Content tagged EN

Learn You a Haskell for Great Good

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This is the first book on Haskell, that really made me want to read it. I had it with me as an e-book on my vacations. I couldn't stop reading it before I finished. It is a very good introduction to the basics of the Haskell programming language. It even contains an understandable explanation of the infamous monads. (Side note: they are a very simple concept, and you shouldn't fear them.)

For me this book was the right amount of introduction to get me started. Everything else I think I will be able to learn while using the language.

The book is available in print at your preferred book shop, or can be read online and free of charge.

Links to resources

Getting Safari Books Online

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I like the books from O'Reilly. For many years I've seen the ad on the backside advertising Safari. Sure, I checked out what this is, but I wasn't really interested to have a digital copy for a limited amount of time. I already had the print version.

I love to read real books made of paper. I use highlighters and add notes, while reading. I make the book mine. And after finishing the book, I can place it on my bookshelf, to show the books I like to others. This doesn't work with my Tolino e-book reader. While I have this device, I still buy most books as a paper copy.

Some days ago, I heard of Safari again on a podcast. I thought, that at least I should check it out. It's not only O'Reilly books anymore and it includes videos and other podcasts as well. There is a free 10 days trial, so I did not have to invest more than some of my time.

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Reactive Programming with RxJava

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RxJava is an implementation of “Reactive Extensions” (Rx) in Java. But what is this? Originally Rx are an implementation of Microsoft to address the increasing complexity of software. It is a model to build large scale asynchronous service architectures.

Another company that has to be mentioned is Netflix: they implemented the Rx in Java which resulted in RxJava.

On the programming side Rx looks very similar to how streams (java.util.stream.Stream) work. The main difference in my opinion is that streams are pull and lazy. They produce only as much data as someone is reading from them. RxJava on the other side is more push style. The source of data is pushing events through a pipe of operators similar to what you know from streams (filter(), map(), and so on) to the sink. And as I know from this book, Java streams are the wrong tool to parallelize anything that is not CPU bound–like network requests. There reason for this is, that (parallel) streams are executed on a thread pool that is shared with several other features of Java. This thread pools is limited to have only that many workers as the system has CPU cores. Therefore this pool gets exhausted very soon, when threads in it get blocked by I/O operations. Any thread waiting for an I/O operation effectively results in a processor core not used by your program.

RxJava on the other hand is not limited to a fixed thread pool. Any source (Observable) and sink (Subscriber) of data can be bound declaratively to user defined Schedulers. As well as Rx favours a model in which I/O operations are done asynchronously and non-blocking. Therefore resulting in a need for much fewer threads. In a traditional model of using one thread per network connection, threads become very soon the first thing that limits scalability.

What is really great about this book

The best part of this book for me were the reflections on Relational Database Access in chapter 5. While as a developer you might be tempted to convert everything to the reactive model, this part of the book shows where it doesn't make sense to do so.

By converting the access to your relational database to an asynchronous model you won't gain anything. Whatever you are doing on the client side, let's say for example your PostgreSQL will run all of your concurrent requests in different processes. This results in a noticeable limit on the number of parallel queries you're able to run. You cannot lift this limit by becoming asynchronous on the client side.

Links to the book

ZooKeeper, Distributed Process Coordination

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ZooKeeper is a component that facilitates building distributed applications. It is:

The data managed by ZooKeeper is presented in a file system like manner with directories and files whose names get separated by slashes (/). The difference to a file system is, that you can store information in the directories as well. Or seen differently: directories are files at the same time. Based on this simple abstraction, users of ZooKeeper can implement things like leader election in a cluster of software instances.

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Microservice Architecture, anligning principles, practices, and culture

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To stay on the right track with microservices, I wanted to revisit the philosophy and organizational recomendations on how to do them right. After reading Building Microservices in april this year, I got Microservice Architecture, aligning principles, practices, and culture by Irakli Nadareishvili et al.; O'Reilly Media, Inc., 2016.

The book can be read on one week-end as the content is very well condensed to 118 pages.

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Developing Web Components, UI from JQuery to Polymer

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It's hard to find sources how to do front-end micro-services in a single page application (SPA). Having a single front-end that faces the user makes it hard to impossible to exploid the full power of going micro-services in the back-end. For every new function you cannot just deploy the corresponding service, but you have the dependency to update and redeploy the service as well.

So I was looking around how to go micro in an SPA. One of the ideas I found on the web was to do so using web components. To evaluate this idea as someone working mainly on the backend I thought I should get some literature and bought the book Developing Web Components by Jarrod Overson and Jason Strimpel, O'Reilly Media, Inc., 2015.

