  parser.add_argument('--verbose', '-v', {action: 'store_true'});
  parser.add_argument('--no-build', '-n', {action: 'store_true'});
  parser.add_argument('--no-wasm', '-W', {action: 'store_true'});
  parser.add_argument('--run-unittests', '-t', {action: 'store_true'});
  parser.add_argument('--run-integrationtests', '-T', {action: 'store_true'});
  parser.add_argument('--debug', '-d', {action: 'store_true'});
  parser.add_argument('--bigtrace', {action: 'store_true'});
  parser.add_argument('--interactive', '-i', {action: 'store_true'});
  parser.add_argument('--rebaseline', '-r', {action: 'store_true'});
  parser.add_argument('--no-depscheck', {action: 'store_true'});
  parser.add_argument('--cross-origin-isolation', {action: 'store_true'});
  parser.add_argument('--test-filter', '-f', {
    help: 'filter Jest tests by regex, e.g. \'chrome_render\'',
  });
  parser.add_argument('--no-override-gn-args', {action: 'store_true'});

  const args = parser.parse_args();
  const clean = !args.no_build;
  cfg.outDir = path.resolve(ensureDir(args.out || cfg.outDir));
  cfg.outUiDir = ensureDir(pjoin(cfg.outDir, 'ui'), clean);
  cfg.outUiTestArtifactsDir = ensureDir(pjoin(cfg.outDir, 'ui-test-artifacts'));
  cfg.outExtDir = ensureDir(pjoin(cfg.outUiDir, 'chrome_extension'));
  cfg.outDistRootDir = ensureDir(pjoin(cfg.outUiDir, 'dist'));
  const proc = exec('python3', [VERSION_SCRIPT, '--stdout'], {stdout: 'pipe'});
  cfg.version = proc.stdout.toString().trim();
  cfg.outDistDir = ensureDir(pjoin(cfg.outDistRootDir, cfg.version));
  cfg.outTscDir = ensureDir(pjoin(cfg.outUiDir, 'tsc'));
  cfg.outGenDir = ensureDir(pjoin(cfg.outUiDir, 'tsc/gen'));
  cfg.testFilter = args.test_filter || '';
  cfg.watch = !!args.watch;
  cfg.verbose = !!args.verbose;
  cfg.debug = !!args.debug;
  cfg.bigtrace = !!args.bigtrace;
  cfg.startHttpServer = args.serve;
  cfg.noOverrideGnArgs = !!args.no_override_gn_args;
  if (args.bigtrace) {
    cfg.outBigtraceDistDir = ensureDir(pjoin(cfg.outDistDir, 'bigtrace'));
  }
  if (args.serve_host) {
    cfg.httpServerListenHost = args.serve_host;
  }
  if (args.serve_port) {
    cfg.httpServerListenPort = args.serve_port;
  }
  if (args.interactive) {
    process.env.PERFETTO_UI_TESTS_INTERACTIVE = '1';
  }
  if (args.rebaseline) {
    process.env.PERFETTO_UI_TESTS_REBASELINE = '1';
  }
  if (args.cross_origin_isolation) {
    cfg.crossOriginIsolation = true;
  }

  process.on('SIGINT', () => {
    console.log('\nSIGINT received. Killing all child processes and exiting');
    for (const proc of subprocesses) {
      if (proc) proc.kill('SIGINT');
    }
    process.exit(130);  // 130 -> Same behavior of bash when killed by SIGINT.
  });

  if (!args.no_depscheck) {
    // Check that deps are current before starting.
    const installBuildDeps = pjoin(ROOT_DIR, 'tools/install-build-deps');
    const checkDepsPath = pjoin(cfg.outDir, '.check_deps');
    let args = [installBuildDeps, `--check-only=${checkDepsPath}`, '--ui'];

    if (process.platform === 'darwin') {
      const result = childProcess.spawnSync('arch', ['-arm64', 'true']);
      const isArm64Capable = result.status === 0;
      if (isArm64Capable) {
        const archArgs = [
          'arch',
          '-arch',
          'arm64',
        ];
        args = archArgs.concat(args);
      }
    }
    const cmd = args.shift();
    exec(cmd, args);
  }

  console.log('Entering', cfg.outDir);
  process.chdir(cfg.outDir);

