Source: invoke.go in package github.com/googleapis/gax-go/v2

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package gax

import (
	"context"
	"strings"
	"time"
)

APICall is a user defined call stub.

type APICall func(context.Context, CallSettings) error

Invoke calls the given APICall, performing retries as specified by opts, if any.

func Invoke(ctx context.Context, call APICall, opts ...CallOption) error {
	var settings CallSettings
	for _, opt := range opts {
		opt.Resolve(&settings)
	}
	return invoke(ctx, call, settings, Sleep)
}

Sleep is similar to time.Sleep, but it can be interrupted by ctx.Done() closing. If interrupted, Sleep returns ctx.Err().

func Sleep(ctx context.Context, d time.Duration) error {
	t := time.NewTimer(d)
	select {
	case <-ctx.Done():
		t.Stop()
		return ctx.Err()
	case <-t.C:
		return nil
	}
}

type sleeper func(ctx context.Context, d time.Duration) error

invoke implements Invoke, taking an additional sleeper argument for testing.

func invoke(ctx context.Context, call APICall, settings CallSettings, sp sleeper) error {
	var retryer Retryer
	for {
		err := call(ctx, settings)
		if err == nil {
			return nil
		}
		if settings.Retry == nil {
			return err

Never retry permanent certificate errors. (e.x. if ca-certificates are not installed). We should only make very few, targeted exceptions: many (other) status=Unavailable should be retried, such as if there's a network hiccup, or the internet goes out for a minute. This is also why here we are doing string parsing instead of simply making Unavailable a non-retried code elsewhere.

		if strings.Contains(err.Error(), "x509: certificate signed by unknown authority") {
			return err
		}
		if retryer == nil {
			if r := settings.Retry(); r != nil {
				retryer = r
			} else {
				return err
			}
		}
		if d, ok := retryer.Retry(err); !ok {
			return err
		} else if err = sp(ctx, d); err != nil {
			return err
		}
	}