EVOLUTION-MANAGER

Edit File: writing_koji_code.rst

================= Writing Koji Code ================= Getting Started Hacking on Koji =============================== This page gives an overview of the Koji code and then describes what needs to change if you want to add a new type of task. A new task could be for a new content type, or assembling the results of multiple builds together, or something else that helps your workflow. New contributors to Koji should leave this page knowing where to begin and have enough understanding of Koji's architecture to be able to estimate how much work is still ahead of them. Task Flow ========= A task starts with a user submitting it with the Koji client, which is a command line interface. This contacts the hub, an apache-based server application. It leaves a row in the database that represents a "free" task, one that has not been assigned to a builder. Periodically, the builders asynchronously ping the hub asking if there are any tasks available, and at some point one will be given the new task. The hub marks this in the database, and the builder begins executing the task (a build). Upon completion, the builder uploads the results to the hub, including logs, binaries, environment information, and whatever else the task handler for the build dictated. The hub moves the results to a permanent shared storage solution, and marks the task as completed (or failed). During this whole time, the webUI can be used to check up on progress. So the flow of work is: :: Client -> Hub -> Builder -> Hub If you wanted to add a new build type or task that was tightly integrated in Koji's data model, you would need to modify the CLI, Hub, Builder, and WebUI at a minimum. Alternatively, you could do this with a plugin, which is far simpler but less flexible. Component Overview ================== Koji is comprised of several components, this section goes into details for each one, and what you potentially may need to change. Every component is written in Python, so you will need to know that language beyond a beginner level. Koji-client ----------- koji-client is a command line interface that provides many hooks into Koji. It allows the user to query much of the data as well as perform actions such as adding users and initiating build requests. Option Handling ~~~~~~~~~~~~~~~ The code is in ``cli/koji``. It uses ``OptionParsers`` extensively with interspersed arguments disabled. That means these two commands are not interpreted the same: :: $ koji -u admin -p password tag-build some-tag --force some-build $ koji tag-build -u admin -p password some-tag --force some-build The second one will generate an error, because -u and -p are not options for tag-build, they must show up before that because they are global options that can be used with any subcommand. There will be two ``OptionParsers`` used with each command. The first is used to pick up arguments to ``koji`` itself, and the second for the subcommand specified. When the first one executes (see ``get_options()``) it will figure out the subcommand and come up with a function name based on it. The convention is to prepend the word ``handle_`` before it, and change all hyphens to underscores. If a command does not require an account with Koji, the function handle will prepended with ``anon_handle_`` instead. The code will dynamically call the derived function handle which is where the second ``OptionParser`` is used to parse the remaining options. To have your code log into Koji (you're writing a handle\_ function), use the ``activate_session`` function. All function signatures in the client code will get a session object, which is your interface to the hub. Profiles ~~~~~~~~ It is possible to run the Koji client with different configuration profiles so that you can interact with multiple Koji instances easily. The ``--profile`` option to the Koji command itself enables this. You should have a ``~/.koji/config`` already, if not just copy from ``/etc/koji.conf`` to get a start. The profile command accepts an argument that matches a section in that config file. So if your config file had this: :: [Fedora] authtype = ssl server = https://koji.fedoraproject.org/kojihub topdir = /mnt/koji weburl = https://koji.fedoraproject.org/koji #pkgurl = https://koji.fedoraproject.org/packages cert = ~/.fedora.cert ca = ~/.fedora-upload-ca.cert serverca = ~/.fedora-server-ca.cert [MyKoji] server = https://koji.mydomain.com/kojihub authtype = kerberos topdir = /mnt/koji weburl = https://koji.mydomain.com/koji topurl = https://download.mydomain.com/kojifiles you could pass Fedora or MyKoji to --profile. Creating Tasks ~~~~~~~~~~~~~~ Once options are processed and understood, a task needs to be created on the hub so that a builder can come along and take it. This is accomplished with the ``makeTask`` method (defined on the Hub, so call it on the ``session`` object). The name of the task should match the name given to the task handler in the builder, which is explained later on. Be sure to process the channel, priority, background, and watch/nowatch parameters too, which should be available to most new tasks. They'll be buried in the first argument to your handler