Context

This projet is part of a Proof of Concept (POC) for a larger private project.

As a result, the code is commented in French — apologies for that.
It is also structured to support automatic documentation generation using Doxygen.

Multiclient TCP Server

I encountered several issues when transitioning from a single‑client TCP server to a multi‑client TCP server.
Sharing the same server instance can lead to socket concurrency problems.
Let’s take a look at the structural differences to better understand this behavior.

Single client

The client connects to the socket.
It can send messages as long as the socket remains open.
A limitation of this architecture is that issues arise when attempting to connect multiple clients simultaneously.

---
Title: TCP Client example
---
flowchart LR


subgraph TCP Client
    Config["`IP: 192.168.0.10
    `"]

    Connect(["client(#quot;192.168.0.50#quot;, 8080);"])

    TCP["TCP exchanges successfull"]
end

subgraph TCP Client 2
    Config2["`IP: 192.168.0.11
    `"]

    Connect2(["client(#quot;192.168.0.50#quot;, 8080);"])

    TCP2["TCP exchanges failed"]
end

subgraph TCP Server
    Config_Server["`IP: 192.168.0.50
    Port: 8080
    `"]

    Socket
end

Connect <--> Socket
Socket <--> Connect2


TCP <==>
Socket x==x TCP2

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Multiclient

Clients connect one by one to the main socket.
This socket listens for incoming client/server connections, then redirects each client to a dedicated thread.
This allows each client to maintain its own individual socket connection.
As a result, there are no inter-client conflicts with this approach.

---
Title: TCP Client example
---
flowchart LR


subgraph TCP Client
    direction TB
    Config["`IP: 192.168.0.10
    `"]

    Connect(["client(#quot;192.168.0.50#quot;, 8080);"])

    TCP["TCP exchanges successfull"]
end

subgraph TCP Client 2
    direction TB
    Config2["`IP: 192.168.0.11
    `"]

    Connect2(["client(#quot;192.168.0.50#quot;, 8080);"])

    TCP2["TCP exchanges successfull"]
end

subgraph TCP Server
    direction TB
    Config_Server["`IP: 192.168.0.50
    Port: 8080
    `"]
    subgraph Main Socket
        Socket["Socket"]
        Queue["`Queue:
        Client 1
        Client 2
        `"]
    end

    subgraph Threads
        direction TB
        subgraph Thread 1
            Socket1["Socket 1"]
        end

        subgraph Thread 2
            Socket2["Socket 2"]
        end
    end
end

Connect -- Client 1 | Step 1 --> Socket
Connect2 -- Client 2 | Step 1 --> Socket

Socket -- Client 1 | Step 2 --> Socket1
Socket -- Client 2 | Step 2 --> Socket2

TCP <== Client 1 | Step 3 ==> Socket1
TCP2 <== Client 2 | Step 3 ==> Socket2 

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