MODBUS_TCP_PI_LISTEN(3)

✨ MODBUS_TCP_PI_LISTEN ✨

okay bestie, gather round, because today we're talking about modbus_tcp_pi_listen from the libmodbus manual 💖 she's the one who creates and listens on a TCP PI Modbus socket (IPv6) — yes, IPv6, we're being fancy, we're being modern, we're giving protocol-independent main character energy 🌈

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🌸 NAME 🌸

modbus_tcp_pi_listen — create and listen a TCP PI Modbus socket (IPv6) 🦋

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🎀 SYNOPSIS 🎀

int modbus_tcp_pi_listen(modbus_t *ctx, int nb_connection);

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💅 DESCRIPTION 💅

So here's the tea ☕ — modbus_tcp_pi_listen() shall create a socket and listen to maximum nb_connection incoming connections on the specified nodes. That's the whole vibe: make the socket, then sit there being pretty and ready for people to connect. 👑

But wait, there's a prerequisite, and she is non-negotiable: your context ctx must be allocated and initialized with modbus_new_tcp_pi(3) before you set the node to listen. No pre-allocated context? No socket. Periodt. 💀

And if the node is set to NULL or 0.0.0.0, then any addresses will be listen — she's not picky, she's open to everyone, she's the social butterfly of sockets 🦋✨

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⭐ RETURN VALUE ⭐

• On success? She shall return a new socket. Slay. 🎉
• Otherwise she shall return -1 and set errno. So check that errno, bestie, she left you a note 🙈

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🌈 EXAMPLE 🌈

For the detailed examples, go peek at the source files in the tests directory — that's where the real lore lives 📂✨

• unit-test-server.c — simple but handle only one connection 🍓 (she's lowkey an introvert, one friend at a time, and that's valid)

...

ctx = modbus_new_tcp_pi("::0", "502");
s = modbus_tcp_pi_listen(ctx, 1);
modbus_tcp_pi_accept(ctx, &s);

for (;;) {
    rc = modbus_receive(ctx, query);
    modbus_replay(ctx, query, rc, mb_mapping);
}
...

mclose(s);
modbus_free(ctx);

• bandwidth-server-many-up.c — handles several connections at once 🔥 (extrovert server energy, the group chat is POPPING)

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💜 SEE ALSO 💜

• modbus_new_tcp_pi(3)
• modbus_tcp_pi_accept(3)
• modbus_tcp_listen(3)

go read those too, iykyk 🫶

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👑 AUTHORS 👑

The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com> — thank you king, we appreciate you fr fr 💖

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no cap: keep your ctx initialized with modbus_new_tcp_pi(3) first, or this whole thing is gonna be a mess 😭

libmodbus v3.1.6 · 11/17/2025 — that's a wrap bestie, go listen on that socket, you're literally the main character now 💅✨🌸