refactor-for-testability (#3)

Co-authored-by: jdl <jdl@desktop>
Co-authored-by: jdl <jdl@crumpington.com>
Reviewed-on: #3

peer/packets.go

@@ -0,0 +1,120 @@
+package peer
+
+import (
+	"net/netip"
+)
+
+const (
+	packetTypeSyn           = 1
+	packetTypeInit          = 2
+	packetTypeAck           = 3
+	packetTypeProbe         = 4
+	packetTypeAddrDiscovery = 5
+)
+
+// ----------------------------------------------------------------------------
+
+type packetInit struct {
+	TraceID uint64
+	Direct  bool
+	Version uint64
+}
+
+func (p packetInit) Marshal(buf []byte) []byte {
+	return newBinWriter(buf).
+		Byte(packetTypeInit).
+		Uint64(p.TraceID).
+		Bool(p.Direct).
+		Uint64(p.Version).
+		Build()
+}
+
+func parsePacketInit(buf []byte) (p packetInit, err error) {
+	err = newBinReader(buf[1:]).
+		Uint64(&p.TraceID).
+		Bool(&p.Direct).
+		Uint64(&p.Version).
+		Error()
+	return
+}
+
+// ----------------------------------------------------------------------------
+
+type packetSyn struct {
+	TraceID       uint64   // TraceID to match response w/ request.
+	SharedKey     [32]byte // Our shared key.
+	Direct        bool
+	PossibleAddrs [8]netip.AddrPort // Possible public addresses of the sender.
+}
+
+func (p packetSyn) Marshal(buf []byte) []byte {
+	return newBinWriter(buf).
+		Byte(packetTypeSyn).
+		Uint64(p.TraceID).
+		SharedKey(p.SharedKey).
+		Bool(p.Direct).
+		AddrPort8(p.PossibleAddrs).
+		Build()
+}
+
+func parsePacketSyn(buf []byte) (p packetSyn, err error) {
+	err = newBinReader(buf[1:]).
+		Uint64(&p.TraceID).
+		SharedKey(&p.SharedKey).
+		Bool(&p.Direct).
+		AddrPort8(&p.PossibleAddrs).
+		Error()
+	return
+}
+
+// ----------------------------------------------------------------------------
+
+type packetAck struct {
+	TraceID       uint64
+	ToAddr        netip.AddrPort
+	PossibleAddrs [8]netip.AddrPort // Possible public addresses of the sender.
+}
+
+func (p packetAck) Marshal(buf []byte) []byte {
+	return newBinWriter(buf).
+		Byte(packetTypeAck).
+		Uint64(p.TraceID).
+		AddrPort(p.ToAddr).
+		AddrPort8(p.PossibleAddrs).
+		Build()
+}
+
+func parsePacketAck(buf []byte) (p packetAck, err error) {
+	err = newBinReader(buf[1:]).
+		Uint64(&p.TraceID).
+		AddrPort(&p.ToAddr).
+		AddrPort8(&p.PossibleAddrs).
+		Error()
+	return
+}
+
+// ----------------------------------------------------------------------------
+
+// A probeReqPacket is sent from a client to a server to determine if direct
+// UDP communication can be used.
+type packetProbe struct {
+	TraceID uint64
+}
+
+func (p packetProbe) Marshal(buf []byte) []byte {
+	return newBinWriter(buf).
+		Byte(packetTypeProbe).
+		Uint64(p.TraceID).
+		Build()
+}
+
+func parsePacketProbe(buf []byte) (p packetProbe, err error) {
+	err = newBinReader(buf[1:]).
+		Uint64(&p.TraceID).
+		Error()
+	return
+}
+
+// ----------------------------------------------------------------------------
+
+type packetLocalDiscovery struct{}