/
dns.go
92 lines (77 loc) · 2.53 KB
/
dns.go
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package gateway
import (
"fmt"
"strings"
"github.com/libp2p/go-doh-resolver"
dns "github.com/miekg/dns"
madns "github.com/multiformats/go-multiaddr-dns"
)
var defaultResolvers = map[string]string{
"eth.": "https://resolver.cloudflare-eth.com/dns-query",
"crypto.": "https://resolver.cloudflare-eth.com/dns-query",
}
func newResolver(url string, opts ...doh.Option) (madns.BasicResolver, error) {
if !strings.HasPrefix(url, "https://") {
return nil, fmt.Errorf("invalid resolver url: %s", url)
}
return doh.NewResolver(url, opts...)
}
// NewDNSResolver creates a new DNS resolver based on the default resolvers and
// the provided resolvers.
//
// The argument 'resolvers' is a map of [FQDNs] to URLs for custom DNS resolution.
// URLs starting with "https://" indicate [DoH] endpoints. Support for other resolver
// types may be added in the future.
//
// Example:
// - Custom resolver for ENS: "eth." → "https://eth.link/dns-query"
// - Override the default OS resolver: "." → "https://doh.applied-privacy.net/query"
//
// [FQDNs]: https://en.wikipedia.org/wiki/Fully_qualified_domain_name
// [DoH]: https://en.wikipedia.org/wiki/DNS_over_HTTPS
func NewDNSResolver(resolvers map[string]string, dohOpts ...doh.Option) (*madns.Resolver, error) {
var opts []madns.Option
var err error
domains := make(map[string]struct{}) // to track overridden default resolvers
rslvrs := make(map[string]madns.BasicResolver) // to reuse resolvers for the same URL
for domain, url := range resolvers {
if domain != "." && !dns.IsFqdn(domain) {
return nil, fmt.Errorf("invalid domain %s; must be FQDN", domain)
}
domains[domain] = struct{}{}
if url == "" {
// allow overriding of implicit defaults with the default resolver
continue
}
rslv, ok := rslvrs[url]
if !ok {
rslv, err = newResolver(url, dohOpts...)
if err != nil {
return nil, fmt.Errorf("bad resolver for %s: %w", domain, err)
}
rslvrs[url] = rslv
}
if domain != "." {
opts = append(opts, madns.WithDomainResolver(domain, rslv))
} else {
opts = append(opts, madns.WithDefaultResolver(rslv))
}
}
// fill in defaults if not overridden by the user
for domain, url := range defaultResolvers {
_, ok := domains[domain]
if ok {
continue
}
rslv, ok := rslvrs[url]
if !ok {
rslv, err = newResolver(url)
if err != nil {
return nil, fmt.Errorf("bad resolver for %s: %w", domain, err)
}
rslvrs[url] = rslv
}
opts = append(opts, madns.WithDomainResolver(domain, rslv))
}
return madns.NewResolver(opts...)
}