  // Enqueue empty task. This is needed only for --no-build --serve. The HTTP
  // server is started when the task queue reaches quiescence, but it takes at
  // least one task for that.
  addTask(() => {});

  if (!args.no_build) {
    updateSymlinks();  // Links //ui/out -> //out/xxx/ui/

    buildWasm(args.no_wasm);
    scanDir('ui/src/assets');
    scanDir('ui/src/chrome_extension');
    scanDir('ui/src/test/diff_viewer');
    scanDir('buildtools/typefaces');
    scanDir('buildtools/catapult_trace_viewer');
    generateImports('ui/src/tracks', 'all_tracks.ts');
    generateImports('ui/src/plugins', 'all_plugins.ts');
    compileProtos();
    genVersion();
    transpileTsProject('ui');
    transpileTsProject('ui/src/service_worker');
    if (cfg.bigtrace) {
      transpileTsProject('ui/src/bigtrace');
    }

    if (cfg.watch) {
      transpileTsProject('ui', {watch: cfg.watch});
      transpileTsProject('ui/src/service_worker', {watch: cfg.watch});
      if (cfg.bigtrace) {
        transpileTsProject('ui/src/bigtrace', {watch: cfg.watch});
      }
    }

    bundleJs('rollup.config.js');
    genServiceWorkerManifestJson();

    // Watches the /dist. When changed:
    // - Notifies the HTTP live reload clients.
    // - Regenerates the ServiceWorker file map.
    scanDir(cfg.outDistRootDir);
  }

  // We should enter the loop only in watch mode, where tsc and rollup are
  // asynchronous because they run in watch mode.
  if (args.no_build && !isDistComplete()) {
    console.log('No build was requested, but artifacts are not available.');
    console.log('In case of execution error, re-run without --no-build.');
  }
  if (!args.no_build) {
    const tStart = Date.now();
    while (!isDistComplete()) {
      const secs = Math.ceil((Date.now() - tStart) / 1000);
      process.stdout.write(
          `\t\tWaiting for first build to complete... ${secs} s\r`);
      await new Promise((r) => setTimeout(r, 500));
    }
  }
  if (cfg.watch) console.log('\nFirst build completed!');

  if (cfg.startHttpServer) {
    startServer();
  }
  if (args.run_unittests) {
    runTests('jest.unittest.config.js');
  }
  if (args.run_integrationtests) {
    runTests('jest.integrationtest.config.js');
  }
}

// -----------
// Build rules
// -----------

function runTests(cfgFile) {
  const args = [
    '--rootDir',
    cfg.outTscDir,
    '--verbose',
    '--runInBand',
    '--detectOpenHandles',
    '--forceExit',
    '--projects',
    pjoin(ROOT_DIR, 'ui/config', cfgFile),
  ];
  if (cfg.testFilter.length > 0) {
    args.push('-t', cfg.testFilter);
  }
  if (cfg.watch) {
    args.push('--watchAll');
    addTask(execModule, ['jest', args, {async: true}]);
  } else {
    addTask(execModule, ['jest', args]);
  }
}

function cpHtml(src, filename) {
  let html = fs.readFileSync(src).toString();
  // First copy the html as-is into the dist/v1.2.3/ directory. This is
  // only used for archival purporses, so one can open
  // ui.perfetto.dev/v1.2.3/ to skip the auto-update and channel logic.
  fs.writeFileSync(pjoin(cfg.outDistDir, filename), html);