function, which captures the options passed to the base Koji command. If the client needs to make locally-available artifacts (config files, sources, kickstarts) accessible to the builder, it must be uploaded to the hub. This is the case with uploading SRPMs or kickstarts. You can easily upload this content with the ``session.uploadWrapper`` method. You can create progress bars as necessary with this snippet: :: if _running_in_bg() or task_opts.noprogress: callback = None else: callback = _progress_callback serverdir = unique_path('cli-image') # create a unique path on the hub session.uploadWrapper(somefile, serverdir, callback=callback) Task Arguments ~~~~~~~~~~~~~~ If you define a new task for Koji, you'll want the task submission output to have the options ordered usefully. This output is automatically generated, but sometimes it does not capture the more important arguments you want displayed. :: Created task 10001810 Watching tasks (this may be safely interrupted)... 10001810 thing (noarch): free 10001810 thing (noarch): free -> closed 0 free 0 open 1 done 0 failed 10001810 thing (noarch) completed successfully In this (fake) example, you can see that "noarch" is the only option being displayed, but maybe you want something more than just the task architecture displayed, like some other options that were passed in. You can fix this behavior in ``koji/__init__.py`` in the \_taskLabel function. Here you can define the string(s) to display when Koji receives status on a task. That is the return value. Using multicall ~~~~~~~~~~~~~~~ Koji supports a multicall feature where many calls are passed to the server wrapped as a single call. This can reduce the overhead when a large number of related calls need to be made. The ``ClientSession`` class provides support for this and there are several examples in the existing client code. Some examples in the cli include: ``edit-host``, ``add-pkg``, ``disable-host``, and ``list-hosts``. There are two ways to use multicall. The original modal method works within the ``ClientSession`` object and prevents making other normal calls until the multicall is completed. The newer method uses a separate ``MultiCallSession`` object and is much more flexible. **Using MultiCallSession** Note: this feature was added in Koji version 1.18. A ``MultiCallSession`` object is used to track an individual multicall attached to a session. To create one, you can simply call your session's ``multicall`` method. Once created, the object can be used like a session, but calls are stored rather than sent immediately. The stored calls are executed by calling the ``call_all()`` method. :: m = session.multicall() for task_id in mylist: m.cancelTask(task_id) m.call_all() This object can also be used as a context manager, so the following is equivalent: :: with session.multicall() as m: for task_id in mylist: m.cancelTask(task_id) Method calls to a ``MultiCallSession`` object return a ``VirtualCall`` object that stands in for the result. Once the multicall is executed, the result of each call can be accessed via the ``result`` property of the ``VirtualCall`` object. Accessing the ``result`` property before the call is executed will result in an error. :: with session.multicall() as m: tags = [m.getTag(tag_id) for tag_id in mylist] for tag in tags: print(tag.result['name']) There are two parameters affecting the behavior of the multicall. If the ``strict`` parameter is set to True, the multicall will raise the first error it encounters, if any. If the ``batch`` parameter is set to a number greater than zero, the multicall will spread the calls across multiple multicall batches of at most that number. These parameters may be passed when the ``MultiCallSession`` is initialized, or they may be passed to the ``call_all`` method. :: with session.multicall(strict=True, batch=500): builds = [m.getBuild(build_id) for build_id in mylist] **Using ClientSession.multiCall** Note: this approach is still supported, but we highly recommend using ``MultiCallSession`` as described above, unless you need to support Koji versions prior to 1.18. To use the feature, you first set the ``multicall`` attribute of the session to ``True``. Once this is done, the session will not immediately process further calls but will instead store their parameters for later. To tell the session to process them, use the ``multiCall()`` method (note the capitalization). The ``multiCall()`` method returns a list of results, one for each call in the multicall. Each result with either be: 1. the result of the call wrapped in a singleton list 2. a dictionary representing the error raised by the call Here is a simple example from the koji-tools package: :: session.multicall = True for host in hosts: session.listChannels(hostID=host['id']) for host, [channels] in zip(hosts, session.multiCall(strict=True)): host['channels'] = channels Note that when using multicall for informational calls, it is important to keep track of which result is which. Here we use the existing hosts list as a unifying index. Python's ``zip`` function is useful here. Also note the unpacking of the singletons. The ``multiCall()`` method supports a few options. Here is its signature: :: multiCall(strict=False, batch=None): If the strict option is set to True, then this method will raise the first error it encounters, if any. If the batch option is set to a number greater than zero, the calls will be spread across multiple multicall batches of at most this number. The hub processes multicalls in a *single database transaction*. Note that if the ``batch`` option is used, then each batch is a separate multicall in the api and therefore a separate transaction. Koji-Hub -------- koji-hub is the center of all Koji operations. It is an XML-RPC server running under mod\_wsgi in Apache. koji-hub is passive in that it only receives XML-RPC calls and relies upon the build daemons and other components to initiate communication. koji-hub is the only component that has direct access to the database and is one of the two components that have write access to the file system. If you want to make changes to the webUI (new pages or themes), you are looking in the wrong section, there is a separate component for that. Implementation Details ~~~~~~~~~~~~~~~~~~~~~~ The **hub/kojihub.py** file is where the server-side code lives. If you need to fix any server problems or want to add any new tasks, you will need to modify this file. Changes to the database schema will almost certainly require code changes too. This file gets deployed to **/usr/share/koji-hub/kojihub.py**, whenever you make changes to that remember to restart **httpd**. Also there are cases where httpd looks for an existing .pyc file and takes it as-is, instead of re-compiling it when the code is changed. In the code there are two large classes: **RootExports** and **HostExports**. RootExports exposes methods using XMLRPC for any client that connects to the server. The Koji CLI makes use of this quite a bit. If you want to expose a new API to any remote system, add your code here. The HostExports class does the same thing except it will ensure the requests are only coming from builders. Attempting to use an API exposed here with the CLI will fail. If your work requires the builders to call a new API, you should implement it here. Any other function defined in this file is inaccessible by remote hosts. It is generally a good practice to have the exposed APIs do very little work, and pass off control to internal functions to do the heavy lifting. Database Interactions ~~~~~~~~~~~~~~~~~~~~~ Database interactions are done with raw query strings, not with any kind of modern ORM. Consider using context objects from the Koji contexts library for thread-safe interactions. The database schema is captured in the **docs** directory in the root of a git clone. A visualization of the schema is not available at the time of this writing. If you plan to introduce schema changes, please update both ``schema.sql`` and provide a migration script if necessary. Troubleshooting ~~~~~~~~~~~~~~~ The hub runs in an Apache service, so you will need to look in Apache logs for error messages if you are encountering 500 errors or the service is failing to start. Specifically you want to check in: - /var/log/httpd/error\_log - /var/log/httpd/ssl\_error\_log If you need more specific tracebacks and debugging data, consider changing the debugging setting in **/etc/koji-hub/hub.conf**. Be advised the hub is very verbose with this setting on, your logs will take up gigabytes of space within several days. Kojid ----- kojid is the build daemon that runs on each of the build machines. Its primary responsibility is polling for incoming build requests and handling them accordingly. Essentially kojid asks koji-hub for work. Koji also has support for tasks other than building. Creating install images is one example. kojid is responsible for handling these tasks as well. kojid uses mock for building. It also creates a fresh buildroot for every build. kojid is written in Python and communicates with koji-hub via XML-RPC. Implementation Details ~~~~~~~~~~~~~~~~~~~~~~ The daemon runs as a service on a host that is traditionally not the same as the hub or webUI. This is a good security practice because the service runs as root, and executes untrusted code to produce builds on a regular basis. Keeping the Hub separate limits the damage a malicious package can do to the build system as a whole. For the same reason, the filesystem that the hub keeps built software on should be mounted Read-Only on the build host. It should call APIs on the hub that are exposed through the ``HostExports`` class in the hub code. Whenever the builder accepts a task, it forks a process to carry out the build. An initscript/unit-file is available for kojid, so it can be stopped and started like a normal service. Remember to do this when you deploy changes! TaskHandlers ^^^^^^^^^^^^ All tasks in kojid have a ``TaskHandler`` class that defines what to do when the task is picked up from the hub. The base class is defined in ``koji/tasks.py`` where a lot of useful utility methods are available. An example is ``uploadFile``, which is used to upload logs and built binaries from a completed build to the hub since the shared filesystem is read only. The daemon code lives in ``builder/kojid``, which is deployed to /usr/sbin/kojid. In