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https://github.com/Kozea/wdb

An improbable web debugger through WebSockets
https://github.com/Kozea/wdb

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An improbable web debugger through WebSockets

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# wdb - Web Debugger

[![Build Status](https://travis-ci.org/Kozea/wdb.svg?branch=master)](https://travis-ci.org/Kozea/wdb)

[![Coverage Status](https://coveralls.io/repos/Kozea/wdb/badge.svg?branch=master&service=github)](https://coveralls.io/github/Kozea/wdb?branch=master)



[![](https://raw.github.com/Kozea/wdb/master/wdb.png)](https://raw.github.com/Kozea/wdb/master/wdb-lg.png)



## Description



**wdb** is a full featured web debugger based on a client-server architecture.



The wdb server which is responsible of managing debugging instances along with browser connections (through websockets) is based on [Tornado](http://www.tornadoweb.org/).

The wdb clients allow step by step debugging, in-program python code execution, code edition (based on [CodeMirror](http://codemirror.net/)) setting breakpoints...



Due to this architecture, all of this is fully compatible with **multithread** and **multiprocess** programs.



**wdb** works with python 2 (2.6, 2.7), python 3 (3.2, 3.3, 3.4, 3.5) and pypy.

Even better, it is possible to debug a python 2 program with a wdb server running on python 3 and vice-versa or debug a program running on a computer with a debugging server running on another computer inside a web page on a third computer!



Even betterer, it is now possible to pause a currently running python process/thread using code injection from the web interface. (This requires gdb and ptrace enabled)



In other words it's a very enhanced version of pdb directly in your browser with nice features.



## Installation:



Global installation:



```

    $ pip install wdb.server

```



In virtualenv or with a different python installation:



```

    $ pip install wdb

```



(You must have the server installed and running)



## Quick test



To try wdb, first you have to start the wdb server:



```

    $ wdb.server.py &

```



Optionally, you can automatically activate daemons with systemd (socket activation):



```

    $ cd /etc/systemd/system

    # curl -O https://raw.githubusercontent.com/Kozea/wdb/master/server/wdb.server.service

    # curl -O https://raw.githubusercontent.com/Kozea/wdb/master/server/wdb.server.socket

    # systemctl enable wdb.server.socket

    # systemctl start wdb.server.socket

```



Next run:



```

    $ python -m wdb your_file.py

```



Wdb will open a debugging window right in your browser, paused at the beginning of your program.



You can access to  to have an overview of the server.



NB: You have to start the server only once. Multiple Debugging sessions can be run simultaneously without problem.



This is not the only way to debug a program, see below.



## Usage



### Setting trace



To debug any program, with the server on, just add:



```python

    import wdb

    wdb.set_trace()

```



anywhere in your code. Your program will stop at the set_trace line. (Just like pdb)



### Tracing code



To inspect your code on exception, you can do the following:



```python

    from wdb import trace

    with trace():

        wrong_code()

```



Any exception during `wrong_code` will launch a debugging session.



You can also use the `start_trace()` and `stop_trace` methods.

(It's better to put the `stop_trace` in a finally block to avoid tracing all your program after an exception.)



### Debugging web servers



wdb provides some tools to make it work nicely with different webservers:



#### Wsgi servers



For wsgi servers you can use the `WdbMiddleware`:



```python

    from wdb.ext import WdbMiddleware

    wsgi_app = Whathever_wsgi_server_lib()

    my_app = WdbMiddleware(wsgi_app)

    my_app.serve_forever()

```



##### Flask



or using Flask:



```python

    from flask import Flask

    from wdb.ext import WdbMiddleware

    app = Flask(__name__)

    app.debug = True

    app.wsgi_app = WdbMiddleware(app.wsgi_app)

    app.run(use_debugger=False) # Disable builtin Werkzeug debugger

```



you can also use the [Flask-Wdb](https://github.com/techniq/flask-wdb/) extension



```python

    from flask import Flask

    from flask_wdb import Wdb



    app = Flask(__name__)

    app.debug = True

    Wdb(app)



    app.run()

```



##### Django



or using django:



Add the middleware in your `wsgi.py`:



After:



```python

    from django.core.wsgi import get_wsgi_application

    application = get_wsgi_application()

```



Add this:



```python

    from wdb.ext import WdbMiddleware

    application = WdbMiddleware(application)

```



And in your `settings.py`, activate exception propagation:



```python

    DEBUG = True

    DEBUG_PROPAGATE_EXCEPTIONS = True