  // Then copy it into the dist/ root by patching the version code.
  // TODO(primiano): in next CLs, this script should take a
  // --release_map=xxx.json argument, to populate this with multiple channels.
  const versionMap = JSON.stringify({'stable': cfg.version});
  const bodyRegex = /data-perfetto_version='[^']*'/;
  html = html.replace(bodyRegex, `data-perfetto_version='${versionMap}'`);
  fs.writeFileSync(pjoin(cfg.outDistRootDir, filename), html);
}

function copyIndexHtml(src) {
  addTask(cpHtml, [src, 'index.html']);
}

function copyBigtraceHtml(src) {
  if (cfg.bigtrace) {
    addTask(cpHtml, [src, 'bigtrace.html']);
  }
}

function copyAssets(src, dst) {
  addTask(cp, [src, pjoin(cfg.outDistDir, 'assets', dst)]);
  if (cfg.bigtrace) {
    addTask(cp, [src, pjoin(cfg.outBigtraceDistDir, 'assets', dst)]);
  }
}

function copyUiTestArtifactsAssets(src, dst) {
  addTask(cp, [src, pjoin(cfg.outUiTestArtifactsDir, dst)]);
}

function compileScss() {
  const src = pjoin(ROOT_DIR, 'ui/src/assets/perfetto.scss');
  const dst = pjoin(cfg.outDistDir, 'perfetto.css');
  // In watch mode, don't exit(1) if scss fails. It can easily happen by
  // having a typo in the css. It will still print an error.
  const noErrCheck = !!cfg.watch;
  const args = [src, dst];
  if (!cfg.verbose) {
    args.unshift('--quiet');
  }
  addTask(execModule, ['sass', args, {noErrCheck}]);
  if (cfg.bigtrace) {
    addTask(cp, [dst, pjoin(cfg.outBigtraceDistDir, 'perfetto.css')]);
  }
}

function compileProtos() {
  const dstJs = pjoin(cfg.outGenDir, 'protos.js');
  const dstTs = pjoin(cfg.outGenDir, 'protos.d.ts');
  // We've ended up pulling in all the protos (via trace.proto,
  // trace_packet.proto) below which means |dstJs| ends up being
  // 23k lines/12mb. We should probably not do that.
  // TODO(hjd): Figure out how to use lazy with pbjs/pbts.
  const inputs = [
    'protos/perfetto/common/trace_stats.proto',
    'protos/perfetto/common/tracing_service_capabilities.proto',
    'protos/perfetto/config/perfetto_config.proto',
    'protos/perfetto/ipc/consumer_port.proto',
    'protos/perfetto/ipc/wire_protocol.proto',
    'protos/perfetto/metrics/metrics.proto',
    'protos/perfetto/trace/perfetto/perfetto_metatrace.proto',
    'protos/perfetto/trace/trace.proto',
    'protos/perfetto/trace/trace_packet.proto',
    'protos/perfetto/trace_processor/trace_processor.proto',
  ];
  // Can't put --no-comments here - The comments are load bearing for
  // the pbts invocation which follows.
  const pbjsArgs = [
    '--no-beautify',
    '--force-number',
    '--no-delimited',
    '--no-verify',
    '-t',
    'static-module',
    '-w',
    'commonjs',
    '-p',
    ROOT_DIR,
    '-o',
    dstJs,
  ].concat(inputs);
  addTask(execModule, ['pbjs', pbjsArgs]);

  // Note: If you are looking into slowness of pbts it is not pbts
  // itself that is slow. It invokes jsdoc to parse the comments out of
  // the |dstJs| with https://github.com/hegemonic/catharsis which is
  // pinning a CPU core the whole time.
  const pbtsArgs = ['--no-comments', '-p', ROOT_DIR, '-o', dstTs, dstJs];
  addTask(execModule, ['pbts', pbtsArgs]);
}

function generateImports(dir, name) {
  // We have to use the symlink (ui/src/gen) rather than cfg.outGenDir
  // below since we want to generate the correct relative imports. For example:
  // ui/src/frontend/foo.ts
  //    import '../gen/all_plugins.ts';
  // ui/src/gen/all_plugins.ts (aka ui/out/tsc/gen/all_plugins.ts)
  //    import '../frontend/some_plugin.ts';
  const dstTs = pjoin(ROOT_DIR, 'ui/src/gen', name);
  const inputDir = pjoin(ROOT_DIR, dir);
  const args = [GEN_IMPORTS_SCRIPT, inputDir, '--out', dstTs];
  addTask(exec, ['python3', args]);
}

