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mmandlis improve default arc selection in devtools (#2625)
* improve default arc selection in devtools

* update strategy-explorer page to also default to the "-null" arc
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config Strict updates for server (#2319) Nov 27, 2018
design Decentralized Planning design doc (#1869) Oct 9, 2018
devtools improve default arc selection in devtools (#2625) Jan 18, 2019
extension constify non runtime/shell directories (#2125) Oct 19, 2018
modalities/dom Strategizer Selected Pipe Processing (#2466) Jan 9, 2019
particles update `UseWishlist` recipe to resolve (#2619) Jan 18, 2019
server update server/README with new shell URL (#2555) Jan 9, 2019
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src Add triggering reason to planning results in DevTools (#2621) Jan 18, 2019
tools convert multiplexer-test and schema-tests to typescript (#2587) Jan 14, 2019
.appveyor.yml Node 10 LTS is coming. Switch build to use it and update docs. (#2153) Oct 29, 2018
.clang-format Run clang-format over extension Jan 5, 2018
.dockerignore The Raulnarok PR of 2018 (#2389) Dec 6, 2018
.editorconfig Add an editorconfig configuration for easier IDE use - http://editorc… Sep 14, 2018
.eslintrc.js Streamling hosted slots, allow recursive inner arcs (#2573) Jan 14, 2019
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.prettierrc PouchDb support for Arcs Storage (#1972) Sep 26, 2018
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Dockerfile Improve CI testing, fix and add server tests (#2182) Nov 5, 2018
LICENSE Various cleanups for package.json (#1735) Aug 8, 2018 Remove Greenkeeper references for now. (#2430) Dec 12, 2018
cloudbuild.yaml Improve CI testing, fix and add server tests (#2182) Nov 5, 2018
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rollup.config.js Switch to using 0.6 planner for server-side planning (#2452) Dec 13, 2018
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Build Status AppVeyor Build status


Particle developers should visit our particle developer website. This document is targeted at Arcs core system developers.

A hosted version of Arcs is available in both tagged and bleeding edge forms. Neither is stable -- the runtime, database and front-end are all iterating rapidly.

Tagged release URLs have the form<release_number>/shell/apps/web/index.html (the list of releases is here). A recent version (latest as of this writing) is v0.4.1.

Bleeding edge often works and is available via github pages:


Arcs is developed with a recent version of Node (v10.0.0 at the time of this writing), in particular as we use new ES6 features. You can check our Travis config to see what version is used for automated build status. More recent versions should work, but if for example you see test errors on a version that's a full release later (ex. v11+) you may want to try rolling back to an earlier version. We welcome patches that will allow more recent versions to operate, ideally without requiring an upgrade to our current version.

Installing from scratch

  1. Install nvm.

    As per the installation instructions, download and run the installation script directly in your terminal (yes, you read that correctly):

    $ curl -o- | bash

    If you're using zsh you may need to source ~/.nvm/ after this.

  2. Install node.

    $ nvm install 10
  3. If you need to update npm to a later version (our build checks for the minimum required version):

    $ npm install -g npm   # can use npm@6.3.0 to install a specific version

Installing within the Arcs project:

$ npm install
$ ./tools/sigh

npm install is required on a fresh checkout. After that it only needs to be re-run infrequently as new dependencies are included, and usually a build failure will be the signal for that.

Windows Installation Notes

  • Git for Windows is one of many Git options.
  • Consider using nvm-windows to allow more easily switching between Node versions.
  • As part of npm install you'll need to build fibers which uses node-gyp which in turn requires windows-build-tools. Follow the node-gyp Windows build instructions. If option 1 hangs or otherwise hits issues, you can try option 2. Note the Microsoft Build Tools 2015 can be downloaded separately from Visual Studio (and the links in the node-gyp documentation are stale), but you'll still need to do the npm config set msvs_version 2015 bit, and similar for Python if you install that manually per node-gyp option 2 instructions.

Starting Arcs

After the full build (npm install && tools/sigh) run: (note that npm start will block, so you'll have to run the second command in a new shell):

$ npm start

Then open http://localhost:8080/shell/apps/web/index.html in a web browser (or, on MacOS, use open 'http://localhost:8080/shell/apps/web/index.html').


Subcomponents have more detailed descriptions. Particularly the extensions also have individual installation steps.


For more information on the shell, see shell.

Chrome Extension

See extension.

Chrome Developer Tools Extension

See devtools.


The simplest way to run tests is to let the targets do all the work. These commands will install all packages, run a build, start a background server, run all the tests, and kill the background server:

$ npm install
$ npm run test-with-start

There are additional targets provided to run subsets of those commands.

  • npm start: spins up a server (and blocks), serving in port 8080.
  • tools/sigh: run a subset of tests and build packed artifacts.
  • npm test: run all tests (using currently built artifacts) against an already-running server (assumed to be port 8080).
  • npm run test-no-web: run all non-web tests.

To run a specific Selenium test using Mocha's 'grep' capability:

  • In one terminal: npm start
  • In another: npm run test-wdio -- --mochaOpts.grep 'regex'

Debugging tests

If you see errors like

    at new RuntimeError (...\node_modules\webdriverio\build\lib\utils\ErrorHandler.js:144:12)
    at Request._callback (...\node_modules\webdriverio\build\lib\utils\RequestHandler.js:327:43)

It may indicate that chromedriver hasn't been installed completely. Run the install script:

node node_modules\chromedriver\install.js

Debugging Selenium Failures

Selenium failures are often easy to cause due to seemingly unrelated changes, and difficult to diagnose.

