The Open Screen Library implements the Open Screen Protocol, Multicast DNS and DNS-SD, and the Chromecast protocols (discovery, application control, and media streaming).
The library consists of feature modules that share a common platform API that must be implemented and linked by the embedding application.
The major feature modules in the library can be used independently and have their own documentation:
Library dependencies are managed using
gclient, from the depot_tools repo.
To get gclient, run the following command in your terminal:
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
drover. However, some
git-cl functions do work, like
git cl try,
git cl format,
git cl lint, and
git cl upload.
From the parent directory of where you want the openscreen checkout (e.g.,
gclient and check out openscreen with the following commands:
cd ~/my_project_dir gclient config https://chromium.googlesource.com/openscreen gclient sync
gclient command will create a default .gclient file in
~/my_project_dir that describes how to pull down the
openscreen repository. The second command creates an
openscreen/ subdirectory, downloads the source code, all third-party dependencies, and the toolchain needed to build things; and at their appropriate revisions.
To update your local checkout from the openscreen reference repository, just run
cd ~/my_project_dir/openscreen git pull gclient sync
This will rebase any local commits on the remote top-of-tree, and update any dependencies that have changed.
The following are the main tools are required for development/builds.
gofrom https://golang.org or your Linux package manager.
go install github.com/neilpa/yajsv@latest
Ensure that libstdc++ 8 is installed, as clang depends on the system instance of it. On Debian flavors, you can run:
sudo apt-get install libstdc++-8-dev libstdc++6-8-dbg
On Mac OS X, the build will use the clang provided by XCode. You can install the XCode command-line tools only or the full version of XCode.
TODO(https://issuetracker.google.com/202964797): Switch to use Chromium clang for Mac builds.
is_gcc=true on Linux enables building using gcc instead.
mkdir out/debug-gcc gn gen out/debug-gcc --args="is_gcc=true"
Note that g++ version 7 or newer must be installed. On Debian flavors you can run:
sudo apt-get install gcc-7
is_debug=true enables debug build.
gn gen out/debug --args="is_debug=true"
gn args opens an editor that allows to create a list of arguments passed to every invocation of
gn args --list will list all of the possible arguments you can set.
gn args out/debug
We use the Open Screen Protocol demo application as an example, however, the instructions are essentially the same for all executable targets.
mkdir out/debug gn gen out/debug # Creates the build directory and necessary ninja files ninja -C out/debug osp_demo # Builds the executable with ninja ./out/debug/osp_demo # Runs the executable
-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:
./gn gen out/debug cd out/debug ninja osp_demo ./osp_demo
After editing a file, only
ninja needs to be rerun, not
gn. If you have edited a
ninja will re-run
gn for you.
We recommend using
autoninja instead of
ninja, which takes the same command-line arguments but automatically parallelizes the build for your system, depending on number of processor cores, amount of RAM, etc.
Also, while specifying build targets is possible while using ninja, typically for development it is sufficient to just build everything, especially since the Open Screen repository is still quite small. That makes the invocation to the build system simplify to:
autoninja -C out/debug
For details on running
osp_demo, see its README.md.
ninja -C out/debug gn_all will build all non-test targets in the repository.
gn ls --type=executable out/debug 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/debug to pull up an editor for build flags.
gn args --list out/debug prints all of the build flags available.
ninja -C out/debug openscreen_unittests ./out/debug/openscreen_unittests
Open Screen library code should follow the Open Screen Library Style Guide.
This library uses Chromium Gerrit for patch management and code review (for better or worse). You will need to register for an account at
chromium-review.googlesource.com to upload patches for review.
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.
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:
git cl format git cl upload
The first command will will auto-format the code changes using
clang-format. Then, the second command runs the
PRESUBMIT.py script to check style and, if it passes, a newcode review will be posted on
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.
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.
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.
Send your patch to one or more committers in the COMMITTERS file for code review. All patches must receive at least one LGTM by a committer before it can be submitted.
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.