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# Snapcraft: Advanced features
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Once you have built [your first snap](your-first-snap.md), you will probably
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want to learn more about snapcraft's more advanced features. Having a look at
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our selection of examples is a good idea, as we want it to be a good showcase
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want to learn more about snapcraft's more advanced features. Having a look at
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our selection of examples is a good idea, as we want it to be a good showcase
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of what is possible and generally relevant.
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Our showcase can be found in the actual source of `snapcraft` itself. Check
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Our showcase can be found in the actual source of `snapcraft` itself. Check
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it out by simply running:
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bzr branch lp:snapcraft
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cd snapcraft/examples
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Inspecting the source locally will make easier to build the examples and
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play around with them. (You can
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Inspecting the source locally will make easier to build the examples and
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play around with them. (You can
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[view them online](https://bazaar.launchpad.net/~snappy-dev/snapcraft/core/files/head:/examples/)
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(like description, vendor information and everything else), naming
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the individual parts will define the stucture of your `snapcraft.yaml` file.
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Think of parts as individual components of your snap: Where do you pull them
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from? How are they built?
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from? How are they built?
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### Prerequisites during the build
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build-packages: [libssl-dev]
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The above will install the `libssl-dev` package from the Ubuntu archive before
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an attempted build. If you need a specific version of libssl-dev or a custom
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an attempted build. If you need a specific version of libssl-dev or a custom
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build, you will need to specify a separate part.
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Also note that the above will not define which libraries are shipped with the
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### Pulling and building
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If you just intend to pull and build the source, take a look at the `gopaste`
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example. In its `snapcraft.yaml` file you can find just this one `parts`
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example. In its `snapcraft.yaml` file you can find just this one `parts`
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source: git://github.com/wisnij/gopaste/gopasted
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It starts off with the name of the specific part (`gopaste` here), the origin
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of the part (it's a `git` URL) and how to build it (plugin: `go-project`).
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of the part (it's a `git` URL) and how to build it (plugin: `go`).
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Other possible scenarios would be Bazaar or Mercurial branches, or local
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### Mixing and matching plugins
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An interesting example is `py2-project` because it defines only one part
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(`spongeshaker`), but uses two different plugins (`python2-project` and
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`make-project) to assemble and build the snap:
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(`spongeshaker`), but uses two different plugins (`python2` and `make`) to
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assemble and build the snap:
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plugin: python2-project
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source: git://github.com/markokr/spongeshaker.git
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The example above mixes and matches parts of different origin. Locally it
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provides a binary we intend to ship (the `sha3sum.py` script) and a
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provides a binary we intend to ship (the `sha3sum.py` script) and a
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`Makefile` (to install our script in the right place).
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`spongeshaker` is a python library we will need to pull from git, build as
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binary which you maintain, but require a library you need to build from git
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as opposed to simply including it from the Ubuntu archives.
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What's happening during the `snapcraft` run is:
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What's happening during the `snapcraft` run is:
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1. Get `spongeshaker` from `git`.
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1. Build it as a python project (which will include installing the python
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1. Build it as a python project (which will include installing the python
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library in the right place).
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1. Running `make` (from the local `Makefile`) and thus installing our
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1. Running `make` (from the local `Makefile`) and thus installing our
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`sha3sum.py` script in the right place.
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### Putting your parts in order
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If your app is comprised of multiple parts, it might be necessary to build
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If your app is comprised of multiple parts, it might be necessary to build
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and stage parts in a particular order. This can be done by using the `after`
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source: lp:~mterry/+junk/pipelinetest
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plugin: autotools-project
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source: lp:~mterry/libpipeline/printf
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In the case of the `libpipeline` example above, the part named `pipelinetest`
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will be built after `libpipeline`. Especially if you need specific
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will be built after `libpipeline`. Especially if you need specific
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functionality during a build or as part of checks during the `snap` phase,
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this will be handy.
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With snapcraft we want to make it easy to learn from other app vendors and
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re-use parts which have worked well for them.
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In the `downloader-with-wiki-parts` example, you can see that the `main`
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In the `downloader-with-wiki-parts` example, you can see that the `main`
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As we never define the `curl` part in the above example, `snapcraft` will
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check the Ubuntu Wiki, which is where we currently host examples of
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check the Ubuntu Wiki, which is where we currently host examples of
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successful snapcraft parts. The build order in this case would be `curl`,
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### Individual files
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If you are planning to provide binaries and services to the users of your
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apps, you need to specify them in your definition first. It's just a matter
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apps, you need to specify them in your definition first. It's just a matter
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of enumerating them.
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The `godd` example has one binary:
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description: "gopaste"
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start: bin/gopasted
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You define a name for the service, describe it (so log messages are more
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descriptive), declare how to run the service and that's it. For more
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You define a name for the service, describe it (so log messages are more
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descriptive), declare how to run the service and that's it. For more
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thoughts on services and their security, visit the
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[snappy policy](https://developer.ubuntu.com/en/snappy/guides/security-policy/).
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### Limiting the number of installed files
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To check the list of files included in your snap, you can use `dpkg -c` on
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To check the list of files included in your snap, you can use `dpkg -c` on
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the resulting `.snap` file. If you find that certain files should not be
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shipped to the user (download size being just one factor), you can
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shipped to the user (download size being just one factor), you can
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explicitly tell `snapcraft` which files to snap:
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docs/snapcraft-advanced-features.md
