status-go/vendor/github.com/multiformats/go-multiaddr-dns/resolve.go

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package madns
import (
"context"
"net"
"strings"
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"github.com/miekg/dns"
ma "github.com/multiformats/go-multiaddr"
)
var ResolvableProtocols = []ma.Protocol{DnsaddrProtocol, Dns4Protocol, Dns6Protocol, DnsProtocol}
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var DefaultResolver = &Resolver{def: net.DefaultResolver}
const dnsaddrTXTPrefix = "dnsaddr="
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// BasicResolver is a low level interface for DNS resolution
type BasicResolver interface {
LookupIPAddr(context.Context, string) ([]net.IPAddr, error)
LookupTXT(context.Context, string) ([]string, error)
}
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// Resolver is an object capable of resolving dns multiaddrs by using one or more BasicResolvers;
// it supports custom per domain/TLD resolvers.
// It also implements the BasicResolver interface so that it can act as a custom per domain/TLD
// resolver.
type Resolver struct {
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def BasicResolver
custom map[string]BasicResolver
}
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var _ BasicResolver = (*Resolver)(nil)
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// NewResolver creates a new Resolver instance with the specified options
func NewResolver(opts ...Option) (*Resolver, error) {
r := &Resolver{def: net.DefaultResolver}
for _, opt := range opts {
err := opt(r)
if err != nil {
return nil, err
}
}
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return r, nil
}
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type Option func(*Resolver) error
// WithDefaultResolver is an option that specifies the default basic resolver,
// which resolves any TLD that doesn't have a custom resolver.
// Defaults to net.DefaultResolver
func WithDefaultResolver(def BasicResolver) Option {
return func(r *Resolver) error {
r.def = def
return nil
}
}
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// WithDomainResolver specifies a custom resolver for a domain/TLD.
// Custom resolver selection matches domains left to right, with more specific resolvers
// superseding generic ones.
func WithDomainResolver(domain string, rslv BasicResolver) Option {
return func(r *Resolver) error {
if r.custom == nil {
r.custom = make(map[string]BasicResolver)
}
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fqdn := dns.Fqdn(domain)
r.custom[fqdn] = rslv
return nil
}
}
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func (r *Resolver) getResolver(domain string) BasicResolver {
fqdn := dns.Fqdn(domain)
// we match left-to-right, with more specific resolvers superseding generic ones.
// So for a domain a.b.c, we will try a.b,c, b.c, c, and fallback to the default if
// there is no match
rslv, ok := r.custom[fqdn]
if ok {
return rslv
}
for i := strings.Index(fqdn, "."); i != -1; i = strings.Index(fqdn, ".") {
fqdn = fqdn[i+1:]
if fqdn == "" {
// the . is the default resolver
break
}
rslv, ok = r.custom[fqdn]
if ok {
return rslv
}
}
return r.def
}
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// Resolve resolves a DNS multiaddr.
func (r *Resolver) Resolve(ctx context.Context, maddr ma.Multiaddr) ([]ma.Multiaddr, error) {
var results []ma.Multiaddr
for i := 0; maddr != nil; i++ {
var keep ma.Multiaddr
// Find the next dns component.
keep, maddr = ma.SplitFunc(maddr, func(c ma.Component) bool {
switch c.Protocol().Code {
case DnsProtocol.Code, Dns4Protocol.Code, Dns6Protocol.Code, DnsaddrProtocol.Code:
return true
default:
return false
}
})
// Keep everything before the dns component.
if keep != nil {
if len(results) == 0 {
results = []ma.Multiaddr{keep}
} else {
for i, r := range results {
results[i] = r.Encapsulate(keep)
}
}
}
// If the rest is empty, we've hit the end (there _was_ no dns component).
if maddr == nil {
break
}
// split off the dns component.
var resolve *ma.Component
resolve, maddr = ma.SplitFirst(maddr)
proto := resolve.Protocol()
value := resolve.Value()
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rslv := r.getResolver(value)
// resolve the dns component
var resolved []ma.Multiaddr
switch proto.Code {
case Dns4Protocol.Code, Dns6Protocol.Code, DnsProtocol.Code:
// The dns, dns4, and dns6 resolver simply resolves each
// dns* component into an ipv4/ipv6 address.
v4only := proto.Code == Dns4Protocol.Code
v6only := proto.Code == Dns6Protocol.Code
// XXX: Unfortunately, go does a pretty terrible job of
// differentiating between IPv6 and IPv4. A v4-in-v6
// AAAA record will _look_ like an A record to us and
// there's nothing we can do about that.
