minstrel/internal/indexer/ratelimit.go

package indexer

import (
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"time"
)

// RateLimited is a source answering 429. Named so the search pacing can hold
// that source back for as long as it asked; still an ErrUnreachable to
// everything else, because this search did not reach it.
type RateLimited struct {
	// RetryAfter is what the source asked for; zero when it did not say.
	RetryAfter time.Duration
	// Who names the source in the sentence, e.g. "Prowlarr".
	Who string
}

func (e *RateLimited) Error() string {
	return fmt.Sprintf("%v: HTTP 429, %s is rate-limiting this search", ErrUnreachable, e.Who)
}

func (e *RateLimited) Unwrap() error { return ErrUnreachable }

// AsRateLimited finds a RateLimited anywhere in err's chain.
func AsRateLimited(err error) (*RateLimited, bool) {
	var rl *RateLimited
	if errors.As(err, &rl) {
		return rl, true
	}
	return nil, false
}

// RetryAfter reads a Retry-After header: seconds, or an HTTP date. Zero when
// absent or unreadable.
func RetryAfter(h http.Header, now time.Time) time.Duration {
	v := h.Get("Retry-After")
	if v == "" {
		return 0
	}
	if s, err := strconv.Atoi(v); err == nil && s > 0 {
		return time.Duration(s) * time.Second
	}
	if t, err := http.ParseTime(v); err == nil && t.After(now) {
		return t.Sub(now)
	}
	return 0
}