feat: add PDF support with page navigation (poppler/pdftoppm)

- HTTP server wrapping zplgfa library (port 4543)
- File upload with drag-and-drop, width/height resize, encoding selection, image edits
- /convert endpoint returns ZPL output; /preview returns image dimensions
- Dockerfile (multi-stage, Alpine) and docker-compose.yml

.github/workflows/go.yml

@@ -0,0 +1,28 @@
+# This workflow will build a golang project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-go
+
+name: Go
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+jobs:
+
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Go
+      uses: actions/setup-go@v4
+      with:
+        go-version: '1.22'
+
+    - name: Build
+      run: go build -v ./cmd/zplgfa
+
+    - name: Test
+      run: go test -v ./...

Dockerfile

@@ -0,0 +1,24 @@
+FROM golang:1.22-alpine AS builder
+
+WORKDIR /src
+
+# Copy module files and download deps
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source
+COPY . .
+
+# Build the web server
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /zplgfa-web ./cmd/web
+
+# ─── Final stage ────────────────────────────────────────────────────────────
+FROM alpine:3.20
+
+RUN apk add --no-cache ca-certificates poppler-utils
+
+COPY --from=builder /zplgfa-web /usr/local/bin/zplgfa-web
+
+EXPOSE 4543
+
+ENTRYPOINT ["/usr/local/bin/zplgfa-web"]

README.md

@@ -1,13 +1,16 @@
+*since I am currently working exclusively in the home office and no longer have to do with labels professionally (only as a hobby), I can unfortunately no longer work on this project.*
+*But if someone would like to provide me a [@Zebra](https://github.com/Zebra) printer, I would be happy to develop it further.*
+*Of course, pull requests are still welcome.*
+
 # ZPLGFA Golang Package
 
 *convert pictures to ZPL compatible ^GF-elements*
 
+[![DOI](https://zenodo.org/badge/153820885.svg)](https://doi.org/10.5281/zenodo.15291211) 
 [![GoDoc](https://godoc.org/github.com/SimonWaldherr/zplgfa?status.svg)](https://godoc.org/github.com/SimonWaldherr/zplgfa) 
-[![Build Status](https://travis-ci.org/SimonWaldherr/zplgfa.svg?branch=master)](https://travis-ci.org/SimonWaldherr/zplgfa) 
 [![Coverage Status](https://coveralls.io/repos/github/SimonWaldherr/zplgfa/badge.svg?branch=master)](https://coveralls.io/github/SimonWaldherr/zplgfa?branch=master) 
 [![Go Report Card](https://goreportcard.com/badge/github.com/SimonWaldherr/zplgfa)](https://goreportcard.com/report/github.com/SimonWaldherr/zplgfa) 
 [![codebeat badge](https://codebeat.co/badges/28d795af-6f9b-453a-94c2-4fafb8b5b0d5)](https://codebeat.co/projects/github-com-simonwaldherr-zplgfa-master) 
-[![BCH compliance](https://bettercodehub.com/edge/badge/SimonWaldherr/zplgfa?branch=master)](https://bettercodehub.com/results/SimonWaldherr/zplgfa) 
 [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bgithub.com%2FSimonWaldherr%2Fzplgfa.svg?type=shield)](https://app.fossa.io/projects/git%2Bgithub.com%2FSimonWaldherr%2Fzplgfa?ref=badge_shield) 
 [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/SimonWaldherr/zplgfa/master/LICENSE) 
 
@@ -83,9 +86,6 @@ If you have dozens of label printers in use and need to fill and print label tem
 
 [![SimonWaldherr/ups - GitHub](https://gh-card.dev/repos/SimonWaldherr/ups.svg?fullname)](https://github.com/SimonWaldherr/ups)
 
-## Is it any good?
-
-[Yes](https://news.ycombinator.com/item?id=3067434)
 
