ping: add a useful error message when pinging self

We don't allow dialing self for many (very good) reasons.

fixes #4542

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

core/commands/ping.go

@@ -3,6 +3,7 @@ package commands
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -26,6 +27,9 @@ type PingResult struct {
 	Text    string
 }
 
+// ErrPingSelf is returned when the user attempts to ping themself.
+var ErrPingSelf = errors.New("error: can't ping self")
+
 var PingCmd = &cmds.Command{
 	Helptext: cmdkit.HelpText{
 		Tagline: "Send echo request packets to IPFS hosts.",
@@ -84,6 +88,11 @@ trip latency information.
 			return
 		}
 
+		if peerID == n.Identity {
+			res.SetError(ErrPingSelf, cmdkit.ErrNormal)
+			return
+		}
+
 		if addr != nil {
 			n.Peerstore.AddAddr(peerID, addr, pstore.TempAddrTTL) // temporary
 		}