qutebrowser/doc/HACKING.asciidoc

qutebrowser HACKING
===================
The Compiler <mail@qutebrowser.org>
:icons:
:data-uri:
:toc:

I `&lt;3` footnote:[Of course, that says `<3` in HTML.] contributors!

This document contains guidelines for contributing to qutebrowser, as well as
useful hints when doing so.

If anything mentioned here would prevent you from contributing, please let me
know, and contribute anyways! The guidelines are only meant to make life easier
for me, but if you don't follow anything in here, I won't be mad at you. I will
probably change it for you then, though.

If you have any problems, I'm more than happy to help! You can get help in
several ways:

* Send a mail to the mailing list at mailto:qutebrowser@lists.qutebrowser.org[]
(optionally
https://lists.schokokeks.org/mailman/listinfo.cgi/qutebrowser[subscribe]
first).
* Join the IRC channel irc://irc.freenode.org/#qutebrowser[`#qutebrowser`] on
http://freenode.net/[Freenode]
(https://webchat.freenode.net/?channels=#qutebrowser[webchat]).

Finding something to work on
----------------------------

Chances are you already know something to improve or add when you're reading
this. It might be a good idea to ask on the mailing list or IRC channel to make
sure nobody else started working on the same thing already.

If you want to find something useful to do, check the
https://github.com/The-Compiler/qutebrowser/issues[issue tracker]. Some
pointers:

* https://github.com/The-Compiler/qutebrowser/milestones/v0.1[Open issues for
the v0.1 release]
* https://github.com/The-Compiler/qutebrowser/labels/easy[Issues which should
be easy to solve]
* https://github.com/The-Compiler/qutebrowser/labels/not%20code[Issues which
require little/no coding]

There are also some things to do if you don't want to write code:

* Help the community, e.g. on the mailinglist and the IRC channel.
* Improve the documentation.
* Help on the website and graphics (logo, etc.).

Using git
---------

qutebrowser uses http://git-scm.com/[git] for its development. You can clone
the repo like this:

----
git clone git://the-compiler.org/qutebrowser
----

If you don't know git, a http://git-scm.com/[git cheatsheet] might come in
handy. Of course, if using git is the issue which prevents you from
contributing, feel free to send normal patches instead, e.g. generated via
`diff -Nur`.

Getting patches
~~~~~~~~~~~~~~~

After you finished your work and did `git commit`, you can get patches of your
changes like this:

----
git format-patch origin/master <1>
----
<1> Replace `master` by the branch your work was based on, e.g.
`origin/develop`.

Useful utilities
----------------

Checkers
~~~~~~~~

In the _scripts/_ subfolder, there is a `run_checks.py` script.

It runs a bunch of static checks on all source files, using the following
checkers:

* Unit tests using the Python
https://docs.python.org/3.4/library/unittest.html[unittest] framework
* https://pypi.python.org/pypi/flake8/1.3.1[flake8]
* https://github.com/GreenSteam/pep257/[pep257]
* http://pylint.org/[pylint]
* A custom checker for the following things:
    - untracked git files
    - VCS conflict markers

If you changed `setup.py` or `MANIFEST.in`, add the `--setup` argument to run
the following additional checkers:

* https://pypi.python.org/pypi/pyroma/0.9.3[pyroma]
* https://github.com/mgedmin/check-manifest[check-manifest]

It needs all the checkers to be installed and also needs
https://pypi.python.org/pypi/colorama/[colorama].

Please make sure this script runs without any warnings on your new
contributions. There's of course the possibility of false-positives, and the
following techniques are useful to handle these:

* Use `_foo` for unused parameters, with `foo` being a descriptive name. Using
`_` is discouraged.
* If you think you have a good reason to suppress a message, add the following
comment:
+
----
# pylint: disable=message-name
----
+
Note you can add this per line, per function/class, or per file. Please use the
smallest scope which makes sense. Most of the time, this will be line scope.
+
* If you really think a check shouldn't be done globally as it yields a lot of
false-positives, let me know! I'm still tweaking the parameters.

