77 lines
1.7 KiB
Go
77 lines
1.7 KiB
Go
package alps
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import (
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"fmt"
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"net"
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"net/url"
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"strings"
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)
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func discoverTCP(service, name string) (string, error) {
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_, addrs, err := net.LookupSRV(service, "tcp", name)
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if dnsErr, ok := err.(*net.DNSError); ok {
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if dnsErr.IsTemporary {
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return "", err
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}
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} else if err != nil {
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return "", err
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}
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if len(addrs) == 0 {
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return "", nil
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}
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addr := addrs[0]
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target := strings.TrimSuffix(addr.Target, ".")
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if target == "" {
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return "", nil
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}
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return fmt.Sprintf("%v:%v", target, addr.Port), nil
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}
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// discoverIMAP performs a DNS-based IMAP service discovery, as defined in
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// RFC 6186 section 3.2.
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func discoverIMAP(domain string) (*url.URL, error) {
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imapsHost, err := discoverTCP("imaps", domain)
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if err != nil {
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return nil, err
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}
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if imapsHost != "" {
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return &url.URL{Scheme: "imaps", Host: imapsHost}, nil
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}
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imapHost, err := discoverTCP("imap", domain)
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if err != nil {
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return nil, err
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}
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if imapHost != "" {
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return &url.URL{Scheme: "imap", Host: imapHost}, nil
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}
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return nil, fmt.Errorf("IMAP service discovery not configured for domain %q", domain)
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}
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// discoverSMTP performs a DNS-based SMTP submission service discovery, as
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// defined in RFC 6186 section 3.1. RFC 8314 section 5.1 adds a new service for
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// SMTP submission with implicit TLS.
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func discoverSMTP(domain string) (*url.URL, error) {
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smtpsHost, err := discoverTCP("submissions", domain)
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if err != nil {
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return nil, err
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}
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if smtpsHost != "" {
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return &url.URL{Scheme: "smtps", Host: smtpsHost}, nil
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}
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smtpHost, err := discoverTCP("submission", domain)
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if err != nil {
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return nil, err
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}
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if smtpHost != "" {
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return &url.URL{Scheme: "smtp", Host: smtpHost}, nil
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}
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return nil, fmt.Errorf("SMTP service discovery not configured for domain %q", domain)
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}
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