```



##### CherryPy



or using CherryPy:



```python

import cherrypy

from wdb.ext import WdbMiddleware



class HelloWorld(object):

    @cherrypy.expose

    def index(self):

        undefined_method() # This will fail

        return "Hello World!"



cherrypy.config.update({'global':{'request.throw_errors': True}})

app = cherrypy.Application(HelloWorld())

app.wsgiapp.pipeline.append(('debugger', WdbMiddleware))



cherrypy.quickstart(app)

```



#### Tornado



In tornado, which is not a wsgi server, you can use the `wdb_tornado` function which will monkey patch the execute method on RequestHandlers:



```python

    from wdb.ext import wdb_tornado

    from tornado.web import Application

    my_app = Application([(r"/", MainHandler)])

    if options.debug:

        wdb_tornado(my_app)

    my_app.listen(8888)

```



#### Page loading time become slow



If wdb slows down too much of your application (tracing all the things takes time), you can start it disabled with:



```python

    my_app = WdbMiddleware(wsgi_app, start_disabled=True)  # or

    wdb_tornado(my_app, start_disabled=True)

```



Then when you get an exception just click on the on/off button.



## Remote debugging



You can easily do remote debugging with wdb:



Let's say you want to run a program `p.py` on computer A and you want to debug it on computer B.



Start wdb server on computer A and launch this:



```

    WDB_NO_BROWSER_AUTO_OPEN=True python -m wdb p.py

```



And open a browser on computer B at the url given by wdb log.



Now you can also run wdb server on a computer C and run on computer A:



```

    WDB_NO_BROWSER_AUTO_OPEN=True WDB_SOCKET_SERVER=computerC.addr WDB_SOCKET_PORT=19840 python -m wdb p.py

```



And go with computer B to http://computerC/debug/session/[uuid in log] there you can step into p.py running in computer A. Yay !



You can use different configurations:



See `wdb.server.py --help` for changing ports on server and these environnement vars for wdb instances:



```

WDB_SOCKET_SERVER         # WDB server host

WDB_SOCKET_PORT           # WDB server socket port

WDB_WEB_SERVER            # WDB server host for browser openning

WDB_WEB_PORT              # WDB server http port

WDB_NO_BROWSER_AUTO_OPEN  # To disable the automagic browser openning (which can't be done if the browser is not on the same machine)

```

### Docker



If you are developing locally with [Docker](http://www.docker.com/), you can

also use wdb to debug a code running inside a container. The basic setup looks

like this:



1. Start `wdb.server.py ` running in a container and expose port `1984` to your

   host computer, this will server the debugging web server.

2. Start debugging in your app container, making sure to set `WDB_SOCKET_SERVER`

   to the address of the server container, and point it to the expoed port

   `19840` on that server.

3. When a trace is reached, open up `http://:1984`



I will walk through this process in detail, using

[Docker Compose](https://docs.docker.com/compose/) to set up the containers.



Let's say your `docker-compose.yml` looks like

[their example for using with Django](https://docs.docker.com/compose/django/):



```yaml

db:

  image: postgres

web:

  build: .

  command: python manage.py runserver 0.0.0.0:8000

  volumes:

    - .:/code

  ports:

    - "8000:8000"

  links:

    - db

```



Next lets add the wdb server part now and tell the web to link to it:



```yaml

db:

  image: postgres

web:

  build: .

  command: python manage.py runserver 0.0.0.0:8000

  volumes:

    - .:/code

  ports:

    - "8000:8000"

  links:

    - db

    - wdb

  environment:

    WDB_SOCKET_SERVER: wdb

    WDB_NO_BROWSER_AUTO_OPEN: True

wdb:

  image: kozea/wdb

  ports:

    - "1984:1984"

```



And add `wdb` to your `requirements.txt` in your web app:



```bash

$ echo 'wdb' >> requirements.txt

```



Now we can use `wdb.set_trace()` in our python app.



```python

# ... some code

import wdb

wdb.set_trace()

```

Then you have to rebuild your web application and start everything up again



```bash

$ docker-compose stop

$ docker-compose build web

$ docker-compose up

```



Now you can access `http://:1984`, to

see the traces as they come up in your app.



## In browser usage



Once you are in a breakpoint or in an exception, you can eval all you want in the prompt under the code.

Multi-lines are partially supported using `[Shift] + [Enter]`.

There is now help available by clicking on the top help button.