Profiling
~~~~~~~~~

In the _scripts/_ subfolder there's a `run_profile.py` which profiles the code
and shows a graphical representation of what takes how much time.

It needs https://pypi.python.org/pypi/pyprof2calltree/[pyprof2calltree] and
http://kcachegrind.sourceforge.net/html/Home.html[KCacheGrind]. It uses the
built-in Python https://docs.python.org/3.4/library/profile.html[cProfile]
module.

Debugging
~~~~~~~~~

In the `qutebrowser.utils.debug` module there are some useful functions for
debugging.

When starting qutebrowser with the `--debug` flag you also get useful debug
logs. You can add +--logfilter _category[,category,...]_+ to restrict logging
to the given categories.

With `--debug` there are also some additional +debug-_*_+ commands available,
for example `:debug-all-objects` and `:debug-all-widgets` which print a list of
all Qt objects/widgets to the debug log -- this is very useful for finding
memory leaks.

Useful websites
~~~~~~~~~~~~~~~

Some resources which might be handy:

* http://qt-project.org/doc/qt-5/classes.html[The Qt5 reference]
* https://docs.python.org/3/library/index.html[The Python reference]
* http://httpbin.org/[httpbin, a test service for HTTP requests/responses]
* http://requestb.in/[RequestBin, a service to inspect HTTP requests]

Documentation of used Python libraries:

* http://jinja.pocoo.org/docs/dev/[jinja2]
* http://pygments.org/docs/[pygments]
* http://fdik.org/pyPEG/index.html[pyPEG2]
* http://pythonhosted.org/setuptools/[setuptools]
* http://cx-freeze.readthedocs.org/en/latest/overview.html[cx_Freeze]
* https://pypi.python.org/pypi/colorama[colorama]
* https://pypi.python.org/pypi/colorlog[colorlog]

Related RFCs and standards:

HTTP
^^^^

* https://tools.ietf.org/html/rfc2616[RFC 2616 - Hypertext Transfer Protocol
-- HTTP/1.1]
(http://www.rfc-editor.org/errata_search.php?rfc=2616[Errata])
* https://tools.ietf.org/html/rfc7230[RFC 7230 - Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing]
(http://www.rfc-editor.org/errata_search.php?rfc=7230[Errata])
* https://tools.ietf.org/html/rfc7231[RFC 7231 - Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content]
(http://www.rfc-editor.org/errata_search.php?rfc=7231[Errata])
* https://tools.ietf.org/html/rfc7232[RFC 7232 - Hypertext Transfer Protocol
(HTTP/1.1): Conditional Requests]
(http://www.rfc-editor.org/errata_search.php?rfc=7232[Errata])
* https://tools.ietf.org/html/rfc7233[RFC 7233 - Hypertext Transfer Protocol
(HTTP/1.1): Range Requests]
(http://www.rfc-editor.org/errata_search.php?rfc=7233[Errata])
* https://tools.ietf.org/html/rfc7234[RFC 7234 - Hypertext Transfer Protocol
(HTTP/1.1): Caching]
(http://www.rfc-editor.org/errata_search.php?rfc=7234[Errata])
* https://tools.ietf.org/html/rfc7235[RFC 7235 - Hypertext Transfer Protocol
(HTTP/1.1): Authentication]
(http://www.rfc-editor.org/errata_search.php?rfc=7235[Errata])
* https://tools.ietf.org/html/rfc5987[RFC 5987 - Character Set and Language
Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters]
(http://www.rfc-editor.org/errata_search.php?rfc=5987[Errata])
* https://tools.ietf.org/html/rfc6266[RFC 6266 - Use of the
Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)]
(http://www.rfc-editor.org/errata_search.php?rfc=6266[Errata])
* http://tools.ietf.org/html/rfc6265[RFC 6265 - HTTP State Management Mechanism
(Cookies)] (http://www.rfc-editor.org/errata_search.php?rfc=6265[Errata])
* http://www.cookiecentral.com/faq/#3.5[Netscape Cookie Format]

Other
^^^^^

* https://tools.ietf.org/html/rfc5646[RFC 5646 - Tags for Identifying
Languages] (http://www.rfc-editor.org/errata_search.php?rfc=5646[Errata])
* http://www.w3.org/TR/CSS2/[Cascading Style Sheets Level 2 Revision 1 (CSS
2.1) Specification]
* http://qt-project.org/doc/qt-4.8/stylesheet-reference.html[Qt Style Sheets
Reference]
* http://mimesniff.spec.whatwg.org/[MIME Sniffing Standard]
* http://spec.whatwg.org/[WHATWG specifications]
* http://www.w3.org/html/wg/drafts/html/master/Overview.html[HTML 5.1 Nightly]
* http://www.w3.org/TR/webstorage/[Web Storage]
* http://www.brynosaurus.com/cachedir/spec.html[Cache directory tagging
standard]
* http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html[XDG
basedir specification]

Hints
-----

Python and Qt objects
~~~~~~~~~~~~~~~~~~~~~

