I was not very familiar with checking an error’s type in Golang, so I spent a few minutes learning about it today. It turns out that it’s incredibly easy to do. Running the below code shows the output: 2009/11/10 23:00:00 got custom error: err1 package main import ( "errors" "log" ) var ( customErr = errors.New("err1") // create a error, identified by its var name ) // oops always returns our custom error. Oops! func oops() error { return customErr } func main() { err := oops() if errors.Is(err, customErr) { // check error type with errors.Is() log.Fatal("got custom error: ", err) } } This is doing more than just matching the string of the error, as this does not show any output: ...

I’ve also been thinking more about unnecessary allocations in my Go code and how to avoid them by pre-declaring the length of a slice up front. Normally, I’d write something like this: var s []int for _, val := otherSlice { s = append(s, val) } Since I don’t specify the size of s, if otherSlice is large, the array underlying s might not be large enough to hold all the values; then a new array will have to be allocated and (I presume) all existing values copied out of it one at a time to fill the new array. ...

I recently went through How To Use Templates in Go to refresh my memory on Golang templates. I was reminded how great they are and learned several things along the way. I learned that the below syntaxes are equivalent: {{ . | len }} {{ (len .) }} Here is the program I wrote and tweaked along the way, to refresh my memory in the future: package main import ( "html/template" "os" "strings" ) type Pet struct { Name string Sex string Intact bool Age string Breed []string } var dogs = []Pet{ { // This is why you should use html/template and not text/template when // rendering HTML. Especially if you don't trust the source of your // data! // // You don't want the template you render to do (potentially) malicious // things in your user's webbrowser. Name: "<script>alert(\"Gotcha!\");</script>Jujube", Sex: "Female", Intact: false, Age: "10 months", Breed: []string{ "German Shepherd", "Pitbull", }, }, { Name: "Zephyr", Sex: "Male", Intact: true, Age: "13 years, 3 months", Breed: []string{ "German Shepherd", "Border Collie", }, }, { Name: "Roger", Sex: "Male", Intact: false, Age: "9 years, 7 months", Breed: []string{ "German Shepherd", "Border Collie", }, }, { Name: "Missi", Sex: "Female", Intact: false, Age: "99 years, 2 months", Breed: []string{ "Teacup Poodle", }, }, } // This is how you add functions to your template. You can add functions from // other packages or define them inline here. // // See petsHtml.tmpl for an example of using "join". var funcMap = template.FuncMap{ "dec": func(i int) int { return i - 1 }, // Inline! "replace": strings.ReplaceAll, // Other package! "join": strings.Join, } func main() { // Create Template, add functions, and load template files. tmpl, err := template.New("").Funcs(funcMap).ParseGlob("*.tmpl") if err != nil { panic(err) } // Create a file. var f *os.File f, err = os.Create("pets.html") if err != nil { panic(err) } defer f.Close() // Execute a template by name with data "dogs" and write to writer "f". err = tmpl.ExecuteTemplate(f, "petsHtml.tmpl", dogs) if err != nil { panic(err) } } And here are the files I wrote and tweaked along the way: ...

While watching a talk by Rob Pike I learned today something about Goroutines which surprised me: Goroutines outlive their calling function. Said another way, if the function which created the goroutine returns, the goroutine will continue running. (main() is the one exception.) This is fantastic! 🎉 Here’s an example of this in practice. package main import ( "fmt" "time" ) func person(msg string) <-chan string { // Function returns a receive-only channel ch := make(chan string) // Create unbuffered channel go func() { // This goroutine lives on after person() returns for i := 0; ; i++ { time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond) ch <- fmt.Sprintf("%s %d", msg, i) } }() return ch } func main() { james := person("james") // Assign returned channel to variable sinah := person("sinah") for i := 0; i < 5; i++ { fmt.Println(<-james) // Block, waiting for value on channel fmt.Println(<-sinah) } fmt.Println("Done!") } Output: ...