 ## License
 

cmd/web/main.go

@@ -0,0 +1,914 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/color"
+	_ "image/gif"
+	_ "image/jpeg"
+	"image/png"
+	"io"
+	"log"
+	"math"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/anthonynsimon/bild/blur"
+	"github.com/anthonynsimon/bild/effect"
+	"github.com/anthonynsimon/bild/segment"
+	"github.com/nfnt/resize"
+
+	"simonwaldherr.de/go/zplgfa"
+)
+
+const maxUploadSize = 20 << 20 // 20 MB
+
+func isPDF(data []byte) bool {
+	return len(data) >= 4 && string(data[:4]) == "%PDF"
+}
+
+// pdfPageToImage renders one page of a PDF to an image using pdftoppm.
+// dpi controls the render resolution (use 150 for thumbnails, 300 for conversion).
+// Returns the image, total page count, and any error.
+func pdfPageToImage(data []byte, page, dpi int) (image.Image, int, error) {
+	tmpDir, err := os.MkdirTemp("", "zplgfa-*")
+	if err != nil {
+		return nil, 0, err
+	}
+	defer os.RemoveAll(tmpDir)
+
+	pdfPath := filepath.Join(tmpDir, "input.pdf")
+	if err := os.WriteFile(pdfPath, data, 0600); err != nil {
+		return nil, 0, err
+	}
+
+	// Get total page count via pdfinfo
+	pageCount := 1
+	if out, err := exec.Command("pdfinfo", pdfPath).Output(); err == nil {
+		for _, line := range strings.Split(string(out), "\n") {
+			if strings.HasPrefix(line, "Pages:") {
+				if n, err := strconv.Atoi(strings.TrimSpace(strings.TrimPrefix(line, "Pages:"))); err == nil {
+					pageCount = n
+				}
+			}
+		}
+	}
+
+	if page < 1 {
+		page = 1
+	}
+	if page > pageCount {
+		page = pageCount
+	}
+
+	// Convert the requested page to PNG
+	outBase := filepath.Join(tmpDir, "out")
+	cmd := exec.Command("pdftoppm",
+		"-png",
+		"-r", strconv.Itoa(dpi),
+		"-f", strconv.Itoa(page),
+		"-l", strconv.Itoa(page),
+		pdfPath, outBase)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return nil, pageCount, fmt.Errorf("pdftoppm: %s", string(out))
+	}
+
+	matches, err := filepath.Glob(filepath.Join(tmpDir, "out-*.png"))
+	if err != nil || len(matches) == 0 {
+		return nil, pageCount, fmt.Errorf("pdftoppm produced no output")
+	}
+
+	f, err := os.Open(matches[0])
+	if err != nil {
+		return nil, pageCount, err
+	}
+	defer f.Close()
+
+	img, _, err := image.Decode(f)
+	return img, pageCount, err
+}
+
+func getGraphicType(t string) zplgfa.GraphicType {
+	switch strings.ToUpper(t) {
+	case "ASCII":
+		return zplgfa.ASCII
+	case "BINARY":
+		return zplgfa.Binary
+	default:
+		return zplgfa.CompressedASCII
+	}
+}
+
+func invertImage(img image.Image) image.Image {
+	b := img.Bounds()
+	out := image.NewNRGBA(b)
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
+			r, g, bv, a := img.At(x, y).RGBA()
+			out.Set(x, y, color.RGBA{
+				R: uint8((65535 - r) >> 8),
+				G: uint8((65535 - g) >> 8),
+				B: uint8((65535 - bv) >> 8),
+				A: uint8(a >> 8),
+			})
+		}
+	}
+	return out
+}
+
+func monochromeImage(img image.Image) image.Image {
+	b := img.Bounds()
+	out := image.NewNRGBA(b)
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
+			r, g, bv, a := img.At(x, y).RGBA()
+			var v uint8
+			if r > math.MaxUint16/2 || g > math.MaxUint16/2 || bv > math.MaxUint16/2 {
+				v = 255
+			}
+			out.Set(x, y, color.RGBA{R: v, G: v, B: v, A: uint8(a >> 8)})
+		}
+	}
+	return out
+}
+
+func processImage(img image.Image, editFlag string, width, height uint) image.Image {
+	if strings.Contains(editFlag, "monochrome") {
+		img = monochromeImage(img)
+	}
+	bounds := img.Bounds()
+	if strings.Contains(editFlag, "blur") {
+		img = blur.Gaussian(img, float64(bounds.Dx())/300)
+	}
+	if strings.Contains(editFlag, "edge") {
+		img = effect.Sobel(img)
+	}
+	if strings.Contains(editFlag, "segment") {
+		img = segment.Threshold(img, 128)
+	}
+	if strings.Contains(editFlag, "invert") {
+		img = invertImage(img)
+	}
+	if width > 0 || height > 0 {
+		img = resize.Resize(width, height, img, resize.MitchellNetravali)
+	}
+	return img
+}
+
+func convertHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	if err := r.ParseMultipartForm(maxUploadSize); err != nil {
+		http.Error(w, "file too large", http.StatusBadRequest)
+		return
+	}
+
+	file, _, err := r.FormFile("file")
+	if err != nil {
+		http.Error(w, "missing file", http.StatusBadRequest)
+		return
+	}
+	defer file.Close()
+
+	data, err := io.ReadAll(file)
+	if err != nil {
+		http.Error(w, "failed to read file", http.StatusBadRequest)
+		return
+	}
+
+	var img image.Image
+	if isPDF(data) {
+		page := 1
+		if p, e2 := strconv.Atoi(r.FormValue("page")); e2 == nil && p > 0 {
+			page = p
+		}
+		img, _, err = pdfPageToImage(data, page, 300)
+		if err != nil {
+			http.Error(w, "PDF conversion failed: "+err.Error(), http.StatusBadRequest)
+			return
+		}
+	} else {
+		img, _, err = image.Decode(bytes.NewReader(data))
+		if err != nil {
+			http.Error(w, fmt.Sprintf("cannot decode image: %s", err), http.StatusBadRequest)
+			return
+		}
+	}
+
+	var w2, h2 uint
+	if v, err := strconv.ParseUint(r.FormValue("width"), 10, 32); err == nil {
+		w2 = uint(v)
+	}
+	if v, err := strconv.ParseUint(r.FormValue("height"), 10, 32); err == nil {
+		h2 = uint(v)
+	}
+
+	editFlag := r.FormValue("edit")
+	graphicType := getGraphicType(r.FormValue("type"))
+
+	img = processImage(img, editFlag, w2, h2)
+	flat := zplgfa.FlattenImage(img)
+	zpl := zplgfa.ConvertToZPL(flat, graphicType)
+
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	w.Header().Set("Content-Disposition", `attachment; filename="label.zpl"`)
+	fmt.Fprint(w, zpl)
+}
+
+func previewHandler(w http.ResponseWriter, r *http.Request) {
+	// Returns image info (dimensions) before conversion
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	if err := r.ParseMultipartForm(maxUploadSize); err != nil {
+		http.Error(w, "file too large", http.StatusBadRequest)
+		return
+	}
+	file, _, err := r.FormFile("file")
+	if err != nil {
+		http.Error(w, "missing file", http.StatusBadRequest)
+		return
+	}
+	defer file.Close()
+
+	var buf bytes.Buffer
+	buf.ReadFrom(file)
+	data := buf.Bytes()
+
+	if isPDF(data) {
+		page := 1
+		if p, e2 := strconv.Atoi(r.FormValue("page")); e2 == nil && p > 0 {
+			page = p
+		}
+		img, pageCount, err := pdfPageToImage(data, page, 150)
+		if err != nil {
+			http.Error(w, "PDF conversion failed: "+err.Error(), http.StatusBadRequest)
+			return
+		}
+		b := img.Bounds()
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprintf(w, `{"width":%d,"height":%d,"pages":%d,"isPDF":true}`, b.Dx(), b.Dy(), pageCount)
+		return
+	}
+
+	cfg, _, err := image.DecodeConfig(bytes.NewReader(data))
+	if err != nil {
+		http.Error(w, "cannot decode image", http.StatusBadRequest)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	fmt.Fprintf(w, `{"width":%d,"height":%d,"pages":1,"isPDF":false}`, cfg.Width, cfg.Height)
+}
+
+func pageThumbHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	if err := r.ParseMultipartForm(maxUploadSize); err != nil {
+		http.Error(w, "file too large", http.StatusBadRequest)
+		return
+	}
+	file, _, err := r.FormFile("file")
+	if err != nil {
+		http.Error(w, "missing file", http.StatusBadRequest)
+		return
+	}
+	defer file.Close()
+
+	data, err := io.ReadAll(file)
+	if err != nil {
+		http.Error(w, "failed to read file", http.StatusBadRequest)
+		return
+	}
+	if !isPDF(data) {
+		http.Error(w, "not a PDF", http.StatusBadRequest)
+		return
+	}
+
+	page := 1
