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dns.go
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dns.go
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package namesys
import (
"context"
"errors"
"net"
"strings"
"time"
opts "github.com/ipfs/go-ipfs/namesys/opts"
path "github.com/ipfs/go-ipfs/path"
isd "gx/ipfs/QmZmmuAXgX73UQmX1jRKjTGmjzq24Jinqkq8vzkBtno4uX/go-is-domain"
)
type LookupTXTFunc func(name string) (txt []string, err error)
// DNSResolver implements a Resolver on DNS domains
type DNSResolver struct {
lookupTXT LookupTXTFunc
// TODO: maybe some sort of caching?
// cache would need a timeout
}
// NewDNSResolver constructs a name resolver using DNS TXT records.
func NewDNSResolver() *DNSResolver {
return &DNSResolver{lookupTXT: net.LookupTXT}
}
// Resolve implements Resolver.
func (r *DNSResolver) Resolve(ctx context.Context, name string, options ...opts.ResolveOpt) (path.Path, error) {
return resolve(ctx, r, name, opts.ProcessOpts(options), "/ipns/")
}
type lookupRes struct {
path path.Path
error error
}
// resolveOnce implements resolver.
// TXT records for a given domain name should contain a b58
// encoded multihash.
func (r *DNSResolver) resolveOnce(ctx context.Context, name string, options *opts.ResolveOpts) (path.Path, time.Duration, error) {
segments := strings.SplitN(name, "/", 2)
domain := segments[0]
if !isd.IsDomain(domain) {
return "", 0, errors.New("not a valid domain name")
}
log.Debugf("DNSResolver resolving %s", domain)
rootChan := make(chan lookupRes, 1)
go workDomain(r, domain, rootChan)
subChan := make(chan lookupRes, 1)
go workDomain(r, "_dnslink."+domain, subChan)
var subRes lookupRes
select {
case subRes = <-subChan:
case <-ctx.Done():
return "", 0, ctx.Err()
}
var p path.Path
if subRes.error == nil {
p = subRes.path
} else {
var rootRes lookupRes
select {
case rootRes = <-rootChan:
case <-ctx.Done():
return "", 0, ctx.Err()
}
if rootRes.error == nil {
p = rootRes.path
} else {
return "", 0, ErrResolveFailed
}
}
var err error
if len(segments) > 1 {
p, err = path.FromSegments("", strings.TrimRight(p.String(), "/"), segments[1])
}
return p, 0, err
}
func workDomain(r *DNSResolver, name string, res chan lookupRes) {
txt, err := r.lookupTXT(name)
if err != nil {
// Error is != nil
res <- lookupRes{"", err}
return
}
for _, t := range txt {
p, err := parseEntry(t)
if err == nil {
res <- lookupRes{p, nil}
return
}
}
res <- lookupRes{"", ErrResolveFailed}
}
func parseEntry(txt string) (path.Path, error) {
p, err := path.ParseCidToPath(txt) // bare IPFS multihashes
if err == nil {
return p, nil
}
return tryParseDnsLink(txt)
}
func tryParseDnsLink(txt string) (path.Path, error) {
parts := strings.SplitN(txt, "=", 2)
if len(parts) == 2 && parts[0] == "dnslink" {
return path.ParsePath(parts[1])
}
return "", errors.New("not a valid dnslink entry")
}