Open Event Server: No (no-wrap) Ellipsis using jquery!

Yes, the title says it all i.e., Enabling multiple line ellipsis. This was used to solve an issue to keep Session abstract view within 200 characters (#3059) on FOSSASIA‘s Open Event Server project.

There is this one way to ellipsis a paragraph in html-css and that is by using the text-overflow property:

.div_class{
white-space: nowrap;
overflow: hidden;
text-overflow: ellipsis;
}’’

But the downside of this is the one line ellipis. Eg: My name is Medozonuo. I am…..

And here you might pretty much want to ellipsis after a few characters in multiple lines, given that your div space is small and you do want to wrap your paragraph. Or maybe not.

So jquery to the rescue.

There are two ways you can easily do this multiple line ellipsis:

1) Height-Ellipsis (Using the do-while loop):

//script:
if ($('.div_class').height() > 100) {
    var words = $('.div_class').html().split(/\s+/);
    words.push('...');

    do {
        words.splice(-2, 1);
        $('.div_class').html( words.join(' ') );
    } while($('.div_class').height() > 100);
}

Here, you check for the div content’s height and split the paragraph after that certain height and add a “…”, do- while making sure that the paragraphs are in multiple lines and not in one single line. But checkout for that infinite loop.

2) Length-Ellipsis (Using substring function):  

//script:
$.each($('.div_class'), function() {
        if ($(this).html().length > 100) {
               var cropped_words = $(this).html();
               cropped_words = cropped_words.substring(0, 200) + "...";
               $(this).html(cropped_words);
        }
 });

Here, you check for the length/characters rather than the height, take in the substring of the content starting from 0-th character to the 200-th character and then add in extra “…”.

This is exactly how I used it in the code.

$.each($('.short_abstract',function() {
   if ($(this).html().length > 200) {
       var  words = $(this).html();
       words = words.substring(0,200 + "...";
       $(this).html(words);
    }
});


So ellipsing paragraphs over heights and lengths can be done using jQuery likewise.

DetachedInstanceError: dealing with Celery, Flask’s app context and SQLAlchemy

In the open event server project, we had chosen to go with celery for async background tasks. From the official website,

What is celery?

Celery is an asynchronous task queue/job queue based on distributed message passing.

What are tasks?

The execution units, called tasks, are executed concurrently on a single or more worker servers using multiprocessing.

After the tasks had been set up, an error constantly came up whenever a task was called

The error was:

DetachedInstanceError: Instance <User at 0x7f358a4e9550> is not bound to a Session; attribute refresh operation cannot proceed

The above error usually occurs when you try to access the session object after it has been closed. It may have been closed by an explicit session.close() call or after committing the session with session.commit().

The celery tasks in question were performing some database operations. So the first thought was that maybe these operations might be causing the error. To test this theory, the celery task was changed to :

@celery.task(name='lorem.ipsum')
def lorem_ipsum():
    pass

But sadly, the error still remained. This proves that the celery task was just fine and the session was being closed whenever the celery task was called. The method in which the celery task was being called was of the following form:

def restore_session(session_id):
    session = DataGetter.get_session(session_id)
    session.deleted_at = None
    lorem_ipsum.delay()
    save_to_db(session, "Session restored from Trash")
    update_version(session.event_id, False, 'sessions_ver')


In our app, the app_context was not being passed whenever a celery task was initiated. Thus, the celery task, whenever called, closed the previous app_context eventually closing the session along with it. The solution to this error would be to follow the pattern as suggested on http://flask.pocoo.org/docs/0.12/patterns/celery/.

def make_celery(app):
    celery = Celery(app.import_name, broker=app.config['CELERY_BROKER_URL'])
    celery.conf.update(app.config)
    task_base = celery.Task

    class ContextTask(task_base):
        abstract = True

        def __call__(self, *args, **kwargs):
            if current_app.config['TESTING']:
                with app.test_request_context():
                    return task_base.__call__(self, *args, **kwargs)
            with app.app_context():
                return task_base.__call__(self, *args, **kwargs)

    celery.Task = ContextTask
    return celery

celery = make_celery(current_app)


The __call__ method ensures that celery task is provided with proper app context to work with.

 

Event-driven programming in Flask with Blinker signals

Setting up blinker:

The Open Event Project offers event managers a platform to organize all kinds of events including concerts, conferences, summits and regular meetups. In the server part of the project, the issue at hand was to perform multiple tasks in background (we use celery for this) whenever some changes occurred within the event, or the speakers/sessions associated with the event.