+	if p, e2 := strconv.Atoi(r.FormValue("page")); e2 == nil && p > 0 {
+		page = p
+	}
+
+	img, _, err := pdfPageToImage(data, page, 150)
+	if err != nil {
+		http.Error(w, "PDF conversion failed: "+err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	w.Header().Set("Content-Type", "image/png")
+	png.Encode(w, img)
+}
+
+var labelaryClient = &http.Client{Timeout: 15 * time.Second}
+
+func renderHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	dpmm := r.URL.Query().Get("dpmm")
+	width := r.URL.Query().Get("width")
+	height := r.URL.Query().Get("height")
+	if dpmm == "" {
+		dpmm = "8"
+	}
+	if width == "" {
+		width = "4"
+	}
+	if height == "" {
+		height = "6"
+	}
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		http.Error(w, "failed to read body", http.StatusBadRequest)
+		return
+	}
+
+	url := fmt.Sprintf("http://api.labelary.com/v1/printers/%s/labels/%sx%s/0/", dpmm, width, height)
+	req, err := http.NewRequest(http.MethodPost, url, bytes.NewReader(body))
+	if err != nil {
+		http.Error(w, "failed to build request", http.StatusInternalServerError)
+		return
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Accept", "image/png")
+
+	resp, err := labelaryClient.Do(req)
+	if err != nil {
+		http.Error(w, "labelary unreachable: "+err.Error(), http.StatusBadGateway)
+		return
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		http.Error(w, "labelary returned "+resp.Status, http.StatusBadGateway)
+		return
+	}
+	w.Header().Set("Content-Type", "image/png")
+	io.Copy(w, resp.Body)
+}
+
+func main() {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/convert", convertHandler)
+	mux.HandleFunc("/preview", previewHandler)
+	mux.HandleFunc("/page-thumb", pageThumbHandler)
+	mux.HandleFunc("/render", renderHandler)
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Write([]byte(indexHTML))
+	})
+
+	addr := ":4543"
+	log.Printf("zplgfa web UI listening on %s", addr)
+	log.Fatal(http.ListenAndServe(addr, mux))
+}
+
+const indexHTML = `<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<title>zplgfa – Image to ZPL Converter</title>
+<style>
+  *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
+  body {
+    font-family: system-ui, sans-serif;
+    background: #0f1117;
+    color: #e2e8f0;
+    min-height: 100vh;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 2rem;
+  }
+  .card {
+    background: #1e2130;
+    border: 1px solid #2d3348;
+    border-radius: 12px;
+    padding: 2rem;
+    width: 100%;
+    max-width: 640px;
+    box-shadow: 0 8px 32px rgba(0,0,0,0.4);
+  }
+  h1 { font-size: 1.5rem; font-weight: 700; margin-bottom: 0.25rem; }
+  .subtitle { color: #718096; font-size: 0.875rem; margin-bottom: 1.75rem; }
+
+  .drop-zone {
+    border: 2px dashed #3a4060;
+    border-radius: 8px;
+    padding: 2.5rem 1rem;
+    text-align: center;
+    cursor: pointer;
+    transition: border-color .2s, background .2s;
+    margin-bottom: 1.5rem;
+  }
+  .drop-zone:hover, .drop-zone.over { border-color: #6366f1; background: #1a1e2e; }
+  .drop-zone input { display: none; }
+  .drop-zone .icon { font-size: 2.5rem; margin-bottom: 0.5rem; }
+  .drop-zone .hint { color: #718096; font-size: 0.85rem; }
+  .preview-info { margin-top: 0.75rem; font-size: 0.8rem; color: #a0aec0; min-height: 1.2em; }
+
+  .grid { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; margin-bottom: 1rem; }
+  .grid3 { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: 1rem; margin-bottom: 1rem; }
+  label { display: block; font-size: 0.8rem; font-weight: 600; color: #a0aec0; margin-bottom: 0.35rem; }
+  input[type=number], select {
+    width: 100%;
+    background: #252a3d;
+    border: 1px solid #3a4060;
+    border-radius: 6px;
+    color: #e2e8f0;
+    padding: 0.5rem 0.75rem;
+    font-size: 0.9rem;
+    outline: none;
+    transition: border-color .2s;
+  }
+  input[type=number]:focus, select:focus { border-color: #6366f1; }
+
+  /* unit toggle */
+  .unit-row {
+    display: flex; align-items: center; gap: 0.5rem;
+    margin-bottom: 0.75rem;
+  }
+  .unit-row span { font-size: 0.8rem; color: #a0aec0; font-weight: 600; }
+  .toggle-group { display: flex; border: 1px solid #3a4060; border-radius: 6px; overflow: hidden; }
+  .toggle-group button {
+    flex: 1; background: #252a3d; color: #a0aec0;
+    border: none; border-radius: 0; padding: 0.3rem 0.8rem;
+    font-size: 0.8rem; font-weight: 600; cursor: pointer; width: auto;
+    transition: background .15s, color .15s;
+  }
+  .toggle-group button.active { background: #6366f1; color: #fff; }
+  .sub-label { font-size: 0.7rem; color: #718096; font-weight: 400; margin-top: 0.15rem; }
+
+  .checks { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-bottom: 1.5rem; }
+  .checks label {
+    display: flex; align-items: center; gap: 0.4rem;
+    background: #252a3d; border: 1px solid #3a4060;
+    border-radius: 6px; padding: 0.35rem 0.7rem;
+    cursor: pointer; font-size: 0.8rem; font-weight: 500; color: #cbd5e0;
+    margin-bottom: 0;
+    transition: border-color .2s, background .2s;
+  }
+  .checks label:hover { border-color: #6366f1; }
+  .checks input[type=checkbox] { accent-color: #6366f1; width: 14px; height: 14px; }
+
+  button {
+    width: 100%;
+    background: #6366f1;
+    color: #fff;
+    border: none;
+    border-radius: 8px;
+    padding: 0.75rem;
+    font-size: 1rem;
+    font-weight: 600;
+    cursor: pointer;
+    transition: background .2s, opacity .2s;
+  }
+  button:hover { background: #4f52d0; }
+  button:disabled { opacity: 0.5; cursor: not-allowed; }
+
+  .output { margin-top: 1.5rem; display: none; }
+  .output-header {
+    display: flex; justify-content: space-between; align-items: center;
+    margin-bottom: 0.5rem;
+  }
+  .output-header span { font-size: 0.8rem; font-weight: 600; color: #a0aec0; }
+  .copy-btn {
+    background: #252a3d; border: 1px solid #3a4060; border-radius: 6px;
+    color: #a0aec0; font-size: 0.75rem; padding: 0.25rem 0.6rem;
+    width: auto; font-weight: 500;
+  }
+  .copy-btn:hover { background: #2d3348; }
+  textarea {
+    width: 100%; height: 220px;
+    background: #0f1117; border: 1px solid #2d3348; border-radius: 6px;
+    color: #7dd3fc; font-family: monospace; font-size: 0.75rem;
+    padding: 0.75rem; resize: vertical; outline: none;
+  }
+  .dl-btn { margin-top: 0.75rem; background: #2d6a4f; }
+  .dl-btn:hover { background: #215040; }
+  .error { color: #fc8181; font-size: 0.85rem; margin-top: 0.75rem; display: none; }
+
+  /* previews */
+  .preview-panel {
+    margin-bottom: 1.5rem; display: none;
+  }
+  .preview-panel .panel-header {
+    font-size: 0.8rem; font-weight: 600; color: #a0aec0; margin-bottom: 0.5rem;
+  }
+  .preview-panel img {
+    max-width: 100%; max-height: 260px; object-fit: contain;
+    border-radius: 6px; border: 1px solid #2d3348; background: #fff;
+    display: block;
+  }
+  .preview-panel .panel-meta {
+    font-size: 0.75rem; color: #718096; margin-top: 0.35rem;
+  }
+  .label-preview-wrap {
+    margin-top: 1.25rem; display: none;
+  }
+  .label-preview-wrap .panel-header {
+    display: flex; justify-content: space-between; align-items: center;
+    font-size: 0.8rem; font-weight: 600; color: #a0aec0; margin-bottom: 0.5rem;
+  }
+  .label-preview-wrap img {
+    max-width: 100%; border-radius: 6px; border: 1px solid #2d3348;
