Learning about computers
Arrays are an interesting case in Go, because you are usually encouraged to not use them and use slices instead. Arrays in Go have a few rules that make them feel counter intuitive but I’m going to start with the parts that look normal. You can declare an array and assign values to it like this:
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var a [3]int
a[0] = 5
a[1] = 11
a[2] = 22
I got asked this question in a code interview and I wanted to make sure my answer was good. Without the pressure of being in an interview I see the problem more clearly and the problem seems pretty easy now.
Lets look at the basics of adding in binary:
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0 1 1
+0 +0 +1
--- --- ---
0 1 10
A few weeks ago I started to learn Go and I wrote an introductory post. I’m going to continue where I left and explain how you can extend structures with methods and later how to use interfaces as arguments.
Go doesn’t have classes or objects as we know them. It uses structs instead to create object-like structures:
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type Animal struct {
color string
size float64
}
This looks very similar to an object but something very important is missing. You can declare properties like this, but not methods. How will our animal do stuff without methods?. Golang actually does have methods, but you have to attach them to the struct after it is created:
I’m having some problems with one of my hobby servers but this time instead of looking at the code to try to figure out what is happening, I decided to try to do it using only tcpdump. I was trying to start my server and I got this error message:
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failed to create GA auth provider: invalid character '\u003c' looking for beginning of value
The character ‘\u003c’ translates to <, so it seemed like the problem was that somewhere in my GA auth library I was getting what looked like an HTML instead of a JSON. The first thing I did was monitor the HTTP traffic using this command:
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tcpdump -c 20 -s 0 -i eth0 -A tcp port http
I have a hobby server that I’m deploying to a digital ocean droplet. I run this server as any other program and it does what it was programmed to do:
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./myserver
The problem is that this server is not perfect and I’m OK with that. Nevertheless, I don’t want to have to restart it manually every time it dies. For that reason I did some googling and found an easy way to restart my server if it unexpectedly dies:
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#!/usr/bin/env bash
until /home/tacos/myserver >> myserver.log 2>> myserver.error.log; do
echo "$(date -u) - Server crashed with exit code $?. Respawning..." >> runner.log
sleep 1
done
echo "$(date -u) - Server manually killed" >> runner.log
My company started using Go for some services and currently there is only one person that is familiar with the language. This means nobody is reviewing the code and nobody can contribute or fix stuff if it is necessary. To fix this, I have decided to learn Go.
The install steps might change depending on your operating system, so you are probably better reading the official documentation. I’m going to show the steps I followed to install on my system just as an example.
I’m running a Fedora machine so I downloaded the binary from the downloads page and extracted it to a folder. The next step is to add the Go binaries to the path. You can achieve this by adding two lines to ~/.bashrc:
On a previous post I wrote about how to write tests for polymer components. Now, I want to hook those tests into my automated test suite that runs for all commits in a repo. The problem is that we are kind of in a low budget so we don’t have a selenium grid we can connect to. What we do have is a machine where we have Jenkins installed. Because we run many different jobs in this machine, we usually use docker to keep our environment isolated.
The problem now is that we can’t run polymer tests in a headless browser like phantomjs, because it is not supported. We have to run our tests in a real browser like Chrome or Firefox. These browsers need a GUI to work which docker doesn’t provide, so we have to do a few things to work around this issue.
Xvfb stands for X virtual framebuffer. It is a display server that implements the X11 protocol, but does everything in memory, so it doesn’t really need a screen to work. This is exactly what we need. To use it we just need to create a Dockerfile that uses xvfb to run the tests:
I have started writing some real life polymer components, and I feel really bad that I haven’t been writing tests for them. In this post I’m going to teach myself how to write and run tests for polymer components so I can stop being a slacker and do some proper TDD.
Lets start by creating a little project. You can leave the defaults for the questions asked by npm init:
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mkdir ~/test
cd ~/test
npm init
Now, lets setup bower. You can again, leave the defaults:
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npm install --save-dev bower
./node_modules/bower/bin/bower init
A few weeks ago I published a post with an introduction to Gerrit. The configuration I explain there is not very scalable, so now I want to explain how to connect it to an external MySQL database so the data is more secure. As in my previous post, I’m going to do everything inside a docker image so it is easy to reuse and share.
Lets start with the Dockerfile from my previous post:
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FROM gerritforge/gerrit-centos7:2.11.4
# Expose gerrit ports
EXPOSE 29418 8080
# Start Gerrit
CMD /var/gerrit/bin/gerrit.sh start && tail -f /var/gerrit/logs/error_log
Sometimes when I’m running a process in the foreground (most commonly, vim). I unintentionally press Ctrl + z and I get a message like this:
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[1]+ Stopped vim
There might be reasons why you want to do this if you are running in a system that gives you a single terminal, but when running a UI where you can have multiple terminal tabs open, this usually happens by mistake. But no reason to panic, if you want to go back you just have to type this command:
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fg
As a matter of fact, you can have different jobs running on the background:
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jobs
[1] Stopped vim
[2]- Stopped vim
[3]+ Stopped less Makefile
And reopen them using fg %n. For example:
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fg %2