Itamar Weiss @itamarthoughts-blog - Tumblr Blog

Broadcasting an OP_RETURN transaction on the Bitcoin blockchain using bitcoinjs-lib

The Bitcoin protocol allows adding metadata to Bitcoin transactions. This is done by adding another output with an OP_RETURN operator. The OP_RETURN operator signals the Bitcoin nodes that this output is not vital for Bitcoin transactions and will never be spent, so that they aren’t obligated to store it.

The steps for putting a transaction containing meta data are as follows:

Get a Bitcoin address with a positive balance

Create an output Bitcoin address that will receive the transaction

Build the transaction

Broadcast the transaction to the Bitcoin network

How much data can you put on each transaction?

Every transaction can have up to one OP_RETURN output according to the Bitcoin protocol. Each OP_RETURN output can contain up to 80 bytes of data, which is equivalent to 80 ASCII characters or 160 hexadecimal symbols.

Step 1 - Get a bitcoin address with a positive balance

If you already have a bitcoin address with a positive balance, your can skip to Step 2. If not, you can first create a new key:

var inputKey = bitcoin.ECKey.makeRandom(); //print your private key (in WIF format) console.log(key.toWIF()); //print your key's public address console.log(key.pub.getAddress().toString());

You can now go ahead and send some satoshis to this address from your Bitcoin wallet. You can use a Bitcoin adress QR code generator to simplify the process.

Step 2- Create an output address

You can repeat the steps from above to create another key that will server as the ouput of our transaction

Step 3 - Building the transaction

var bitcoin = require ('bitcoinjs-lib'); var tx = new bitcoin.TransactionBuilder(); var transactionId, //a transaction that has the unspent output unspentOutputId, //the serial id of the unspent output in the transaction inputKey, //the key that corresponds to the unspent output address outputKey,//the key that corresponds to the recipient of the transaction amount; //the amount to be transferred - should be the entire unspent output minus a reasonable fee //Creating the OP_RETURN script var data = new Buffer(”Your message here”); var dataScript = bitcoin.scripts.nullDataOutput(data); //Building the transaction tx.addInput(transaction_id, unused_output); tx.addOutput(dataScript, nspentOutputId); tx.addOutput(outputKey.pub.getAddress().toString(), amount); tx.sign(0, inputKey); //Printing the signed transaction console.log(tx.build().toHex());

Step 4 -Broadcasting the transaction

There are many ways to broadcast your transaction. For example, you could use your own bitcoind using the JSON-RPC API. But easiest, is to use an online service to post the transactions. We'll demonstrate how to use chain.com.

First, you'll need to sign up on chain.com and generate your API token. Then, you need to install the chain.com package from npm.

npm install -S chain-node

Then, in your code you can broadcast the transaction as follows:

Chain = require('chain-node'); chain = new Chain({ keyId: 'your_key', keySecret: 'your_secret', blockChain: 'bitcoin'}); chain.sendTransaction(tx.build().toHex(), function(err, res){ //do something with the repsonse });

If you have any questions, or need any help developing your Bitcoin application, contact me at weiss.itamar at gmail com.

#bitcoin #blockchain #bitcoinjs #op_return

Writing a debouncer service with Angular.js

Let's say that you would like to have an input field where each time the user changes the input, your app updates the url, and fetches the search results from the server.

The best user experience will be provided if you let the user finish typing, and show the results straight afterwards.

To do that, you can create a simple debouncer service, that will execute a function of your choice, after a certain time that the user hasn't typed anything.

$scope.$watch('searchInput', function(newVal, oldVal){ if (newVal===oldVal) return; debouncer('search', function(){doSearch(newVal);},500); });

Using the code above, you can call your search time everytime searchInput changes, but only 500ms after the user stopped typing, to provide a smoother, better user experience.

And here's my code for the debouncer service:

myApp.factory('debouncer', function($timeout){ var timeout = {}; return function(debouncer, cb, timeoutMs){ if (timeout[debouncer]){ $timeout.cancel(timeout[debouncer]); } timeout[debouncer] = $timeout(cb, timeoutMs); }; });

You can see a working example on: jsfiddle.net/itamarwe/cFECf/

#angular.js #search #debouncer

Raising a moral child - Key take-aways

Here is a short summary of the blog post "Raising a moral child".

Praise effort vs. ability? Praise effort!

Praise effort rather than ability: children develop a stronger work ethic and become more motivated.

A quarter to half of our propensity to be giving and caring is inherited. That's significant, but still leaves enough room for nurture.

Praise vs. rewards? Praise!

To reinforce caring as the right behavior, praise is more effective than rewards. Rewards run the risk of leading children to be kind only when a carrot is offered, whereas praise communicates that sharing is intrinsically worthwhile for its own sake.

Praise character vs. actions? Praise character!

Praising their character helps children internalize it as part of their identities. The children learn who they are from observing their own actions: I am a helpful person.

"Be a helper" was more effective than inviting children "to help". "Don't be a cheater" was more effective than "don't cheat".