+    background: #fff; display: block;
+  }
+  .render-status { font-size: 0.75rem; color: #718096; font-weight: 400; }
+  .spinner {
+    display: none; width: 18px; height: 18px;
+    border: 2px solid #ffffff40; border-top-color: #fff;
+    border-radius: 50%; animation: spin .6s linear infinite;
+    margin: 0 auto;
+  }
+  @keyframes spin { to { transform: rotate(360deg); } }
+</style>
+</head>
+<body>
+<div class="card">
+  <h1>zplgfa</h1>
+  <p class="subtitle">Convert images to ZPL Graphic Fields for Zebra label printers</p>
+
+  <div class="drop-zone" id="dropZone">
+    <input type="file" id="fileInput" accept="image/png,image/jpeg,image/gif,application/pdf,.pdf">
+    <div class="icon">🖼️</div>
+    <div>Drop an image here or <strong>click to browse</strong></div>
+    <div class="hint">PNG, JPEG, GIF, PDF — max 20 MB</div>
+    <div class="preview-info" id="previewInfo"></div>
+  </div>
+
+  <!-- PDF page selector (shown only for PDFs) -->
+  <div id="pdfPageRow" style="display:none; margin-bottom:1rem;">
+    <label for="pdfPage">PDF Page <span id="pdfPageMax" style="font-weight:400;color:#718096"></span></label>
+    <div style="display:flex; gap:0.5rem; align-items:center;">
+      <input type="number" id="pdfPage" min="1" value="1" style="width:100px">
+      <button id="pdfPageBtn" style="width:auto;padding:0.45rem 1rem;font-size:0.85rem;">Load Page</button>
+    </div>
+  </div>
+
+  <!-- Image preview (original) -->
+  <div class="preview-panel" id="imgPreviewPanel">
+    <div class="panel-header">Image Preview</div>
+    <img id="imgPreviewEl" alt="preview">
+    <div class="panel-meta" id="imgPreviewMeta"></div>
+  </div>
+
+  <!-- Unit toggle + DPI -->
+  <div class="unit-row">
+    <span>Dimensions in</span>
+    <div class="toggle-group">
+      <button id="btnPx" class="active" onclick="setUnit('px')">px</button>
+      <button id="btnCm" onclick="setUnit('cm')">cm</button>
+    </div>
+    <span style="margin-left:auto">Printer DPI</span>
+    <select id="dpi" style="width:110px">
+      <option value="203" selected>203 dpi</option>
+      <option value="300">300 dpi</option>
+      <option value="600">600 dpi</option>
+    </select>
+  </div>
+
+  <div class="grid">
+    <div>
+      <label id="labelW">Width (px)</label>
+      <input type="number" id="width" min="0" step="1" value="0" placeholder="0">
+      <div class="sub-label" id="subW"></div>
+    </div>
+    <div>
+      <label id="labelH">Height (px)</label>
+      <input type="number" id="height" min="0" step="1" value="0" placeholder="0">
+      <div class="sub-label" id="subH"></div>
+    </div>
+  </div>
+
+  <div class="grid" style="margin-bottom:1rem">
+    <div>
+      <label for="enctype">Encoding</label>
+      <select id="enctype">
+        <option value="CompressedASCII" selected>CompressedASCII (default)</option>
+        <option value="ASCII">ASCII</option>
+        <option value="Binary">Binary</option>
+      </select>
+    </div>
+  </div>
+
+  <div class="checks">
+    <label><input type="checkbox" name="edit" value="monochrome"> Monochrome</label>
+    <label><input type="checkbox" name="edit" value="invert"> Invert</label>
+    <label><input type="checkbox" name="edit" value="blur"> Blur</label>
+    <label><input type="checkbox" name="edit" value="edge"> Edge detect</label>
+    <label><input type="checkbox" name="edit" value="segment"> Segment</label>
+  </div>
+
+  <button id="convertBtn" disabled>Convert to ZPL</button>
+  <div class="spinner" id="spinner"></div>
+  <div class="error" id="error"></div>
+
+  <div class="output" id="output">
+    <div class="output-header">
+      <span>ZPL Output</span>
+      <button class="copy-btn" id="copyBtn">Copy</button>
+    </div>
+    <textarea id="zplOutput" readonly></textarea>
+    <button class="dl-btn" id="dlBtn">⬇ Download .zpl</button>
+
+    <!-- Labelary rendered preview -->
+    <div class="label-preview-wrap" id="labelPreviewWrap">
+      <div class="panel-header">
+        <span>Label Preview <span style="font-weight:400;color:#718096">(rendered by Labelary)</span></span>
+        <span class="render-status" id="renderStatus"></span>
+      </div>
+      <img id="labelPreviewImg" alt="label preview">
+    </div>
+  </div>
+</div>
+
+<script>
+const dropZone = document.getElementById('dropZone');
+const fileInput = document.getElementById('fileInput');
+const previewInfo = document.getElementById('previewInfo');
+const convertBtn = document.getElementById('convertBtn');
+const spinner = document.getElementById('spinner');
+const output = document.getElementById('output');
+const zplOutput = document.getElementById('zplOutput');
+const errorEl = document.getElementById('error');
+
+let selectedFile = null;
+let currentUnit = 'px'; // 'px' or 'cm'
+let origPxW = 0, origPxH = 0; // image native pixel dimensions
+let imgObjectURL = null;
+let fileIsPDF = false;
+let pdfPageCount = 1;
+
+function getDPI() { return parseInt(document.getElementById('dpi').value, 10); }
+
+// cm ↔ px helpers
+function pxToCm(px) { return +(px * 2.54 / getDPI()).toFixed(3); }
+function cmToPx(cm) { return Math.round(cm * getDPI() / 2.54); }
+
+function setUnit(unit) {
+  const wEl = document.getElementById('width');
+  const hEl = document.getElementById('height');
+  const curW = parseFloat(wEl.value) || 0;
+  const curH = parseFloat(hEl.value) || 0;
+
+  if (unit === 'cm' && currentUnit === 'px') {
+    wEl.step = '0.01';
+    hEl.step = '0.01';
+    wEl.value = curW > 0 ? pxToCm(curW) : 0;
+    hEl.value = curH > 0 ? pxToCm(curH) : 0;
+  } else if (unit === 'px' && currentUnit === 'cm') {
+    wEl.step = '1';
+    hEl.step = '1';
+    wEl.value = curW > 0 ? cmToPx(curW) : 0;
+    hEl.value = curH > 0 ? cmToPx(curH) : 0;
+  }
+  currentUnit = unit;
+  document.getElementById('btnPx').classList.toggle('active', unit === 'px');
+  document.getElementById('btnCm').classList.toggle('active', unit === 'cm');
+  updateLabels();
+}
+
+function updateLabels() {
+  const unit = currentUnit;
+  document.getElementById('labelW').textContent = 'Width (' + unit + ')' + (unit === 'px' ? ' — 0 = auto' : '');
+  document.getElementById('labelH').textContent = 'Height (' + unit + ')' + (unit === 'px' ? ' — 0 = auto' : '');
+  updateSubLabels();
+}
+
+function updateSubLabels() {
+  if (!origPxW) return;
+  if (currentUnit === 'px') {
+    document.getElementById('subW').textContent = pxToCm(origPxW) + ' cm at ' + getDPI() + ' dpi';
+    document.getElementById('subH').textContent = pxToCm(origPxH) + ' cm at ' + getDPI() + ' dpi';
+  } else {
+    document.getElementById('subW').textContent = origPxW + ' px native';
+    document.getElementById('subH').textContent = origPxH + ' px native';
+  }
+}
+
+// Recalc sub-labels when DPI changes
+document.getElementById('dpi').addEventListener('change', () => {
+  if (currentUnit === 'cm') {
+    // re-fill cm fields based on original px
+    if (origPxW) {
+      document.getElementById('width').value = pxToCm(origPxW);
+      document.getElementById('height').value = pxToCm(origPxH);
+    }
+  }
+  updateSubLabels();
+});
+
+dropZone.addEventListener('click', () => fileInput.click());
+dropZone.addEventListener('dragover', e => { e.preventDefault(); dropZone.classList.add('over'); });