For many tasks, there are solutions in both Qt and the Python standard libary
available.

In qutebrowser, the policy is usually using the Python libraries, as they
provide exceptions and other benefits.

There are some exceptions to that:

* `QThread` is used instead of Python threads because it provides signals and
slots.
* `QProcess` is used instead of Python's `subprocess` if certain actions (e.g.
cleanup) when the process finished are desired, as it provides signals for
that.
* `QUrl` is used instead of storing URLs as string, see the
<<handling-urls,handling URLs>> section for details.

When using Qt objects, two issues must be taken care of:

* Methods of Qt objects report their status by using their return values,
instead of using exceptions.
+
If a function gets or returns a Qt object which
has an `.isValid()` method such as `QUrl` or `QModelIndex`, there's a helper
function `ensure_valid` in `qutebrowser.utils.qt` which should get called on
all such objects. It will raise `qutebrowser.utils.qt.QtValueError` if the
value is not valid.
+
If a function returns something else on error, the return value should
carefully be checked.

* Methods of Qt objects have certain maximum values, based on their underlying
C++ types.
+
When passing a numeric parameter to a Qt function, all numbers should be
range-checked using `qutebrowser.utils.check_overflow`, or passing a value
which is too large should be avoided by other means (e.g. by setting a maximum
value for a config object).

[[object-registry]]
The object registry
~~~~~~~~~~~~~~~~~~~

The object registry in `qutebrowser.utils.objreg` is a collection of
dictionaries which map object names to the actual long-living objects.

There are currently these object registries, also called 'scopes':

* The `global` scope, with objects which are used globally (`config`,
`cookie-jar`, etc.)
* The `tab` scope with objects which are per-tab (`hintmanager`, `webview`,
etc.). Passing this scope to `objreg.get()` selects the object in the currently
focused tab by default. A tab can be explicitely selected by passing
+tab=_tab-id_, window=_win-id_+ to it.

A new object can be registered by using
+objreg.register(_name_, _object_[, scope=_scope_, window=_win-id_,
tab=_tab-id_])+. An object should not be registered twice. To update it,
`update=True` has to be given.

An object can be retrieved by using +objreg.get(_name_[, scope=_scope_,
window=_win-id_, tab=_tab-id_])+. The default scope is `global`.

All objects can be printed by starting with the `--debug` flag and using the
`:debug-all-objects` command.

The registry is mainly used for <<commands,command handlers>> but also can be
useful in places where using Qt's
http://qt-project.org/doc/qt-5/signalsandslots.html[signals and slots]
mechanism would be difficult.

Logging
~~~~~~~

Logging is used at various places throughout the qutebrowser code. If you add a
new feature, you should also add some strategic debug logging.