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records, err := rslv.LookupIPAddr(ctx, value)
if err != nil {
return nil, err
}
// Convert each DNS record into a multiaddr. If the
// protocol is dns4, throw away any IPv6 addresses. If
// the protocol is dns6, throw away any IPv4 addresses.
for _, r := range records {
var (
rmaddr ma.Multiaddr
err error
)
ip4 := r.IP.To4()
if ip4 == nil {
if v4only {
continue
}
rmaddr, err = ma.NewMultiaddr("/ip6/" + r.IP.String())
} else {
if v6only {
continue
}
rmaddr, err = ma.NewMultiaddr("/ip4/" + ip4.String())
}
if err != nil {
return nil, err
}
resolved = append(resolved, rmaddr)
}
case DnsaddrProtocol.Code:
// The dnsaddr resolver is a bit more complicated. We:
//
// 1. Lookup the dnsaddr txt record on _dnsaddr.DOMAIN.TLD
// 2. Take everything _after_ the `/dnsaddr/DOMAIN.TLD`
// part of the multiaddr.
// 3. Find the dnsaddr records (if any) with suffixes
// matching the result of step 2.
// First, lookup the TXT record
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records, err := rslv.LookupTXT(ctx, "_dnsaddr."+value)
if err != nil {
return nil, err
}
// Then, calculate the length of the suffix we're
// looking for.
length := 0
if maddr != nil {
length = addrLen(maddr)
}
for _, r := range records {
// Ignore non dnsaddr TXT records.
if !strings.HasPrefix(r, dnsaddrTXTPrefix) {
continue
}
// Extract and decode the multiaddr.
rmaddr, err := ma.NewMultiaddr(r[len(dnsaddrTXTPrefix):])
if err != nil {
// discard multiaddrs we don't understand.
// XXX: Is this right? It's the best we
// can do for now, really.
continue
}
// If we have a suffix to match on.
if maddr != nil {
// Make sure the new address is at least
// as long as the suffix we're looking
// for.
rmlen := addrLen(rmaddr)
if rmlen < length {
// not long enough.
continue
}
// Matches everything after the /dnsaddr/... with the end of the
// dnsaddr record:
//
// v----------rmlen-----------------v
// /ip4/1.2.3.4/tcp/1234/p2p/QmFoobar
// /p2p/QmFoobar
// ^--(rmlen - length)--^---length--^
if !maddr.Equal(offset(rmaddr, rmlen-length)) {
continue
}
}
resolved = append(resolved, rmaddr)
}
// consumes the rest of the multiaddr as part of the "match" process.
maddr = nil
default:
panic("unreachable")
}
if len(resolved) == 0 {
return nil, nil
} else if len(results) == 0 {
results = resolved
} else {
// We take the cross product here as we don't have any
// better way to represent "ORs" in multiaddrs. For
// example, `/dns/foo.com/p2p-circuit/dns/bar.com` could
// resolve to:
//
// * /ip4/1.1.1.1/p2p-circuit/ip4/2.1.1.1
// * /ip4/1.1.1.1/p2p-circuit/ip4/2.1.1.2
// * /ip4/1.1.1.2/p2p-circuit/ip4/2.1.1.1
// * /ip4/1.1.1.2/p2p-circuit/ip4/2.1.1.2
results = cross(results, resolved)
}
}
return results, nil
}
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func (r *Resolver) LookupIPAddr(ctx context.Context, domain string) ([]net.IPAddr, error) {
return r.getResolver(domain).LookupIPAddr(ctx, domain)
}
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func (r *Resolver) LookupTXT(ctx context.Context, txt string) ([]string, error) {
return r.getResolver(txt).LookupTXT(ctx, txt)
}