Design
Design
The design separates byte transport from protocol semantics.
classDiagram
class Ecr17Client {
+configure(config)
+connect()
+pay(request)
+sendLastResult()
}
class Ecr17Session {
+runTransaction(command)
+runAckOnly(command)
}
class PacketCodec {
+encode(payload)
+decode(frame)
}
class Transport {
+connect(host, port)
+send(bytes)
+setOnData(callback)
}
Ecr17Client --> Ecr17Session
Ecr17Session --> PacketCodec
Ecr17Session --> Transport
Design principles
- Validate local request fields before transport send.
- Decode defensively and never read past malformed payloads.
- Keep ACK/NAK retransmission inside the session boundary.
- Make business-level recovery explicit through
sendLastResult(). - Emit terminal progress without making UI code parse protocol bytes.
Design tradeoff: one transaction at a time
ECR17 is a synchronous request-response protocol. The client serializes commands because parallel transactions on one terminal would create ambiguous terminal state and unsafe recovery behavior.
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