As of now the following special commands are supported during breakpoint:



    * .s or [Ctrl] + [↓] or [F11]    : Step into

    * .n or [Ctrl] + [→] or [F10]    : Step over (Next)

    * .r or [Ctrl] + [↑] or [F9]     : Step out (Return)

    * .c or [Ctrl] + [←] or [F8]     : Continue

    * .u or [F7]                     : Until (Next over loops)

    * .j lineno                      : Jump to lineno (Must be at bottom frame and in the same function)

    * .b arg                         : Set a session breakpoint, see below for what arg can be*

    * .t arg                         : Set a temporary breakpoint, arg follow the same syntax as .b

    * .z arg                         : Delete existing breakpoint

    * .l                             : List active breakpoints

    * .f                             : Echo all typed commands in the current debugging session

    * .d expression                  : Dump the result of expression in a table

    * .w expression                  : Watch expression in current file (Click on the name to remove)

    * .q                             : Quit

    * .h                             : Get some help

    * .e                             : Toggle file edition mode

    * .g                             : Clear prompt

    * .i [mime/type;]expression      : Display the result in an embed, mime type is auto detected on linux and defaults to "text/html" otherwise

    * iterable!sthg                  : If cutter is installed, executes cut(iterable).sthg

    * expr >! file                   : Write the result of expr in file

    * !< file                        : Eval the content of file

    * [Enter]                        : Eval the current selected text in page, useful to eval code in the source

    *

    * * arg is using the following syntax:

    *   [file/module][:lineno][#function][,condition]

    * which means:

    *   - [file]                    : Break if any line of `file` is executed

    *   - [file]:lineno             : Break on `file` at `lineno`

    *   - [file][:lineno],condition : Break on `file` at `lineno` if `condition` is True (ie: i == 10)

    *   - [file]#function           : Break when inside `function` function

    *

    * File is always current file by default and you can also specify a module like `logging.config`.



You can also eval a variable in the source by middle clicking on it.

You can add/remove a breakpoint by clicking on the line number.



NB: Hotkeys with arrows are purposely not triggered in the eval prompt to avoid conflicts when typing.



## Wdb Server



To see which debugging session are currently open, open your browser at .

You can also close crashed session.



From there you should also see all python process and their threads running and you can try to pause them during their execution to do step by step debugging and current variable inspection. **This is highly experimental and requires gdb and a kernel with ptrace enabled to inject python code into a running python process.**

If you get `ptrace: Operation not permitted.` you will have to enable it.



Depending on your system it might work with:

```bash

echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

```



Make sure that wdb is installed for the python version running the program too.



## Importing wdb each time is exhausting



Yes to avoid that, you can add a `w` builtin at the beggining of your application:



```python

    from wdb.ext import add_w_builtin

    add_w_builtin()

```



you can now use the `w` object any where in your code:



```python

    my_code()

    w.tf  # Stop next line

    doubtful_code()

```



```python

    my_code()

    with w.trace():

        doubtful_code()

```



## Code completion



Wdb has dynamic code completion in eval prompt thanks to [jedi](https://github.com/davidhalter/jedi).



## FAQ



### In Firefox opened debugging pages are not closed when done



It's a firefox config flag, visit `about:config` and set:

`dom.allow_scripts_to_close_windows` to `true`



### The logs are spammed with 'parsing Python module'



If your logging configuration is set to display DEBUG logs, you may see a log for every imported file in your project any time WDB is active, like so:



```

DEBUG 2017-07-16 13:15:03,772 index 49835 123145573191680 parsing Python module /project/.virtualenv/python-3.6.1/lib/python3.6/site-packages/package/file.py for indexing

```



To silence only this message, add a config for the importmagic module. For example: 



```    

LOGGING = {

    ...

    'loggers': {

        ...

        'importmagic.index': {

            'level': 'ERROR',

            'propagate': False,

        },

    },

}

```



## Contribute



All contributions are more than welcomed, use the fork luke !



Or you still can use your money =)



[![Flattr](http://api.flattr.com/button/flattr-badge-large.png)](https://flattr.com/submit/auto?user_id=paradoxxx_zero&url=https://github.com/Kozea/wdb&title=Wdb&tags=github&category=software)

[![gittip](http://i.imgur.com/IKcQB2P.png)](https://www.gittip.com/paradoxxxzero/)



## Test



Wdb is now partially tested, so if you want to contribute be sure to run the test suite:



```

    $ pip install pytest

    $ pip install -e client -e server

    $ cd test

    $ py.test

```



Feel free to add tests !



## Author



[Florian Mounier](http://github.com/paradoxxxzero) @ [Kozea](http://kozea.fr/)



## Licence



This library is licensed under GPLv3



wdb - An improbable web debugger through WebSockets



    wdb Copyright (c) 2012-2016  Florian Mounier, Kozea



    This program is free software: you can redistribute it and/or modify

    it under the terms of the GNU General Public License as published by

    the Free Software Foundation, either version 3 of the License, or

    (at your option) any later version.



    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 this program.  If not, see .