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// Copyright (C) 2019-2024 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package dnssec
import (
"context"
"fmt"
"net"
"strconv"
"strings"
)
// Dialer wraps net.Dialer and provides a custom DNSSEC-aware resolver
type Dialer struct {
InnerDialer *net.Dialer
Resolver ResolverIf
}
// DialContext connects to the address on the named network using the provided context.
// It waits if needed not to exceed connectionsRateLimitingCount.
// Idea:
//
// net.Dialer.DialContext calls net.Dialer.resolver().resolveAddrList
// that calls net.Resolver.internetAddrList
// that ends up in LookupIPAddr -> lookupIPAddr -> parseIPZone -> return
// So this DialContext:
// 1. Parses address to host and port
// 2. If the host is not IPv4/IPv6 address then resolves it with DNSSEC
// 3. Calls original net.DialContext knowing that the name already resolved
// and the control flow would be as described above
func (d *Dialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
// snipped below is from net.Resolver.internetAddrList
var (
err error
host, port string
portnum int
)
switch network {
case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
if address != "" {
if host, port, err = net.SplitHostPort(address); err != nil {
return nil, err
}
if portnum, err = d.Resolver.LookupPort(ctx, network, port); err != nil {
return nil, err
}
}
default:
return nil, net.UnknownNetworkError(network)
}
// end snippet
if host == "" {
return nil, fmt.Errorf("Empty host")
}
var resolvedAddr string
// check if address is IPv4 or IPv6 address
var zone string
if i := strings.LastIndex(host, "%"); i > 0 {
host, zone = host[:i], host[i+1:]
}
if netIP := net.ParseIP(host); netIP != nil {
resolvedAddr = netIP.String()
if zone != "" {
resolvedAddr = fmt.Sprintf("%s%%%s", resolvedAddr, zone)
}
} else {
// not an address, lookup with DNS
var ipAddrs []net.IPAddr
if ipAddrs, err = d.Resolver.LookupIPAddr(ctx, host); err != nil {
return nil, err
}
resolvedAddr = ipAddrs[0].String() // LookupIPAddr returns non-empty list
}
resolvedAddr = net.JoinHostPort(resolvedAddr, strconv.Itoa(portnum))
return d.InnerDialer.DialContext(ctx, network, resolvedAddr)
}
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