As always – a commit!

Here’s a thing I struggled while doing previous commit – decoding command to something more structurized – according to docs it’s composed of command name and body – all coming in one binary. I had to get the name and body (if any)

It seems like you have to use ::binary-size for the first one, and just ::binary for the rest – I may be wrong thou and I will have to research that more in the future.

It’s slowly starting to be a mess – that’s why I refactored enconding a bit to make a use of pattern matching. Not it’s more “elixir style”. Still I feel the lack of the bigger picture – I guess rushing into it wasn’t as good idea as first though 😉 I will have to do some more research and maybe a post on a protocol – it will surely help me. For example – turns out that command will never have “more” frames incoming – as you can see in changes in code – now all command have “more” set as false (with is quite redundant).

Erlang Factory Lite Rome 2017 #1

Hello for the second (and last) part of EFL Rome2017 post! You can find previous one here

Music and Message Passing Concurrency by Joe Armstrong

Here goes the big name, Joe himself. While it may suggest a lot about music, it was more about messaging and integration. Joe showed how he could remotely control Sonic Pi. He was glad that there’s an other way to control a program “than clicking a bloody mouse!”.

He did that sending properly coded messages to UDP port. And here it all started. Joe is a big supporter of messaging based communication. API suposes a programming language, so it’s not a best way – you’re tied to programming language. As the main topic emerged once again – how to integrate and there are some programming languages better to do other things – so you’d naturally like to use them for specific purposes and not be stuck with one.

You should also treat specific parts/modules/apps like a black boxes – you know nothing (even the language used) except for how to communicate (using messages, of course 😉 ) – “the protocol only matters.”

  1. Pick transport (TCP/UDP)
  2. Pick encoding (XML/JSON/YAML/etc)
  3. Pick protocol description (RFC/UBF/etc)
Some combinations for you to pick from
With the Joe himself!

Joe picked OSC over TCP/UPD with some English to describe it. OSC is a very simple encoding – and it has “simplicity by design”, as Joe said, “if you can’t create complex data structures, the interface will be simple and easy to understand”.

“if you can’t create complex data structures, the interface will be simple and easy to understand”

Which is another way worth remebering. Complicated systems are easy – you just keep adding stuff. Simple systems are difficult to make.

I think thou – if one thing should be remembered from this talk it’s fact, that we should be able to understand the system by looking on the messages going in and out.

Adopting Elixir in a 10 Year Old Codebase by Michael Klishin

While it seems like adding Elixir to some Ruby ecosystem, it was actually using Elixir in Erlang project. They did a CLI tool in Elixir as a “check” with ~8k LOC, ~750 tests and 70 CL commands available.

I will just point out good:

  1. It’s more approachable than Erlang
  2. It’s a recriutment honeypot – easier to lure people into project
  3. Has decent standard lib
  4. Potentian contributors could have not contributed if it was in Erlang

And bad things he learned:

  1. Integration with is a pain
  2. Elixir/Erlang data type mismatches
  3. String vs Binary
  4. Some Elixir libs are a one man show ( 😉 )

Overall Michael feels like Elixir was worth adopting as sees a bright future for it – and you can utilize it even without agents, macros and sweet libs. He was even more optimistic for Elixir than for Erlang itself.

A Little Replica of the Internet in Elixir by Ju Liu

He describes himself as a Mad Scientist – and, boy, he is!

Basically it was a little trivia on the Internet and his attempt to do a small replica of it’s routing system using Elixir (and nerves). He had 2 RP3s connected, simulating North America and Europe with routing links. There’s a bit of how the Internet works and how it connects – he used that common knowledge to simulate it and it worked like a charm. There a code online if you want to look at it!

This is the Internet! Be careful not to break it!

The real show started when he took the router, connected third Rasp and added Asia – it all worked! It was a nice show for the Nerves project to show what you can do with them. Funny thing – the most problems, and the slowest part was HTML+JS frontend where all the arrows where hacked as separate CSS elements – so it crashed when connection number rose. Still, great project and you can look at it on github!

Embrace the Database with Ecto by Josh Branchaud

Basically it was how to use the Ecto and how to query the database. I really don’t know if it was the high temperature in the room, or it was just quite obvious to me – but I cannot say that I didn’t find anything at all – there was one statement that I won’t say if I find true or false – because it’s strengh is that it provokes some interesting conversations:

“The database should be the ultimate gatekeeper – it should validate the data coming in”

Monitoring and Pre-emptive support: The road to five nines on the Beam by Francesco Cesarini

It was a great talk with a lot of focusing on “no single point of failure” “we need at least 2 of everything”. He showed 2 types of monitoring usefulness – you can prevent failures, or do quick post-mortems. With monitoring you can prove your innocence in 1.5 minutes – without trying to replicate the bug and trying to debug. While there’s a lot to be said – he said so many cool stories I guess you have to go and give it a listen yourself – this one seems almost identical.

And this was it – it was a great experience and possibility to talk with those people was sometimes eye-opening.


As always – commit!

I really need to spend more time. Today I struggled a lot with bitstrings. And still didn’t find an answer for what I was looking for, but I created a map for command without redundant info. So no more flags, only command name, data and size.

After push thou I saw a better solution – I could do pattern match on functions, so I could eliminate switch. I get a lot of mess with all those maps. I think that rethinking/refactoring it should happen sooner than I initially thought.

