GoSteps

GoSteps is a go library that helps in running functions as steps and reminds you to step out and get active (kidding!).

The idea behind gosteps is to define set of functions as steps-chain (kind of a linked list) and execute them in a sequential fashion by piping output (other than error) from previous step, as arguments, into the next steps (not necessarily using the args).

Usage

The Step type contains the requirments to execute a step function and move to next one.

type Step struct {
	Name              StepName
	Function          StepFn
	UseArguments      stepArgChainingType
	StepArgs          []interface{}
	NextStep          *Step
	PossibleNextSteps PossibleNextSteps
	NextStepResolver  interface{}
	ErrorsToRetry     []error
	StrictErrorCheck  bool
	SkipRetry         bool
	MaxAttempts       int
	RetrySleep        time.Duration
}

Field	Description
Name	Name of step
Function	The function to execute
StepArgs	any additional arguments need to pass to te step
UseArguments	Choosing Arguments to Use from previous step's return or current step's arguments or both.
NextStep	Next Step for the current step. If next step needs to be conditional dont set this and use PossibleNextSteps field instead
PossibleNextSteps	Candidate functions for next step (pick from multiple possible next steps based on condition)
NextStepResolver	A function that returns the step name, based on conditions, that is used to pick the NextStep from PossibleNextSteps
ErrorsToRetry	A list of error to retry step for
StrictErrorCheck	If set to true exact error is matched, else only presence of error is checked
SkipRetry	If set to true step is not retried for any error
MaxAttempts	Max attempts are the number of times the step is tried (first try + subsequent retries). If not set, it'll run 100 times
RetrySleep	Sleep duration (type time.Duration) between each re-attempts

Step Function

Define a step function using the following function signature. You can also use the StepFn type.

// StepFn Type
type StepFn func(...interface{}) ([]interface{}, error)

// sample Step function
func Add(args ...any) ([]interface{}, error) {
	fmt.Printf("Adding %v\n", args)
	return []interface{}{args[0].(int) + args[1].(int)}, nil
}

To see all the types available in go-steps see types.go

Defining Steps

To define steps, use the gosteps.Step type and link the next steps in the NextStep field like a Linked List.

var steps = gosteps.Step{
	Name: "add",
	Function: funcs.Add,
	StepArgs: []interface{}{2, 3},
	NextStep: gosteps.Steps{
		Name: "sub",
		Function:       funcs.Sub,
		StepArgs: []interface{}{4},
	},
}

Here the first step is Add and next step (and final) is Sub, so the output of Add is piped to Sub and that gives the final output.

Choosing Arguments to Use

Arguments to use in the current step function's execution is determined using the previous step returned values and the current step arguments specified.

You can choose if you want to use previous step returned values as arguments to current step, or you want to use only current step arguments or both. You can also choose the order in which the returns from previous step, and step arguments are passed as arguments.

This can be done so by passing the "strategy" to the UseArguments field. There are four directives defined in the library

 // only previous step return will be passed to current step as arguments
 PreviousStepReturns stepArgChainingType = "PreviousStepReturns"

 // only current step arguments (StepArgs) will be passed to current step as arguments
 CurrentStepArgs stepArgChainingType = "CurrentStepArgs"

 // both previous step returns and current step arguments (StepArgs) will be passed
 // to current step as arguments - previous step returns, followed by current step args,
 PreviousReturnsWithCurrentStepArgs stepArgChainingType = "PreviousReturnsWithCurrentStepArgs"

 // both previous step returns and current step arguments (StepArgs) will be passed
 // to current step as arguments - current step args, followed by previous step returns
 CurrentStepArgsWithPreviousReturns stepArgChainingType = "CurrentStepArgsWithPreviousReturns"

These values can be used in the step chain as

var steps = gosteps.Step{
	Name: "add",
	Function: funcs.Add,
	StepArgs: []interface{}{2, 3},
	NextStep: gosteps.Steps{
		Name: "sub",
		Function:       funcs.Sub,
		StepArgs: []interface{}{4, 6},
		UseArguments: gosteps.CurrentStepArgs,
	},
}

Conditional Steps

Some steps might have multiple candidates for next step and the executable next step is to be picked based on the output of the current step. Define the possible next steps in the PossibleNextSteps field, as an array of Steps.

