Read Go documentation

A few weeks ago I’ve finished reading the Go documentation. The Go 1.10 documentation Android app is very helpful! It’s very easy to read and it has auto bookmarks; whenever you get back into the app, you can return to the chapter you were reading, at the same line you were before closing it.

It was very nice to find out a lot of details. Of course, I don’t remember all of them after just one reading, but when I bump into some situations (performance, how slices really work, libraries, the memory model etc) it’s easier to start researching further if I don’t remember the point exactly.

I don’t want to write Go without understanding as best as I can its way of getting things done.

PHP backward compatibility

Could PHP 7 inherit Go’s philosophy of not introducing breaking changes in future versions? I’ve asked this myself today.

PHP is on a really nice path since version 7, with its courageous changes, and I believe more is yet to come. Because things must evolve, there were some incompatible changes from 5 to 7, and that’s great. And now that it’s more mature, I would like to see more stability and more of those hardcore changes that will keep the language in its good position.

Regarding this, something that I really wish for PHP 7 is to approach Go’s idea of not introducing incompatibilities with future versions. The programs should run flawless when upgrading PHP. It would be a great encouragement for everyone to safely upgrade as soon as a new version is released.

Configurable implementation hidden behind a contract

Some concrete implementations are better to be hidden behind contracts, in a specific package. A layer of abstraction can save you later, mostly on unstable projects that often change requirements, or maybe you just want to test an idea, maybe you don’t have the necessary time to finish a task in a way you’d like to.

A good contract will save you. You can “throw” your implementation behind it and come back later to refine it. Sometimes later means in a few years. But if you’re behind a well designed contract, most probably you’re going to alter only the concrete implementation, without touching large areas of the projects.

I had to filter some user input. Some strings had to be HTML escaped, some sanitized to prevent different attacks. I’ve wrapped everything into a package, behind a contract. For escaping I’ve used Go’s html.EscapeString function, while for sanitizing I’ve found the bluemonday package, which is inspired by an OWASP sanitizier for Java. Continue reading Configurable implementation hidden behind a contract

Using channels to control flow

When I first met channels in Go, I thought they were just data containers. When you want to send data between routines, they are the go to. But later I saw they can be used to control an application flow, like waiting until something happens and only after that go on with the normal flow.

Here’s an approach to wait until some tasks have finished. Let me consider some input data that can come from anywhere: HTTP requests, files, sockets etc. That data can come in fast, but processing can take some time. If the application needs to exit (you restart it, stop it) but you want to wait until all the data you have in memory is processed, you can use channels.

First, I have a routine which processes input data read from a buffered channel. I simulate the slow processing with a sleep. Continue reading Using channels to control flow

Converting seconds from float to int

Another small one on time precision that I’ve noticed.

package main

import (
	"fmt"
	"math"
	"time"
)

func main() {
	now := time.Now().Add(time.Hour)
	seconds = time.Now().Sub(now).Seconds()
	fmt.Println(int(seconds))
	fmt.Println(int(math.Floor(seconds)))
}

Line 12 will print -3599, line 13 will print -3600 (tested on Ubuntu). So watch out when converting the number of seconds to an integer, you might not always get what you need.

Time precision on Linux and Windows

Unit tests were needed on a new project I’m working on and a few weeks ago I wrote some. Last week, a colleague wrote some more, and when he ran all of them, mine were failing. Same code base, up to date, same tests. On my machine they were still passing. We jumped on the situation and saw math.Floor was giving a result on my machine, which runs on Ubuntu, and another one on his, on Windows.

The code is larger, but I’ve extracted and adapted what’s needed:

package main

import (
	"time"
	"math"
)

func main() {
	datetime := time.Now().Add(time.Hour * 24 * 7 * 4 * 12 * 3)
	seconds := -1 * int(time.Now().Sub(datetime).Seconds())
	a := 29030400
	x := float64(seconds)/float64(a)

	println("input:", x, "floor:", math.Floor(x))
}

Result on Ubuntu:

input: +3.000000e+000 floor: +2.000000e+000

Result on Windows:

input: +3.000000e+000 floor: +3.000000e+000

Continue reading Time precision on Linux and Windows

Handling API errors

The past days I’ve practiced Go by writing a package for Apixu weather service. They have a a straightforward REST service to offer their weather information.

Their service also returns an error response if it can’t offer data based on your needs, if you use an invalid API key, or for other cases. Of course, the Go package should also return errors if the case.

No problem with returning data, but I had some issues handling errors. There can be general errors that have nothing to do with Apixu (but with the package internals) and errors returned by them. My first approach was to return three values for each API method:

Search(q string) (Search, ApixuError, error)

But it smelled right away. There had to be another way. Continue reading Handling API errors

Reloading Go apps automatically while developing

There are some ways to automatically reload Go apps while developing, to not have to manually stop your app, build it, run it. Recently I ran into this article about a nice tool called Fresh.

I wanted to start using live reload (or hot reload) for a project of mine, but it had a particularity which gave me troubles when I tried Fresh. My case was:

  • I had a multiple apps Git repository
  • The apps were sharing some packages
  • If I edited app1 and the packages it used, I didn’t want both app1 and app2 to be restarted, only app1 (similar for app2)

Continue reading Reloading Go apps automatically while developing

Counting number of items in a concurrent map

Lately I’ve been using Go’s concurrent map. And sometimes I needed to count the items I’ve stored in the map. I have ranged over the items and incremented a counter, and it was done:

package main

import (
       "sync"
       "log"
)

func main() {
       m := sync.Map{}
       
       m.Store("k1", "v1")
       m.Store("k2", "v2")
       
       count := 0
       m.Range(func(key, value interface{}) bool{
              count++
              return true
       })

       log.Println(count)
}

But I didn’t want to range over the items each time I wanted to count them. So I thought of incrementing the counter every time an element was added, and to decrementing it when one was removed. The following is just for practice, I didn’t perform any advanced tests. Continue reading Counting number of items in a concurrent map

Go HTTP server duplicate handler call

It took me a minute or two to figure out why, while doing some experiments, for the following built-in HTTP server use case, the handler was called two times, and so printing the log message two times.

package main

import (
       "log"
       "net/http"
)

func main() {
       http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
              log.Println("call")
       })

       http.ListenAndServe(":8800", nil)
}

The path “/” catches all requests, thus it catches the “/favicon.ico” request sent by the browser. So I’ve just used another path.