// Generates a .ts source that defines the VERSION and SCM_REVISION constants.
function genVersion() {
  const cmd = 'python3';
  const args =
      [VERSION_SCRIPT, '--ts_out', pjoin(cfg.outGenDir, 'perfetto_version.ts')];
  addTask(exec, [cmd, args]);
}

function updateSymlinks() {
  // /ui/out -> /out/ui.
  mklink(cfg.outUiDir, pjoin(ROOT_DIR, 'ui/out'));

  // /ui/src/gen -> /out/ui/ui/tsc/gen)
  mklink(cfg.outGenDir, pjoin(ROOT_DIR, 'ui/src/gen'));

  // /out/ui/test/data -> /test/data (For UI tests).
  mklink(
      pjoin(ROOT_DIR, 'test/data'),
      pjoin(ensureDir(pjoin(cfg.outDir, 'test')), 'data'));

  // Creates a out/dist_version -> out/dist/v1.2.3 symlink, so rollup config
  // can point to that without having to know the current version number.
  mklink(
      path.relative(cfg.outUiDir, cfg.outDistDir),
      pjoin(cfg.outUiDir, 'dist_version'));

  mklink(
      pjoin(ROOT_DIR, 'ui/node_modules'), pjoin(cfg.outTscDir, 'node_modules'));
}

// Invokes ninja for building the {trace_processor, traceconv} Wasm modules.
// It copies the .wasm directly into the out/dist/ dir, and the .js/.ts into
// out/tsc/, so the typescript compiler and the bundler can pick them up.
function buildWasm(skipWasmBuild) {
  if (!skipWasmBuild) {
    if (!cfg.noOverrideGnArgs) {
      let gnVars = `is_debug=${cfg.debug}`;
      if (childProcess.spawnSync('which', ['ccache']).status === 0) {
        gnVars += ` cc_wrapper="ccache"`;
      }
      const gnArgs = ['gen', `--args=${gnVars}`, cfg.outDir];
      addTask(exec, [pjoin(ROOT_DIR, 'tools/gn'), gnArgs]);
    }

    const ninjaArgs = ['-C', cfg.outDir];
    ninjaArgs.push(...cfg.wasmModules.map((x) => `${x}_wasm`));
    addTask(exec, [pjoin(ROOT_DIR, 'tools/ninja'), ninjaArgs]);
  }

  const wasmOutDir = pjoin(cfg.outDir, 'wasm');
  for (const wasmMod of cfg.wasmModules) {
    // The .wasm file goes directly into the dist dir (also .map in debug)
    for (const ext of ['.wasm'].concat(cfg.debug ? ['.wasm.map'] : [])) {
      const src = `${wasmOutDir}/${wasmMod}${ext}`;
      addTask(cp, [src, pjoin(cfg.outDistDir, wasmMod + ext)]);
    }
    // The .js / .ts go into intermediates, they will be bundled by rollup.
    for (const ext of ['.js', '.d.ts']) {
      const fname = `${wasmMod}${ext}`;
      addTask(cp, [pjoin(wasmOutDir, fname), pjoin(cfg.outGenDir, fname)]);
    }
  }
}

