Build

This chapter lays out the rules of the file system for bnd projects. It discusses the workspace layout and the projects layout as well as the properties.

Workspace

A Workspace is a single directory with all its sub-directories and their files, similar to a git workspace. The core idea of the workspace is that it is easy to move around, that is, it allows the use of relative file names. It also prevents a lot of potential problems that occur when you allow projects to be anywhere on the file system. KISS!

Workspaces should be named according to the bundle symbolic names of its projects. Using such a naming strategy will simplify finding the correct namespace given a bundle symbolic name.

A bndlib workspace is a valid workspace when it contains a cnf file. If this is a text file, its content is read and interpreted as a path to the cnf directory (which can again be a path to a cnf directory, ad infinitum). The retrieved path is trimmed after which it is resolved relative to its parent directory.

However, the advised model is to use a directory with a cnf/build.bnd file. The purpose of the cnf directory is to provide a place for shared information. Though this includes bndlib setup information, it also can be used to define for example shared licensing, copyright, and vendor headers for your organization.

The cnf/ext directory

The cnf directory can have an ext directory. Files in this directory are added to the properties of the workspace. They can have the following extensions:

• .bnd – Contain bnd properties
• .pmvn – An index file for a Maven Bnd Repository. The first lines can contain properties for this plugin in the format of # key = value, e.g. # name = OSGi R8.
• .pobr – An OSGi Repository file in XML.

Automatically registering repositories

Files with .pmvn or .pobr will be automatically registered as a Repository and show up in the Repository browser (means, no Plugin configuration needed). This is a convenience shortcut to add a repository with almost no configuration.

Example /cnf/ext/central.pmvn file:

# name = My Maven Central Repo
# releaseUrl = https://repo.maven.apache.org/maven2/
# tags = resolve
biz.aQute.bnd:biz.aQute.bndlib:7.0.0
biz.aQute.bnd:aQute.libg:7.0.0

The ext directory is a convenient way to add add reusable components. See template fragments how they can be used to manage workspaces. When files change in this directory the workspace will be reloaded.

The cnf/cache directory

To cache some intermediate files, bndlib will create a cnf/cache/ directory, this file should not be under source control. E.g. in Git it should be defined in the .gitignore file.

Folder structure

Overall, this gives us the following layout for a workspace:

com.acme.prime/                     workspace
  cnf/                              configuration/setup
    ext/                            extensions
      maven.bnd                     maven setup extension
    build.bnd                       organization setup
    plugins/                        directory for plugins
    cache/                          bnd cache directory, should not be saved in an scm
  com.acme.prime.speaker/           project directory	  

The root of the workspace is generally used to hold other files. For example the .git directory for Git, or gradle and ant files for continuous integration. However, designers that add functionality to the workspace should strive to minimize the clutter in the root. For example, the bnd gradle support adds a few files to the root but these link to a cnf/gradle directory for their actual content.

Other directories in the workspace represent projects. The name of the project is the bundle symbolic name of the bundle that it produces (or the prefix of the bundle symbolic name when it produces multiple bundles).

Workspace Properties

Properties are used for headers, macros, and instructions in bndlib, they are quite fundamental. To simplify maintenance, bndlib provides an elaborate mechanism to provide these properties from different places and inherit them. The workspace resides at the top of this inheritance chain (ok, after the built-in defaults).

When a workspace is created, it will first read in the properties in the .bnd files in the cnf/ext directory. These are called the extension files since they in general setup plugins and other extensions. The order in which they are read is the lexical sorting order of their file names.

Target build directory

The target-dir defines where the build process places the build output artifacts. By default this folder is named generated.

Avoiding target-dir conflicts between different build tools

In the default setup of the workspace, the gradle build tool & eclipse share the same output directories. In general, this means you always have to clean in each tool and in the case of Eclipse stop the incremental builder (otherwise eclipse will start rebuilding the whole workspace when you do a gradle clean build).

All the output directories are defined in macros. In general, the ${target-dir} is the main output directory and the ${bin} and ${testbin} are placed inside this directory. So by redefining ${target-dir} in cnf/build.bnd we can redirect all output.

bnd has a macro ${driver} that indicates which build tool (a.k.a. the driver) is used. We can then use this as follows, to use a separate output directory for each build tool (e.g. eclipse, gradle, maven):

target-dir              generated${if;${driver;eclipse};;/${driver}}
bin                     ${target-dir}/classes
testbin                 ${target-dir}/test-classes

This example configuration, placed in cnf/build.bnd means:

• eclipse build puts the build output directly into the generated folder of each project.
• gradle build puts the build outputs in generated/gradle.

Extension Files

Extension files allow you to separate configuration concerns. Its primary purpose is to allow third party extensions. These extensions can then put their properties in one place. The contents of these files should therefore not be touched so that a new version can override them. Each extension file is read as a bnd file, this means that full power of bndlib is available. The bnd command line tool has facilities to add and remove files from this directory.

