smpp34

A pure-Rust implementation of the SMPP 3.4 protocol (Short Message Peer-to-Peer): a PDU codec plus an asynchronous (tokio) client and server built on a listener-trait model.

The same engine ships two ways from one source tree, one version: a Rust crate (cargo add smpp34, zero Python dependencies) and a Rust-backed Python wheel (pip install smpp34) that exposes the identical async client/server to asyncio. The whole SMPP machinery — framing, windowing, timers, codec — runs in the Rust/tokio core; Python crosses the GIL only once per message, and the extension is free-threaded ("no-GIL") ready. See Python below.

• Client — bind to an SMSC as an ESME (transmitter, receiver or transceiver), send submit_sm / data_sm, and receive deliver_sm and session events through your own SmppClientListener.
• Server — accept ESME binds and dispatch submit_sm, data_sm, cancel_sm, … to your SmppServerListener; push MT traffic back out with deliver_sm.
• Codec — encode/decode every SMPP 3.4 PDU, including optional TLV parameters.

Sessions handle the SMPP timers (session_init, enquire_link, inactivity, response), sequence-number windowing, and optional TLS.

Supported PDUs

bind_transmitter · bind_receiver · bind_transceiver (+ resps) · outbind · unbind · enquire_link · submit_sm · submit_sm_multi · deliver_sm · data_sm · query_sm · cancel_sm · replace_sm · alert_notification · generic_nack, plus arbitrary TLV (optional parameter) encode/decode.

Install

cargo add smpp34

Quick start — server

Implement SmppServerListener and hand it to an SmppServer. Every trait method has a default, so you override only the PDUs you care about — typically on_bind_transceiver and on_submit_sm.

use std::sync::Arc;
use std::net::{IpAddr, Ipv4Addr};
use async_trait::async_trait;
use smpp34::{
    SmppServer, SmppServerListener, SmppConnectionInformation, SmppError,
    bind_transceiver, bind_transceiver_resp, submit_sm, submit_sm_resp,
};

struct MyEsmeHandler;

#[async_trait]
impl SmppServerListener for MyEsmeHandler {
    async fn on_bind_transceiver(
        &self, req: bind_transceiver, _c: &SmppConnectionInformation, _s: &String,
    ) -> bind_transceiver_resp {
        if req.system_id == "esme1" && req.password == "secret" {
            req.accept("MySMSC".to_string(), Some(0x34))   // 0x34 = SMPP v3.4
        } else {
            req.reject(SmppError::ESME_RINVPASWD)
        }
    }

    async fn on_submit_sm(
        &self, req: submit_sm, _c: &SmppConnectionInformation, _s: &String,
    ) -> submit_sm_resp {
        // ... route the message ...
        req.accept("message-id-1".to_string())
    }

    // Every other method has a sensible default (binds reject, on_data_sm /
    // on_cancel_sm reject, on_unbind acks, notifications no-op), so you override
    // only what you need.
}

#[tokio::main]
async fn main() {
    let listener = Arc::new(MyEsmeHandler);
    let mut server = SmppServer::new(IpAddr::V4(Ipv4Addr::LOCALHOST), 2775, listener);
    server.start().await;          // spawns the accept loop
    tokio::signal::ctrl_c().await.unwrap();
    server.stop().await;
}

Quick start — client

Bind to an SMSC, then submit once the bind completes (the on_smsc_bound callback hands you an SMSC you can submit through).

use std::sync::Arc;
use smpp34::client::{SmppClient, BIND_TYPE};

// `listener` implements SmppClientListener; its on_smsc_bound callback hands
// you the bound `SMSC` handle to submit through.
let listener = Arc::new(MyClientHandler::new());
let mut client = SmppClient::new(
    "smsc.example.net".to_string(), 2775, /* tls = */ false,
    BIND_TYPE::TRX,
    "esme1".to_string(), "secret".to_string(), "GATEWAY".to_string(),
    /* addr_ton */ 0, /* addr_npi */ 0, /* address_range */ String::new(),
    listener.clone(),
    /* window_size */ 20,
);
client.start().await;
// inside on_smsc_bound(smsc, _): use the fluent builder (only set what you need)
//   smsc.submit_sm()
//       .source_addr("12345")
//       .destination_addr("31600000000")
//       .short_message(b"hello")
//       .send().await?;

