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Hacker's guide to NAV

If you are contributing code to Network Administration Visualized, please read this first.

Contributing to NAV

Originally, NAV was a closed source project, initiated by the Norwegian University of Science and Technology (NTNU), and eventually sponsored by UNINETT on behalf of the Norwegian higher education community. In 2004, however, NTNU and UNINETT started distributing NAV under the GNU General Public License, making it a truly free software system.

While UNINETT and NTNU are still the main contributors to NAV, developing NAV to support the needs of the Norwegian higher education community, contributions from third parties is highly appreciated.

We communicate mainly through mailing lists, Launchpad and the #nav IRC channel on FreeNode. At times, UNINETT also arranges workshops and gatherings for its customers: Norwegian universities, university colleges and research institutions.

To contribute:

Go to http://metanav.uninett.no/ and

  • Join the mailing lists. The nav-dev mailing list in

particular is for discussing NAV development. So far, this is a

  low traffic list. We can only hope this will change ;-)
* Get a copy of the latest development sources by cloning the
  Mercurial repository at http://metanav.uninett.no/hg/default/.
  Most new development takes place on this branch.
* Take a look at the [[:navprojects|project reports from previous
  development projects at NTNU]] (NAVMe, NAVMore, tigaNAV and
  others) - design specifications and other useful bits of historic
  NAV information is mostly to be found in these.  Unfortunately,
  some of the oldest project documentation is in Norwegian only.  Do
  not hesitate to ask for help on the mailing lists.

If you wish to contribute code to the project, see the submitting patches section.

Directory layout

A rough guide to the source tree:

conf/ Files related to the autoconf build system.
doc/ User and developer documentation, SQL scripts and example NAV configuration files.
tools/ Tool scripts for the build and release processes.
contrib/ User contributed NAV tools. NAV doesn't depend on these, and any maintenance of them is left up to the original developers. We do not offer support for these tools.
packages/ Stuff to help packaging NAV for various platforms, such as RedHat, CentOS, FreeBSD, Debian and soforth.
src/ Source code to Java subsystems of NAV (here for historic reasons).
subsystem/ Source code to the rest of NAV - most of it Python. NAV is loosely divided into subsystems, and each one of these has its own subdirectory in here.
subsystem/lib-python/ Python libraries & APIs. Please check what's already there before you roll your own.
subsystem/lib-perl/ Perl libraries & APIs. Only a single piece of Perl code remains in NAV; once this has been replaced, this directory will cease to exist.
subsystem/webfront/ Python libraries for the web interface and front-page handler modules for mod_python.

Development languages and frameworks

For historic reasons, different parts of NAV are written in different programming languages (Perl, Java, PHP and Python). This has been unfortunate in may ways, not at least for the sake of consistency and maintenance, but fortunately we have a long-term goal of reducing the number of languages and dependencies. The last few years we've spent a significant amount of time rewriting parts that were written in Perl and PHP to Python, which is the language we are currently gravitating towards.

Currently (as of February 2009), major parts of NAV are written in Python and Java, while only a single Perl program remains (makecricketconfig.pl).

  • When contributing patches to existing code, or plugins to existing

subsystems, use the language that subsystem was written in.

  • When writing entirely new subsystems, the following rules apply:
    1. If your subsystem is a new tool for the web interface, use

Python and Django. The legacy parts of the web system interface

    directly with ''mod_python'', using Cheetah for HTML templating.
    Anything written in 2008 and later uses Django.  There is also
    [[devel:django_introduction|a guide for interfacing Django
    applications with the legacy web code]].
  - If your subsystem is a new back-end tool/daemon, please use
    Python.  The NAV Python API is more complete than for any of the
    other languages, and you will receive a lot for free.

If these rules are not followed, your patches will not be accepted into NAV (but if they are really good, we will consider including them in the contrib directory).

If YOU are willing to invest in porting some of the existing Java/Perl code to Python, then you will be celebrated as a NAV hero!

Coding style

Much of the legacy NAV code was written without using any coding style guidelines. This has resulted in some chaotic combination of styles, which we hope to reduce in the future. For new code, please follow these guidelines:

  • For Java code, please refer to SUN's “Code conventions for the

Java Programming Language”: http://java.sun.com/docs/codeconv/

  • For Python code, please refer to PEP-8, “Style Guide for Python

Code” http://www.python.org/doc/peps/pep-0008/

If you see violations of these guidelines, don't hesitate to fix them. If you fix file-wide indentation problems etc., please submit this as a separate patch to make your other patches look clean and readable.

Python boilerplate headers

We will generally only accept code into NAV if it is licensed under GPL v2, but we may make individual exceptions for code licensed under compatible licenses. Each Python source code file should contain the following boilerplate at the top:

#
# Copyright (C) 2008,2009 Somebody
#
# This file is part of Network Administration Visualized (NAV).
#
# NAV is free software: you can redistribute it and/or modify it under the
# terms of the GNU General Public License version 2 as published by the Free
# Software Foundation.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
# more details.  You should have received a copy of the GNU General Public
# License along with NAV. If not, see <http://www.gnu.org/licenses/>.
#

If a file uses non-ASCII characters, it must be encoded as UTF-8, and an encoding statement should be inserted at the top:

# -*- coding: utf-8 -*-

Database connections

NAV uses PostgreSQL as its database backend. Namespaces (schemas) are employed to logically group tables and relations. NAV versions prior to 3.5 employed separate PostgreSQL databases instead of namespaces.

