NSBSimClient (C++)

Simulator-side client. Inherits from NSBClient.

Constructor

nsb::NSBSimClient nsb_conn(identifier, serverAddress, serverPort);

Parameters: Same as NSBAppClient — see NSBAppClient → Constructor.

note

In System-Wide mode, only one NSBSimClient may connect. In PUSH mode, the client must remain connected throughout the simulation.

fetch()

Fetches a payload waiting to be transmitted through the simulated network.

// Default — fetch the most recent message, default timeout
MessageEntry entry = nsb_conn.fetch();

// With explicit source and timeout
MessageEntry entry = nsb_conn.fetch(&src_id, timeout);

// With timeout only
MessageEntry entry = nsb_conn.fetch(timeout);

Signatures:

MessageEntry fetch(std::string* srcId, int timeout = DAEMON_RESPONSE_TIMEOUT);
MessageEntry fetch(int timeout = DAEMON_RESPONSE_TIMEOUT);

Parameters:

Parameter	Type	Default	Description
srcId	std::string*	nullptr	Pointer to source identifier to fetch from. nullptr = fetch most recent regardless of source. In Per-Node mode, this is overwritten with own ID.
timeout	int	DAEMON_RESPONSE_TIMEOUT (30s)	Seconds to wait. Use 0 for non-blocking poll.

Returns: MessageEntry — Populated if message found.

Behavior: Sends FETCH request to daemon. Daemon responds with MESSAGE or NO_MESSAGE.

Per-Node override: In Per-Node mode, srcId is automatically set to the client's own identifier.

Example:

MessageEntry entry = nsb_conn.fetch();
if (entry.exists()) {
    std::string src = entry.source;
    std::string dst = entry.destination;
    std::string payload = entry.payload_obj;
    // Simulate network transmission...
    nsb_conn.post(src, dst, payload);
}

post(src_id, dest_id, payload)

Posts a payload as arrived at its destination in the simulated network.

std::string result = nsb_conn.post(src_id, dest_id, payload);

Parameters:

Parameter	Type	Description
src_id	std::string	Identifier of the source application client.
dest_id	std::string	Identifier of the destination application client.
payload	std::string&	The payload data to post.

Returns: std::string — Status or key from the post operation.

Behavior: Creates a POST message with source, destination, and payload, then transmits to the daemon. Makes the payload available for NSBAppClient(dest_id).receive().

listenFetch()

Blocking listener — for use in dedicated fetcher threads.

MessageEntry entry = nsb_conn.listenFetch();

Returns: MessageEntry

Purpose: Designed for a dedicated thread that blocks waiting for the next payload to simulate, as an alternative to polling fetch() in a loop.

Complete Example

Application Side (app_node.cpp)

#include "nsb_client.h"
#include <iostream>

int main() {
    // Initialize
    std::string server = "127.0.0.1";
    int port = 65432;
    nsb::NSBAppClient app("node0", server, port);

    // Send
    std::string outgoing = "Hello, World!";
    app.send("node1", outgoing);

    // Receive
    nsb::MessageEntry entry = app.receive();
    if (entry.exists()) {
        std::cout << "Source: "  << entry.source      << "\n"
                  << "Dest: "    << entry.destination  << "\n"
                  << "Payload: " << entry.payload_obj  << "\n";
    }
    return 0;
}

Simulator Side (sim_node.cpp)

#include "nsb_client.h"
#include <iostream>

int main() {
    std::string server = "127.0.0.1";
    int port = 65432;
    nsb::NSBSimClient sim("node0", server, port);

    // Fetch payload from NSB
    nsb::MessageEntry entry = sim.fetch();
    if (entry.exists()) {
        std::string src = entry.source;
        std::string dst = entry.destination;
        std::string payload = entry.payload_obj;

        std::cout << "Simulating: " << src << " -> " << dst << "\n";

        // ... simulate network transmission ...

        // Post back when "arrived"
        sim.post(src, dst, payload);
    }
    return 0;
}

Note on AI Assistance

Portions of this C++ documentation were generated with assistance from Anthropic's Claude, based on internal code documentation, and were heavily reviewed and edited by human contributors. The NSB team takes full responsibility for accuracy.

Go Deeper

• MessageEntry — the struct returned by fetch()
• NSBAppClient — the application-side counterpart
• Python NSBSimClient — the equivalent class in Python
• Tutorials → Build a Mock Simulator — a hands-on walkthrough (Python version)