Praising character is most effective around the age of 8, when children start to crystalize their identities.

Reacting to bad behavior

Shame vs. guilt: guilt!

Shame is the feeling that I am a bad person, whereas guilt is the feeling that I have done a bad thing. Shame is a negative judgment about the core self, which is devastating: Shame makes children feel small and worthless, and they respond either by lashing out at the target or escaping the situation altogether. In contrast, guilt is a negative judgment about an action, which can be repaired by good behavior. When children feel guilt, they tend to experience remorse and regret, empathize with the person they have harmed, and aim to make it right.

If we want our children to care about others, we need to teach them to feel guilt rather than shame when they misbehave.

Expressing disappointment and explaining

The most effective response to bad behavior is to express disappointment. Parents raise caring children by expressing disappointment and explaining why the behavior was wrong, how it affected others, and how they can rectify the situation. This enables children to develop standards for judging their actions, feelings of empathy and responsibility for others, and a sense of moral identity, which are conducive to becoming a helpful person.

Teaching by example

Children learn by action. Actions speak louder than words. You need to act as a role model to be one.

The most powerful effect is by teaching by example and not talking about it.

It's not their job to get convinced, it's your job to convince them.

Parsley is a dead simple javascript form validation, powerful and UX aware

I've been looking for a good front end form validation for a long time. Parsely.js seems like a complete and elegant solution.

#parsely.js #front-end

A cookbook for Coffescript. Containing recipes for common problems and useful design patterns.

#coffeescript #design patterns

Switches for radio buttons and checkboxes

A nice project for creating great looking switches with Bootstrap.

#boostrap

Error handling in node.js express

What are the best practices for handling errors in Express?

How should they be bubbled up?

Express suggests the following. In the "Examples" directory in its github repository we can find the "error-pages" example.

app.use(app.router); // Since this is the last non-error-handling // middleware use()d, we assume 404, as nothing else // responded. // $ curl http://localhost:3000/notfound // $ curl http://localhost:3000/notfound -H "Accept: application/json" // $ curl http://localhost:3000/notfound -H "Accept: text/plain" app.use(function(req, res, next){ res.status(404); // respond with html page if (req.accepts('html')) { res.render('404', { url: req.url }); return; } // respond with json if (req.accepts('json')) { res.send({ error: 'Not found' }); return; } // default to plain-text. send() res.type('txt').send('Not found'); }); // error-handling middleware, take the same form // as regular middleware, however they require an // arity of 4, aka the signature (err, req, res, next). // when connect has an error, it will invoke ONLY error-handling // middleware. // If we were to next() here any remaining non-error-handling // middleware would then be executed, or if we next(err) to // continue passing the error, only error-handling middleware // would remain being executed, however here // we simply respond with an error page. app.use(function(err, req, res, next){ // we may use properties of the error object // here and next(err) appropriately, or if // we possibly recovered from the error, simply next(). res.status(err.status || 500); res.render('500', { error: err }); });

What actually happens here is the following:

After the router middleware is called app.use(app.router) We call the 404 error handler

If the requested url didn't hit any route we defined in the app, the error handler will be called and will return a 404 error page

For any other error in the application we should create a new error, and call next(err)

If we want to set the error code of the error (for example for 403 not found errors), we should set the 'status' of the error (eg err.status=403) before sending it to next

And to be able to test the pages, we can add the following code:

app.get('/404', function(req, res, next){ // trigger a 404 since no other middleware // will match /404 after this one, and we're not // responding here next(); }); app.get('/403', function(req, res, next){ // trigger a 403 error var err = new Error('not allowed!'); err.status = 403; next(err); }); app.get('/500', function(req, res, next){ // trigger a generic (500) error next(new Error('keyboard cat!')); });

#express #error handling #node.js

I'll be presenting in {{Soft-Shake}} 2013

I'm going to present serviceathome's dev stack and will be demonstrating the creation and deployment of a simple web app on Heroku.

#softshake

A great article about how Airbnb improved their search

How data powers search and location relevance at airbnb

#airbnb #search

Integrating Node.js, Mongoose and Elastic Search

I tried to integrate Elastic Search into my app which is based on a node.js and MongoDB infrastructure.

I use Mongoose as a framework to manage my models with MongoDb.

As a framework to work with Elastic Search I chose Mongoosastic, which provides a plugin for working with Elastic Search "out-of-the-box" if you use Mongoose.

Or at least that's what I thought. Apparently, my application wasn't so simple to integrate....

What I was looking for

What I needed is a way to search based on both a parent document and a child document.

For example, let's assume that we have a collection of users, and each user has an array of comments.

I wanted to be able to search according to the name of the user, and the content of the comments.

Setting a custom analyzer

To be continued....

#node.js #mongoose #mongodb #elasticsearch #mongoosastic

Hybrid Democracy

I don't know what about you guys, but I am excited about the possibilities that the Pirate parties all over the world are offering. Don't get me wrong, it's not that I can relate to everything that they offer, but that some of the principals of the Pirate parties inspired me to think about the future of democracy.

