NSBSimClient (Python)

The simulator-side client. Integrates into network simulator code to route payloads through a simulated network.

Constructor

nsb_conn = nsb.NSBSimClient(identifier, server_address, server_port)

Parameters:

Parameter	Type	Description
`identifier`	`str`	Unique identifier for this simulator client. Must match the corresponding `NSBAppClient` identifier in Per-Node mode. In System-Wide mode, one identifier is used for all.
`server_address`	`str`	IP address or hostname of the NSB Daemon.
`server_port`	`int`	Port number of the NSB Daemon.

note

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

`fetch(src_id=None, timeout=None)`

Fetches a payload that was sent by an application client and is waiting to be routed through the simulated network.

entry = nsb_conn.fetch()
# or
entry = nsb_conn.fetch(src_id="node0", timeout=10)

Parameters:

Parameter	Type	Default	Description
`src_id`	`str \| None`	`None`	Identifier of the source to fetch from. `None` = fetch the most recent message regardless of source. Overwritten with own ID in Per-Node mode.
`timeout`	`int \| None`	`None`	Seconds to wait. `None` = wait indefinitely. `0` = non-blocking poll.

Returns: MessageEntry | None

Behavior by mode:

PULL mode: Sends a FETCH request to the daemon. Daemon responds with MESSAGE or NO_MESSAGE.
PUSH mode: Waits for forwarded payloads from the daemon/broker.

Per-Node override: When sim_mode is PER_NODE, src_id is automatically overwritten with the client's own identifier — it only fetches on its own behalf.

Example:

entry = nsb_conn.fetch()
if entry:
    src = entry.source
    dst = entry.destination
    payload = entry.payload
    # Route payload through simulated network...
    nsb_conn.post(src, dst, processed_payload)

`listen()`

An asynchronous coroutine for fetching payloads.

async def simulator_loop():
    entry = await nsb_conn.listen()
    if entry:
        src_id = entry.source
        dest_id = entry.destination
        payload = entry.payload
        # Send through simulated network...

Returns: MessageEntry | None

Behavior: Similar to fetch() but for async/await contexts. See Async Listeners for a complete runnable example.

`post(src_id, dest_id, payload)`

Notifies NSB that a payload has arrived at its destination within the simulated network and makes it available for reception by the application client.

nsb_conn.post(src_id, dest_id, payload)

Parameters:

Parameter	Type	Description
`src_id`	`str`	Identifier of the original source application client.
`dest_id`	`str`	Identifier of the destination application client.
`payload`	`bytes`	The payload data (may have been processed/modified by the simulator).

Behavior: Creates an NSB POST message with the source, destination, and payload, then transmits it to the daemon. The daemon stores or routes it so that NSBAppClient(dest_id).receive() can retrieve it.

Example:

nsb_conn.post(src_id="node0", dest_id="node1", payload=b"delivered payload")

Go Deeper

MessageEntry — the object returned by fetch()
NSBAppClient — the application-side counterpart
Async Listeners — full asyncio usage pattern
C++ NSBSimClient — the equivalent class in C++

Constructor​

fetch(src_id=None, timeout=None)​

listen()​

post(src_id, dest_id, payload)​

Go Deeper​

Constructor

`fetch(src_id=None, timeout=None)`

`listen()`

`post(src_id, dest_id, payload)`

Go Deeper