For example, the Maven plugin that is built-in to bndlib has an extension file called maven.bnd which looks as follows:

#
# Plugin maven setup
#
-plugin.maven = aQute.bnd.plugin.maven.MavenPlugin


#
# Change disk layout to fit maven
#

-outputmask = ${@bsn}-${versionmask;===S;${@version}}.jar
src=src/main/java
bin=target/classes
testsrc=src/test/java
testbin=target/test-classes
target-dir=target

We will not explain this plugin here (you can find it in the plugin sections), it only illustrates here how it is possible to setup the environment for a specific optional functionality like a plugin.

If you create local extension files then you should use a prefix to identify this is your file, like:

com.acme-local.bnd

It is possible to use file links to maintain these files in one place when you have many workspaces.

Extension File loading mechanism and order

Extension files will be loaded in alphabetical order. If a files defines a property that was already defined in another previously loaded file or the build.bnd, the property will be assigned a namespace. -plugin in /cnf/ext/test.bnd will become -plugin.test. Please note that this mechanism is just a best guess courtesy and has its limits. If -plugin.test was already defined previously, the old value will be overwritten.

Local customizations

After reading the extension files, bndlib reads the cnf/build.bnd file, this file is supposed to hold the organization specific properties. Out of the box, this file comes empty, ready to be filled by you.

Workspace Plugins

A plugin is a piece of code that runs inside bnd. The workspace provides a number of standard built-in plugins like an Executor, a Randum number generator, itself, etc. Additional plugins can be added with the -plugin.* instructions.

Project Properties

There are a number of built in properties that are set by bnd:

Run instructions

Run instructions are used to start OSGi tests and OSGi runs.

Launching

Launching is needed when the project’s run action or test action is executed. The project creates a Project Launcher. A Project Launcher must launch a new VM and set up this VM correctly. The VM is launched with the following information:

• java - The command to launch a new VM is by default java. However, this can be overridden by setting a property called java.
• classpath - The classpath set for the VM is derived from the -runpath property. Notice that this is supposed to contain the JAR with the framework. The -runpath requires bundle symbolic names for the JAR and an optional version range. bnd will use the latest version found in the repository. Any packages that should be exported by the system bundle should have an export attribute containing the exported packages, like junit.osgi;version=3.8;export="junit.framework;version=3.8,junit.misc;version=3.8".
• VM options - These options can be set in the -runvm property. They are usually in the form of -Dxya=15 or -X:agent=bla. Options should be separated by commas.
• main - The class implementing the main type is defined by the launcher plugin.

An example of a launcher set is:

-runvm:   -Xmn100M, -Xms500M, -Xmx500M
-runpath: \
	org.apache.felix.framework; version=3.0, \
	junit.osgi;export="junit.framework;version=3.8"
-runtrace: true
-runproperties: launch=42, trace.xyz=true
-runbundles: org.apache.felix.configadmin,\
	org.apache.felix.log,\
	org.apache.felix.scr,\
	org.apache.felix.http.jetty,\
	org.apache.felix.metatype,\
	org.apache.felix.webconsole

Debugging the launcher is greatly simplified with the -runtrace property set to true. This provides a lot of feedback what the launcher is doing.

Access to arguments

When the Framework is started the Launcher will register itself as a service of type java.lang.Object with the property launcher.arguments to provide access the arguments handed to the launcher. After all Bundles have been installed and started the ServiceRegistration will be updated with the property launcher.ready=true.

Access to main thread

In certain cases it is necessary to grab the main thread after launching. The default launcher will launch all the bundles and then wait for any of those bundles to register a Runnable service with a service property main.thread=true. If such service is registered, the launcher will call the run method and exit when this method returns.

Timeout

The launcher will timeout after an hour. There is currently no way to override this timeout.

Mini Framework

The bnd launcher contains a mini framework that implements the bare bones of an OSGi framework. The purpose of this mini framework is to allow tests and runs that want to launch their own framework. A launch that wants to take advantage of this can launch with the following property:

-runframework: none

Ant

In Ant, the following task provides the run facility.

<target name="run" depends="compile">
	<bnd command="run" exceptions="true" basedir="${project}" />
</target>

These targets provide commands for ant run.

Testing

Testing is in principle the same as launching, it actually uses the launcher. Testing commences with the test action in the project. This creates a Project Tester. bnd carries a default Project Tester but this can be overridden.

The basic model of the default Project Tester plugin is to look for bundles that have a Test-Cases manifest header after launching. The value of this header is a comma separated list of JUnit test case class names. For example:

Test-Cases: test.LaunchTest, test.OtherTest

Maintaining this list can be cumbersome and for that reason the ${classes} macro can be used to calculate its contents:

Test-Cases: ${classes;extending;junit.framework.TestCase;concrete}

See classes macro for more information.

Ant

<target name="test" depends="compile">
	<bnd command="test" exceptions="true" basedir="${project}" />
</target>

Overriding the plugins

Both the Project Launcher and Project Tester are plugins. Defaults are provided by bnd itself (bnd carries a mini cache repo that is expanded in the cnf directory), it is possible to add new launchers and testers as needed.

Launcher or tester plugins are found on the -runpath or the -testpath properties, respectively. To detect a plugin, bnd will look for an appropriate manifest header. The header value is a class name. Bnd will then instantiate the class and use it as a launcher/tester. The classes must extend an abstract base class. Each plugin has access to the Project object, containing all the details of the project.

The plugin gets complete control and can implement many different strategies.