Python

pip install smpp34 gives a Rust-backed wheel exposing the same async client/server to asyncio. The hot path stays in the Rust/tokio core; the Python layer is an event-pull bridge that crosses the GIL once per message. abi3 wheels cover CPython 3.9+, plus free-threaded ("no-GIL") builds.

pip install smpp34

Client — connect() binds and returns an Smsc; await sends and inbound events:

import asyncio, smpp34

async def main():
    client = smpp34.Client(host="smsc.example.net", port=2775,
                           system_id="esme1", password="secret", bind_type="TRX")
    smsc = await client.connect()
    resp = await smsc.submit_sm(destination_addr="31600000000",
                                source_addr="12345", short_message=b"hello")
    print(resp.message_id, resp.is_success)

    # pull inbound deliver_sm (MO / DLR) — one GIL crossing per message
    ev = await smsc.next()                       # DeliverSmEvent | Disconnected
    if isinstance(ev, smpp34.DeliverSmEvent):
        print(ev.source_addr, ev.short_message)
    await smsc.unbind()

asyncio.run(main())

Server — await next() yields an Esme when a client binds, a SubmitSmEvent per inbound message (answer with accept/reject), or Unbound:

import asyncio, smpp34

async def main():
    server = smpp34.Server(host="0.0.0.0", port=2775, system_id="MySMSC")
    await server.start()
    sessions = {}
    while True:
        ev = await server.next()
        if isinstance(ev, smpp34.Esme):
            sessions[ev.session_id] = ev          # stash the MT send handle
        elif isinstance(ev, smpp34.SubmitSmEvent):
            ev.accept(message_id="abc")           # or ev.reject(smpp34.ESME_RMSGQFUL)
            # push MT back to that ESME (here, a delivery receipt):
            await sessions[ev.session_id].deliver_sm(
                source_addr=ev.destination_addr, destination_addr=ev.source_addr,
                esm_class=0x04, short_message=b"id:abc stat:DELIVRD")

asyncio.run(main())

Codec — encode/decode PDUs without any I/O:

pdu = smpp34.SubmitSm(source_addr="12345", destination_addr="31600000000",
                      short_message=b"hello")
wire = pdu.encode()
msg = smpp34.decode(wire)        # -> typed SubmitSm / DeliverSm / RawPdu

Runnable samples: python/examples/ (and the Rust equivalents in examples/ — client.rs / server.rs). A throughput and leak harness lives in python/perf/, mirroring the Rust examples/{perf_loopback,leak_check}.rs.

Optional parameters (TLVs)

Inbound TLVs are on pdu.tlvs in wire order, with typed accessors from the TlvList trait. Outbound, the builders take them directly:

use smpp34::{Tlv, TlvTag, TlvList};

// ESME -> SMSC
smsc.submit_sm()
    .source_addr("12345")
    .destination_addr("31600000000")
    .tlv(TlvTag::MessagePayload, "a body past the 254-byte short_message limit")
    .tlv(TlvTag::UserMessageReference, 42u16.to_be_bytes())
    .tlv_raw(0x1403, [0xAA, 0xBB])          // vendor-specific tag
    .send().await?;

// SMSC -> ESME: a delivery receipt is TLVs, nothing else
esme.deliver_sm()
    .source_addr("31600000000")
    .destination_addr("12345")
    .esm_class(0x04)
    .tlvs([
        Tlv::from_c_string(TlvTag::ReceiptedMessageId, "abc"),
        Tlv::from_u8(TlvTag::MessageStateTlv, 2),   // DELIVERED
    ])
    .send().await?;

// reading, on either side
let dlr_id = request.tlvs.receipted_message_id();

For a PDU built up front (relaying a decoded one, or data_sm, whose message body only exists as the message_payload TLV) use the *_pdu send methods — the session assigns the sequence number:

let pdu = data_sm::new(0, String::new(), 1, 1, "12345".into(), 1, 1, "31600000000".into(), 0, 0, 8)
    .with_tlvs([Tlv::from_tag(TlvTag::MessagePayload, body)]);
smsc.send_data_sm_pdu(pdu).await?;

In Python, tlvs= takes a list of Tlv(tag, value) and the tag constants are on the module:

await smsc.submit_sm("31600000000", b"hi", source_addr="12345", tlvs=[
    smpp34.Tlv(smpp34.TLV_USER_MESSAGE_REFERENCE, (42).to_bytes(2, "big")),
    smpp34.Tlv(smpp34.TLV_MESSAGE_PAYLOAD, b"the real body"),
])

ev = await smsc.next()
print([(hex(t.tag), t.value) for t in ev.tlvs])

All 44 spec-defined tags are in TlvTag / smpp34.TLV_*; unknown and vendor-specific tags (0x1400-0x3FFF) pass through byte for byte.