The usual approach to this would be applying a function call after any relevant changes are made. But the statements making these changes were distributed all over the project at multiple places. It would be cumbersome to add 3-4 function calls (which are irrelevant to the function they are being executed) in so may places. Moreover, the code would get unstructured with this and it would be really hard to maintain this code over time.

That’s when signals came to our rescue. From Flask 0.6, there is integrated support for signalling in Flask, refer http://flask.pocoo.org/docs/latest/signals/ . The Blinker library is used here to implement signals. If you’re coming from some other language, signals are analogous to events.

Given below is the code to create named signals in a custom namespace:


from blinker import Namespace

event_signals = Namespace()
speakers_modified = event_signals.signal('event_json_modified')

If you want to emit a signal, you can do so by calling the send() method:


speakers_modified.send(current_app._get_current_object(), event_id=event.id, speaker_id=speaker.id)

From the user guide itself:

“ Try to always pick a good sender. If you have a class that is emitting a signal, pass self as sender. If you are emitting a signal from a random function, you can pass current_app._get_current_object() as sender. “

To subscribe to a signal, blinker provides neat decorator based signal subscriptions.


@speakers_modified.connect
def name_of_signal_handler(app, **kwargs):

 

Some Design Decisions:

When sending the signal, the signal may be sending lots of information, which your signal may or may not want. e.g when you have multiple subscribers listening to the same signal. Some of the information sent by the signal may not be of use to your specific function. Thus we decided to enforce the pattern below to ensure flexibility throughout the project.


@speakers_modified.connect
def new_handler(app, **kwargs):
# do whatever you want to do with kwargs['event_id']

In this case, the function new_handler needs to perform some task solely based on the event_id. If the function was of the form def new_handler(app, event_id), an error would be raised by the app. A big plus of this approach, if you want to send some more info with the signal, for the sake of example, if you also want to send speaker_name along with the signal, this pattern ensures that no error is raised by any of the subscribers defined before this change was made.

When to use signals and when not ?

The call to send a signal will of course be lying in another function itself. The signal and the function should be independent of each other. If the task done by any of the signal subscribers, even remotely affects your current function, a signal shouldn’t be used, use a function call instead.

How to turn off signals while testing?

When in testing mode, signals may slow down your testing as unnecessary signals subscribers which are completely independent from the function being tested will be executed numerous times. To turn off executing the signal subscribers, you have to make a small change in the send function of the blinker library.

Below is what we have done. The approach to turn it off may differ from project to project as the method of testing differs. Refer https://github.com/jek/blinker/blob/master/blinker/base.py#L241 for the original function.


def new_send(self, *sender, **kwargs):
    if len(sender) == 0:
        sender = None
    elif len(sender) > 1:
        raise TypeError('send() accepts only one positional argument, '
                        '%s given' % len(sender))
    else:
        sender = sender[0]
    # only this line was changed
    if not self.receivers or app.config['TESTING']:
        return []
    else:
        return [(receiver, receiver(sender, **kwargs))
                for receiver in self.receivers_for(sender)]
                
Signal.send = new_send

event_signals = Namespace
# and so on ....

That’s all for now. Have some fun signaling 😉 .

 

Open Source Developer Guide and Best Practices at FOSSASIA

I would request you to please guide me as to how can I collaborate with you and also how can I contribute effectively to the organization.

At times I might get up to 20 private mails per day about “How to contribute to Open Source”. Usually I will direct developers to our mailing list or chat channels if they are asking about a specific project. But, how do contributions work at FOSSASIA? How can new developers join projects effectively? We have tried many different ways and spent a lot of time communicating with newcomers, many of them new to Git and Open Source development.

Over the years we have gotten better at helping new developers, designers and other contributors to join up. We have more than 1300 registered developers in our GitHub organization today. Not all of them can contribute every day, but we do have thousands of commits every year.

So, how are we able to scale up? I believe one reason are our Best Practices. We didn’t have a document “FOSSASIA Best Practices” yet, but in our daily work we have established excellent (mostly unwritten) best practices, that I would like to share in a concise form here now as a reference for new developers.

Happy to get your feedback and comments.