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Locked-in by Google

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For several years now WhatsApp is spreading on the smart phones of my contacts. Of course my friends are asking me to install the software as well. But I hate using a proprietary service if there are open alternatives. This open and comprehensive alternative was and is Jabber respectively XMPP (two names for the same thing).

But this is nothing more then a protocol. Especially nothing anybody could use. What a Jabber user needs is software and a service provider. Until now my recommendation for both was Google Talk. The software perfectly integrated and pre-installed on every Android phone. An easy to use user interface, comprehensible to John Doe. Nothing made for freaks by nerds. And as an operator Google provided a rock solid service.

That was a smasher: you could get everything well co-ordinated from Google, you could chat with users of other providers, and you could even operate our own server if you wanted to. Real class!

With my denial of using a closed system and my continuing referral to free alternatives, I brought several contacts to Google Talk.

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History of Matthias Wimmer's PGP and GPG keys

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PGP-signed version of this history.

KeyID Fingerprint Date Expires (sign/encrypt) Status
70D6C898 CAEC A12D CE23 37A6 6DFD 17B0 7AC7 631D 70D6 C898 2006-08-10 2010-01-01/2010-01-01 This is my main GPG key since 2006-08-10.
C9CD24F7 85A0 801A 2392 424F 69AB 5A63 C6D6 197D C9CD 24F7 2003-03-06 2008-03-04/2008-03-04 Key in use for special purposes. Please don't use it for e-mail.
4E59C7E6 B0F5 9D8C 28A8 34B6 FDE1 410A 3D27 3DDA 4E59 C7E6 2003-01-21 2007-01-01/2006-01-01 Key still exists, but only used for migration-signing to new key anymore.
8D8B4A2E 6F81 B414 B8A1 1806 A333 A18E 0142 F366 8D8B 4A2E 2001-01-11 *** revoked *** Public and private key still exist, never used for e-mail/not used anymore
AA839AF9 85E8 0EE5 C852 363C FC19 BD5F 27FE 6356 AA83 9AF9 2000-03-06 *** revoked *** Public and private key still exist, but not used anymore.
034FDE2A EA16 DEA8 4146 12EE 3B56 68D8 0A70 794E 034F DE2A 1999-09-15 *** revoked *** Public and private key still exist.
55DB8129 AF 14 32 B5 69 38 30 6E 3A B8 13 8D 66 A8 66 AE 1999-04-27 never :-( Lost private key!
B3D1AF25 8C 79 81 AA ED 95 4D 0B 8F 53 09 52 9A 39 32 49 1998-05-25 *** revoked *** Public and private key still exist, revoked because e-mail address is not used anymore.
730BD791 ??? 1997-07-05 never Lost public key, private key still exists.
D9954A11 ??? 1996-10-23 never Lost public key, private key still exists.
3336E4E9 ??? 1996-07-24 never Shared key (for the sysops of my former mailbox), I am not the only one that has the private key. Public key lost.
8B674F75 DE 51 C1 7E E4 99 4B 9D 5B 76 06 B2 DF 00 64 F1 1996-07-18 *** revoked *** Public and private key still exist, revoked because e-mail address is not used anymore.

There exist some even older keys that I have never used in the internet and that only contain FidoNet addresses. These keys are completely lost. I neither have the public nor the private keys anymore.

Change history

2006-08-10: Marked key AA839AF9 as revoked, updated signing-expire-date for key 4E59C7E6, added new key 70D6C898
2003-12-04: Updated expiry information for 4e59c7e6

IMUnified - protocol

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In 2000, IM Unified announced to create a protocol that enables an instant messaging client to join different IM services. Founding members were MSN, Odigo, Yahoo! and others.

Since then I have not heard much of IMU. I don't even think that their IMIP protocol will ever be used really. But it does exist and e.g. the Yahoo! messenger client supports it. You only have to change some values in the Windows registry. Afterwards, you're client is able to join other IM services like Odigo with the Y! messenger.

For no other reason than to see how IMIP works I've dumped some IMIP sessions with a network sniffer. The IMIP protocol is very simple structured and looks a bit like SMTP or http.

All data is exchanged over a TCP/IP connection. The clients connects to port 11319 at the server. Firstly, it performs the login handshake and afterswards, it is exchanging messages, presences and other data. All data is exchanged in blocks.

All blocks have a structure of lines. Every line is finished by \r\n (carriage return, line feed). The first line contains the type of a block, the second line contains the size of the block (first two lines not counted). It is a decimal ASCII number containing the size in bytes. Starting at the third line, there are head lines, optionally followed by an empty line, optionally followed by a block body. If the body is empty, the empty line can be absent. (The Y! messenger is allways sending the empty line, the Odigo server isn't.)

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Unless otherwise credited all material Creative Commons License by Matthias Wimmer