// This transpiles all the sources (frontend, controller, engine, extension) in
// one go. The only project that has a dedicated invocation is service_worker.
function transpileTsProject(project, options) {
  const args = ['--project', pjoin(ROOT_DIR, project)];

  if (options !== undefined && options.watch) {
    args.push('--watch', '--preserveWatchOutput');
    addTask(execModule, ['tsc', args, {async: true}]);
  } else {
    addTask(execModule, ['tsc', args]);
  }
}

// Creates the three {frontend, controller, engine}_bundle.js in one invocation.
function bundleJs(cfgName) {
  const rcfg = pjoin(ROOT_DIR, 'ui/config', cfgName);
  const args = ['-c', rcfg, '--no-indent'];
  if (cfg.bigtrace) {
    args.push('--environment', 'ENABLE_BIGTRACE:true');
  }
  args.push(...(cfg.verbose ? [] : ['--silent']));
  if (cfg.watch) {
    // --waitForBundleInput is sadly quite busted so it is required ts
    // has build at least once before invoking this.
    args.push('--watch', '--no-watch.clearScreen');
    addTask(execModule, ['rollup', args, {async: true}]);
  } else {
    addTask(execModule, ['rollup', args]);
  }
}

function genServiceWorkerManifestJson() {
  function makeManifest() {
    const manifest = {resources: {}};
    // When building the subresource manifest skip source maps, the manifest
    // itself and the copy of the index.html which is copied under /v1.2.3/.
    // The root /index.html will be fetched by service_worker.js separately.
    const skipRegex = /(\.map|manifest\.json|index.html)$/;
    walk(cfg.outDistDir, (absPath) => {
      const contents = fs.readFileSync(absPath);
      const relPath = path.relative(cfg.outDistDir, absPath);
      const b64 = crypto.createHash('sha256').update(contents).digest('base64');
      manifest.resources[relPath] = 'sha256-' + b64;
    }, skipRegex);
    const manifestJson = JSON.stringify(manifest, null, 2);
    fs.writeFileSync(pjoin(cfg.outDistDir, 'manifest.json'), manifestJson);
  }
  addTask(makeManifest, []);
}

function startServer() {
  console.log(
      'Starting HTTP server on',
      `http://${cfg.httpServerListenHost}:${cfg.httpServerListenPort}`);
  http.createServer(function(req, res) {
        console.debug(req.method, req.url);
        let uri = req.url.split('?', 1)[0];
        if (uri.endsWith('/')) {
          uri += 'index.html';
        }

        if (uri === '/live_reload') {
          // Implements the Server-Side-Events protocol.
          const head = {
            'Content-Type': 'text/event-stream',
            'Connection': 'keep-alive',
            'Cache-Control': 'no-cache',
          };
          res.writeHead(200, head);
          const arrayIdx = httpWatches.length;
          // We never remove from the array, the delete leaves an undefined item
          // around. It makes keeping track of the index easier at the cost of a
          // small leak.
          httpWatches.push(res);
          req.on('close', () => delete httpWatches[arrayIdx]);
          return;
        }

        let absPath = path.normalize(path.join(cfg.outDistRootDir, uri));
        // We want to be able to use the data in '/test/' for e2e tests.
        // However, we don't want do create a symlink into the 'dist/' dir,
        // because 'dist/' gets shipped on the production server.
        if (uri.startsWith('/test/')) {
          absPath = pjoin(ROOT_DIR, uri);
        }

        // Don't serve contents outside of the project root (b/221101533).
        if (path.relative(ROOT_DIR, absPath).startsWith('..')) {
          res.writeHead(403);
          res.end('403 Forbidden - Request path outside of the repo root');
          return;
        }

        fs.readFile(absPath, function(err, data) {
          if (err) {
            res.writeHead(404);
            res.end(JSON.stringify(err));
            return;
          }

