Yet Another CLi Spinner (for Go)

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

License

Because this package adopts the spinner character sets from https://github.com/briandowns/spinner, this package is released under the Apache 2.0 License.

Yet Another CLi Spinner?

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 spinner ties 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 means you need to trade off animation aesthetics to show "realtime" information. It was a goal to avoid this problem.

In addition, there were also some API design choices that have made it 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 other 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.

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 takes inspiration from that other project, and takes a new approach to address the challenges above.

Features

Provided Spinners

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.

Dynamic Width of Animation

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

yacspin

other spinners

Success and Failure Results

The spinner has both a Stop() and StopFail() method, which allows 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.

Stop

StopFail

Animation At End of Line

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.

Concurrency

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.

Live Updates

Most spinners tie the ability to show new messages with the animation of the spinner. 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.

This spinner 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:

Pausing for Updates

Sometimes you want to change a few settings, and don't want the 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.

Supporting non-TTY Output Targets

yacspin also has native support for non-TTY output targets. This is detected automatically within the constructor, or can be specified via the NotTTY Config struct field, and results in a different mode of operation.

Specifically, when this is 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.

Usage

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.

Example

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()

Spinners

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