errgroup.Groupの亜種(一時的なエラーの場合は部分的に再試行し、そうでなければ全て中止する)

main.go

package main

import (
	"context"
	"errors"
	"fmt"
	"os"
	"strings"
	"sync"
	"time"
)

type errorTransientFailure struct {
}

func (e errorTransientFailure) Error() string {
	return "transient failure"
}

type errorPermanentFailure struct {
}

func (e errorPermanentFailure) Error() string {
	return "permanent failure"
}

func main() {
	fmt.Println("Hello, playground")

	var errOnce sync.Once

	var cause error

	var wg sync.WaitGroup

	ch1 := make(chan string)
	ch2 := make(chan string)

	defer close(ch1)
	defer close(ch2)

	go func() {
		ch1 <- "to1: a"
		ch2 <- "to2: a"
		ch1 <- "to1: b"
		ch1 <- "warn"
		ch2 <- "warn"
		ch1 <- "transient failure"
		ch2 <- "permanent failure"
	}()

	ctx := context.Background()
	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()

	wg.Add(1)
	go func() {
		defer wg.Done()

		for {
			if err := procCh(ctx, "proc1", ch1); err != nil {
				if errorAny(err, errorTransientFailure{}) {
					continue
				}

				errOnce.Do(func() {
					cause = err
					cancel()
				})

				break
			}

			if ctx.Err() != nil {
				break
			}
		}
	}()

	wg.Add(1)
	go func() {
		defer wg.Done()

		for {
			if err := procCh(ctx, "proc2", ch2); err != nil {
				if errorAny(err, errorTransientFailure{}) {
					continue
				}

				errOnce.Do(func() {
					cause = err
					cancel()
				})

				break
			}

			if ctx.Err() != nil {
				break
			}
		}
	}()

	wg.Wait()
	if cause != nil {
		println("main", cause.Error())
		os.Exit(1)
	}
}

func errorAny(err error, options ...error) bool {
	for _, e := range options {
		if errors.Is(err, e) {
			return true
		}
	}
	return false
}

func procCh(ctx context.Context, text string, ch chan string) error {
	println(text, "starting")
	defer println(text, "stopping")

	for {
		select {
		case <-ctx.Done():
			return nil
		case t := <-ch:
			if strings.HasSuffix(t, " failure") {
				println(text, "failed with", t)

				if t == "transient failure" {
					return errorTransientFailure{}
				} else if t == "permanent failure" {
					return errorPermanentFailure{}
				}
				return errors.New(t)
			}
			println(text, "received", t)
		}
	}
}