          const mimeMap = {
            'html': 'text/html',
            'css': 'text/css',
            'js': 'application/javascript',
            'wasm': 'application/wasm',
          };
          const ext = uri.split('.').pop();
          const cType = mimeMap[ext] || 'octect/stream';
          const head = {
            'Content-Type': cType,
            'Content-Length': data.length,
            'Last-Modified': fs.statSync(absPath).mtime.toUTCString(),
            'Cache-Control': 'no-cache',
          };
          if (cfg.crossOriginIsolation) {
            head['Cross-Origin-Opener-Policy'] = 'same-origin';
            head['Cross-Origin-Embedder-Policy'] = 'require-corp';
          }
          res.writeHead(200, head);
          res.write(data);
          res.end();
        });
      })
      .listen(cfg.httpServerListenPort, cfg.httpServerListenHost);
}

function isDistComplete() {
  const requiredArtifacts = [
    'frontend_bundle.js',
    'engine_bundle.js',
    'traceconv_bundle.js',
    'trace_processor.wasm',
    'perfetto.css',
  ];
  const relPaths = new Set();
  walk(cfg.outDistDir, (absPath) => {
    relPaths.add(path.relative(cfg.outDistDir, absPath));
  });
  for (const fName of requiredArtifacts) {
    if (!relPaths.has(fName)) return false;
  }
  return true;
}

// Called whenever a change in the out/dist directory is detected. It sends a
// Server-Side-Event to the live_reload.ts script.
function notifyLiveServer(changedFile) {
  for (const cli of httpWatches) {
    if (cli === undefined) continue;
    cli.write(
        'data: ' + path.relative(cfg.outDistRootDir, changedFile) + '\n\n');
  }
}

function copyExtensionAssets() {
  addTask(cp, [
    pjoin(ROOT_DIR, 'ui/src/assets/logo-128.png'),
    pjoin(cfg.outExtDir, 'logo-128.png'),
  ]);
  addTask(cp, [
    pjoin(ROOT_DIR, 'ui/src/chrome_extension/manifest.json'),
    pjoin(cfg.outExtDir, 'manifest.json'),
  ]);
}

// -----------------------
// Task chaining functions
// -----------------------

function addTask(func, args) {
  const task = new Task(func, args);
  for (const t of tasks) {
    if (t.identity === task.identity) {
      return;
    }
  }
  tasks.push(task);
  setTimeout(runTasks, 0);
}

function runTasks() {
  const snapTasks = tasks.splice(0);  // snap = std::move(tasks).
  tasksTot += snapTasks.length;
  for (const task of snapTasks) {
    const DIM = '\u001b[2m';
    const BRT = '\u001b[37m';
    const RST = '\u001b[0m';
    const ms = (new Date(Date.now() - tStart)).toISOString().slice(17, -1);
    const ts = `[${DIM}${ms}${RST}]`;
    const descr = task.description.substr(0, 80);
    console.log(`${ts} ${BRT}${++tasksRan}/${tasksTot}${RST}\t${descr}`);
    task.func.apply(/* this=*/ undefined, task.args);
  }
}

// Executes all the RULES that match the given |absPath|.
function scanFile(absPath) {
  console.assert(fs.existsSync(absPath));
  console.assert(path.isAbsolute(absPath));
  const normPath = path.relative(ROOT_DIR, absPath);
  for (const rule of RULES) {
    const match = rule.r.exec(normPath);
    if (!match || match[0] !== normPath) continue;
    const captureGroup = match.length > 1 ? match[1] : undefined;
    rule.f(absPath, captureGroup);
  }
}

