Package yacspin provides yet another CLi spinner for Go, taking inspiration (and some utility code) from the github.com/briandowns/spinner project. Specifically yacspin borrows the default character sets and color name mappings to github.com/fatih/color colors.

Because this package adopts the spinner character sets from github.com/briandowns/spinner, this package is released under the Apache 2.0 License. The full content of the Apache 2.0 license is available in the included LICENSE file in the root of this repository.

This project was created after it was realized that the most popular spinner library for Go had some limitations, that couldn't be fixed without a massive overhaul of the API.

The other spinners tie the ability to show updated messages to the spinner's animation, meaning you can't always show all the information you want to the end user without changing the animation speed. This results in having to trade off animation aesthetics to show "realtime" information. It was a goal to avoid this problem and instead render the animation independently from the contents being updated. An example of this is shown below.

In addition, there were also some API design choices that have made github.com/briandowns/spinner unsafe for concurrent use, which presents challenges when trying to update the text in the spinner while it's animating. This could result in undefined behavior due to data races.

There were also some variable-width spinners in that project that did not render correctly. Because the width of the spinner animation would change, so would the position of the message on the screen. yacspin uses a dynamic width when animating, so your message should appear static relative to the animating spinner. There is also an example of this feature blow.

Finally, there was an interest in the spinner being able to represent a task, and to indicate whether it failed or was successful. This would have further compounded the API changes needed above to support in an intuitive way.

This project is inspired by github.com/briandowns/spinner, and takes a new approach to address some of the challenges and limitations it has.

There are over 90 spinners available in the CharSets package variable. They were borrowed from github.com/briandowns/spinner. There is a table with most of the spinners at the bottom of this README.

Because of how some spinners are animated, they may have different widths at different frames in the animation. yacspin calculates the maximum width of the animation, and then adds padding to ensure the text's position on the screen doesn't change. This results in a smoother looking animation:

The spinner has both Stop() and StopFail() methods, which allow the spinner to result in a success message or a failure message. The messages, colors, and even the character used to denote success or failure are customizable in either the initial config or via the spinner's methods.

By doing this you can use a single yacspin spinner to display the status of a list of tasks being executed serially:

The SpinnerAtEnd field of the Config struct allows you to specify whether the spinner is rendered at the end of the line instead of the beginning. The default value (false) results in the spinner being rendered at the beginning of the line.

The spinner is safe for concurrent use, so you can update any of its settings via methods whether the spinner is stopped or is currently animating.

Many spinners tie the ability to show new messages to the animation of the spinner itself. So if the spinner animates every 200ms, you can only show updated information every 200ms. If you wanted more frequent updates, you'd need to tradeoff the asthetics of the animation to display more data.

yacspin updates the printed information of the spinner immediately on change, without the animation updating. This allows you to use an animation speed that looks astheticaly pleasing, while also knowing the data presented to the user will be updated live.

You can see this in action in the following gif, where the filenames being uploaded are rendered independent of the spinner being animated:

Sometimes you want to change a few settings, and don't want the yacspin spinner to render your partially applied configuration. If your spinner is running, and you want to change a few configuration items via method calls, you can Pause() the spinner first. After making the changes you can call Unpause(), and it will continue rendering like normal with the newly applied configuration. yacspin will then continue rendering the animation, while triggering the next animation to happen as close as possible to the next Frequency period if it hasn't already passed.

yacspin also has native support for non-interactive (TTY) output targets. By default this is detected in the constructor, or can be overriden via the TerminalMode Config struct field. When detecting the application is not running withn a TTY session, the behavior of the spinner is different.

Specifically, when this is automatically detected the spinner no longer uses colors, disables the automatic spinner animation, and instead only animates the spinner when updating the message. In addition, each animation is rendered on a new line instead of overwriting the current line.

This should result in human-readable output without any changes needed by consumers, even when the system is writing to a non-TTY destination.

If you'd like to manually animate the spinner, you can do so by setting the TerminalMode to ForceNoTTYMode | ForceSmartTerminalMode. In this mode the spinner will still use colors and other text stylings, but the animation only happens when data is updated and on individual lines. You can accomplish this by calling the Message() method with the same used previously.

go get github.com/theckman/yacspin

Within the yacspin package there are some default spinners stored in the yacspin.CharSets variable, and you can also provide your own. There is also a list of known colors in the yacspin.ValidColors variable.

There are runnable examples in the examples/ directory, with one simple example and one more advanced one. Here is a quick snippet showing usage from a very high level, with error handling omitted:

cfg := yacspin.Config{
	Frequency:       100 * time.Millisecond,
	CharSet:         yacspin.CharSets[59],
	Suffix:          " backing up database to S3",
	SuffixAutoColon: true,
	Message:         "exporting data",
	StopCharacter:   "✓",
	StopColors:      []string{"fgGreen"},
}

spinner, err := yacspin.New(cfg)
// handle the error

err = spinner.Start()

// doing some work
time.Sleep(2 * time.Second)

spinner.Message("uploading data")

// upload...
time.Sleep(2 * time.Second)

err = spinner.Stop()

The spinner animations below are recorded at a refresh frequency of 200ms. Some animations may look better at a different speed, so play around with the frequency until you find a value you find aesthetically pleasing.

yacspin.CharSets index	sample gif (Frequency: 200ms)
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