TLS

Pass tls = true to SmppClient::new to bind over TLS. The TLS transport is rustls (via tokio-rustls, ring backend), so no system TLS library is needed to build or run.

• TLS 1.2 and 1.3, ECDHE key exchange with AEAD ciphers only. A peer limited to RSA key exchange or CBC suites cannot be reached.
• The server certificate is verified against the operating system's trust store (SSL_CERT_FILE / SSL_CERT_DIR are honoured), and against the address you passed, hostname or IP. It must carry a matching subjectAltName; a certificate that only names the host in its CN is rejected.
• No client certificate (mTLS) and no per-client CA yet.

Timers & windowing

SmppServer::new / SmppClient::new use sensible default timers. Use the *_with_default_timers constructors to set session_init, enquire_link, inactivity and response timers (milliseconds) and the buffer / window size explicitly.

Performance

Measured on a 24-core AMD Ryzen AI 9 HX 370 (single box — the SMSC and ESME are co-located, so the load generator competes for cores; separate hosts scale further). Reproduce with cargo bench and perf/docker-compose.yml.

Codec — single core, criterion (cargo bench):

End-to-end — real TCP, full submit_sm round-trip (send → submit_sm_resp):

The SMSC server sustains 625k+ submit_sm/s even pinned to half the cores; past a few sessions the single-box benchmark is bound by the co-located load generator, not by smpp34.

Rust vs Python (and free-threading)

Both languages drive the same Rust/tokio engine, so the protocol work — framing, windowing, timers, codec — runs at full Rust speed either way. The difference is the Python boundary: the event-pull bridge crosses the GIL once per message.

A few things worth knowing:

• Build matters. A maturin develop debug build is ~3× slower; published wheels are --release. The ~25k/s figure is a release build.
• Tune the tokio pool with SMPP34_WORKER_THREADS (default 2). On a many-core box, a large pool thrashes the GIL on every future completion and throughput drops (24 threads ≈ 17k/s vs 1 thread ≈ 28k/s); on a free-threaded build, raise it.
• Free-threaded ("no-GIL") is correctness-clean — the full test suite passes with the GIL off (sys._is_gil_enabled() == False) — and lets CPU-bound Python work (the codec, your per-message handlers) run in parallel, as the codec row shows. Single-process async I/O is bounded by the shared tokio runtime, so scale that across processes.
• ~25k submit_sm/s on one event loop is already well above the per-bind rate limits carriers typically impose.

Reproduce: python/perf/perf_loopback.py (COUNT=200000 SESSIONS=4 WINDOW=64), the thread-scaling demo python/perf/perf_threads.py, and the leak check python/perf/leak_check.py — all after a release build (maturin develop --release).

Profiling

A CPU flamegraph of the loopback under load (scripts/flamegraph.sh) puts ~99.98% of samples in the kernel (the socket/syscall path) — the user-space codec barely appears. smpp34 is syscall-bound, not CPU-bound: at these rates the cost is the ~600k+ read/write syscalls per second plus the runtime's wakeups, not parsing (the codec runs at millions of PDUs/sec). The remaining headroom is therefore I/O batching — coalescing writes and cutting wakeups — not faster code.

Memory

scripts/mem_leak_test.sh installs a counting global allocator and asserts live bytes stay flat (exact — unlike noisy RSS) across both codec round-trips and bind/unbind churn. RSS holds at single-digit MB while pushing millions of PDUs. (The bind/unbind check found and now guards a real session-teardown leak — see the changelog.)

SMPP 3.4 compliance

The PDU / TLV / session support matrix is in docs/COMPLIANCE.md; docs/COMPARISON.md maps smpp34 against other SMPP stacks.

MSRV

Rust 1.80.

Stability

The SMPP 3.4 codec and the client/server session handling are used in production, and the crate follows Semantic Versioning: the public Rust API is the contract. The 17-argument send_submit_sm / send_deliver_sm remain available, but the submit_sm() / deliver_sm() builders are the recommended way to send.

License

MIT © Real Time Telecom B.V.

Maintained by Real Time Telecom B.V. — carrier-grade telecom infrastructure in Rust.