+dropZone.addEventListener('dragleave', () => dropZone.classList.remove('over'));
+dropZone.addEventListener('drop', e => {
+  e.preventDefault();
+  dropZone.classList.remove('over');
+  if (e.dataTransfer.files[0]) setFile(e.dataTransfer.files[0]);
+});
+fileInput.addEventListener('change', () => { if (fileInput.files[0]) setFile(fileInput.files[0]); });
+
+function setFile(file) {
+  selectedFile = file;
+  previewInfo.textContent = 'Loading…';
+  convertBtn.disabled = true;
+  fileIsPDF = file.type === 'application/pdf' || file.name.toLowerCase().endsWith('.pdf');
+
+  // For non-PDFs show the image immediately; for PDFs we wait for the server thumb
+  if (!fileIsPDF) {
+    if (imgObjectURL) URL.revokeObjectURL(imgObjectURL);
+    imgObjectURL = URL.createObjectURL(file);
+    document.getElementById('imgPreviewEl').src = imgObjectURL;
+    document.getElementById('imgPreviewPanel').style.display = 'block';
+  }
+  document.getElementById('pdfPageRow').style.display = fileIsPDF ? 'block' : 'none';
+
+  const fd = new FormData();
+  fd.append('file', file);
+  fetch('/preview', { method: 'POST', body: fd })
+    .then(r => r.ok ? r.json() : Promise.reject())
+    .then(info => {
+      origPxW = info.width;
+      origPxH = info.height;
+
+      if (info.isPDF) {
+        pdfPageCount = info.pages;
+        document.getElementById('pdfPageMax').textContent = '(1 – ' + info.pages + ')';
+        document.getElementById('pdfPage').max = info.pages;
+        document.getElementById('pdfPage').value = 1;
+        loadPDFPageThumb(1);
+      }
+
+      const wEl = document.getElementById('width');
+      const hEl = document.getElementById('height');
+      if (currentUnit === 'px') {
+        wEl.value = origPxW;
+        hEl.value = origPxH;
+      } else {
+        wEl.value = pxToCm(origPxW);
+        hEl.value = pxToCm(origPxH);
+      }
+
+      const cmW = pxToCm(origPxW), cmH = pxToCm(origPxH);
+      const pageInfo = info.isPDF ? '  —  ' + info.pages + ' page' + (info.pages !== 1 ? 's' : '') : '';
+      previewInfo.textContent =
+        file.name + pageInfo + '  —  ' + origPxW + ' × ' + origPxH + ' px' +
+        '  (' + cmW + ' × ' + cmH + ' cm at ' + getDPI() + ' dpi)';
+
+      document.getElementById('imgPreviewMeta').textContent =
+        origPxW + ' × ' + origPxH + ' px  |  ' + cmW + ' × ' + cmH + ' cm at ' + getDPI() + ' dpi';
+
+      updateSubLabels();
+      convertBtn.disabled = false;
+    })
+    .catch(() => {
+      previewInfo.textContent = file.name;
+      convertBtn.disabled = false;
+    });
+}
+
+async function loadPDFPageThumb(page) {
+  if (!selectedFile) return;
+  const fd = new FormData();
+  fd.append('file', selectedFile);
+  fd.append('page', page);
+  document.getElementById('imgPreviewPanel').style.display = 'block';
+  document.getElementById('imgPreviewMeta').textContent = 'Loading page ' + page + '…';
+  try {
+    const res = await fetch('/page-thumb', { method: 'POST', body: fd });
+    if (!res.ok) throw new Error(await res.text());
+    const blob = await res.blob();
+    if (imgObjectURL) URL.revokeObjectURL(imgObjectURL);
+    imgObjectURL = URL.createObjectURL(blob);
+    document.getElementById('imgPreviewEl').src = imgObjectURL;
+    const cmW = pxToCm(origPxW), cmH = pxToCm(origPxH);
+    document.getElementById('imgPreviewMeta').textContent =
+      'Page ' + page + '  —  ' + origPxW + ' × ' + origPxH + ' px  |  ' + cmW + ' × ' + cmH + ' cm at ' + getDPI() + ' dpi';
+  } catch(e) {
+    document.getElementById('imgPreviewMeta').textContent = 'Preview failed: ' + e.message;
+  }
+}
+
+document.getElementById('pdfPageBtn').addEventListener('click', () => {
+  const page = parseInt(document.getElementById('pdfPage').value, 10) || 1;
+  loadPDFPageThumb(page);
+});
+
+// Returns pixel values regardless of current unit
+function getPixelDimensions() {
+  const w = parseFloat(document.getElementById('width').value) || 0;
+  const h = parseFloat(document.getElementById('height').value) || 0;
+  if (currentUnit === 'cm') {
+    return { w: cmToPx(w), h: cmToPx(h) };
+  }
+  return { w: Math.round(w), h: Math.round(h) };
+}
+
+function dpmmFromDPI(dpi) {
+  const map = { 203: 8, 300: 12, 600: 24 };
+  return map[dpi] || 8;
+}
+
+async function fetchLabelPreview(zpl, pxW, pxH) {
+  const dpi = getDPI();
+  const dpmm = dpmmFromDPI(dpi);
+  // Labelary needs label size in inches; clamp minimum to avoid API errors
+  const wIn = Math.max(pxW / dpi, 0.1).toFixed(4);
+  const hIn = Math.max(pxH / dpi, 0.1).toFixed(4);
+
+  const wrap = document.getElementById('labelPreviewWrap');
+  const status = document.getElementById('renderStatus');
+  wrap.style.display = 'block';
+  status.textContent = 'Rendering…';
+  document.getElementById('labelPreviewImg').src = '';
+
+  try {
+    const res = await fetch(
+      '/render?dpmm=' + dpmm + '&width=' + wIn + '&height=' + hIn,
+      { method: 'POST', headers: { 'Content-Type': 'text/plain' }, body: zpl }
+    );
+    if (!res.ok) throw new Error(await res.text());
+    const blob = await res.blob();
+    const url = URL.createObjectURL(blob);
+    document.getElementById('labelPreviewImg').src = url;
+    status.textContent = wIn + '" × ' + hIn + '" at ' + dpi + ' dpi';
+  } catch (e) {
+    status.textContent = 'Preview unavailable: ' + e.message;
+  }
+}
+
+convertBtn.addEventListener('click', async () => {
+  if (!selectedFile) return;
+  errorEl.style.display = 'none';
+  convertBtn.style.display = 'none';
+  spinner.style.display = 'block';
+  output.style.display = 'none';
+  document.getElementById('labelPreviewWrap').style.display = 'none';
+
+  const { w, h } = getPixelDimensions();
+  const edits = [...document.querySelectorAll('input[name=edit]:checked')].map(c => c.value);
+  const fd = new FormData();
+  fd.append('file', selectedFile);
+  fd.append('width', w);
+  fd.append('height', h);
+  fd.append('type', document.getElementById('enctype').value);
+  fd.append('edit', edits.join(','));
+  if (fileIsPDF) {
+    fd.append('page', document.getElementById('pdfPage').value || '1');
+  }
+
+  try {
+    const res = await fetch('/convert', { method: 'POST', body: fd });
+    if (!res.ok) {
+      const msg = await res.text();
+      throw new Error(msg);
+    }
+    const text = await res.text();
+    zplOutput.value = text;
+    output.style.display = 'block';
+    fetchLabelPreview(text, w || origPxW, h || origPxH);
+  } catch (e) {
+    errorEl.textContent = 'Error: ' + e.message;
+    errorEl.style.display = 'block';
+  } finally {
+    spinner.style.display = 'none';
+    convertBtn.style.display = 'block';
+  }
+});
+
+document.getElementById('copyBtn').addEventListener('click', () => {
+  navigator.clipboard.writeText(zplOutput.value);
+  document.getElementById('copyBtn').textContent = 'Copied!';
+  setTimeout(() => document.getElementById('copyBtn').textContent = 'Copy', 1500);
+});
+
+document.getElementById('dlBtn').addEventListener('click', () => {
+  const blob = new Blob([zplOutput.value], { type: 'text/plain' });
+  const a = document.createElement('a');
+  a.href = URL.createObjectURL(blob);
+  a.download = (selectedFile ? selectedFile.name.replace(/\.[^.]+$/, '') : 'label') + '.zpl';
+  a.click();
+});
+
+// init labels
+updateLabels();
+</script>
+</body>
+</html>
+`

