# Open Screen Library The openscreen library implements the Open Screen Protocol and the Chromecast protocols (both control and streaming). Information about the protocol and its specification can be found [on GitHub](https://github.com/webscreens/openscreenprotocol). ## Getting the code ### Installing depot_tools openscreen library dependencies are managed using `gclient`, from the [depot_tools](https://www.chromium.org/developers/how-tos/depottools) repo. To get gclient, run the following command in your terminal: ```bash git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git ``` Then add the `depot_tools` folder to your `PATH` environment variable. Note that openscreen does not use other features of `depot_tools` like `repo` or `drover`. However, some `git-cl` functions *do* work, like `git cl try`, `git cl lint` and `git cl upload.` ### Checking out code From the parent directory of where you want the openscreen checkout, configure `gclient` and check out openscreen with the following commands: ```bash gclient config https://chromium.googlesource.com/openscreen gclient sync ``` Now, you should have `openscreen/` repository checked out, with all dependencies checked out to their appropriate revisions. ### Syncing your local checkout To update your local checkout from the openscreen master repository, just run ```bash git pull gclient sync ``` This will rebase any local commits on the remote top-of-tree, and update any dependencies that have changed. ## Building ### Installing build dependencies The following tools are required for building: - Build file generator: `gn` - Code formatter (optional): `clang-format` - Builder: `ninja` ([GitHub releases](https://github.com/ninja-build/ninja/releases)) `clang-format` and `ninja` can be downloaded to `buildtools/` root by running `./tools/install-build-tools.sh`. `clang-format` is only used for presubmit checks and optionally used on generated code from the CDDL tool. `gn` will be installed in `buildtools//` automatically by DEPS. You also need to ensure that you have the compiler toolchain dependencies. Currently, both Linux and Mac OS X build configurations use clang by default. ### Linux On Linux, the build will automatically download the Clang compiler from the Google storage cache, the same way that Chromium does it. Ensure that libstdc++ 8 is installed, as clang depends on the system instance of it. On Debian flavors, you can run: ```bash sudo apt-get install libstdc++-8-dev ``` ### Mac On Mac OS X, the build will use the clang provided by [XCode](https://apps.apple.com/us/app/xcode/id497799835?mt=12), which must be installed. ### gcc support Setting the `gn` argument "is_gcc=true" on Linux enables building using gcc instead. Note that g++ must be installed. ```bash gn gen out/Default --args="is_gcc=true" ``` ### Debug build Setting the `gn` argument "is_debug=true" enables debug build. ```bash gn gen out/Default --args="is_debug=true" ``` To install debug information for libstdc++ 8 on Debian flavors, you can run: ```bash sudo apt-get install libstdc++6-8-dbg ``` ### gn configuration Running `gn args` opens an editor that allows to create a list of arguments passed to every invocation of `gn gen`. ```bash gn args out/Default ``` ### Building the sample executable The following commands will build a sample executable and run it. ``` bash mkdir out/Default gn gen out/Default # Creates the build directory and necessary ninja files ninja -C out/Default demo # Builds the executable with ninja ./out/Default/demo # Runs the executable ``` The `-C` argument to `ninja` works just like it does for GNU Make: it specifies the working directory for the build. So the same could be done as follows: ``` bash ./gn gen out/Default cd out/Default ninja ./demo ``` After editing a file, only `ninja` needs to be rerun, not `gn`. If you have edited a `BUILD.gn` file, `ninja` will re-run `gn` for you. For details on running `demo`, see its [README.md](demo/README.md). ### Building other targets Running `ninja -C out/Default gn_all` will build all non-test targets in the repository. `gn ls --type=executable out/Default/` will list all of the executable targets that can be built. If you want to customize the build further, you can run `gn args out/Default` to pull up an editor for build flags. `gn args --list out/Default` prints all of the build flags available. ## Running unit tests ```bash ninja -C out/Default unittests ./out/Default/unittests ``` ## Continuous build and try jobs openscreen uses [LUCI builders](https://ci.chromium.org/p/openscreen/builders) to monitor the build and test health of the library. Current builders include: | Name | Arch | OS | Toolchain | Build | Notes | |------------------------|--------|--------------------|-----------|---------|--------------| | linux64_debug | x86-64 | Linux Ubuntu 16.04 | clang | debug | ASAN enabled | | linux64_tsan | x86-64 | Linux Ubuntu 16.04 | clang | release | TSAN enabled | | mac_debug | x86-64 | Mac OS X/Xcode | clang | debug | | | chromium_linux64_debug | x86-64 | Linux Ubuntu 16.04 | clang | debug | built within chromium | | chromium_mac_debug | x86-64 | Mac OS X/Xcode | clang | debug | built within chromium | You can run a patch through the try job queue (which tests it on all non-chromium builders) using `git cl try`, or through Gerrit (details below). The chromium builders only run as continuous-integration FYI bots, testing HEAD vs. HEAD. ## Submitting changes openscreen library code should follow the [Open Screen Library Style Guide](docs/style_guide.md). openscreen uses [Chromium Gerrit](https://chromium-review.googlesource.com/) for patch management and code review (for better or worse). The following sections contain some tips about dealing with Gerrit for code reviews, specifically when pushing patches for review, getting patches reviewed, and committing patches. ### Uploading a patch for review The `git cl` tool handles details of interacting with Gerrit (the Chromium code review tool) and is recommended for pushing patches for review. Once you have committed changes locally, simply run: ```bash git cl upload ``` This will run our `PRESUBMIT.sh` script to check style, and if it passes, a new code review will be posted on `chromium-review.googlesource.com`. If you make additional commits to your local branch, then running `git cl upload` again in the same branch will merge those commits into the ongoing review as a new patchset. It's simplest to create a local git branch for each patch you want reviewed separately. `git cl` keeps track of review status separately for each local branch. ### Addressing merge conflicts If conflicting commits have been landed in the repository for a patch in review, Gerrit will flag the patch as having a merge conflict. In that case, use the instructions above to rebase your commits on top-of-tree and upload a new patchset with the merge conflicts resolved. ### Tryjobs Clicking the `CQ DRY RUN` button (also, confusingly, labeled `COMMIT QUEUE +1`) will run the current patchset through all LUCI builders and report the results. It is always a good idea get a green tryjob on a patch before sending it for review to avoid extra back-and-forth. You can also run `git cl try` from the commandline to submit a tryjob. ### Code reviews Send your patch to one or more committers in the [COMMITTERS](https://chromium.googlesource.com/openscreen/+/refs/heads/master/COMMITTERS) file for code review. All patches must receive at least one LGTM by a committer before it can be submitted. ### Submission After your patch has received one or more LGTM commit it by clicking the `SUBMIT` button (or, confusingly, `COMMIT QUEUE +2`) in Gerrit. This will run your patch through the builders again before committing to the main openscreen repository. ## Chromium Build Differences Currently, openscreen is also built in Chromium, with some build differences. The files that are built are determined by the following build variables: - `build_with_chromium`: `true` when building as part of a Chromium checkout, `false` otherwise. Set by `//build_overrides/build.gni`. - `use_mdns_responder`: `true` by default, `false` when `build_with_chromium` is `true`. Controls whether the default mDNSResponder mDNS implementation is used. Set by `//build/config/services.gni`. - `use_chromium_quic`: `true` by default, `false` when `build_with_chromium` is `true`. Controls whether the Chromium QUIC implementation clone is used. Set by `//build/config/services.gni`.