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iscp.go
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iscp.go
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package eiscp
import (
"bufio"
"bytes"
"encoding/binary"
"fmt"
)
// DeviceType - device destination code in ISCP
type DeviceType byte
// Destination code
const (
Receiver DeviceType = 0x31
)
// Message eISCP
type Message struct {
Version byte
Destination byte
ISCP []byte
}
// Parse eISCP message from reader (one-way)
func (msg *Message) Parse(reader *bufio.Reader) error {
chunk := make([]byte, 4)
_, err := reader.Read(chunk)
if err != nil {
return err
}
if string(chunk) != "ISCP" {
return fmt.Errorf("This is not EISCP message")
}
_, err = reader.Read(chunk) //Header size
if err != nil {
return err
}
if binary.BigEndian.Uint32(chunk) != 16 {
return fmt.Errorf("Invalid header size")
}
reader.Read(chunk) // Data size
dataSize := binary.BigEndian.Uint32(chunk)
msg.Version, err = reader.ReadByte()
if err != nil {
return err
}
reserved := make([]byte, 3)
_, err = reader.Read(reserved) // Skip reserved
if err != nil {
return err
}
_, err = reader.ReadByte() // Skip start character
if err != nil {
return err
}
msg.Destination, err = reader.ReadByte()
if err != nil {
return err
}
msg.ISCP = make([]byte, dataSize-2) // Trim leading control characters
_, err = reader.Read(msg.ISCP)
msg.ISCP = msg.ISCP[:len(msg.ISCP)-3] // Trim trailing EOF and EOL characters
return err
}
// BuildISCP - Build ISCP message
func (msg *Message) BuildISCP() []byte {
buffer := bytes.Buffer{}
buffer.WriteRune('!') // Start character
buffer.WriteByte(msg.Destination) // Receiver
buffer.Write(msg.ISCP)
buffer.Write([]byte{0x0D})
return buffer.Bytes()
}
// BuildEISCP - Build ISCP message into ethernet frame
func (msg *Message) BuildEISCP() []byte {
iscp := msg.BuildISCP()
sizebuf := make([]byte, 4)
buffer := bytes.Buffer{}
buffer.WriteString("ISCP")
buffer.Write([]byte{0, 0, 0, 0x10}) // Header size
binary.BigEndian.PutUint32(sizebuf, uint32(len(iscp)))
buffer.Write(sizebuf) // Data size
buffer.WriteByte(msg.Version) // Version
buffer.Write([]byte{0, 0, 0}) // Reserved
buffer.Write(iscp) //Data
return buffer.Bytes()
}