Development Best Practices at FOSSASIA

Culture and Communication

  • Please adapt your language to non-native English speakers and be super friendly. Remember we are an international community with contributors mainly from Asia and Europe. We are not used to swearing and will mostly understand words literally. At all times ensure your tone stays appropriate and friendly in the FOSSASIA community.
  • Stay modest. Sometimes newcomers already have an amazing knowledge in some areas. Still remember, it is no reason to be arrogant. Even the best developer does not know everything.
  • Be nice and welcoming. Why not add “please” in an issue or a comment “Thank you” in a pull request if someone did a good job? Show your appreciation for the good work of your co-developers.
  • If you are involved in a topic you don’t understand yet, try to learn yourself as much as possible from public channels (wikipedia, stackoverflow) but also do not hesitate to ask questions to other developers.

Communication Channels

Every project at FOSSASIA has its own channels. Many projects use Gitter, some Slack or IRC. Usually you will find information of the main communication channels of a project in the Readme.md.

While we are a community of Open Source and Free Software developers we still reserve our right to use whatever tools we deem necessary to help us to achieve our goal of developing the best possible Open Technologies – software and hardware. It is one step at a time 🙂

Private and Public Chat or Issue Tracker

Chat is a great way to connect with other contributors, but not all contributors are there all the time (consider time difference and personal schedules) and they are not always available to chat. Chat tends to be unstructured and with lots of people in a room there are often a number of threads. Therefore chat is great for help on setup issues and things where you got stuck.

Do not use chat for feature requests and detailed discussions on issues. These things are best for the issue tracker, where people from different timezones can join and where a focused conversation on one specific topic can happen.

Some people try to overcome the unstructured chats by switching to private communication. This shuts out other contributors who might have similar issues. A result I often observed is also, that contributors will bring up arguments in discussions like “I have discussed this already with xyz privately and he agrees”. Other contributors have not seen this discussion if it has not been taken place in public and we haven’t seen the arguments. We don’t know if xyz really agrees or if it was misunderstood. Private conversations are not transparent. Surely, there are cases where private chat is needed, e.g. for specific deployment questions of projects, but whenever you talk about development, please switch to public chat or open an issue.

Feature Requests and Bug Reports

  • Some newcomers are not accustomed to issue trackers and might try to inform developers on the mailing list, chat or even write private emails about bugs and features, but the right place to do this is: The issue tracker of a project.
  • Any bug or feature, please open an issue in the issue tracker right away and indicate if you want to work on it yourself.
  • Please include all relevant information when you submit an issue and wherever possible a link, information about the code that has issues and a screenshot.
  • When you file a bug report on the issue tracker, make sure you add steps to reproduce it. Especially if that bug is some weird/rare one.

Join Development

  • Before you join development, please set up the project on your local machine, run it and go through the application completely. Press on any button you can find and see where it leads to. Explore. (Don’t worry. Nothing will happen to the app or to you due to the exploring. Only thing that will happen is, you’ll be more familiar with what is where and might even get some cool ideas on how to improve various aspects of the app.).
  • If you would like to work on an issue, drop in a comment at the issue. If it is already assigned to someone, but there is no sign of any work being done, please free to drop in a comment so that the issue can be assigned to you if the previous assignee has dropped it entirely.

Commits/Pull Requests

  • All pull requests need to be associated to an issue.
  • All PRs need to be assigned to the person working on it.
  • If an issue cannot be completed in less than a day, it should be broken up into multiple issues.
  • Make pull requests from your own forks (even if you have write rights to the repository, do not create new branches, develop on your own branches).
  • State the actual change or enhancement in the commit message of PRs (do not just state “Fixes issue #123”).
  • Add the issue number into the description (this helps to speed up reviews as reviewers can simply click to get more info in the issue itself).
  • Write clear meaningful git commit messages (Do read http://chris.beams.io/posts/git-commit/).
  • Match pull requests with issues and make sure your pull requests description contains GitHub’s special keyword references that automatically close the related issue when the pull request is merged. (More info at https://github.com/blog/1506-closing-issues-via-pull-requests).
  • When you make very minor changes to a pull request of yours (like for example fixing a failing travis build or some small style corrections or minor changes requested by reviewers) make sure you squash your commits afterwards so that you don’t have an absurd number of commits for a very small fix (Learn how to squash at https://davidwalsh.name/squash-commits-git).
  • Add a screenshot if you changed anything in the UI of a project. When you’re submitting a pull request for a UI-related issue, please add a screenshot of your change or a link to a deployment where it can be tested out along with your pull request. It makes it much easier for the reviewers and helps to speed up the process. You’ll also get reviews quicker.
  • Add a link to your deployment of the project, where reviewers can check out what you have changed (especially for smaller changes this is very helpful as the reviewer might not even need to set up the system itself and test it. Again this speeds up the review process a lot).
  • Always ensure CI and tests are successful.
  • Help to resolve merge conflicts (especially if there are several PRs at the same time, merge conflicts are common. Help the reviewers and solve merge conflicts to speed up the process.).
  • Merging Pull Requests should only happen if at least two contributors reviewed the PR and approved it.