there you'll notice that each task handler class has a ``Methods`` member and ``_taskWeight`` member. These must be defined, and the former is used to match the name of a waiting task (on the hub) with the task handler code to execute. Each task handler object must have a ``handler`` method defined, which is the entry point for the forked process when a builder accepts a task. Tasks can have subtasks, which is a typical model when a build can be run on multiple architectures. In this case, developers should write 2 task handlers: one handles the build for exact one architecture, and one that assembles the results of those tasks into a single build, and sends status information to the hub. You can think of the latter handler as the parent task. All task handler objects have a ``session`` object defined, which is the interface to use for communications with the hub. So, parent tasks should kick off child tasks using the session object's subtask method (which is part of HostExports). It should then call ``self.wait`` with ``all=True`` to wait for the results of the child tasks. Here's a stub of what a new build task might look like: :: class BuildThingTask(BaseTaskHandler): Methods = ['thing'] _taskWeight = 0.5 def handler(self, a, b, arches, options): subtasks = {} for arch in arches: subtasks[arch] = session.host.subtask(method='thingArch', a, b, arch) results = self.wait(subtasks.values(), all=True) # parse results and put rows in database # put files in their final resting place return 'Build successful' class BuildThingArchTask(BaseTaskHandler): Methods = ['thingArch'] _taskWeight = 2.0 def handler(self, a, b, arch): # do the build, capture results in a variable self.uploadFile('/path/to/some/log') self.uploadFile('/path/to/binary/file') return result Source Control Managers ^^^^^^^^^^^^^^^^^^^^^^^ If you your build needs to check out code from a Source Control Manager (SCM) such as git or subversion, you can use SCM objects defined in ``koji/daemon.py``. They take a specially formed URL as an argument to the constructor. Here's an example use. The second line is important, it makes sure the SCM is in the whitelist of SCMs allowed in ``/etc/kojid/kojid.conf``. :: scm = SCM(url) scm.assert_allowed(self.options.allowed_scms) directory = scm.checkout('/checkout/path', session, uploaddir, logfile) Checking out takes 4 arguments: where to checkout, a session object (which is how authentication is handled), a directory to upload the log to, and a string representing the log file name. Using this method Koji will checkout (or clone) a remote repository and upload a log of the standard output to the task results. Build Root Objects ^^^^^^^^^^^^^^^^^^ It is encouraged to build software in mock chroots if appropriate. That way Koji can easily track precise details about the environment in which the build was executed. In ``builder/kojid`` a BuildRoot class is defined, which provides an interface to execute mock commands. Here's an example of their use: :: broot = BuildRoot(self.session, self.options, build_tag, arch, self.id) A session object, task options, and a build tag should be passed in as-is. You should also specify the architecture and the task ID. If you ever need to pass in specialized options to mock, look in the ImageTask.makeImgBuildRoot method to see how they are defined and passed in to the BuildRoot constructor. Troubleshooting ~~~~~~~~~~~~~~~ The daemon writes a log file to ``/var/log/kojid.log``. Debugging output can be turned on in ``/etc/kojid/kojid.conf``. Koji-Web -------- koji-web is a set of scripts that run in mod\_wsgi and use the Cheetah templating engine to provide a web interface to Koji. It acts as a client to koji-hub providing a visual interface to perform a limited amount of administration. koji-web exposes a lot of information and also provides a means for certain operations, such as cancelling builds. The web pages are derived from Cheetah templates, the syntax of which you can read up on `here <http://cheetahtemplate.org/users_guide/>`__. These templates are the ``chtml`` files sitting in ``www/kojiweb``. You'll notice quickly that these templates are referencing variables, but where do they come from? The ``www/kojiweb/index.py`` file provides them. There are several functions named after the templates they support, and in each one a dictionary called ``values`` is populated. This is how data is gathered about the task, build, archive, or whatever the page is about. Take your time with ``taskinfo.chtml`` in particular, as the conditionals there have gotten quite long. If you are adding a new task to Koji, you will need to extend this at a minimum. A new type of build task would require this, and possibly another that is specific to viewing the archived information about the build. (taskinfo vs. buildinfo) If your web page needs to display the contents of a list or dictionary, use the ``$printMap`` function to help with that. It is often sensible to define a function that easily prints options and values in a dictionary. An example of this is in taskinfo.chtml. :: #def printOpts($opts) #if $opts <strong>Options:</strong><br/> $printMap($opts, '&nbsp;&nbsp;') #end if #end def