Unless other Python projects, qutebrowser doesn't use a logger per file,
instead it uses custom-named loggers.

The existing loggers are defined in `qutebrowser.utils.log`. If your feature
doesn't fit in any of the logging categories, simply add a new line like this:

[source,python]
----
foo = getLogger('foo')
----

Then in your source files, do this:

[source,python]
----
from qutebrowser.utils import log
...
log.foo.debug("Hello World")
----

The following logging levels are available for every logger:

[width="75%",cols="25%,75%"]
|=======================================================================
|criticial |Critical issue, qutebrowser can't continue to run.
|error     |There was an issue and some kind of operation was abandoned.
|warning   |There was an issue but the operation can continue running.
|info      |General informational messages.
|debug     |Verbose debugging informations.
|=======================================================================

[[commands]]
Commands
~~~~~~~~

qutebrowser has the concept of functions which are exposed to the user as
commands.

Creating a new command is straightforward:

[source,python]
----
import qutebrowser.commands.cmdutils

...

@cmdutils.register(...)
def foo():
    ...
----

The commands arguments are automatically deduced by inspecting your function.

If the function is a method of a class, the `@cmdutils.register` decorator
needs to have an `instance=...` parameter which points to the (single/main)
instance of the class.

The `instance` parameter is the name of an object in the object registry, which
then gets passed as the `self` parameter to the handler. The `scope` argument
selects which object registry (global, per-tab, etc.) to use.  See the
<<object-registry,object registry>> section for details.

There are also other arguments to customize the way the command is registered,
see the class documentation for `register` in `qutebrowser.commands.utils` for
details.

The types of the function arguments are inferred based on their default values,
e.g. an argument `foo=True` will be converted to a flag `-f`/`--foo` in
qutebrowser's commandline.

This behaviour can be overridden using Python's
http://legacy.python.org/dev/peps/pep-3107/[function annotations]. The
annotation should always be a `dict`, like this:

[source,python]
----
@cmdutils.register(...)
def foo(bar: {'type': int}, baz=True):
    ...
----

The following keys are supported in the dict:

* `type`: The type this value should have. The value entered by the user is
then automatically checked. Possible values:
    - A callable (`int`, `float`, etc.): Gets called to validate/convert the
      value.
    - A string: The value must match exactly (mainly useful with tuples to get
      a choice of values, see below).
    - A python enum type: All members of the enum are possible values.
    - A tuple of multiple types above: Any of these types are valid values,
      e.g. `('foo', 'bar')` or `(int, 'foo')`.
* `flag`: The flag to be used, as 1-char string (default: First char of the
long name).
* `name`: The long name to be used, as string (default: Name of the parameter).
* `special`: The string `count` or `win_id` if the parameter should be
auto-filled (with the count given by the user and the window ID the command was
executed in, respectively).
* `nargs`: Gets passed to argparse, see
https://docs.python.org/dev/library/argparse.html#nargs[its documentation].

[[handling-urls]]
Handling URLs
~~~~~~~~~~~~~

qutebrowser handles two different types of URLs: URLs as a string, and URLs as
the Qt `QUrl` type. As this can get confusing quickly, please follow the
following guidelines:

* Convert a string to a QUrl object as early as possible, i.e. directly after
the user did enter it.
    - Use `utils.urlutils.fuzzy_url` if the URL is entered by the user
      somewhere.
    - Be sure you handle `utils.urlutils.FuzzyError` and display an error
      message to the user.
* Convert a `QUrl` object to a string as late as possible, e.g. before
displaying it to the user.
    - If you want to display the URL to the user, use `url.toDisplayString()`
      so password information is removed.
    - If you want to get the URL as string for some other reason, you most
      likely want to add the `QUrl.EncodeFully` and `QUrl.RemovePassword`
      flags.
* Name a string URL something like `urlstr`, and a `QUrl` something like `url`.
* Mention in the docstring whether your function needs a URL string or a
`QUrl`.
* Call `ensure_valid` from `utils.qtutils` whenever getting or creating a
`QUrl` and take appropriate action if not. Note the URL of the current page
always could be an invalid QUrl (if nothing is loaded yet).