The namespaces currently in use are:

manage The core knowledge database of NAV, containing all sorts of information about the monitored IP Devices, events, alerts, network topology and machine tracking data.
profiles Contains NAV user accounts and groups, user preferences and alert profiles.
logger Anything related to NAV's syslog parser/browser system.
arnold The port detention system Arnold stores it's data here.
radius Radius accounting logs, updated directly by FreeRadius' PostgreSQL module.

NOTE: The following is Python-specific, more info should be added for the other languages used in NAV.

Raw SQL

To obtain a connection to the NAV database, use the API accordingly, e.g.:

import nav.db
# Get a connection to the NAV database
connection = nav.db.getConnection('default')

The above code will open a connection to NAV's database, or, if a previous connection with these parameters is already open, returns the already existing connection from a connection cache.

The default parameter is there for legacy reasons; it specifies the name of a subsystem. The db.conf file allows configuration of separate database users for each subsystem (known as a script in db.conf) of NAV. The default db.conf file specifies a database user for a subsystem called default, and also specifies the same database user for all known subsystem names. At present, using a subsystem name that is not configured in db.conf will raise an exception in nav.db.getConnection().

Django models

NAV 3.5 and on includes Django models for the most widely used database tables. If no SQL magic is needed to perform your database voodoo, it is recommended that you use these models, located in the module nav.models. You do not need to explicitly establish a db connection to use these models, as Django takes care of all that.

Legacy web code

When making changes to NAV's legacy web code, a few special considerations need to be made.

Legacy web code interfaces directly with mod_python, and uses Cheetah for HTML templating.

Cheetah templates

Global Cheetah templates are found in subsystem/webfront/nav/web/templates/, while local templates are located in the subdirectories of their respective subsystems. All Python modules compiled from Cheetah templates should be installed in the nav.web.templates package.

Database connections

Use the nav.db.getConnection() call to open or retrieve an existing database connection. All NAV web modules share the same interpreter and namespace per Apache process, which also means that database connections will be shared between the modules running in each process. Therefore, the following conventions apply for connections obtained from nav.db.getConnection():

  • Do not, under any circumstances, retain references to a database

connection between client requests. Make sure to retrieve a new

  connection at the start of each request cycle - the API will cache
  connections between requests, and will automagically re-open
  broken connections.  As the connection is shared between several
  modules, retained references may be invalid in the next request
  cycle.
* **Do not explicitly close database connections.**  Although the API
  will try to reopen any closed or broken connections, you create
  extra overhead, and you don't play nice with the other web
  modules.
* **The obtained connections will use an isolation level of //read
  committed//**, i.e. no autocommits.  Be careful to commit the
  current transaction if you modify any data.  A mod_python
  cleanuphandler will try to automatically commit all open
  transactions as the request cycle ends, but this may change
  in the future, so you must not rely on it.
* **Do not change the isolation level of a connection** without
  restoring it to its original value before the end of the request
  cycle.

Writing new web code

If you are writing a new web application / tool for NAV, please use the Django framework. Here's a quick primer.

Version Control

NAV uses Mercurial for distributed version control. Official repositories are located at http://metanav.uninett.no/hg/ .

Guide to the repository jungle

The official repositories represent three types of branches

Unstable (default)

New, bleeding edge development occurs on the default branch, which is considered unstable (although we try to always keep it buildable).

Feature branches

New features that take a while (and a lot of changesets) to implement and test will often be published as separate feature branches. For all intents and purposes, the feature branches will look like the default branch with some added feature. They will merge changes from the default branch regularly. Once a feature is considered “ready”, the feature branch will be merged onto the default branch.

Stable (series)

Once we are nearing a new series release of NAV (such as 3.5 or 3.6), a new series branch is created from the default branch. Once this branch is stabilized, the first version is tagged and released. After this point, we accept only bug fixes in this branch. Further point releases in this series are tagged on this branch, and all changes are merged back onto the default branch.

When someone writes a patch for a bug, this should usually be committed to the latest active series branch which is affected by the bug. Once a new series is released, we do not usually maintain the older series branches. We may push bug fixes to these branches, but we are unlikely to create a new point release from it.

Push access

Push access to the official repositories is limited to developers employed or commisioned by UNINETT.

Submitting patches

Unless you are submitting one-off fixes for bugs and small issues, please take the time to discuss your change proposals on the nav-dev mailing list. This will increase the chances of having your patches accepted.

Base your patches on the relevant Mercurial branches. If you are submitting a patch for an issue that affects the latest stable series, base your patch on that series branch. If you are submitting patches containing new features, base them on the default branch.

There are three common options for submitting patches:

  • The best way to submit your patches would be using Mercurial. Publish

your own Mercurial branch, and mail its URL to the nav-dev mailing

  list.
* If unable to host a public Mercurial branch, export your changes
  as a Mercurial bundle and attach it to an email addressed to the
  //nav-dev// mailing list.  
* If you have a single patch to submit, attach it to an email
  addressed to the //nav-dev// mailing list.  Please **do not
  patchbomb** the mailing list with multiple emails.
devel/hacking.1296734562.txt.gz · Last modified: 2011/02/03 12:02 by morten