Scope of Issues and Commits

  • Stay focused on the issue and its specifics: Sometimes it is tempting to do more changes in a pull request and simply add a nice little feature after mentioning it in the issue tracker. Please do not do this. Contributors will look at the title of issues usually to check if it is relevant for them. For example, if an issue is about changing a font, do not also change the color even if this seems like small change to you. Many projects have a design template and standard colors etc. that they want to achieve. So your changes might need to be discussed in a bigger setting even if they seem small to you. Same applies to many other areas.
  • Do only the changes in a pull request that are mentioned in the issue. Do not change anything else without ever mentioning it (remember match issues with pull requests).

Branch Policies

Most FOSSASIA Projects have:

  • a development branch (which is the working branch. Please commit to this branch.) and
  • a master branch (which is the stable branch).

Some projects also keep additional branches e.g.:

  • gh-pages for documentation purposes (often autogenerated from md-files in docs folder)
  • apk branches for Android apps (often autogenerated with travis).

Getting Started

  • Newcomers are sometimes afraid to make a pull request. Don’t be! It is the responsibility of reviewers to review them. And Git is a beautiful tool when it comes to reverting pull requests with errors.
  • In simple issues keep it simple and “simply” contribute, e.g. in an issue “change the color of the button from green to red”, there is no need to mention and ask “here is a screenshot where I changed the color to red. Should I make a PR now?”. Just make the pull request and wait for the feedback of the reviewer.
  • Take on responsibility early and help to review other contributions. Even though you do not have write access in a repository you can already help to review other commits.

Documentation

  • Please ensure you provide information about your code and the functioning of your app as part of every code contribution.
  • Add information on technologies and the code into the code itself and into documentation files e.g. into the Readme.md or /docs folder. Documentation is not a thing that should be done at the end after a few weeks or months of coding! Documentation is a continuous effort at every step of software development.
  • If you add new libraries or technologies add information about them into the Readme file.
  • If you implement a different design or change the css in a web project, please add information to the design specifications/template. If there are not any design specifications in the project yet, why not start them and add a section into the Readme.md to start with?
  • Always help to keep documentation up to date and make it easy for new contributors to join the project.

 

Thank you for helping to define many of the practices while working on the Open Event project to the developer team and for additional input and links to Niranjan Rajendran.

Links to Other Resources

The Mission Mars Challenge with NodeJS and Open Source Bot Framework Emulator

Commissioned under the top-secret space project, our first human team had set foot months ago. This mission on the red planet begun with the quest to establish civilization by creating our first outpost on an extraterrestrial body. Not so long ago, the mission control lost contact with the crew, and we are gathering the best of mankind to help save this mission.

In this rescue mission, you will learn to create a bot using an open source framework and tools. You will be given access to our code repositories and other technical resources. We have 3 mission and 2 code challenge to solve in order to bring the Mars mission back on track.

We need you! Be the first to crack the problems and rescue the compromised mission! Your bounty awaits! Receive your mission briefing at the control centre after checking-in at the FOSS Asia Summit!

How to enter:

  1. Join us on March 18 at Foss Asia Summit (Singapore Science Center), Tinker Lab (Hall E) at the following timeslots:3
    • 9:30
    • 11:30
    • 13:30
  1. Bring your own PC or load one from the mission control. We provide internet access at the lab room.
  2. Fill up the registration form and check in with the form at the Mission Control.
  3. Mission briefing will be provided, you will be given access to the github where you mission resources will be provided, and you can proceed to crack the challenges.
  4. Badge of honors to be earned and bounty awaits the team with the best-time!
  5. Winners to be announced at 17:30! Be there!

