Better error log when dialing without internet connection (#5466)

Co-authored-by: Cheuk <90270663+cheukt@users.noreply.github.com>

Author: allisonschiang

robot/client/client.go

@@ -535,6 +535,18 @@ func (rc *RobotClient) connectWithLock(ctx context.Context) error {
 			conn = grpcConn
 			err = nil
 		} else {
+			// A context.DeadlineExceeded from the WebRTC dial implies the client is unable to reach
+			// the signaling server, which likely means that the client is offline. In that case, if the errors returned from
+			// grpc dials are also timeouts or mDNS failing to find a candidate, we should remind clients to double-check their internet
+			// connection and that the machine is on. This should be more helpful than simply returning a chain of context.DeadlineExceeded
+			// and candidate not found errors.
+			const connTimeoutURL = "https://docs.viam.com/dev/tools/common-errors/#conn-time-out"
+			if errors.Is(err, context.DeadlineExceeded) &&
+				errors.Is(grpcErr, context.DeadlineExceeded) &&
+				errors.Is(grpcErr, rpc.ErrMDNSNoCandidatesFound) {
+				return fmt.Errorf("failed to connect to machine within time limit. check network connection, whether the viam-server is running, " +
+					"and try again. see " + connTimeoutURL + " for troubleshooting steps")
+			}
 			err = multierr.Combine(err, grpcErr)
 		}
 	}