Refactor image handling and dither mode in receipt printing logic

Author: Codaea

README.md

@@ -179,7 +179,7 @@ Prints an image from base64-encoded data.
   "type": "image",
   "data": "data:image/png;base64,iVBORw0KGgoAAAANSU...",
   "alignment": "center",
-  "dither-mode": "floydsteinberg"
+  "dither_mode": "floydsteinberg"
 }
 ```
 

handlers.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"image"
 	"sync"
 
 	"github.com/gin-gonic/gin"
@@ -48,7 +49,8 @@ type Image struct {
 	Type       string        `json:"type"`
 	Data       string        `json:"data"`
 	Alignment  AlignmentType `json:"alignment"`
-	DitherMode DitherMode    `json:"dither_mode"`
+	DitherMode string        `json:"dither_mode"`
+	img        image.Image   // decoded image, not directly unmarshaled
 }
 
 // Global mutex to serialize printer access
@@ -107,6 +109,7 @@ func handlePrint(c *gin.Context) {
 			p.QR(v.Code, v.Size)
 		case Image:
 			// Print image (you'll need to decode base64 and process)
+			p.Align(v.Alignment.ToEscposAlignment())
 			p.Image(processImage(v))
 		}
 	}

main.go

@@ -1,13 +1,10 @@
 package main
 
 import (
-	"encoding/base64"
 	"fmt"
 	"image"
 	"image/color"
-	"image/png"
 	"os"
-	"strings"
 
 	"github.com/gin-contrib/cors"
 	"github.com/gin-gonic/gin"
@@ -50,32 +47,24 @@ func main() {
 	router.Run() // listen and serve on 0.0.0.0:8080 (or whatever is set as PORT environment variable)
 }
 
-func processImage(image Image) image.Image {
+func processImage(i Image) image.Image {
 
 	palette := []color.Color{
 		color.Black, color.White,
 	}
-
 	d := dither.NewDitherer(palette)
 
-	reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(image.Data))
-	img, err := png.Decode(reader)
-	if err != nil {
-		fmt.Printf("failed to decode image: %v", err)
-		return nil
-	}
-
-	// Create a new image from the decoded data
-
 	// Apply dither mode if specified
-	switch image.DitherMode {
-	case FloydSteinberg:
+	switch i.DitherMode {
+	case "floydsteinberg":
 		d.Matrix = dither.FloydSteinberg
-	case None:
-		return img // No dithering, return original image
+		return d.Dither(i.img)
+	case "none":
+		return i.img
+	default:
+		return i.img
 	}
 
-	return d.Dither(img)
 }
 
 /*

models.go

@@ -1,8 +1,12 @@
 package main
 
 import (
+	"bytes"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"image/png"
+	"strings"
 
 	"github.com/mect/go-escpos"
 )
@@ -181,26 +185,37 @@ func (t BarcodeType) ToEscposBarcodeType() escpos.BarcodeType {
 
 }
 
-type DitherMode string
-
-const (
-	None           DitherMode = "none"
-	FloydSteinberg DitherMode = "floydsteinberg"
-)
+func (i *Image) UnmarshalJSON(data []byte) error {
+	var aux struct {
+		Data       string        `json:"data"`
+		DitherMode string        `json:"dither_mode"`
+		Alignment  AlignmentType `json:"alignment"`
+	}
 
-func (d *DitherMode) UnmarshalJSON(data []byte) error {
-	var s string
-	if err := json.Unmarshal(data, &s); err != nil {
+	if err := json.Unmarshal(data, &aux); err != nil {
 		return err
 	}
 
-	switch s {
-	case "none", "floydsteinberg":
-		*d = DitherMode(s)
-		return nil
-	default:
-		return fmt.Errorf("invalid dither mode: %s", s)
+	i.Data = aux.Data
+	i.DitherMode = strings.ToLower(aux.DitherMode)
+	i.Alignment = aux.Alignment
+
+	b64 := aux.Data
+	if after, ok := strings.CutPrefix(b64, "data:image/png;base64,"); ok {
+		b64 = after
+	}
+	decoded, err := base64.StdEncoding.DecodeString(b64)
+	if err != nil {
+		return err
+	}
+	img, err := png.Decode(bytes.NewReader(decoded))
+	if err != nil {
+		return err
 	}
+
+	i.img = img
+	return nil
+
 }
 
 // Helper functions to convert custom types to escpos types

sample.service

@@ -6,8 +6,8 @@ StartLimitIntervalSec=0
 Type=simple
 Restart=always
 RestartSec=1
-User=coda
-ExecStart=/home/coda/simpleprint/simpleprint
+User=root
+ExecStart=/usr/bin/simpleprint
 EnvironmentFile=/home/coda/simpleprint/.env
 
 [Install]