Installations needed:

  1. NodeJS (https://nodejs.org/en/)
  2. Any Code Editor (Visual Studio Code/Atom/Sublime Text etc.)
  3. Open Source Bot Framework Emulator (https://emulator.botframework.com/)

Apply for Your Free Stay during the FOSSASIA Summit 2017 with our 100 #OpenTechNights Program

The FOSSASIA Summit 2017 takes place from Friday March 17 – Sunday March 19 at the Science Centre Singapore. We are now inviting Open Source contributors to apply for a free stay in a Singapore hostel and a free ticket to the event. All you have to do is convince us, that you are an awesome Open Source contributor!

The details

Developers from all over the world are joining the FOSSASIA Summit. We want to connect established and new Open Tech contributors alike. Therefore FOSSASIA is supporting the Open Source community to join the event by offering 100 free nights stay at a hostel in the centre of Singapore and a free ticket to the event. All you have to do is to fill in the form with information that convinces us that you are an awesome contributor in the Open Source community.

The Process

Step 1: Please fill in our form here before February 17 (23:00 Singapore Time).

Step 2: We will get back to you at latest within 3 days after the deadline if you are selected. But, also we are choosing very convincing applicants on an ongoing basis. So, the earlier you apply the higher your chances to get a free stay might be.

Step 3: The selected applicants will need to confirm their itinerary and tickets before March 1st to re-assure their free stay in Singapore.

Expectations of Participants – Share what you learn

1. Please support volunteers, speakers and participants at the event. Let’s bring all this good spirit of sharing Open Technologies and learning together!

2. Help to reach out to participants who cannot join us at the event. For example make some tweets, share what you learn on social media, publish photos and put up blog posts about the summit.

Our Team

Our team of “100 #OpenTechNights” – Hong Phuc Dang, Mario Behling, and Roland Turner – is excited to meet you in Singapore!

Apply Now

Apply for a free stay with #FOSSASIA #OpenTechNights and participation at the FOSSASIA Summit 2017 now here!

More Information

More updates, tickets and information on speakers also on our #OpenEvent system: https://eventyay.com/e/45da88b7/

FOSSASIA Summit 2017 Singapore – Call for Speakers

The FOSSASIA OpenTechSummit is Asia’s leading Open Technology conference for developers, startups, and IT professionals. In 2017 the event will take place from March 17th – 19th at the Science Centre Singapore.

During three days, thousands of developers, technologists, scientists, entrepreneurs and artists get together to showcase latest technologies, communicate, exchange ideas, learn from each other, and collaborate. Topics range from information technology and Open Source software development to hardware and maker projects, open design tools, machine learning, DevOps, knowledge tools, and citizen science.

For our 2017 feature event we are looking for speaker submissions for the following tracks:

* Open Source Software
* Design, Art & Culture,
* Internet, Society & Politics,
* Hardware & Making,
* Health and Technology
* Science
* Kernel Track and
* Startup and Business Development

Apart from the conference program, the FOSSASIA Summit offers an exhibition space for company and project stands and areas for community assemblies, and developer meetings.

Submission Guidelines

Please propose your session as early as possible and include a description of your session proposal that is as complete as possible. The description is of particular importance for the selection. Once accepted, speakers will receive a code for a speakers ticket. Please indicate on the submissions form if you would like to apply for a sponsored community ticket.

Submission Link: 2017.fossasia.org/speaker-registration

Dates & deadlines

Please send us your proposal as soon as possible via the FOSSASIA Summit speaker registration.

December 20th, 2016: Deadline for submissions
January 18th, 2017: Notification of acceptance
March 17th – 19th, 2017: FOSSASIA OpenTechSummit

Sessions and Tracks

Talks and Workshops
Talk slots are 20 minutes long plus 5-10 minutes for questions and answers. You can also sign up for either a 1-hour long or a 2-hours workshop. Longer sessions are possible in principle. Please tell us the proposed length of your session at the time of submission.

Lightning talks
You have some interesting ideas but do not want to submit a full talk? We suggest you go for a lightning talk which is a 5 minutes slot to present your idea or project. You are welcome to continue the discussion in break out areas. There are tables and chairs to serve your get-togethers.

Stands and assemblies
We offer spaces in our exhibition area for companies, community projects, installations, workshops, team gatherings and other fun activities. We are curious to know what you would like to make, bring or show. Please add details in the submission form.

Developer Rooms/Track Hosts
Get in touch early if you plan to organize a developer room at the event. FOSSASIA is also looking for team members who are interested to co-host and moderate tracks. Please sign up to become a host here.

