net: implement ResolveIPAddr with stub for lookupProtocol, take #2

This is a rework of PR#24 based on review comments.  The rework mostly
involved moving changes to the proper files, aligning with upstream Go
src/net file layout.

dial.go

@@ -16,6 +16,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"internal/bytealg"
 	"syscall"
 	"time"
 )
@@ -191,6 +192,38 @@ func (lc *ListenConfig) ListenPacket(ctx context.Context, network, address strin
 	return nil, errors.New("dial:ListenConfig:ListenPacket not implemented")
 }
 
+func parseNetwork(ctx context.Context, network string, needsProto bool) (afnet string, proto int, err error) {
+	i := bytealg.LastIndexByteString(network, ':')
+	if i < 0 { // no colon
+		switch network {
+		case "tcp", "tcp4", "tcp6":
+		case "udp", "udp4", "udp6":
+		case "ip", "ip4", "ip6":
+			if needsProto {
+				return "", 0, UnknownNetworkError(network)
+			}
+		case "unix", "unixgram", "unixpacket":
+		default:
+			return "", 0, UnknownNetworkError(network)
+		}
+		return network, 0, nil
+	}
+	afnet = network[:i]
+	switch afnet {
+	case "ip", "ip4", "ip6":
+		protostr := network[i+1:]
+		proto, i, ok := dtoi(protostr)
+		if !ok || i != len(protostr) {
+			proto, err = lookupProtocol(ctx, protostr)
+			if err != nil {
+				return "", 0, err
+			}
+		}
+		return afnet, proto, nil
+	}
+	return "", 0, UnknownNetworkError(network)
+}
+
 // Listen announces on the local network address.
 //
 // See Go "net" package Listen() for more information.

iprawsock.go

@@ -63,6 +63,23 @@ func (a *IPAddr) opAddr() Addr {
 	return a
 }
 
+// ResolveIPAddr returns an address of IP end point.
+//
+// The network must be an IP network name.
+//
+// If the host in the address parameter is not a literal IP address,
+// ResolveIPAddr resolves the address to an address of IP end point.
+// Otherwise, it parses the address as a literal IP address.
+// The address parameter can use a host name, but this is not
+// recommended, because it will return at most one of the host name's
+// IP addresses.
+//
+// See func [Dial] for a description of the network and address
+// parameters.
+func ResolveIPAddr(network, address string) (*IPAddr, error) {
+	return nil, errors.New("ResolveIPAddr not implemented")
+}
+
 // IPConn is the implementation of the Conn and PacketConn interfaces
 // for IP network connections.
 type IPConn struct {

lookup_unix.go

@@ -0,0 +1,20 @@
+// TINYGO: The following is copied and modified from Go 1.22.0 official implementation.
+
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix || js || wasip1
+
+package net
+
+import (
+	"context"
+	"errors"
+)
+
+// lookupProtocol looks up IP protocol name in /etc/protocols and
+// returns correspondent protocol number.
+func lookupProtocol(_ context.Context, name string) (int, error) {
+	return 0, errors.New("net:lookupProtocol not implemented")
+}