Style conventions
-----------------

qutebrowser's coding conventions are based on
http://legacy.python.org/dev/peps/pep-0008/[PEP8] and the https://google-styleguide.googlecode.com/svn/trunk/pyguide.html[Google Python style guidelines] with some additions:

* The _Raise:_ section is not added to the docstring.
* Methods overriding Qt methods (obviously!) don't follow the naming schemes.
* Everything else does though, even slots.
* Docstrings should look like described in
http://legacy.python.org/dev/peps/pep-0257/[PEP257] and the google guidelines.
* Class docstrings have additional _Attributes:_, _Class attributes:_ and
  _Signals:_ sections.
* In docstrings of command handlers (registered via `@cmdutils.register`), the
description should be split into two parts by using `//` - the first part is
the description of the command like it will appear in the documentation, the
second part is "internal" documentation only relevant to people reading the
sourcecode.
+
Example for a class docstring:
+
[source,python]
----
"""Some object.

Attributes:
    blub: The current thing to handle.

Signals:
    valueChanged: Emitted when a value changed.
                  arg: The new value
"""
----
+
Example for a method/function docstring:
+
[source,python]
----
"""Do something special.

This will do something.

//

It is based on http://example.com/.

Args:
    foo: ...

Return:
    True if something, False if something else.
"""
----
+
* The layout of a module should be roughly like this:
  - Shebang (`#!/usr/bin/python`, if needed)
  - vim-modeline (`# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et`)
  - Copyright
  - GPL boilerplate
  - Module docstring
  - Python standard library imports
  - PyQt imports
  - qutebrowser imports
  - functions
  - classes
* The layout of a class should be like this:
  - docstring
  - `__magic__` methods
  - properties
  - _private methods
  - public methods
  - `on_*` methods
  - overrides of Qt methods

Checklists
----------

These are mainly intended for myself, but they also fit in here well.

New Qt release
~~~~~~~~~~~~~~

* Run all tests and check nothing is broken.
* Check the
https://bugreports.qt-project.org/issues/?jql=reporter%20%3D%20%22The%20Compiler%22%20ORDER%20BY%20fixVersion%20ASC[Qt bugtracker]
and make sure all bugs marked as resolved are actually fixed.
* Update own PKGBUILDs based on upstream Archlinux updates.
* Build developer packages.
* Build non-developer symbol packages.
* Upload symbols patch to http://www.qutebrowser.org/qt-symbols.patch
* Upload symbols packages to http://www.qutebrowser.org/qt-symbols-pkg/
* Update recommended Qt version in `README`
* Update OS X instructions in `README`
* Make sure Gentoo instructions are up to date.
* Grep for `WORKAROUND` in the code and test if fixed stuff works without the
workaround.

qutebrowser release
~~~~~~~~~~~~~~~~~~~

* Make sure there are no unstaged changes.
* Run `src2asciidoc.py` and commit changes if necessary.
* Run `asciidoc2html.py`.
* Adjust `__version_info__` in `qutebrowser/__init__.py`.

* Run all tests on all supported systems.
* Test an upgrade from the previous version (no manual intervention).
* Test an upgrade from the first version (no manual intervention).

* Create annotated git tag (`git tag -s "v0.1" -m "Release v0.1"`)
* Create git branch `v0.1.x`
* Push including `--tags`
* Create release on github
* Mark the milestone at https://github.com/The-Compiler/qutebrowser/milestones
as closed.

* Create standalone Windows package (32/64bit) in Windows VM
* Upload to PyPI: `python setup.py register sdist upload --sign`
* Maybe upload to http://qt-apps.org/
* Upload to webpage with checksum/GPG (when/if it exists)

* Announce to qutebrowser mailinglist
* Maybe annouce at other places?