Publication

Audio and video recordings of the lectures will be published in various formats under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. This license allows commercial use by media institutions as part of their reporting. If you do not wish for material from your lecture to be published or streamed, please let us know in your submission.

Sponsorship & Contact

If you would like to sponsor FOSSASIA or have any questions, please contact us via [email protected]

Links

FOSSASIA Summit 2017: 2017.fossasia.org

FOSSASIA Summit 2016 Event: Wrap-Up

FOSSASIA Photos: flickr.com/photos/fossasia/

FOSSASIA Videos: Youtube FOSSASIA

FOSSASIA on Twitter: twitter.com/fossasia

FOSSASIA Coding Contest: codeheat.org

PayPal Express Checkout in Python

As per the PayPal documentation …

Express Checkout is a fast, easy way for buyers to pay with PayPal. Express Checkout eliminates one of the major causes of checkout abandonment by giving buyers all the transaction details at once, including order details, shipping options, insurance choices, and tax totals.

The basic steps for using express checkout to receive one-time payments are:

  1. Getting the PayPal API credentials.
  2. Making a request to the API with the transaction details to get a token
  3. Using the token to send the users to the PayPal payment page
  4. Capturing the payment and charging the user after the user completes the payment at PayPal.

We will be using PayPal’s Classic NVP (Name-value pair) API for implementing this.

Getting PayPal API Credentials

To begin with, we’ll need API Credentials.
We’ll be using the Signature API credentials which consists of

  • API Username
  • API Password
  • Signature

To obtain these, you can follow the steps at Creating and managing NVP/SOAP API credentials – PayPal Developer.

You’ll be getting two sets of credentials. Sandbox and Live. We’ll just stick to the Sandbox for now.

Now, we need sandbox test accounts for making and receiving payments. Head over to Creating Sandbox Test Accounts – PayPal Developer and create two sandbox test accounts. One would be the facilitator and one would be the buyer.

PayPal NVP Servers

All the API actions will take place by making a request to the PayPal server. PayPal has 4 different NVP servers for 4 different purposes.

  1. https://api-3t.sandbox.paypal.com/nvp – Sandbox “testing” server for use with API signature credentials.
  2. https://api-3t.paypal.com/nvp– PayPal “live” production server for use with API signature credentials.
  3. https://api.sandbox.paypal.com/nvp – Sandbox “testing” server for use with API certificate credentials.
  4. https://api.paypal.com/nvp – PayPal “live” production server for use with API certificate credentials.

We’ll be using the Sandbox “testing” server for use with API signature credentials.

Creating a transaction and obtaining the token

To create a transaction, we’ll need to make a request with all the transaction details. We can use Python requests library to easily make the requests. All requests are POST.

We’ll be calling the SetExpressCheckout method of the NVP API to obtain the token.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'SetExpressCheckout',
    'VERSION': 93,
    'PAYMENTREQUEST_0_PAYMENTACTION': 'SALE',
    'PAYMENTREQUEST_0_AMT': 100,
    'PAYMENTREQUEST_0_CURRENCYCODE': 'USD',
    'RETURNURL': 'http://localhost:5000/paypal/return/',
    'CANCELURL': 'http://localhost:5000/paypal/cancel/'
}
response = requests.post('https://api-3t.sandbox.paypal.com/nvp', data=data)  
token = dict(urlparse.parse_qsl(response.text))['TOKEN']

Here,

  • USER represents your Sandbox API Username.
  • PWD represents your Sanbox API Password.
  • SIGNATURE represents your Sandbox Signature.
  • SUBJECT represents the facilitator’s email ID.
  • PAYMENTREQUEST_0_AMT is the total transaction amount.
  • PAYMENTREQUEST_0_CURRENCYCODE is the 3 digit ISO 4217 Currency code.
  • RETURNURL is where the user will be sent to after the transaction
  • CANCELURL is where the user will be sent to if he/she cancels the transaction.

A URL-Encoded, Name-value pair response would be obtained. We can decode that into a dict by using Python’s urlparse modules.

From the response, we’re extracting the TOKEN which we will use to generate the payment URL for the user.

This token has to be retained since we’ll be using it in further steps of the process.

Redirecting the user to PayPal for Approval

With the token we obtained, we can form the payment URL.

https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_express-checkout&token=<TOKEN>

We’ll have to send the user to that URL. Once the user completes the transaction at PayPal, he/she will be returned to the RETURNURL where we’ll further process the transaction.

