core: add X-Sequence header supportv1.2.2

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.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/core.c b/src/core.c
index 8b2832a..bb76df0 100644
--- a/src/core.c
+++ b/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;
 }