53 lines
1.4 KiB
Go
53 lines
1.4 KiB
Go
package probe
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import (
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"context"
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"fmt"
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"net"
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"net/netip"
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"time"
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)
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// DNSResult contains the outcome of one DNS lookup.
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type DNSResult struct {
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Reachable bool
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Duration time.Duration
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IPs []net.IP
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Err error
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}
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// Resolve checks whether a domain can be resolved against a specific DNS server.
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func Resolve(ctx context.Context, server string, domain string, timeout time.Duration) DNSResult {
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start := time.Now()
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lookupCtx, cancel := context.WithTimeout(ctx, timeout)
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defer cancel()
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dialer := net.Dialer{Timeout: timeout}
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resolver := net.Resolver{
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PreferGo: true,
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Dial: func(ctx context.Context, network string, address string) (net.Conn, error) {
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conn, err := dialer.DialContext(ctx, network, dnsServerAddress(server))
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if err != nil {
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return nil, fmt.Errorf("dialing dns server %s: %w", server, err)
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}
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return conn, nil
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},
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}
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ips, err := resolver.LookupIP(lookupCtx, "ip", domain)
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duration := time.Since(start)
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if err != nil {
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return DNSResult{Duration: duration, Err: fmt.Errorf("resolving %s with %s: %w", domain, server, err)}
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}
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return DNSResult{Reachable: len(ips) > 0, Duration: duration, IPs: ips}
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}
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func dnsServerAddress(server string) string {
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if _, err := netip.ParseAddrPort(server); err == nil {
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return server
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}
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if addr, err := netip.ParseAddr(server); err == nil {
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return net.JoinHostPort(addr.String(), "53")
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}
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return net.JoinHostPort(server, "53")
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}
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