Obtaining approved payment details and capturing the payment

Once the user completes the transaction and gets redirected back to RETURNURL, we’ll have to obtain the confirmed payment details from PayPal. For that we can again use the token ID that we obtained before.

We’ll now be making a request to the GetExpressCheckoutDetails method of the API.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'GetExpressCheckoutDetails',
    'VERSION': 93,
    'TOKEN': TOKEN
}

response = requests.post('https://api-3t.sandbox.paypal.com/nvp', data=data)  
result = dict(urlparse.parse_qsl(response.text))  
payerID = result['PAYERID']

A URL-Encoded, Name-value pair response would be obtained. We can decode that into a dict by using Python’s urlparse modules.

This will provide us with information about the transaction such as transaction time, transaction amount, charges, transaction mode, etc.

But, we’re more interested in the PAYERID which we’ll need to capture/collect the payment. The money is not transferred to the facilitators account until it is captured/collected. So, be sure to collect it.

To collect it, we’ll be making another request to the DoExpressCheckoutPaymentmethod of the API using the token and the PAYERID.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'DoExpressCheckoutPayment',
    'VERSION': 93,
    'TOKEN': TOKEN,
    'PAYERID': payerID,
    'PAYMENTREQUEST_0_PAYMENTACTION': 'SALE',
    'PAYMENTREQUEST_0_AMT': 100,
    'PAYMENTREQUEST_0_CURRENCYCODE': 'USD',
}

response = requests.post('https://api-3t.sandbox.paypal.com/nvp', data=data)  
result = dict(urlparse.parse_qsl(response.text))  
status = result['ACK']

All the details have to be the same as the ones provided while obtaining the token. Once we make the request, we’ll again get a URL-Encoded, Name-value pair response. We can decode that into a dict by using Python’s urlparsemodules.

From the response, ACK (Acknowledgement status) will provide us with the status of the payment.

  • Success — A successful operation.
  • SuccessWithWarning — A successful operation; however, there are messages returned in the response that you should examine.
  • Failure — The operation failed; the response also contains one or more error messages explaining the failure.
  • FailureWithWarning — The operation failed and there are messages returned in the response that you should examine.

And, we have completed the PayPal transaction flow for Express Checkout. These are just the basics and might miss a few stuff. I suggest you go through the following links too for a better understanding of everything:

For Reference:
  1. PayPal Name-Value Pair API Basics – PayPal Developer
  2. How to Create One-Time Payments Using Express Checkout – PayPal Developer

Writing linux commands

sTeam includes a number of tools namely steam-shell, debug, edit, import and export from git. These tools are only accessible from the tools folder in the sTeam installation. My task is to make a steam command for linux so that all these tools can be accessible from anywhere just like any other linux application.

Problem: https://github.com/societyserver/sTeam/issues/126

The command structure decided is that we have a global sTeam command and sub commands for each of the tools. This structure can be though of as similar to the structure of the git command. The central git command has many sub commands like branch, checkout, reset, merge, etc. I started with making a pike executable and then changing the installation files to copy this executable to /usr/bin. Now this pike executable becomes accessible from anywhere in the system and acts like a linux command.

https://github.com/societyserver/sTeam/pull/127

I wrote the main function to accept the command line arguments and passed them to a function named resolveParam. In this function I am using an if-else structure to segregate the different sub commands. For shell and debug I started a child process to execute the file for these tools present in /usr/local/lib/steam/tools. The following code snippet gives an example.

void resolveParam(int argc,array(string) argv)
{
if(argv[1]=="shell")
{
array command =({"/usr/local/lib/steam/tools/steam-shell.pike"});
object shell = Process.create_process(command, (["stdin":Stdio.stdin,"stdout":Stdio.stdout,"stderr":Stdio.stderr]));
shell->wait();
}
}

I had some problem when I had to accept more arguments than just the sub command. Foe example the edit command works as ./edit <filename1> <filename2> <filename3>… Using the global command it becomes steam edit <filename1> <filename2> <filename3>… I had to pass all the rest of the arguments to the edit scripts. I had to add them in the command array. The first solution would be to loop through the arguments array and add them all, however pike has a very easy and elegant way of doing it in one sentence.

array command = ({"/usr/local/lib/steam/tools/edit.pike"})+argv[2..];

This gets our global command up and running. Rest of the time I spend on resolving merge conflicts while merging all my previous Pull Requests.

https://github.com/Siddhant085/sTeam/tree/gsoc2016

linux command
output showing the use of steam command

Building a logger interface for FlightGear using Python: Part One

{ Repost from my personal blog @ https://blog.codezero.xyz/python-logger-interface-for-flightgear-part-one/ }

The FlightGear flight simulator is an open-source, multi-platform, cooperative flight simulator developed as a part of the FlightGear project. I have been using this Flight simulator for a year for Virtual Flight testing, running simulations and measuring flight parameters during various types of maneuvers. I have noticed that, logging the data, (figuring out how to log in the first place) has been quite difficult for users with less technical knowledge in such softwares.

