From 10594498c5db2cb5715c770053eb3f701c09da66 Mon Sep 17 00:00:00 2001
From: Javier Peletier <jm@epiclabs.io>
Date: Wed, 16 Dec 2020 00:08:23 +0100
Subject: [PATCH] modbus module

---
 modbus/mock.go   | 44 ++++++++++++++++++++++++++++++
 modbus/modbus.go | 70 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 114 insertions(+)
 create mode 100644 modbus/mock.go
 create mode 100644 modbus/modbus.go

diff --git a/modbus/mock.go b/modbus/mock.go
new file mode 100644
index 0000000..5d516b6
--- /dev/null
+++ b/modbus/mock.go
@@ -0,0 +1,44 @@
+package modbus
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+type Mock struct {
+	State map[byte][]uint16
+}
+
+func NewMock() Modbus {
+	return &Mock{
+		State: map[byte][]uint16{
+			49: {3, 68, 41, 41, 3, 68, 41, 41, 3, 68, 41, 45, 3, 68, 41, 45, 3, 68, 41, 42, 3, 52, 41, 40, 3, 52, 41, 44, 3, 68, 41, 41, 3, 68, 41, 40, 3, 68, 41, 41, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0},
+			50: {3, 68, 41, 41, 3, 68, 41, 41, 3, 68, 41, 45, 3, 68, 41, 45, 3, 68, 41, 42, 3, 52, 41, 40, 3, 52, 41, 44, 3, 68, 41, 41, 3, 68, 41, 40, 3, 68, 41, 41, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0, 0, 68, 0, 0},
+		},
+	}
+}
+
+func (ms *Mock) ReadRegister(slaveID byte, address uint16, quantity uint16) (results []byte, err error) {
+	state, ok := ms.State[slaveID]
+	if !ok {
+		return nil, errors.New("Unknown slave")
+	}
+	for a := address; a < address+quantity; a++ {
+		b := make([]byte, 2)
+		binary.BigEndian.PutUint16(b, state[a])
+		results = append(results, b...)
+	}
+	return results, nil
+}
+func (ms *Mock) WriteRegister(slaveID byte, address uint16, value uint16) (results []byte, err error) {
+	state, ok := ms.State[slaveID]
+	if !ok {
+		return nil, errors.New("Unknown slave")
+	}
+	state[address] = value
+	results = make([]byte, 2)
+	binary.BigEndian.PutUint16(results, value)
+	return results, nil
+}
+
+func (ms *Mock) Close() error { return nil }
diff --git a/modbus/modbus.go b/modbus/modbus.go
new file mode 100644
index 0000000..c773b91
--- /dev/null
+++ b/modbus/modbus.go
@@ -0,0 +1,70 @@
+package modbus
+
+import (
+	"sync"
+	"time"
+
+	gmodbus "github.com/goburrow/modbus"
+)
+
+type Modbus interface {
+	ReadRegister(slaveID byte, address uint16, quantity uint16) (results []byte, err error)
+	WriteRegister(slaveID byte, address uint16, value uint16) (results []byte, err error)
+	Close() error
+}
+
+type Config struct {
+	Port     string
+	BaudRate int
+	DataBits int
+	Parity   string
+	StopBits int
+	Timeout  time.Duration
+}
+
+type modbus struct {
+	handler *gmodbus.RTUClientHandler
+	client  gmodbus.Client
+	lock    sync.RWMutex
+}
+
+func New(config *Config) (Modbus, error) {
+	handler := gmodbus.NewRTUClientHandler(config.Port)
+	handler.BaudRate = config.BaudRate
+	handler.DataBits = config.DataBits
+	handler.Parity = config.Parity
+	handler.StopBits = config.StopBits
+	handler.Timeout = config.Timeout
+
+	err := handler.Connect()
+	if err != nil {
+		return nil, err
+	}
+
+	return &modbus{
+		handler: handler,
+		client:  gmodbus.NewClient(handler),
+	}, nil
+}
+
+func (mb *modbus) Close() error {
+	return mb.handler.Close()
+}
+
+func (mb *modbus) ReadRegister(slaveID byte, address uint16, quantity uint16) (results []byte, err error) {
+	mb.lock.Lock()
+	defer mb.lock.Unlock()
+	mb.handler.SlaveId = slaveID
+	results, err = mb.client.ReadHoldingRegisters(address-1, quantity)
+	return results, err
+
+}
+
+func (mb *modbus) WriteRegister(slaveID byte, address uint16, value uint16) (results []byte, err error) {
+	mb.lock.Lock()
+	defer mb.lock.Unlock()
+	mb.handler.SlaveId = slaveID
+	results, err = mb.client.WriteSingleRegister(address-1, value)
+	return results, err
+
+}