71 lines
1.7 KiB
Go
71 lines
1.7 KiB
Go
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package dnsxl
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import (
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"context"
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"errors"
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"net"
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"strings"
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)
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// Result of a lookup from a single server.
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type Result struct {
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// Server is the name of the DNSxL server that produced this result.
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Server string
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// InList is true if the IP address that was lookup up is in the list.
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InList bool
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// Weight is the server's present/not present weight, as appropriate, or
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// 0 on error.
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Weight int
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// Reason may be set if the IP address is in the server's list, and the
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// server has a reason TXT record present for it.
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Reason string
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// Error is set if there was an error looking up the IP address on this
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// server.
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Error error
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}
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// server implements a single DNSxL server. It holds the server's DNS name and
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// the configured weights for found / not found results.
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type server struct {
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Addr string
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WeightInList, WeightNotInList int
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}
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// Lookup performs a (synchronous) DNSxL lookup.
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func (s server) Lookup(ctx context.Context, res *net.Resolver, reversed string) Result {
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r := Result{
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Server: s.Addr,
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}
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addr := reversed + "." + s.Addr
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ips, err := res.LookupIP(ctx, "ip4" /* DNSxL entries are A records */, addr)
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switch {
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case isNXDOMAIN(err):
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r.Weight = s.WeightNotInList
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return r
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case err != nil:
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r.Error = err
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return r
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case len(ips) == 0:
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r.Weight = s.WeightNotInList
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return r
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}
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txts, _ := res.LookupTXT(ctx, addr)
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r.InList = true
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r.Weight = s.WeightInList
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r.Reason = strings.Join(txts, "\n")
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return r
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}
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// isNXDOMAIN catches the error that Go returns when getting an NXDOMAIN
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// response. This just means "not on list" in our case.
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func isNXDOMAIN(err error) bool {
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var d *net.DNSError
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return errors.As(err, &d) && d.IsNotFound
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}
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