Also, the Property Tree of FlightGear is pretty extensive making it difficult to properly traverse the huge tree to get the parameters that are actually required.

That’s when I got the idea of making a simple, easy to use, user friendly logging interface for FlightGear. I gave it a name ‘FlightGear Command Center’:wink: and the project was born at github.com/niranjan94/flightgear-cc.

After 44 commits, this is what I have now.

1. A simple dashboard to connect to FlightGear, open FlightGear with a default plane, Getting individual parameter values or to log a lot of parameters continuously

2. An interface to choose the parameters to log and the interval

  1. The User interface is a web application written in HTML/javascript.
  2. The Web application communicates with a python bridge using WebSockets.
  3. The python bridge communicates with FlightGear via telnet.
  4. The data is logged to a csv file continuously (until the user presses stop) by the bridge once the web application requests it.
The interface with FlightGear

FlightGear has an internal “telnet” command server which provides us “remote shell” into the running FlightGear process which we can exploit to interactively view or modify any property/variable of the simulation.

FlightGear can be instructed to start the server and listen for commands by passing the --telnet=socket,out,60,localhost,5555,udp command line argument while starting FlightGear. (The argument is of format --telnet=medium,direction,speed_in_hertz,localhost,PORT,style.)

Communication with that server can be done using any simple telnet interface. But FlightGear also provides us with a small wrapper class that makes retrieving and setting properties using the telnet server even more easier.

The wrapper can be obtained from the official repository atsourceforge.net/p/flightgear/flightgear/ci/master/tree/scripts/python/FlightGear.py

Using the wrapper is straightforward. Initialize an instance of the class with the hostname and port. The class will then make a connection to the telnet server.

from FlightGear import FlightGear

flightgear_server = 'localhost'  
flightgear_server_port = 5555  
fg = FlightGear(flightgear_server, flightgear_server_port)

The wrapper makes use of python’s magic methods __setitem__ and __getitem__ to make it easy for us to read or manipulate the property tree.

For example, getting the current altitude of the airplane is as easy as

print fg['/position[0]/altitude-ft']

and setting the altitude is as simple as

fg['/position[0]/altitude-ft'] = 345.2

But the important thing here is, knowing the path to the data you want in the FlightGear property tree. Most of the commonly used properties are available over at Aircraft properties reference – FlightGear Wiki.

Now that we have basic interface between python and FlightGear in place, the next step would be to setup a link between the user interface (a small web app) and the python bridge. We would be using WebSockets for that so as to have a Real-time and an always on link to the bridge which would enable us to in turn communicate with FlightGear in realtime.

We need a WebSocket server in place. So, I used the SimpleWebSocketServer.pyclass from github.com/dpallot/simple-websocket-server.

A websocket server can be created by,

from SimpleWebSocketServer import SimpleWebSocketServer, WebSocket

hostname = 'localhost'  
websocket_server_port = 8888

class SocketHandler(WebSocket):

    def handleMessage(self):
        # print the message when received 
        print self.data

    def handleConnected(self):
        print self.address, 'connected'

    def handleClose(self):
        print self.address, 'closed'

server = SimpleWebSocketServer(hostname, websocket_server_port, SocketHandler)  
server.serveforever()
  • handleMessage is called whenever a client sends a message to the server
  • handleConnected is called when a new client connects to the server
  • handleClose is called when a client disconnects from the server

A message can be sent to the clients by using the sendMessage method from within the SocketHandler.

class SocketHandler(WebSocket):

    def handleMessage(self):
        # send a hello whenever a message is received  
        print self.data
        self.sendMessage('Hello')

    def handleConnected(self):
        print self.address, 'connected'

    def handleClose(self):
        print self.address, 'closed'

We now have a WebSocket server in place. Now the web app can easily talk to this server using javascript websockets API. Which would be continued in upcoming blog articles.