cmd/zplgfa/main.go

@@ -19,154 +19,146 @@ import (
 	"simonwaldherr.de/go/zplgfa"
 )
 
-func specialCmds(zebraCmdFlag, networkIpFlag, networkPortFlag string) bool {
-	var cmdSent bool
-	if networkIpFlag == "" {
-		return cmdSent
+func handleZebraCommands(cmd, ip, port string) bool {
+	if ip == "" {
+		return false
 	}
-	if strings.Contains(zebraCmdFlag, "cancel") {
-		if err := sendCancelCmdToZebra(networkIpFlag, networkPortFlag); err == nil {
-			cmdSent = true
+
+	// Define a map of command strings to functions that return error only
+	cmdActionsErr := map[string]func(string, string) error{
+		"cancel": sendCancelCmdToZebra,
+		"calib":  sendCalibCmdToZebra,
+		"feed":   sendFeedCmdToZebra,
+	}
+
+	// Define a map of command strings to functions that return (string, error)
+	cmdActionsStr := map[string]func(string, string) (string, error){
+		"info":   getInfoFromZebra,
+		"config": getConfigFromZebra,
+		"diag":   getDiagFromZebra,
+	}
+
+	for key, action := range cmdActionsErr {
+		if strings.Contains(cmd, key) {
+			if err := action(ip, port); err == nil {
+				return true
+			}
 		}
 	}
-	if strings.Contains(zebraCmdFlag, "calib") {
-		if err := sendCalibCmdToZebra(networkIpFlag, networkPortFlag); err == nil {
-			cmdSent = true
+
+	for key, action := range cmdActionsStr {
+		if strings.Contains(cmd, key) {
+			result, err := action(ip, port)
+			if err == nil {
+				fmt.Println(result)
+				return true
+			}
 		}
 	}
-	if strings.Contains(zebraCmdFlag, "feed") {
-		if err := sendFeedCmdToZebra(networkIpFlag, networkPortFlag); err == nil {
-			cmdSent = true
-		}
+
+	return false
+}
+
+func parseFlags() (string, string, string, string, string, string, float64) {
+	var filename, zebraCmd, graphicType, imageEdit, ip, port string
+	var resizeFactor float64
+
+	flag.StringVar(&filename, "file", "", "filename to convert to zpl")
+	flag.StringVar(&zebraCmd, "cmd", "", "send special command to printer [cancel,calib,feed,info,config,diag]")
+	flag.StringVar(&graphicType, "type", "CompressedASCII", "type of graphic field encoding")
+	flag.StringVar(&imageEdit, "edit", "", "manipulate the image [invert,monochrome]")
+	flag.StringVar(&ip, "ip", "", "send zpl to printer")
+	flag.StringVar(&port, "port", "9100", "network port of printer")
+	flag.Float64Var(&resizeFactor, "resize", 1.0, "zoom/resize the image")
+
+	flag.Parse()
+	return filename, zebraCmd, graphicType, imageEdit, ip, port, resizeFactor
+}
+
+func openImageFile(filename string) (image.Image, image.Config, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return nil, image.Config{}, fmt.Errorf("could not open the file \"%s\": %s", filename, err)
 	}
-	if strings.Contains(zebraCmdFlag, "info") {
-		info, err := getInfoFromZebra(networkIpFlag, networkPortFlag)
-		if err == nil {
-			fmt.Println(info)
-			cmdSent = true
-		}
+	defer file.Close()
+
+	config, format, err := image.DecodeConfig(file)
+	if err != nil {
+		return nil, config, fmt.Errorf("image not compatible, format: %s, config: %v, error: %s", format, config, err)
 	}
-	if strings.Contains(zebraCmdFlag, "config") {
-		info, err := getConfigFromZebra(networkIpFlag, networkPortFlag)
-		if err == nil {
-			fmt.Println(info)
-			cmdSent = true
-		}
+
+	file.Seek(0, 0)
+	img, _, err := image.Decode(file)
+	if err != nil {
+		return nil, config, fmt.Errorf("could not decode the file, %s", err)
 	}
-	if strings.Contains(zebraCmdFlag, "diag") {
-		info, err := getDiagFromZebra(networkIpFlag, networkPortFlag)
-		if err == nil {
-			fmt.Println(info)
-			cmdSent = true
-		}
+
+	return img, config, nil
+}
+
+func processImage(img image.Image, editFlag string, resizeFactor float64, config image.Config) image.Image {
+	if strings.Contains(editFlag, "monochrome") {
+		img = editImageMonochrome(img)
+	}
+	if strings.Contains(editFlag, "blur") {
+		img = blur.Gaussian(img, float64(config.Width)/300)
+	}
+	if strings.Contains(editFlag, "edge") {
+		img = effect.Sobel(img)
+	}
+	if strings.Contains(editFlag, "segment") {
+		img = segment.Threshold(img, 128)
+	}
+	if strings.Contains(editFlag, "invert") {
+		img = editImageInvert(img)
+	}
+
+	if resizeFactor != 1.0 {
+		img = resize.Resize(uint(float64(config.Width)*resizeFactor), uint(float64(config.Height)*resizeFactor), img, resize.MitchellNetravali)
+	}
+
+	return img
+}
+
+func getGraphicType(typeFlag string) zplgfa.GraphicType {
+	switch strings.ToUpper(typeFlag) {
+	case "ASCII":
+		return zplgfa.ASCII
+	case "BINARY":
+		return zplgfa.Binary
+	case "COMPRESSEDASCII":
+		return zplgfa.CompressedASCII
+	default:
+		return zplgfa.CompressedASCII
 	}
-	return cmdSent
 }
 
 func main() {
-	var filenameFlag string
-	var zebraCmdFlag string
-	var graphicTypeFlag string
-	var imageEditFlag string
-	var networkIpFlag string
-	var networkPortFlag string
-	var imageResizeFlag float64
-	var graphicType zplgfa.GraphicType
+	filename, zebraCmd, graphicTypeFlag, imageEdit, ip, port, resizeFactor := parseFlags()
 
-	flag.StringVar(&filenameFlag, "file", "", "filename to convert to zpl")
-	flag.StringVar(&zebraCmdFlag, "cmd", "", "send special command to printer [cancel,calib,feed,info,config,diag]")
-	flag.StringVar(&graphicTypeFlag, "type", "CompressedASCII", "type of graphic field encoding")
-	flag.StringVar(&imageEditFlag, "edit", "", "manipulate the image [invert,monochrome]")
-	flag.StringVar(&networkIpFlag, "ip", "", "send zpl to printer")
-	flag.StringVar(&networkPortFlag, "port", "9100", "network port of printer")
-	flag.Float64Var(&imageResizeFlag, "resize", 1.0, "zoom/resize the image")
+	if handleZebraCommands(zebraCmd, ip, port) && filename == "" {
+		return
+	}
 
-	// load flag input arguments
-	flag.Parse()
-
-	// send special commands to printer
-	cmdSent := specialCmds(zebraCmdFlag, networkIpFlag, networkPortFlag)
-
-	// check input parameter
-	if filenameFlag == "" {
-		if cmdSent {
-			return
-		}
+	if filename == "" {
 		log.Printf("Warning: no input file specified\n")
 		return
 	}
 
-	// open file
-	file, err := os.Open(filenameFlag)
+	img, config, err := openImageFile(filename)
 	if err != nil {
-		log.Printf("Warning: could not open the file \"%s\": %s\n", filenameFlag, err)
+		log.Printf("Warning: %s\n", err)
 		return
 	}
 
-	// close file when complete
-	defer file.Close()
+	img = processImage(img, imageEdit, resizeFactor, config)
 
