Add mDNS API for updating TXT data

This change adds an API to MdnsResponderAdapter to update the TXT data
of a registered service that is being published.  It also removes the
friendly name API that would have used this (as it's been removed from
the spec).  The future use of the TXT update API will be for updating
the service certificate fingerprint or, more likely, updating the
metadata timestamp.  This also adds config parameters for the publisher
hostname and service instance.

Change-Id: I04a04f61cf68c53d08019b4958781fc16bf36fb8
Commit-Queue: Brandon Tolsch <>
Reviewed-by: mark a. foltz <>
16 files changed
tree: b48319c3fe98c77ab082e3b938f21abefec6a1ef
  1. .clang-format
  2. .gitignore
  3. .gitmodules
  4. .gn
  12. api/
  13. base/
  14. build/
  15. codereview.settings
  16. demo/
  17. discovery/
  18. docs/
  19. infra/
  20. msgs/
  21. platform/
  22. sample/
  23. third_party/
  24. tools/

Open Screen Library

This library implements the Open Screen Protocol. Information about the protocol can be found in the Open Screen GitHub repository.

Continuous Build

Open Screen uses LUCI builders to monitor the build and test health of the library.

Coming soon: tryjob and submit queue integration with Gerrit code review.

Build guide

Open Screen Library code should follow the Open Screen Library Style Guide. In addition, you should also run // before uploading changes for review (which primarily checks formatting).

Build dependencies

Run ./tools/ from the root source directory to obtain a copy of the following build tools:

  • Build file generator: gn
  • Code formatter: clang-format

You will have to obtain and install these yourself:

  • Compiler toolchain: Currently, this is gcc on Linux, and clang on Mac (from Xcode).

  • Builder: ninja

    GitHub releases

Building an example with GN and Ninja

After checking out the Open Screen library, make sure to initialize the submodules for the dependencies. The following commands will checkout all the necessary submodules:

  git submodule init
  git submodule update

The following commands will build the current example executable and run it.

  ./gn gen out/Default    # Creates the build directory and necessary ninja files
  ninja -C out/Default  # Builds the executable with ninja
  ./out/Default/hello     # 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:

  ./gn gen out/Default
  cd out/Default

After editing a file, only ninja needs to be rerun, not gn.


The following sections contain some tips about dealing with Gerrit for code reviews, specifically when pushing patches for review.

Uploading a new change

There is official Gerrit documentation for this which essentially amounts to:

  git push origin HEAD:refs/for/master

You may also wish to install the Change-Id commit-msg hook. This adds a Change-Id line to each commit message locally, which Gerrit uses to track changes. Once installed, this can be toggled with git config gerrit.createChangeId <true|false>.

To download the commit-msg hook for the Open Screen repository, use the following command:

  curl -Lo .git/hooks/commit-msg

Gerrit keeps track of changes using a Change-Id line in each commit.

When there is no Change-Id line, Gerrit creates a new Change-Id for the commit, and therefore a new change. Gerrit's documentation for replacing a change describes this. So if you want to upload a new patchset to an existing review, it should contain the matching Change-Id line in the commit message.

Adding a new patchset to an existing change

By default, each commit to your local branch will get its own Gerrit change when pushed, unless it has a Change-Id corresponding to an existing review.

If you need to modify commits on your local branch to ensure they have the correct Change-Id, you can do one of two things:

After committing to the local branch, run:

  git commit --amend
  git show

to attach the current Change-Id to the most recent commit. Check that the correct one was inserted by comparing it with the one shown on for the existing review.

If you have made multiple local commits, you can squash them all into a single commit with the correct Change-Id:

  git rebase -i HEAD~4
  git show

where ‘4’ means that you want to squash three additional commits onto an existing commit that has been uploaded for review.