94 lines
2.6 KiB
Go
94 lines
2.6 KiB
Go
package send
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import (
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stdcontext "context"
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"errors"
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"fmt"
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"net"
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"net/textproto"
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"sort"
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"strings"
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"time"
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"git.pcux.cn/xuans/Smail/utils/smtp"
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)
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var errNullMX = errors.New("收件域名声明不接收邮件")
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type mxLookup func(stdcontext.Context, string) ([]*net.MX, error)
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func resolveMX(domain string, lookup mxLookup) ([]string, error) {
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ctx, cancel := stdcontext.WithTimeout(stdcontext.Background(), 10*time.Second)
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defer cancel()
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records, err := lookup(ctx, domain)
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if err != nil {
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var dnsErr *net.DNSError
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if !errors.As(err, &dnsErr) || !dnsErr.IsNotFound || dnsErr.IsTemporary || dnsErr.IsTimeout {
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return nil, fmt.Errorf("查询收件域名 MX 失败: %w", err)
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}
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// 无 MX 时使用域名自身的地址记录，不猜测 smtp 子域名。
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return []string{domain}, nil
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}
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if len(records) == 0 {
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return []string{domain}, nil
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}
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records = append([]*net.MX(nil), records...)
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for _, record := range records {
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if record == nil || record.Host == "" {
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return nil, errors.New("收件域名 MX 记录无效")
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}
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if record.Host == "." {
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return nil, errNullMX
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}
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}
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sort.SliceStable(records, func(i, j int) bool { return records[i].Pref < records[j].Pref })
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hosts := make([]string, 0, len(records))
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seen := make(map[string]bool)
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for _, record := range records {
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host := strings.ToLower(strings.TrimSuffix(record.Host, "."))
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if !seen[host] {
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hosts = append(hosts, host)
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seen[host] = true
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}
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}
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return hosts, nil
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}
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func stopFallback(err error) bool {
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return smtp.IsDeliveryUncertain(err) || isCertificateVerificationError(err) || isPermanentSMTPResponse(err) || errors.Is(err, smtp.ErrUnsafeRemoteAddress)
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}
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// deliverMX 只在确认本次未接收时切换安全通道，DATA 不确定结果不进入下一条路由。
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func deliverMX(hosts []string, attempt func(host, port string) error) error {
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var lastErr error
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for _, host := range hosts {
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for _, port := range []string{"25", "587", "465"} {
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lastErr = attempt(host, port)
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if lastErr == nil || stopFallback(lastErr) {
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return lastErr
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}
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}
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}
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if lastErr == nil {
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lastErr = errors.New("收件域名没有可用邮件服务器")
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}
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return lastErr
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}
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// Retryable 仅允许有明确临时失败语义的结果进入持久队列重试。
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func Retryable(err error) bool {
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if err == nil || stopFallback(err) {
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return false
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}
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var response *textproto.Error
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if errors.As(err, &response) {
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return response.Code >= 400 && response.Code <= 499
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}
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var dnsErr *net.DNSError
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if errors.As(err, &dnsErr) {
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return dnsErr.IsTimeout || dnsErr.IsTemporary
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}
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var networkErr net.Error
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return errors.As(err, &networkErr)
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}
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