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_test.go

@@ -17,6 +17,7 @@
 package discover
 
 import (
+	"bytes"
 	"fmt"
 	"math/big"
 	"math/rand"
@@ -192,6 +193,35 @@ func TestHexID(t *testing.T) {
 	}
 }
 
+func TestNodeID_textEncoding(t *testing.T) {
+	ref := NodeID{
+		0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x10,
+		0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x20,
+		0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x30,
+		0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x40,
+		0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x50,
+		0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x60,
+		0x61, 0x62, 0x63, 0x64,
+	}
+	hex := "01020304050607080910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364"
+
+	text, err := ref.MarshalText()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(text, []byte(hex)) {
+		t.Fatalf("text encoding did not match\nexpected: %s\ngot:      %s", hex, text)
+	}
+
+	id := new(NodeID)
+	if err := id.UnmarshalText(text); err != nil {
+		t.Fatal(err)
+	}
+	if *id != ref {
+		t.Fatalf("text decoding did not match\nexpected: %s\ngot:      %s", ref, id)
+	}
+}
+
 func TestNodeID_recover(t *testing.T) {
 	prv := newkey()
 	hash := make([]byte, 32)