Go 1.18 added a feature to easily get the Git commit version that the binary was built from. This is so much easier than the old way of doing it! 🎉 package main import ( "fmt" "runtime/debug" ) func main() { info, _ := debug.ReadBuildInfo() for _, setting := range info.Settings { if setting.Key == "vcs.revision" || setting.Key == "vcs.time" { fmt.Printf("%s:\t%s\n", setting.Key, setting.Value) } } } $ go build git-version $ ./git-version vcs.revision: 4d47dd39d1debbdf10715fd9ff967e09d4347f02 vcs.time: 2023-09-02T00:21:21Z More info here. warning For this to work, you must build with go build -o ./build/foo. Using go build -o ./build/foo/main.go will not work. ...

The other day I ran into a situation where I wanted my function to block until it received data from a Go channel. But I didn’t want it to block indefinitely. I wanted it to timeout after a few seconds if it didn’t get any data. My coworker Dan showed me a technique I didn’t know about to easily accomplish this. It wasn’t surprising to learn how easy it was, given that Go has strong support for concurrency out the gate. ...

Example 1 In the below code, <-messages will block until it gets something on the channel. This prevents main() from exiting until one item is received on the channel. package main import ( "fmt" "time" ) func waitThenSend(msg chan string) { time.Sleep(2 * time.Second) msg <- "badwolf" } func main() { messages := make(chan string) // make unbuffered channel go func() { waitThenSend(messages) // make goroutine, pass in channel }() <-messages // blocks until channel receives a value fmt.Println("done") } Example 2 The below example demonstrates using a sync.WaitGroupto keep the program running until all of the goroutines have exited. Data is sent to the function via the unbuffered channel named numbers. ...

At work, I’ve been using both Golang and Ruby to render Nomad jobspec files in a consistent manner across environments. But Python is my one true love and I wanted to learn how to do it in Python. Turns out I already knew how… you can do it in Jinja2! I’ve used Jinja2 in the past a lot for Django and Ansible, so this was pretty easy to pick up. Here are some notes for future me when I want to inevitably do this again. ...

These are useful and I’m putting them here so I can find them easily wherever I am. Latency Comparison Numbers (~2012) ---------------------------------- L1 cache reference 0.5 ns Branch mispredict 5 ns L2 cache reference 7 ns 14x L1 cache Mutex lock/unlock 25 ns Main memory reference 100 ns 20x L2 cache, 200x L1 cache Compress 1K bytes with Zippy 3,000 ns 3 us Send 1K bytes over 1 Gbps network 10,000 ns 10 us Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD Read 1 MB sequentially from memory 250,000 ns 250 us Round trip within same datacenter 500,000 ns 500 us Read 1 MB sequentially from SSD* 1,000,000 ns 1,000 us 1 ms ~1GB/sec SSD, 4X memory Disk seek 10,000,000 ns 10,000 us 10 ms 20x datacenter roundtrip Read 1 MB sequentially from disk 20,000,000 ns 20,000 us 20 ms 80x memory, 20X SSD Send packet CA->Netherlands->CA 150,000,000 ns 150,000 us 150 ms Notes ----- 1 ns = 10^-9 seconds 1 us = 10^-6 seconds = 1,000 ns 1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns Credit ------ By Jeff Dean: http://research.google.com/people/jeff/ Originally by Peter Norvig: http://norvig.com/21-days.html#answers Contributions ------------- 'Humanized' comparison: https://gist.github.com/hellerbarde/2843375 Visual comparison chart: http://i.imgur.com/k0t1e.png Source: https://gist.github.com/jboner/2841832 ...

Last week, I was working on some Python at work and I found myself wishing for an equivalent to Golang’s structs. Rather than passing in a bunch of core data types (string, dict, int, etc.) in an out of methods, I wanted to pass in a single object with predictable attributes. But…. I didn’t want to go through all the trouble of creating a class with a constructor, and passing in all the various attributes. ...