// Walks the passed |dir| recursively and, for each file, invokes the matching
// RULES. If --watch is used, it also installs a fswatch() and re-triggers the
// matching RULES on each file change.
function scanDir(dir, regex) {
  const filterFn = regex ? (absPath) => regex.test(absPath) : () => true;
  const absDir = path.isAbsolute(dir) ? dir : pjoin(ROOT_DIR, dir);
  // Add a fs watch if in watch mode.
  if (cfg.watch) {
    fswatch(absDir, {recursive: true}, (_eventType, filePath) => {
      if (!filterFn(filePath)) return;
      if (cfg.verbose) {
        console.log('File change detected', _eventType, filePath);
      }
      if (fs.existsSync(filePath)) {
        scanFile(filePath, filterFn);
      }
    });
  }
  walk(absDir, (f) => {
    if (filterFn(f)) scanFile(f);
  });
}

function exec(cmd, args, opts) {
  opts = opts || {};
  opts.stdout = opts.stdout || 'inherit';
  if (cfg.verbose) console.log(`${cmd} ${args.join(' ')}\n`);
  const spwOpts = {cwd: cfg.outDir, stdio: ['ignore', opts.stdout, 'inherit']};
  const checkExitCode = (code, signal) => {
    if (signal === 'SIGINT' || signal === 'SIGTERM') return;
    if (code !== 0 && !opts.noErrCheck) {
      console.error(`${cmd} ${args.join(' ')} failed with code ${code}`);
      process.exit(1);
    }
  };
  if (opts.async) {
    const proc = childProcess.spawn(cmd, args, spwOpts);
    const procIndex = subprocesses.length;
    subprocesses.push(proc);
    return new Promise((resolve, _reject) => {
      proc.on('exit', (code, signal) => {
        delete subprocesses[procIndex];
        checkExitCode(code, signal);
        resolve();
      });
    });
  } else {
    const spawnRes = childProcess.spawnSync(cmd, args, spwOpts);
    checkExitCode(spawnRes.status, spawnRes.signal);
    return spawnRes;
  }
}

function execModule(module, args, opts) {
  const modPath = pjoin(ROOT_DIR, 'ui/node_modules/.bin', module);
  return exec(modPath, args || [], opts);
}

// ------------------------------------------
// File system & subprocess utility functions
// ------------------------------------------

class Task {
  constructor(func, args) {
    this.func = func;
    this.args = args || [];
    // |identity| is used to dedupe identical tasks in the queue.
    this.identity = JSON.stringify([this.func.name, this.args]);
  }

  get description() {
    const ret = this.func.name.startsWith('exec') ? [] : [this.func.name];
    const flattenedArgs = [].concat(...this.args);
    for (const arg of flattenedArgs) {
      const argStr = `${arg}`;
      if (argStr.startsWith('/')) {
        ret.push(path.relative(cfg.outDir, arg));
      } else {
        ret.push(argStr);
      }
    }
    return ret.join(' ');
  }
}

function walk(dir, callback, skipRegex) {
  for (const child of fs.readdirSync(dir)) {
    const childPath = pjoin(dir, child);
    const stat = fs.lstatSync(childPath);
    if (skipRegex !== undefined && skipRegex.test(child)) continue;
    if (stat.isDirectory()) {
      walk(childPath, callback, skipRegex);
    } else if (!stat.isSymbolicLink()) {
      callback(childPath);
    }
  }
}

function ensureDir(dirPath, clean) {
  const exists = fs.existsSync(dirPath);
  if (exists && clean) {
    console.log('rm', dirPath);
    fs.rmSync(dirPath, {recursive: true});
  }
  if (!exists || clean) fs.mkdirSync(dirPath, {recursive: true});
  return dirPath;
}

function cp(src, dst) {
  ensureDir(path.dirname(dst));
  if (cfg.verbose) {
    console.log(
        'cp', path.relative(ROOT_DIR, src), '->', path.relative(ROOT_DIR, dst));
  }
  fs.copyFileSync(src, dst);
}

function mklink(src, dst) {
  // If the symlink already points to the right place don't touch it. This is
  // to avoid changing the mtime of the ui/ dir when unnecessary.
  if (fs.existsSync(dst)) {
    if (fs.lstatSync(dst).isSymbolicLink() && fs.readlinkSync(dst) === src) {
      return;
    } else {
      fs.unlinkSync(dst);
    }
  }
  fs.symlinkSync(src, dst);
}

main();