libgofunc/printer.go

package libgofunc

import (
	/*
		#include <stdint.h>
	*/
	"C"
	_ "image/png"
	"os"
	"strings"

	"bufio"
	"log"
	"net"

	"time"

	"errors"

	"github.com/kenshaw/escpos"
)
import "io"

//export PrintImg
func PrintImg(printer *C.char, imagePath *C.char) *C.char {
	goPrinter := C.GoString(printer)
	goImagePath := C.GoString(imagePath)
	err := Print(goPrinter, goImagePath)
	if err != nil {
		return NewErr(err)
	}
	return NewOk(nil)
}

//export CheckPrinter
func CheckPrinter(printer *C.char) *C.char {
	goPrinter := C.GoString(printer)
	err := Check(goPrinter)
	if err != nil {
		return NewErr(err)
	}
	return NewOk(nil)
}

func Print(printer, imagePath string) error {
	conn, err := connect(printer)
	if err != nil {
		return err
	}
	defer conn.Close()
	w := bufio.NewReadWriter(bufio.NewReader(conn), bufio.NewWriter(conn))

	prt := escpos.New(w)

	prt.Init()
	prt.SetSmooth(1)
	prt.SetAlign("left")

	imgBytes, err := imgData(imagePath)
	if err != nil {
		return err
	}
	err = writeChunk(w, prt, imgBytes)
	if err != nil {
		return err
	}
	time.Sleep(500 * time.Millisecond)
	w.Flush()

	prt.WriteRaw([]byte{0x1B, 0x64, 0x03})
	prt.Cut()
	prt.End()
	w.Flush()
	time.Sleep(1 * time.Second)
	return nil
}

func Check(printer string) error {
	conn, err := connect(printer)
	if err != nil {
		return err
	}
	defer conn.Close()

	var w *bufio.ReadWriter
	w = bufio.NewReadWriter(bufio.NewReader(conn), bufio.NewWriter(conn))
	prt := escpos.New(w)

	prt.Init()
	prt.SetSmooth(1)
	prt.SetAlign("left")
	time.Sleep(100 * time.Millisecond)
	return w.Flush()
}

func connect(printer string) (io.ReadWriteCloser, error) {
	if strings.HasPrefix(printer, "tcp:") {
		location := strings.TrimLeft(printer, "tcp:")
		conn, err := net.Dial("tcp", location)
		if err != nil {
			log.Println("error net.Dial tcp:", err.Error())
			return nil, err
		}
		return conn, nil
	} else if strings.HasPrefix(printer, "usb:") {
		location := strings.TrimLeft(printer, "usb:")
		f, err := os.OpenFile(location, os.O_WRONLY, 0666)
		if err != nil {
			log.Println("error os.OpenFile usb:", err.Error())
			return nil, err
		}
		return f, nil
	}
	return nil, errors.New("invalid printer")
}

// writeChunk breaks the large byte array into smaller chunks
func writeChunk(w *bufio.ReadWriter, prt *escpos.Escpos, data []byte) error {
	chunkSize := 1024 // 1 KB chunks work best for network printers
	for i := 0; i < len(data); i += chunkSize {
		end := min(i+chunkSize, len(data))

		_, err := prt.WriteRaw(data[i:end])
		if err != nil {
			log.Println("Error writing image chunk:", err)
			return err
		}
		if err := w.Flush(); err != nil {
			log.Println("Error flushing buffer:", err)
			return err
		}
		// Give the printer's network chip a microsecond to breathe
		time.Sleep(5 * time.Millisecond)
	}
	return nil
}