net-test: packetdrill: for wire mode have client send WIRE_LIVE_REMOTE_IP to server

For wire mode have the client send WIRE_LIVE_REMOTE_IP to server.

This fixes a significant bug from the May 2023 wire mode patch series.
That bug caused the wire server to inject packets with a source IP of
the DEFAULT_V4_LIVE_REMOTE_IP_STRING (192.0.2.1) instead of a source
IP of the wire server machine. That bug prevented wire mode from
working properly.

This fixes behavior so that the following simple usage works as
intended for remote/wire-server mode:

server_machine# ./packetdrill --wire_server
client_machine# ./packetdrill --wire_server_at=10.240.0.42 test.pkt

This method of configuring the client and server now works properly
because:

+ set_wire_client_defaults() will set live_remote_ip_string from
  wire_server_ip

+ the client will communicate this live_remote_ip_string value to the
  server

+ the server will use this live_remote_ip_string as the source IP for
  injected packets

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Change-Id: Icda2f8040b3d69a1c23813e9d94e94cc3be88a36

Author: nealcardwell

gtests/net/packetdrill/wire_client.c

@@ -151,6 +151,18 @@ static void wire_client_send_live_local_ip(struct wire_client *wire_client,
 				"error sending WIRE_LIVE_LOCAL_IP");
 }
 
+/* Send the IP live_remote address from which the server should send packets. */
+static void wire_client_send_live_remote_ip(struct wire_client *wire_client,
+					   const struct config *config)
+{
+	if (wire_conn_write(wire_client->wire_conn,
+			    WIRE_LIVE_REMOTE_IP,
+			    config->live_remote_ip_string,
+			    strlen(config->live_remote_ip_string)))
+		wire_client_die(wire_client,
+				"error sending WIRE_LIVE_REMOTE_IP");
+}
+
 /* Receive server's message that the server is ready to execute the script. */
 static void wire_client_receive_server_ready(struct wire_client *wire_client)
 {
@@ -279,6 +291,8 @@ int wire_client_init(struct wire_client *wire_client,
 
 	wire_client_send_live_local_ip(wire_client, config);
 
+	wire_client_send_live_remote_ip(wire_client, config);
+
 	wire_client_receive_server_ready(wire_client);
 
 	return STATUS_OK;

gtests/net/packetdrill/wire_protocol.c

@@ -37,6 +37,7 @@ const char *wire_op_to_string(enum wire_op_t op)
 	case WIRE_SCRIPT:		return "WIRE_SCRIPT";
 	case WIRE_HARDWARE_ADDR:	return "WIRE_HARDWARE_ADDR";
 	case WIRE_LIVE_LOCAL_IP:	return "WIRE_LIVE_LOCAL_IP";
+	case WIRE_LIVE_REMOTE_IP:	return "WIRE_LIVE_REMOTE_IP";
 	case WIRE_SERVER_READY:		return "WIRE_SERVER_READY";
 	case WIRE_CLIENT_STARTING:	return "WIRE_CLIENT_STARTING";
 	case WIRE_PACKETS_START:	return "WIRE_PACKETS_START";

gtests/net/packetdrill/wire_protocol.h

@@ -35,6 +35,7 @@ enum wire_op_t {
 	WIRE_SCRIPT,		/* "here's the script we're going to start" */
 	WIRE_HARDWARE_ADDR,	/* "here's my ethernet MAC address" */
 	WIRE_LIVE_LOCAL_IP,	/* "here's the client live_local_ip_string */
+	WIRE_LIVE_REMOTE_IP,	/* "here's the live_remote_ip_string to use */
 	WIRE_SERVER_READY,	/* "server ready to start script execution" */
 	WIRE_CLIENT_STARTING,	/* "i'm starting script execution... now!" */
 	WIRE_PACKETS_START,	/* "please start handling packet events" */

gtests/net/packetdrill/wire_server.c

@@ -236,6 +236,35 @@ static int wire_server_receive_live_local_ip(struct wire_server *wire_server)
 	return STATUS_OK;
 }
 
+/* Receive the live_remote IP from which the server should send packets. */
+static int wire_server_receive_live_remote_ip(struct wire_server *wire_server)
+{
+	enum wire_op_t op = WIRE_INVALID;
+	void *buf = NULL;
+	int buf_len = -1;
+	struct config *config = &wire_server->config;
+
+	if (wire_conn_read(wire_server->wire_conn, &op, &buf, &buf_len))
+		return STATUS_ERR;
+	if (op != WIRE_LIVE_REMOTE_IP) {
+		fprintf(stderr,
+			"bad wire client: expected WIRE_LIVE_REMOTE_IP\n");
+		return STATUS_ERR;
+	}
+	if (buf_len + 1 > sizeof(config->live_remote_ip_string)) {
+		fprintf(stderr,
+			"bad wire client: ip address too long\n");
+		return STATUS_ERR;
+	}
+
+	memcpy(config->live_remote_ip_string, buf, buf_len);
+	config->live_remote_ip_string[buf_len] = '\0';  /* NULL-terminate str */
+	DEBUGP("got WIRE_LIVE_REMOTE_IP: [%s]\n",
+	       config->live_remote_ip_string);
+
+	return STATUS_OK;
+}
+
 /* Send a message to tell the client we're ready to excecute the script. */
 static int wire_server_send_server_ready(struct wire_server *wire_server)
 {
@@ -488,6 +517,9 @@ static void *wire_server_thread(void *arg)
 	if (wire_server_receive_live_local_ip(wire_server))
 		goto error_done;
 
+	if (wire_server_receive_live_remote_ip(wire_server))
+		goto error_done;
+
 	if (parse_script_and_set_config(wire_server->argc,
 						wire_server->argv,
 						&wire_server->config,