There are 2 main avenues to debug them in this system. The first is to have the browser run in a graphical manner (as opposed to the default headless configuration). The second is to actually debug the running selenium instance.

There are some debugging hints (code and configuration you can uncomment to make debugging easier) in test/specs/starter-test.js and test/wdio.conf.js marked with the phrase debug hint.

To activate a sane set of helpful debugging flags, there's a wdio-debug command line argument that you can pass in. This will run Chrome in a non-headless fashion, and will increase timeouts.

Through npm: npm run test-wdio --wdio-debug=true (or npm test --wdio-debug=true). Directly through wdio: node_modules/.bin/wdio --wdio-debug=true shell/test/wdio.conf.js.

Webdriver takes screenshots of failures, which are saved to the ./shell/test/errorShots/ directory. When running on Travis, the screenshots are uploaded to the Arcs Webdriver Screenshots team drive.

Graphical (non-headless)

It may be easiest to see the problem in a browser window to diagnose it. Edit wdio.conf.js in the branch with failures, comment out the '--headless' option and increase the mocha timeout. In combination, these two changes will allow you to see what's happening on the screen, and will give you enough time to debug the situation.

arcs/shell> vi test/wdio.conf.js
arcs/shell> git diff test/wdio.conf.js
diff --git a/test/wdio.conf.js b/test/wdio.conf.js
index 0e36452..8ecf3d6 100644
--- a/test/wdio.conf.js
+++ b/test/wdio.conf.js
@@ -50,7 +50,7 @@ exports.config = {
       chromeOptions: {
         args: [
           // arcs note: comment this out to see the system running
-          '--headless'
+          // '--headless'
@@ -139,7 +139,7 @@ exports.config = {
   mochaOpts: {
     ui: 'bdd',
     // arcs note: increase this timeout for debugging
-    timeout: 20003
+    timeout: 2000003
   // =====

Then, in your test, you can add a breakpoint (via browser.debug();) to pause execution so you can debug in the browser. It may be worthwhile to add several browser.debug() invocations through your flow to trace execution (.exit will exit the debugger and continue execution of the test).

At that point you can open up DevTools in the browser to debug the current state, or inspect it visually. Some utilities (those in selenium-utils.js, including pierceShadows) have already been loaded.

There are also some commands available natively at that point, including .help and the browser variable (including methods such as browser.execute()).

Attaching a Debugger

To attach a debugger, uncomment the execArgv --inspect configuration option. It's likely that you'll still want to have increased the mochaTimeout and to be running graphically, so those are in the example as well:

arcs/shell> git diff test/wdio.conf.js
diff --git a/test/wdio.conf.js b/test/wdio.conf.js
index 0e36452..4240c0a 100644
--- a/test/wdio.conf.js
+++ b/test/wdio.conf.js
@@ -50,11 +50,12 @@ exports.config = {
       chromeOptions: {
         args: [
           // arcs note: comment this out to see the system running
-          '--headless'
+          // '--headless'
+  execArgv: ['--inspect'],
   // ===================
   // Test Configurations
@@ -139,7 +140,7 @@ exports.config = {
   mochaOpts: {
     ui: 'bdd',
     // arcs note: increase this timeout for debugging
-    timeout: 20003
+    timeout: 2000003
   // =====

When starting, you should see log item like debugger listening on ws:// as normally appears for node debugging. Passing the --inspect argument will also enable the V8 Inspector Integration which may be easier to use (to activate this, look for a node icon in a Chrome DevTools process).

Adding debugger; statements may be the easiest way to activate the debugger. Using browser.debug(); statements to pause execution to give you time to attach a debugger may be helpful as well.


Our release process is pretty minimal, but requires a few steps across the arcs and arcs-live repositories.

Our standard is to have the stable versions start with clean (empty) databases, but to continue a single mainline/unstable database.

  1. Decide what your new mainline and stable versions will be. For an example here, I'll use 0.3.5-alpha as the old mainline, 0.3.6-alpha as the new mainline, and 0.3.5 as the new stable version.

  2. In order to keep the mainline data roughly consistent, clone the data at the current firebase key to the new mainline release number. To do this, I used the firebase web interface to "Export JSON" for the current tree, and "Import JSON" to the new tree.

For example, clone from <snip>/database/arcs-storage/data/0_3_5-alpha to <snip>/database/arcs-storage/data/0_3_6-alpha.

If the web interface is read-only due to too many nodes, you can visit the new version's URL directly to Import JSON.

  1. Update the version in shell/apps/common/firebase-config.js to a reasonable stable version (in our example, 0.3.5). See #1114 for an example. Update the links (this file) to reflect this new version.

  2. Once the deploy is done to arcs-live, create a new release. Note that we remap the versions slightly between the two systems for legibility in different systems - a version of 0_3_5 (in firebase-config.js) becomes v0.3.5 (in the arcs-live repo).

  3. Update the version in shell/apps/common/firebase-config.js to the new mainline development version (perhaps using the -alpha suffix; in our example, 0.3.6-alpha). See #1155 for an example.