Finally, if you need to expand the drop-down menus of "method" types when searching for tasks in the WebUI, you will need to add them to the ``_TASKS`` list in ``www/kojiweb/index.py``. Add values where appropriate to ``_TOPLEVEL_TASKS`` and ``_PARENT_TASKS`` as well so that parent-child relationships show up correctly too. Remember whenever you update a template or index.py, you will need to deploy and restart apache/httpd! Troubleshooting ~~~~~~~~~~~~~~~ Like the hub, this component is backed by apache, so you should follow the same techniques for debugging Koji-Web as `Koji-Hub <#Troubleshooting>`__. Kojira ------ kojira is a daemon that keeps the build root repodata updated. It is responsible for removing redundant build roots and cleaning up after a build request is completed. Building and Deploying Changes ============================== The root of the git clone for Koji code contains a ``Makefile`` that has a few targets to make building and deployment a little easier. Among them are: - tarball: create a bz2 tarball that could be consumed in an rpm build - rpm: create Koji rpms. The NVRs will be defined by the spec file, which is also in the same directory. The results will appear in a ``noarch`` directory. - test-rpm: like rpm, but append the Release field with a date and time stamp for easy upgrade-deployment Writing Koji plugins ==================== .. toctree:: :hidden: writing_a_plugin There is a separate documentation page :doc:`writing_a_plugin`. Submitting Changes ================== To submit code changes for Koji, please file a pull request in Pagure. https://pagure.io/koji/pull-requests Here are some guidelines on producing preferable pull requests. - Each request should be a coherent whole, e.g. a single feature or bug fix. Please do not bundle a series of unrelated changes into a single PR - Pull requests in Pagure come from a branch in your personal fork of Koji (either in Pagure or a remote git repo). Please use an appropriately named branch for this. Do not use the master branch of your fork. Also, please be aware that Pagure will automatically update the pull request if you modify the source branch - Your branch should be based against the current HEAD of the target branch - Please adhere to `PEP8 <https://www.python.org/dev/peps/pep-0008/>`__. While much of the older code in Koji does not, we try to stick to it with new code - Code which is imported into CLI or needed for stand-alone API calls must run in both 2.6+ and 3.x python versions. We use the python-six library for compatibility. The affected files are: - ``cli/*`` - ``koji/__init__.py`` - ``koji/auth.py`` - ``koji/tasks.py`` - ``koji/util.py`` - ``tests/test_lib/*`` - ``tests/test_cli/*`` - Check, that unit tests are not broken. Simply run ``make test`` in main directory of your branch to check both python2/3 compatible-code. Or you can also use ``make test2`` or ``make test3`` target for each of them. Note that the core development team for Koji is small, so it may take a few days for someone to reply to your request. Partial work ------------ Pull requests are for changes that are complete and ready for inclusion, but sometimes you have partial work that you may want feedback on. Please don't submit a PR before your code is complete. The preferred way to request early feedback is to push your changes to a your own koji fork and then send an email to `koji-devel AT lists.fedorahosted.org <https://lists.fedorahosted.org/mailman/listinfo/koji-devel>`__ requesting review. This approach is one step short of a PR, making it easy to upgrade to a PR once the changes are ready. Unit Tests ========== Koji comes with a small test suite, that you should always run when making changes to the code. To do so, just run ``make test`` in your terminal. You will need to install the following packages to actually run the tests. * ``findutils`` * ``pyOpenSSL`` * ``python-coverage`` * ``python-krbV`` * ``python-mock`` * ``python-psycopg2`` * ``python-requests`` * ``python-requests-mock`` * ``python-qpid-proton`` Please note that it is currently not supported to use *virtualenv* when hacking on Koji. Unit tests are run automatically for any commit in master branch. We use Fedora's jenkins instance for that. Details are given here: :doc:`Unit tests in Fedora's Jenkins <configuring_jenkins>`. Further testing =============== Currently we automatically build two versions of rpms in Fedora's `Copr <https://copr.fedorainfracloud.org/>`__. First one is simple "master" branch and is available `here <https://copr.fedorainfracloud.org/coprs/tkopecek/koji/>`__. These RPMs are early release candidates before we tag each final release. Second one lives `here <https://copr.fedorainfracloud.org/coprs/tkopecek/koji-testing/>`__ and contains the "master" branch with all the in-progress pull requests that have "testing-ready" flag. Both repos are built once per four hours if there are new changes in pagure. Code Style ========== We are using ``flake8`` to check the code style. Please refer to ``.flake8`` to find the PEP8 and extra rules we are following/ignoring. You will need to install the packages below to run the check. * ``python-flake8`` * ``python-flake8-import-order``