publisher.h File Reference

Write-side primitive of the VLink event communication model. More...

#include <memory>
#include <string>
#include <type_traits>
#include "./impl/publisher_impl.h"
#include "./node.h"
#include "./internal/publisher-inl.h"

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Classes
class	vlink::Publisher< MsgT, SecT >
	Type-safe topic emitter for the VLink event communication model. More...
class	vlink::SecurityPublisher< MsgT >
	Convenience alias of Publisher with per-message security enabled. More...

Namespaces
	vlink

Detailed Description

Write-side primitive of the VLink event communication model.

Publisher<MsgT, SecT> is the message emitter for VLink topics. Each call to publish() serialises an instance of MsgT according to the compile-time-detected codec and hands the resulting payload to the active transport back-end, which fans the bytes out to every connected Subscriber that shares the same topic URL.

The class is a thin, header-only template wrapper around PublisherImpl; all runtime work is delegated to the impl. Codec selection is fully resolved at compile time so the runtime dispatch is zero-cost.

Event-model Data Flow

*   Publisher<MsgT>               Transport Back-end              Subscriber<MsgT>
*   ----------------              ------------------              -----------------
*      |                                  |                              |
*      |-- publish(msg, force) ---------->|                              |
*      |   Serializer::serialize          |                              |
*      |   (loan-aware on shm/zenoh)      |                              |
*      |                                  |--- frame on wire ----------->|
*      |                                  |                              |
*      |                                  |                              |--> callback
*      |                                  |                              |    Serializer::
*      |                                  |                              |    deserialize
* 

Supported Message Types

Category	Example C++ Type	Serializer::Type	Notes
Raw bytes	Bytes	kBytesType	Pass-through, no codec call.
Protobuf value	MyProto	kProtoType	Uses SerializeToArray.
Protobuf pointer	MyProto*	kProtoPtrType	Caller owns lifetime.
FlatBuffers obj	MyTableT (NativeTable)	kFlatTableType	Object API.
FlatBuffers ptr	MyTable* (Table pointer)	kFlatPtrType	Zero-copy read view.
FlatBuffers build	MyBuilder (fbb_ + Finish)	kFlatBuilderType	Finishes builder on publish.
DDS CDR	type with serialize(Cdr&)	kCdrType	DDS fast path.
POD struct	trivial standard-layout type	kStandardType	sizeof(T) byte copy.
UTF-8 text	std::string	kStringType	Length-prefixed.
Custom	type with operator>>/<<	kCustomType	User-supplied codec.

Subscriber Detection

Use the detection API to gate writes on the presence of at least one matching subscriber. This is purely informational; pass force=true to publish() if you wish to write regardless of detection state.

vlink::Publisher<MyMsg> pub("dds://sensor/imu");
 
pub.detect_subscribers([&pub](bool present) {
  if (present) { pub.publish(MyMsg{}); }
});
 
if (pub.wait_for_subscribers(std::chrono::milliseconds(500))) {
  pub.publish(MyMsg{});
}
 
if (pub.has_subscribers()) { pub.publish(MyMsg{}); }

Zero-copy Loan on Loan-capable Transports

vlink::Publisher<vlink::Bytes> pub("shm://image/raw");
if (pub.is_support_loan()) {
  vlink::Bytes buf = pub.loan(sizeof(FrameHeader) + payload_size);
  ::memcpy(buf.data(), &header, sizeof(header));
  pub.publish(buf);
}

Note

Loans bypass an extra copy by writing directly into transport-managed memory. Loans are not used when security is enabled because ciphertext length differs from plaintext length.

See also

subscriber.h, node.h, serializer.h, extension/security.h