p2p: add network simulation framework (#14982)

This commit introduces a network simulation framework which
can be used to run simulated networks of devp2p nodes. The
intention is to use this for testing protocols, performing
benchmarks and visualising emergent network behaviour.

p2p/discover/node.go

@@ -225,6 +225,11 @@ func (n *Node) UnmarshalText(text []byte) error {
 // The node identifier is a marshaled elliptic curve public key.
 type NodeID [NodeIDBits / 8]byte
 
+// Bytes returns a byte slice representation of the NodeID
+func (n NodeID) Bytes() []byte {
+	return n[:]
+}
+
 // NodeID prints as a long hexadecimal number.
 func (n NodeID) String() string {
 	return fmt.Sprintf("%x", n[:])
@@ -240,6 +245,41 @@ func (n NodeID) TerminalString() string {
 	return hex.EncodeToString(n[:8])
 }
 
+// MarshalText implements the encoding.TextMarshaler interface.
+func (n NodeID) MarshalText() ([]byte, error) {
+	return []byte(hex.EncodeToString(n[:])), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface.
+func (n *NodeID) UnmarshalText(text []byte) error {
+	id, err := HexID(string(text))
+	if err != nil {
+		return err
+	}
+	*n = id
+	return nil
+}
+
+// BytesID converts a byte slice to a NodeID
+func BytesID(b []byte) (NodeID, error) {
+	var id NodeID
+	if len(b) != len(id) {
+		return id, fmt.Errorf("wrong length, want %d bytes", len(id))
+	}
+	copy(id[:], b)
+	return id, nil
+}
+
+// MustBytesID converts a byte slice to a NodeID.
+// It panics if the byte slice is not a valid NodeID.
+func MustBytesID(b []byte) NodeID {
+	id, err := BytesID(b)
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
 // HexID converts a hex string to a NodeID.
 // The string may be prefixed with 0x.
 func HexID(in string) (NodeID, error) {