Add sequence diagram for client connection flow

src/SUMMARY.md

@@ -63,6 +63,7 @@ Robust Toolbox
 - [ECS](en/robust-toolbox/ecs.md)
 - [Netcode]()
   - [Net Entities](en/robust-toolbox/netcode/net-entities.md)
+  - [Connection Sequence](en/robust-toolbox/netcode/connection-sequence.md)
   - [Potentially Visible Set]()
 - [Coordinate Systems](en/robust-toolbox/coordinate-systems.md)
 - [Transform]()

src/en/robust-toolbox/netcode/connection-sequence.md

@@ -0,0 +1,68 @@
+# RobustToolbox Connection Sequence
+
+This is a complete sequence of what steps get taken when a client connects in RobustToolbox (and to some extent, Space Station 14). This is an incredibly involved and messy system that evolved over multiple years, and has many moving parts and sets of state. Oof.
+
+## Basic overview
+
+```mermaid
+sequenceDiagram
+    participant C as Client
+    participant S as Server
+    
+    C->>S: Lidgren Connection Attempt
+    S->>C: Lidgren Connection Approval
+    
+    rect
+        Note over C,S: Initial handshake
+        
+        C->>S: MsgLoginStart
+        Note left of S: Server decides to auth or not
+        opt Authentication
+            S->>C: MsgEncryptionRequest
+            create participant A as Auth Server
+            C->>A: POST /api/session/join
+            C->>S: MsgEncryptionResponse
+            %% I'd use <<->> but my Trilium doesn't have Mermaid v11.0.0 yet.
+            destroy A
+            S->A: GET /api/session/hasJoined
+        end
+        Note over S: Connecting event is raised,<br/>content can deny connection if desired
+        S->>C: MsgLoginSuccess
+        Note over C,S: Both sides enable encryption if necessary
+        Note over C,S: Both sides create NetChannel
+    end
+    S->>C: MsgStringTableEntries
+    rect
+        Note over C,S: Serializer handshake
+        S->>C: MsgMapStrServerHandshake
+        C->>S: MsgMapStrClientHandshake
+        opt Client needs strings
+            S->>C: MsgMapStrStrings
+            C->>S: MsgMapStrClientHandshake
+        end
+    end
+    Note over S,C: NetManager.Connected event<br/>Non-handshake messages are now allowed
+    C-->>S: MsgConVars
+    C-->>S: MsgConCmdReg
+    par PlayerManager.NewSession
+        Note over S: Server-side player session gets created,<br/>PlayerStatusChanged gets ran for first time
+        S->>C: MsgSyncTimeBase
+        Note over S: NetConfigurationManager.SyncConnectingClient
+        S->>C: MsgConVars
+        Note over C: Client-side player session gets created
+        C->>S: MsgPlayerListReq
+    and UploadedContentManager
+        loop Send uploaded resources
+            S->>C: NetworkResourceUploadMessage
+        end
+        loop Send uploaded prototypes
+            S->>C: GamePrototypeLoadMessage
+        end
+    end
+    Note over S: Player session is set to Connected
+    S->>C: MsgPlayerList<br/>Contains Connected Status
+    Note over C: Player session is set to Connected
+    Note over S: Content sets client session to InGame
+    S->>C: Starts sending game states
+    Note over C: Player session is set to InGame
+```