-	// load image head information
-	config, format, err := image.DecodeConfig(file)
-	if err != nil {
-		log.Printf("Warning: image not compatible, format: %s, config: %v, error: %s\n", format, config, err)
-	}
-
-	// reset file pointer to the beginning of the file
-	file.Seek(0, 0)
-
-	// load and decode image
-	img, _, err := image.Decode(file)
-	if err != nil {
-		log.Printf("Warning: could not decode the file, %s\n", err)
-		return
-	}
-
-	// select graphic field type
-	switch strings.ToUpper(graphicTypeFlag) {
-	case "ASCII":
-		graphicType = zplgfa.ASCII
-	case "BINARY":
-		graphicType = zplgfa.Binary
-	case "COMPRESSEDASCII":
-		graphicType = zplgfa.CompressedASCII
-	default:
-		graphicType = zplgfa.CompressedASCII
-	}
-
-	// apply image manipulation functions
-	if strings.Contains(imageEditFlag, "monochrome") {
-		img = editImageMonochrome(img)
-	}
-	if strings.Contains(imageEditFlag, "blur") {
-		img = blur.Gaussian(img, float64(config.Width)/300)
-	}
-	if strings.Contains(imageEditFlag, "edge") {
-		img = effect.Sobel(img)
-	}
-	if strings.Contains(imageEditFlag, "segment") {
-		img = segment.Threshold(img, 128)
-	}
-	if strings.Contains(imageEditFlag, "invert") {
-		img = editImageInvert(img)
-	}
-
-	// resize image
-	if imageResizeFlag != 1.0 {
-		img = resize.Resize(uint(float64(config.Width)*imageResizeFlag), uint(float64(config.Height)*imageResizeFlag), img, resize.MitchellNetravali)
-	}
-
-	// flatten image
 	flat := zplgfa.FlattenImage(img)
+	gfimg := zplgfa.ConvertToZPL(flat, getGraphicType(graphicTypeFlag))
 
-	// convert image to zpl compatible type
-	gfimg := zplgfa.ConvertToZPL(flat, graphicType)
-
-	if networkIpFlag != "" {
-		// send zpl to printer
-		sendDataToZebra(networkIpFlag, networkPortFlag, gfimg)
+	if ip != "" {
+		sendDataToZebra(ip, port, gfimg)
 	} else {
-		// output zpl with graphic field data to stdout
 		fmt.Println(gfimg)
 	}
 }

docker-compose.yml

@@ -0,0 +1,6 @@
+services:
+  zplgfa:
+    build: .
+    ports:
+      - "4543:4543"
+    restart: unless-stopped

example_test.go

@@ -52,5 +52,5 @@ func ExampleConvertToZPL() {
 
 	fmt.Println(zplstr)
 
-	// Output: ^XA,^FS^FO0,0^GFA,52,51,3,FFFF00::FE3F00::FFFF00FFE300::FFFF00E22300::FFFF00::^FS,^XZ
+	// Output: ^XA,^FS^FO0,0^GFA,52,51,3,FFFF80::FE3F80::FFFF80FFE380::FFFF80E22380::FFFF80::^FS,^XZ
 }

go.mod

@@ -0,0 +1,8 @@
+module simonwaldherr.de/go/zplgfa
+
+go 1.22
+
+require (
+	github.com/anthonynsimon/bild v0.13.0
+	github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646
+)

go.sum

@@ -0,0 +1,35 @@
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/anthonynsimon/bild v0.13.0 h1:mN3tMaNds1wBWi1BrJq0ipDBhpkooYfu7ZFSMhXt1C8=
+github.com/anthonynsimon/bild v0.13.0/go.mod h1:tpzzp0aYkAsMi1zmfhimaDyX1xjn2OUc1AJZK/TF0AE=
+github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6/go.mod h1:grANhF5doyWs3UAsr3K4I6qtAmlQcZDesFNEHPZAzj8=
+github.com/coreos/etcd v3.3.10+incompatible/go.mod h1:uF7uidLiAD3TWHmW31ZFd/JWoc32PjwdhPthX9715RE=
+github.com/coreos/go-etcd v2.0.0+incompatible/go.mod h1:Jez6KQU2B/sWsbdaef3ED8NzMklzPG4d5KIOhIy30Tk=
+github.com/coreos/go-semver v0.2.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
+github.com/cpuguy83/go-md2man v1.0.10/go.mod h1:SmD6nW6nTyfqj6ABTjUi3V3JVMnlJmwcJI5acqYI6dE=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
+github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
+github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
+github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
+github.com/mitchellh/go-homedir v1.1.0/go.mod h1:SfyaCUpYCn1Vlf4IUYiD9fPX4A5wJrkLzIz1N1q0pr0=
+github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646 h1:zYyBkD/k9seD2A7fsi6Oo2LfFZAehjjQMERAvZLEDnQ=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646/go.mod h1:jpp1/29i3P1S/RLdc7JQKbRpFeM1dOBd8T9ki5s+AY8=
+github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/russross/blackfriday v1.5.2/go.mod h1:JO/DiYxRf+HjHt06OyowR9PTA263kcR/rfWxYHBV53g=
+github.com/spf13/afero v1.1.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
+github.com/spf13/cast v1.3.0/go.mod h1:Qx5cxh0v+4UWYiBimWS+eyWzqEqokIECu5etghLkUJE=
+github.com/spf13/cobra v0.0.5/go.mod h1:3K3wKZymM7VvHMDS9+Akkh4K60UwM26emMESw8tLCHU=
+github.com/spf13/jwalterweatherman v1.0.0/go.mod h1:cQK4TGJAtQXfYWX+Ddv3mKDzgVb68N+wFjFa4jdeBTo=
+github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
+github.com/spf13/viper v1.3.2/go.mod h1:ZiWeW+zYFKm7srdB9IoDzzZXaJaI5eL9QjNiN/DMA2s=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/ugorji/go/codec v0.0.0-20181204163529-d75b2dcb6bc8/go.mod h1:VFNgLljTbGfSG7qAOspJ7OScBnGdDN/yBr0sguwnwf0=
+github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77/go.mod h1:aYKd//L2LvnjZzWKhF00oedf4jCCReLcmhLdhm1A27Q=
+golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/image v0.0.0-20190703141733-d6a02ce849c9/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
+golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

zplgfa.go

@@ -21,179 +21,173 @@ const (
 	CompressedASCII
 )
 
-// ConvertToZPL is just a wrapper for ConvertToGraphicField which also includes the ZPL
-// starting code ^XA and ending code ^XZ, as well as a Field Separator and Field Origin.
+// ConvertToZPL wraps ConvertToGraphicField, adding ZPL start and end codes.
 func ConvertToZPL(img image.Image, graphicType GraphicType) string {
+	if img.Bounds().Size().X/8 == 0 {
+		return ""
+	}
 	return fmt.Sprintf("^XA,^FS\n^FO0,0\n%s^FS,^XZ\n", ConvertToGraphicField(img, graphicType))
 }
 
-// FlattenImage optimizes an image for the converting process
+// FlattenImage optimizes an image for the converting process.
 func FlattenImage(source image.Image) *image.NRGBA {
 	size := source.Bounds().Size()
-	background := color.White
 	target := image.NewNRGBA(source.Bounds())
+	background := color.White
+
 	for y := 0; y < size.Y; y++ {
 		for x := 0; x < size.X; x++ {
 			p := source.At(x, y)
-			flat := flatten(p, background)
-			target.Set(x, y, flat)
+			target.Set(x, y, flatten(p, background))
 		}
 	}
 	return target
 }
 
-func flatten(input color.Color, background color.Color) color.Color {
-	source := color.NRGBA64Model.Convert(input).(color.NRGBA64)
-	r, g, b, a := source.RGBA()
+// flatten blends a pixel with the background color based on its alpha value.
+func flatten(input, background color.Color) color.Color {
+	src := color.NRGBA64Model.Convert(input).(color.NRGBA64)
+	r, g, b, a := src.RGBA()
 	bgR, bgG, bgB, _ := background.RGBA()
 	alpha := float32(a) / 0xffff
-	conv := func(c uint32, bg uint32) uint8 {
-		val := 0xffff - uint32((float32(bg) * alpha))
-		val = val | uint32(float32(c)*alpha)
+
+	blend := func(c, bg uint32) uint8 {
+		val := 0xffff - uint32(float32(bg)*alpha)
+		val |= uint32(float32(c) * alpha)
 		return uint8(val >> 8)
 	}
-	c := color.NRGBA{
-		conv(r, bgR),
-		conv(g, bgG),
-		conv(b, bgB),
-		uint8(0xff),
+
+	return color.NRGBA{
+		R: blend(r, bgR),
+		G: blend(g, bgG),
+		B: blend(b, bgB),
+		A: 0xff,
 	}
-	return c
 }
 