PossibleNextSteps: gosteps.Step{
	Function:       funcs.Add,
		StepArgs: []interface{}{2},
		NextStep: &gosteps.Step{
			Function:         funcs.Sub,
			StepArgs:   []interface{}{4},
			NextStepResolver: nextStepResolver,
			PossibleNextSteps: gosteps.PossibleNextSteps{
				{
					Name:           "multiply",
					Function:       funcs.Multiply,
				},
				{
				Name:           "divide",
					Function:       funcs.Divide,
				},
			}
	}
}

To pick the required next step based on conditions, we must use the NextStepResolver field passing a resolver function that returns the Name of the function to use as next step.

The resolver function should be of type func(args ...any) string, where args are the output of current step and returned string is the name of the step to use.

func nextStepResolver(args ...any) string {
	if args[0].(int) < 5 {
		fmt.Printf("StepResolver [%v]: Arguments is Negative, going with Multiply\n", args)
		return "add"
	}

	fmt.Printf("StepResolver [%v]: Arguments is Positive, going with Divide\n", args)
	return "sub"
}

Executing Steps

To execute steps use the Execute(initArgs ...any) method, passing the (optional) initializing arguments.

import (
	gosteps "github.com/TanmoySG/go-steps"
	funcs "github.com/TanmoySG/go-steps/example/funcs"
)

func main() {
	initArgs := []interface{}{1, 2}
	finalOutput, err := steps.Execute(initArgs...)
	if err != nil {
		fmt.Printf("error executing steps: %s, final output: [%s]\n", err, finalOutput)
	}

	fmt.Printf("Final Output: [%v]\n", finalOutput)
}

Retrying for Error

To retry a step for particular erors, use the ErrorsToRetry field passing the list of errors. To make sure the error matches exactly as that of the Errors to retry, pass true for the StrictErrorCheck field, otherwise only error-substring presense will be checked.

{
	ErrorsToRetry: []error{
		fmt.Errorf("error to retry"),
	},
	StrictErrorCheck: true,
	MaxAttempts: 5,
	RetrySleep:  1 * time.Second,
}

To skip retry on error pass true to the SkipRetry field.

Additionally,

• To limit the number of tries, use the MaxAttempts field, passing the number of max tries. If not set then Default Max Attempts (of 100 tries) is used. To avoid infinite runs due to the MaxAttempts not being set, we're keeping the default attempts to 100. If required, import and use the gosteps.MaxMaxAttempts. Please note that the Max value is 9223372036854775807, which is not infinite but a huge number of attempts, please use cautiously.
• To add sleep between each attempts, use the RetrySleep parameter passing the duration of sleep (of type time.Duration) like 2 * time.Second.

Constraints

To keep the step execution same, all step functions must be of type func(args ..any) ([]interface{}, error)

Here all arguments passed to the step function need to be type asserted within the step function, as

func Multiply(args ...any) ([]interface{}, error) {
	return []interface{}{args[0].(int) * args[1].(int)}, nil
}

The step function must also return all parameters (other than error) as type []interface{ret1, ret2, ...} and error must be returned for all functions even if nil.

Help Wanted

If you want to help fix the above constraint or other bugs/issues, feel free to raise an Issue or Pull Request with the changes. It'd be an immense help!

Example

In this example, we've used a set of complex steps with conditional step and retry. The flow of the same is

Execute the example steps

go run example/main.go

// output
Adding [1 2]
Sub [3 4]
StepResolver [[-1]]: Arguments is Negative, going with Multiply
Multiply [-1 -5]
Adding [5 100]
Running fake error function for arg [[105]]
Running fake error function for arg [[105]]
Running fake error function for arg [[105]]
Running fake error function for arg [[105]]
Multiply [3150 5250]
Final Output: [[16537500]]

Please Note: This example flow might change and can be out-of-date. Please check the example.