smpp-core Overview
smpp-core is a modern Java 21 implementation of the SMPP 3.4 protocol, designed as a clean-room replacement for the abandoned Cloudhopper library.
Features
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Java 21 LTS - Virtual threads, records, sealed classes, pattern matching
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Immutable PDUs - Thread-safe records with fluent builders
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Netty Transport - Zero-copy buffers, efficient memory management
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Virtual Thread Handlers - Business logic runs on lightweight threads
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Clean API - Intuitive builder patterns and CompletableFuture async
Architecture
smpp-core (parent)
├── smpp-core # PDUs, codecs, types (zero dependencies)
├── smpp-netty # Netty transport layer
├── smpp-server # Server with virtual threads
├── smpp-client # Client with auto-reconnect
└── smpp-metrics # Optional Micrometer integrationDesign Principles
Immutable PDUs
All PDUs are immutable records with builders:
SubmitSm pdu = SubmitSm.builder()
.sourceAddress(source)
.destAddress(dest)
.shortMessage(message)
.build();
// PDUs are immutable - create modified copies
SubmitSm modified = pdu.toBuilder()
.shortMessage(newMessage)
.build();Sealed Interfaces
PDU types use sealed interfaces for exhaustive pattern matching:
switch (pdu) {
case SubmitSm s -> handleSubmit(s);
case DeliverSm d -> handleDeliver(d);
case EnquireLink e -> handleEnquireLink(e);
// Compiler ensures all cases covered
}Virtual Threads
Handler callbacks run on virtual threads, allowing blocking operations without blocking platform threads:
// This blocks a virtual thread, not a platform thread
SubmitSmResult handleSubmitSm(SmppServerSession session, SubmitSm pdu) {
// Safe to do blocking I/O here
database.save(pdu);
kafka.send(pdu);
return SubmitSmResult.success(messageId);
}