Democracy Is Broken

Current democratic system all over the world are fundamentally broken, or at least, not as great as they can be. I don't know if the democratic systems worked better in the past and now they are being exploited, or that they just look pale in the light of the future opportunities.

Some of the things that bother me with modern democracy:

1. It doesn't seem that representatives work for the public anymore. They work for powerful corporates and lobbies, for themselves and for their friends, much more than they work for us.

2. There is no follow up. Representatives say whatever we like to hear on the election day, but are not obliged to hold that line during their term.

3. In order to keep their position, politicians have to spend at least half of their time in getting re-elected. Not to mention not telling their real opinions, hiding data, using manipulative tricks (if not lying) in order to keep everyone happy.

3. Why should my views about the economy, foreign policy, education, state and religion be tied up? Why can we only vote for parties that represent a bundle of independent issues? There definitely cannot be a party that accurately represents my opinions in all of these matters at the same time. Why should I do the trade-off between a more social economy and a more strict foreign policy?

4. There is no transparency. When we were kids, we were told to read newspapers so that we know what is happening in the world around us. I don't think that kids should be given this advice anymore. I read newspapers and I have no clue what is happening around me. It seems that the media is so shallow, yellow and manipulated, that you cannot really know what to believe in anymore. And really, we don't have the most basic data about the most burning issues, and most of the times we don't even know what are our representatives are thinking about these issues and how they are handling them.

5. When there is no data, there cannot be a data-driven approach. Data driven approaches changed the world. When you have data, you can make much better decisions. Since the data today is missing, both the public and the representatives lack the tools to make better decisions.

6. Discussion is shallow. In the lack of data, the level of discussion is shallow and no real progress can be made. Knowing the facts about the world and the opinions of our representatives about them allows a deep discussion that can have fruitful results.

7. Short term thinking. Since the politicians' main concern is to get re-elected, mostly decisions with short-term outcomes are being taken.

Recent Breakthroughs

Even if the current structure of democracy was great back in the day, a few amazing breakthroughs happened in recent times that can very much be adopted. The rise of open source and crowd sourced communities around us demonstrate the power of these tools.

Wikipedia has just made traditional encyclopedias obsolete and it is more detailed, accurate, unbiased and concurrent than any other encyclopedia has ever been or will ever be. It is a great demonstration of how a crowd can collaborate and reach an agreement through discussion, and can be curated to be much more powerful than any single person or organization.

Open source projects rule today's web development tools. There is no website that isn't using open sourced programs. Open source programs are more stable, elegant and powerful than any other program, since they are developed, tested, fixed and updated by thousands of people. Open source communities developed methods and tools so that thousands of people can collaborate in order to create better software.

And in general, the internet has allowed people to securely collaborate from all 4 corners of the earth.

What I Suggest

There are definitely things that need to be done: Transparency should be dramatically increased, the public should be more directly involved in the decision making so that their fragmented opinions about independent matters are well represented, the representatives should represent the public and should stop wasting their time in getting re-elected, long-term goals should get back on the table, decision making should be data driven.

How it can be done?

Creating a party, with no agenda. Everyone with a voting right can become a member. The elected representatives of this party directly represent their voters. Every vote goes through the party before being voted, and the representatives split their votes according to the internal vote. On top of voting according to the internal vote, the main responsibilities of the representatives are to represent the voice of the public (the party members) by curating the different public opinions on different matters, increasing the two-way transparency by providing the public with data and access to the parliament and government, by providing the parliament and the government data about the public opinion and by collecting relevant data from all over the world to allow everyone in the public, the parliament and government to make better data driven decisions for higher short term and long term benefits.

In my vision, I see the party's representatives as intelligent analysts, "spies" of the public, working for no one else but the public, working to expose everything that is happening in the government and in the parliament to the public, collecting relevant unbiased data from any available source, and representing the various public opinions on various matters in the parliament and in the government.

Really? No agenda?

Yes and no. The method is the agenda, but there is no political agenda. Exactly like democracy is not an agenda but a method. It is a new form of democracy. Nevertheless, exactly like democracy is not just the voting system, but a larger system of values, such as freedom of speech, pluralism, peaceful conflict resolution, human rights etc, the party should have a set of non political values to complement the new method.

Such values are, for instance: reaching agreement through open discussion, data driven decision making, supervision through transparency.

#hybrid-democracy #pirate

If you don’t go forward, you go backwards.

#quotes

Browser the profiles of great service providers. Book them from wherever you are.

My current main project. A trusted marketplace for home service - cleaning, babysitting, tutoring, fitness (Yoga, Pilates etc), wellness (massage), beauty and more.

Find Kosher stores, Kosher restaurants, synagogues and Jewish memorial sites and create a custom map for planning your trip to the world's most popular cities. We also help you find a local tour guide.

A side project I was working on this summer. A website to help you find Kosher shops and restaurants and Jewish related attractions in Europe. Shows all locations on a map to help you better plan your trip.

Trending Blogs

Recently Viewed Blogs

Itamar Weiss