devguide/transactions: update & refine diagrams

- DNS sequence diagram was incorrect (transactions should be
unidirectional). After changing it, it made sense to rename the file.
Adjusted spacing, too. Updated transactions.rst accordingly.
- TLS sequence diagram was refined to illustrate how Suricata actually
implements the protocol.

doc/devguide/extending/app-layer/img/DnsUnidirectionalTransactions.msc

@@ -9,7 +9,8 @@ msc {
 
     # Message Flow
     a =>> b [ label = "DNS Request" ];
-    b =>> a [ label = "DNS Response" ];
+    --- [ label = "Transaction 1 Completed" ];
     |||;
-    --- [ label = "Transaction Completed" ];
+    b =>> a [ label = "DNS Response" ];
+    --- [ label = "Transaction 2 Completed" ];
 }

doc/devguide/extending/app-layer/img/TlsHandshake.msc

@@ -5,17 +5,27 @@ msc {
     arcgradient = "10";
 
     # Entities
-    a [ label = "Client" ], b [ label = "Server"];
+    a [ label = "Client" ], b [ label = "Server" ];
 
     # Message Flow
-    a =>> b [ label = "ClientHello"];
+    # TLS_STATE_IN_PROGRESS = 0,
-    b =>> a [ label = "ServerHello"];
+    a abox b [ label = "TLS_STATE_IN_PROGRESS" ];
-    b =>> a [ label = "ServerCertificate"];
+    a =>> b [ label = "ClientHello" ];
-    b =>> a [ label = "ServerHello Done"];
+    b =>> a [ label = "ServerHello" ];
-    a =>> b [ label = "ClientCertificate"];
+    b =>> a [ label = "ServerCertificate" ];
-    a =>> b [ label = "ClientKeyExchange"];
+    b =>> a [ label = "ServerHello Done" ];
+
+    a =>> b [ label = "ClientCertificate" ];
+    # TLS_STATE_CERT_READY = 1,
+    a abox b [ label = "TLS_STATE_CERT_READY" ];
+    a =>> b [ label = "ClientKeyExchange" ];
+
     a =>> b [ label = "Finished" ];
     b =>> a [ label = "Finished" ];
-
+    # TLS_HANDSHAKE_DONE = 2,
+    a abox b [ label = "TLS_HANDSHAKE_DONE" ];
+    ...;
+    # TLS_STATE_FINISHED = 3
+    a abox b [ label = "TLS_STATE_FINISHED" ];
     --- [ label = "Transaction Completed" ];
 }

doc/devguide/extending/app-layer/transactions.rst

@@ -216,7 +216,7 @@ Sequence Diagrams
 
 A DNS transaction in Suricata can be considered unidirectional:
 
-.. image:: img/DnsRequestUnidirectionalTransaction.png
+.. image:: img/DnsUnidirectionalTransactions.png
   :width: 600
   :alt: A sequence diagram with two entities, Client and Server, with an arrow going from the Client to the Server, labeled "DNS Request". After that, there is a dotted line labeled "Transaction Completed".