Also “size” field seems a bit off. Additionally I don’t feel as comfortable enough with specification as I was expecting, so I guess I’ll spend some more time with it – this should also get me up to speed.

Erlang Factory Lite Rome 2017 #0

Week ago I went to Rome to take part in Erlang Factory Lite, and, as promised, here is blogpost about it (the first part)

Starting with venue – it was near the centre of the city, easy to get with decent views. While inside was quite small (not a lot of people were there as well), the outside…

What a place to take a break!


Sadly, there were no recordings, but from what I saw speakers had the same talks as in some future (and maybe past?) events, so not all is lost.

Pilgrim’s Progress to the Promised Land by Robert Virding

Opening talk by Erlang co-creator. It was a nice opening, showing learning Elixir as a pilgrimage. And it’s quite good analogy. You begin your journey influenced by some prophets. It’s important to validate their words – to decide if Elixir is the right tool for your job. Also the way of learning it is a bit like arriving to different interesting places.

Because of it’s similarity to Ruby you quickly arrive to “Village of Confusion” as things don’t seem to work they should. It’s not an OO language (Joe had different opinion here 😉 Erlang is the only OO language ).

Robert told us that people doing Erlang/Elixir are not scared of crashing things. And there are 3 ways of crashing things:

  1. Just crash
  2. Crash and clean – for example process holding database connection won’t close it if it dies
  3. Crash and restart – if process is critical to the system

Because of all this talking about crashing, you do a lot of upfront error handling – so you have it localized and easy.

“You have to accept that things go wrong it you want to build fault-tolerant systems” – Robert

Stepping into a new era: injecting Elixir in a Ruby app by Andrea Leopardi

This was the talk about replacing some parts of the existing Ruby + Python system with Elixir (and adding new ones with Elixir). This was quite full of examples (like issues going down significantly and performance going up), but I think that the most important thing is:

Prepare your system: Split it into services first, or at least one monolith service and one small (it’s a good start).

It’s the Type Theory Baby! by Michele Finelli

This was talk full with nice theory. Michele defined a formula something that is always true or false. If you depend on external (I/O, DB, etc) logical formulas are no longer eternal – so this describes functional programming.

Nice thingies:

  1. One thing to remember? Read this paper
  2. Basically wiki article around this talk
  3. Duck typing? No! It’s untyped and it’s fine!

Cook your distributed in memory KV store by Gianluca Padovani

Basically a explanation how Riak Core works with concrete idea to implement. It was with some demos how to make a distributed KV store. And it worked like charm 😉 I guess reading throu the code of this masterless cluster (nice idea btw) will be better than me describing it, but there one important quote

Always timeout!

I’ve covered 5 out of 9 talks, so there’s still material for next part, stay tuned!

Today I Learned #0

This is Today I Learned – some nice things I learned, too short to be valid blog post, but too important/interesting/etc to not be written down

While exposing classes to WCF service, you have to use [DataContract] (for class) and [DataMember] (for properties) attributes. Or do you?

Turns out that around 3.5 you don’t have to do it. If you provide class with no attributes it will work out of the box! Where’s the catch? There are two:

  1. You will lose some of features, like naming, being able to serialize private properties, declaring something as required. While some can be more useful than others in specific scenarios – just ask yourself – should you really send private data? 😉
  2. And this is important! If you dare to use [DataMember] on some properties – only those will be serialized.

OpenSettlersII #3

As always, commit to look at!

Today even smaller changes as I had little to no time, but at least moving slowly forward.

I added encoding of long frames. I did the same thing as in decoding, pattern match on flags and then construct proper binary data.

In tests file I added 2 tests for long frames and changed body: property in input to be binary as well. I think it’s starting to be a good time to introduce some struct for my frames, but I will worry about this later. I’m also not happy with return values – they should be more “elixiry”, so next step will be worrying about this (with some explanation what does it mean).

As I dislike post trailers – I’m going to Erlang Factory Lite tomorrow. I will try to write down as much as possible and make a interesting review next week, so stay tuned!

OpenSettlersII #2

Here’s a commit for you to look at!

I didn’t do much this week but progess is progress 🙂

I added the support for long frames. According documentation, long frame is defined by flag (Bit 1, “second one from right” must be 1). If the flag is set, size will be 8 octets, and body will be size octets. (So if size is 256, body will be 256 octets).

First lets look at tests. First change you can see is that I removed “reserved” from flags as it is not needed at all and obscured the data.
Next I renamed “command” key to “type” – as it reflects better what it is – it indicated the type of frame – if it is a command or message.
Next change (in decode) is that body is still in binary (inside << >>). I guess I will work on that later, but was needed in some changes.
I added 2 tests to correctly decode long frames, for both command and message. What’s important is :: size(64). It indicates the size of binary element. If not specified it will be default (8). What’s also important (and quite logical) size have to be divisible by 8.

Now onward to code itself. There’s only one public decode function, but it calls one of the private ones depending of the flag. There’s a pattern matching on long key, and binary data. As you can see here I used ::size accordingly.
What’s worth noting is if you want to match against unknown sized binary data you can use ::binary. Here I used it for body and for “rest” in main function – as before getting flags I don’t care about size and body.

And that’s it! Not a lot, but I learnt a bit when it comes to working with binary data in Elixir and made code a bit “better”.