tor: add onion address implementation

Co-Authored-By: Eugene <crypt-iq@users.noreply.github.com>

tor/onionaddr.go

@@ -0,0 +1,63 @@
+package tor
+
+import (
+	"encoding/base32"
+	"net"
+	"strconv"
+)
+
+const (
+	// base32Alphabet is the alphabet used for encoding and decoding v2 and
+	// v3 onion addresses.
+	base32Alphabet = "abcdefghijklmnopqrstuvwxyz234567"
+
+	// OnionSuffix is the ".onion" suffix for v2 and v3 onion addresses.
+	OnionSuffix = ".onion"
+
+	// OnionSuffixLen is the length of the ".onion" suffix.
+	OnionSuffixLen = len(OnionSuffix)
+
+	// V2DecodedLen is the length of a decoded v2 onion service.
+	V2DecodedLen = 10
+
+	// V2Len is the length of a v2 onion service including the ".onion"
+	// suffix.
+	V2Len = 22
+
+	// V3DecodedLen is the length of a decoded v3 onion service.
+	V3DecodedLen = 35
+
+	// V3Len is the length of a v2 onion service including the ".onion"
+	// suffix.
+	V3Len = 62
+)
+
+var (
+	// Base32Encoding represents the Tor's base32-encoding scheme for v2 and
+	// v3 onion addresses.
+	Base32Encoding = base32.NewEncoding(base32Alphabet)
+)
+
+// OnionAddr represents a Tor network end point onion address.
+type OnionAddr struct {
+	// OnionService is the host of the onion address.
+	OnionService string
+
+	// Port is the port of the onion address.
+	Port int
+}
+
+// A compile-time check to ensure that OnionAddr implements the net.Addr
+// interface.
+var _ net.Addr = (*OnionAddr)(nil)
+
+// String returns the string representation of an onion address.
+func (o *OnionAddr) String() string {
+	return net.JoinHostPort(o.OnionService, strconv.Itoa(o.Port))
+}
+
+// Network returns the network that this implementation of net.Addr will use.
+// In this case, because Tor only allows TCP connections, the network is "tcp".
+func (o *OnionAddr) Network() string {
+	return "tcp"
+}