micro/resolver/dns/dns.go

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// Package dns resolves names to dns records
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package dns
import (
"context"
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"net"
"github.com/unistack-org/micro/v3/resolver"
"github.com/miekg/dns"
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)
// Resolver is a DNS network resolve
type Resolver struct {
// The resolver address to use
Address string
}
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// Resolve assumes ID is a domain name e.g micro.mu
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func (r *Resolver) Resolve(name string) ([]*resolver.Record, error) {
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host, port, err := net.SplitHostPort(name)
if err != nil {
host = name
port = "8085"
}
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if len(host) == 0 {
host = "localhost"
}
if len(r.Address) == 0 {
r.Address = "1.0.0.1:53"
}
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//nolint:prealloc
var records []*resolver.Record
// parsed an actual ip
if v := net.ParseIP(host); v != nil {
records = append(records, &resolver.Record{
Address: net.JoinHostPort(host, port),
})
return records, nil
}
m := new(dns.Msg)
m.SetQuestion(dns.Fqdn(host), dns.TypeA)
rec, err := dns.ExchangeContext(context.Background(), m, r.Address)
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if err != nil {
return nil, err
}
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for _, answer := range rec.Answer {
h := answer.Header()
// check record type matches
if h.Rrtype != dns.TypeA {
continue
}
arec, _ := answer.(*dns.A)
addr := arec.A.String()
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// join resolved record with port
address := net.JoinHostPort(addr, port)
// append to record set
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records = append(records, &resolver.Record{
Address: address,
})
}
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// no records returned so just best effort it
if len(records) == 0 {
records = append(records, &resolver.Record{
Address: net.JoinHostPort(host, port),
})
}
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return records, nil
}