core: add X-Sequence header support

Add non-standard HTTP header "X-Sequence" to the header section of
requests (og_send_request) sent to a connected client.

Define a starting sequence number when creating a new instance of struct
og_client inside og_server_accept_cb. This sequence number is
incremented by one for each outgoing request from ogServer.

This sequence number is checked when receiving a response from a
connected client, if they do not match the connection is dropped.

Use sequence 0 for out-of-band commands (reboot, poweroff, stop). Any
client response with header "X-Sequence: 0" bypasses sequence check.

src/core.c

@@ -160,6 +160,7 @@ enum og_agent_state {
 
 static int og_agent_state_recv_hdr_rest(struct og_client *cli)
 {
+	uint32_t seq;
 	char *ptr;
 
 	ptr = strstr(cli->buf, "\r\n\r\n");
@@ -176,6 +177,20 @@ static int og_agent_state_recv_hdr_rest(struct og_client *cli)
 		cli->msg_len += cli->content_length;
 	}
 
+	ptr = strstr(cli->buf, "X-Sequence: ");
+	if (ptr) {
+		if (sscanf(ptr, "X-Sequence: %i[^\r\n]", &seq) != 1) {
+			syslog(LOG_ERR, "Invalid sequence value from client %s. Payload:\n%s",
+			       inet_ntoa(cli->addr.sin_addr), cli->buf);
+			return -1;
+		}
+		if (cli->seq != 0 && cli->seq != seq) {
+			syslog(LOG_ERR, "Unexpected sequence %u from client %s, expecting %u.",
+			       seq, inet_ntoa(cli->addr.sin_addr), cli->seq);
+			return -1;
+		}
+	}
+
 	return 1;
 }
 

src/rest.c

@@ -296,6 +296,7 @@ int og_send_request(enum og_rest_method method, enum og_cmd_type type,
 	const char *uri;
 	unsigned int i;
 	int client_sd;
+	bool has_seq;
 
 	if (method == OG_METHOD_GET)
 		snprintf(method_str, 5, "GET");
@@ -312,9 +313,17 @@ int og_send_request(enum og_rest_method method, enum og_cmd_type type,
 					    JSON_COMPACT);
 
 	uri = og_cmd_to_uri[type];
-	snprintf(buf, OG_MSG_REQUEST_MAXLEN,
-		 "%s /%s HTTP/1.1\r\nContent-Length: %d\r\n%s\r\n\r\n%s",
-		 method_str, uri, content_length, content_type, content);
+
+	switch (type) {
+		case OG_CMD_POWEROFF:
+		case OG_CMD_REBOOT:
+		case OG_CMD_STOP:
+			has_seq = false;
+			break;
+		default:
+			has_seq = true;
+			break;
+	}
 
 	for (i = 0; i < params->ips_array_len; i++) {
 		cli = og_client_find(params->ips_array[i]);
@@ -331,6 +340,13 @@ int og_send_request(enum og_rest_method method, enum og_cmd_type type,
 			continue;
 		}
 
+		if (++cli->seq == 0)
+			cli->seq++;
+
+		snprintf(buf, OG_MSG_REQUEST_MAXLEN,
+			 "%s /%s HTTP/1.1\r\nContent-Length: %d\r\nX-Sequence: %u\r\n%s\r\n\r\n%s",
+			 method_str, uri, content_length, has_seq ? cli->seq : 0, content_type, content);
+
 		if (send(client_sd, buf, strlen(buf), 0) < 0)
 			continue;
 

src/rest.h

@@ -68,6 +68,7 @@ struct og_client {
 	enum og_cmd_result	last_cmd_result;
 	bool			autorun;
 	uint32_t		speed;
+	uint32_t		seq;
 	const char		*shell_output;
 };