+// getRepeatCode generates ZPL repeat codes for character compression.
 func getRepeatCode(repeatCount int, char string) string {
-	repeatStr := ""
-	if repeatCount > 419 {
-		repeatCount -= 419
-		repeatStr += getRepeatCode(repeatCount, char)
-		repeatCount = 419
-	}
-
-	high := repeatCount / 20
-	low := repeatCount % 20
-
-	lowString := " GHIJKLMNOPQRSTUVWXY"
+	const maxRepeat = 419
 	highString := " ghijklmnopqrstuvwxyz"
+	lowString := " GHIJKLMNOPQRSTUVWXY"
 
-	if high > 0 {
-		repeatStr += string(highString[high])
-	}
-	if low > 0 {
-		repeatStr += string(lowString[low])
+	encode := func(count int) string {
+		var singleRepeatStr strings.Builder
+		high := count / 20
+		low := count % 20
+
+		if high > 0 {
+			singleRepeatStr.WriteByte(highString[high])
+		}
+		if low > 0 {
+			singleRepeatStr.WriteByte(lowString[low])
+		}
+
+		singleRepeatStr.WriteString(char)
+		return singleRepeatStr.String()
 	}
 
-	repeatStr += char
+	if repeatCount > maxRepeat {
+		var repeatStr strings.Builder
+		remainder := repeatCount % maxRepeat
+		quotient := repeatCount / maxRepeat
 
-	return repeatStr
+		if remainder > 0 {
+			repeatStr.WriteString(encode(remainder))
+		}
+
+		maxEncoding := encode(maxRepeat)
+		for i := 0; i < quotient; i++ {
+			repeatStr.WriteString(maxEncoding)
+		}
+
+		return repeatStr.String()
+	}
+
+	return encode(repeatCount)
 }
 
-// CompressASCII compresses the ASCII data of a ZPL Graphic Field using RLE
-func CompressASCII(in string) string {
-	var curChar string
+// CompressASCII compresses the ASCII data of a ZPL Graphic Field using RLE.
+func CompressASCII(input string) string {
+	if input == "" {
+		return ""
+	}
+
+	var output strings.Builder
 	var lastChar string
 	var lastCharSince int
-	var output string
-	var repCode string
 
-	for i := 0; i < len(in)+1; i++ {
-		if i == len(in) {
-			curChar = ""
-			if lastCharSince == 0 {
-				switch lastChar {
-				case "0":
-					output = ","
-					return output
-				case "F":
-					output = "!"
-					return output
-				}
-			}
-		} else {
-			curChar = string(in[i])
+	for i := 0; i <= len(input); i++ {
+		curChar := ""
+		if i < len(input) {
+			curChar = string(input[i])
 		}
+
 		if lastChar != curChar {
 			if i-lastCharSince > 4 {
-				repCode = getRepeatCode(i-lastCharSince, lastChar)
-				output += repCode
+				output.WriteString(getRepeatCode(i-lastCharSince, lastChar))
 			} else {
-				for j := 0; j < i-lastCharSince; j++ {
-					output += lastChar
-				}
+				output.WriteString(strings.Repeat(lastChar, i-lastCharSince))
 			}
-
 			lastChar = curChar
 			lastCharSince = i
 		}
+
+		if curChar == "" && lastCharSince == 0 {
+			switch lastChar {
+			case "0":
+				return ","
+			case "F":
+				return "!"
+			}
+		}
 	}
 
-	if output == "" {
-		output += getRepeatCode(len(in), lastChar)
-	}
-
-	return output
+	return output.String()
 }
 
-// ConvertToGraphicField converts an image.Image picture to a ZPL compatible Graphic Field.
-// The ZPL ^GF (Graphic Field) supports various data formats, this package supports the
-// normal ASCII encoded, as well as a RLE compressed ASCII format. It also supports the
-// Binary Graphic Field format. The encoding can be chosen by the second argument.
+// ConvertToGraphicField converts an image.Image to a ZPL compatible Graphic Field.
 func ConvertToGraphicField(source image.Image, graphicType GraphicType) string {
-	var gfType string
-	var lastLine string
+	var gfType, graphicFieldData string
 	size := source.Bounds().Size()
-	width := size.X / 8
+	width := (size.X + 7) / 8 // round up division
 	height := size.Y
-	if size.Y%8 != 0 {
-		width = width + 1
-	}
+	var lastLine string
 
-	var GraphicFieldData string
-
-	for y := 0; y < size.Y; y++ {
+	for y := 0; y < height; y++ {
 		line := make([]uint8, width)
-		lineIndex := 0
-		index := uint8(0)
-		currentByte := line[lineIndex]
 		for x := 0; x < size.X; x++ {
-			index = index + 1
-			p := source.At(x, y)
-			lum := color.Gray16Model.Convert(p).(color.Gray16)
-			if lum.Y < math.MaxUint16/2 {
-				currentByte = currentByte | (1 << (8 - index))
+			if x%8 == 0 {
+				line[x/8] = 0
 			}
-			if index >= 8 {
-				line[lineIndex] = currentByte
-				lineIndex++
-				if lineIndex < len(line) {
-					currentByte = line[lineIndex]
-				}
-				index = 0
+			if lum := color.Gray16Model.Convert(source.At(x, y)).(color.Gray16).Y; lum < math.MaxUint16/2 {
+				line[x/8] |= 1 << (7 - uint(x)%8)
 			}
 		}
 
-		hexstr := strings.ToUpper(hex.EncodeToString(line))
-
+		hexStr := strings.ToUpper(hex.EncodeToString(line))
 		switch graphicType {
 		case ASCII:
-			GraphicFieldData += fmt.Sprintln(hexstr)
+			graphicFieldData += fmt.Sprintln(hexStr)
 		case CompressedASCII:
-			curLine := CompressASCII(hexstr)
+			curLine := CompressASCII(hexStr)
 			if lastLine == curLine {
-				GraphicFieldData += ":"
+				graphicFieldData += ":"
 			} else {
-				GraphicFieldData += curLine
+				graphicFieldData += curLine
 			}
 			lastLine = curLine
 		case Binary:
-			GraphicFieldData += fmt.Sprintf("%s", line)
+			graphicFieldData += string(line)
 		}
 	}
 
-	if graphicType == ASCII || graphicType == CompressedASCII {
+	switch graphicType {
+	case ASCII, CompressedASCII:
 		gfType = "A"
-	} else if graphicType == Binary {
+	case Binary:
 		gfType = "B"
 	}
 
-	return fmt.Sprintf("^GF%s,%d,%d,%d,\n%s", gfType, len(GraphicFieldData), width*height, width, GraphicFieldData)
+	return fmt.Sprintf("^GF%s,%d,%d,%d,\n%s", gfType, len(graphicFieldData), width*height, width, graphicFieldData)
 }

zplgfa_test.go

@@ -23,73 +23,80 @@ type zplTest struct {
 var zplTests []zplTest
 
 func init() {
-	jsonstr, _ := ioutil.ReadFile("./tests/tests.json")
-	json.Unmarshal(jsonstr, &zplTests)
+	jsonstr, err := ioutil.ReadFile("./tests/tests.json")
+	if err != nil {
+		log.Fatalf("Failed to read test cases: %s", err)
+	}
+	if err := json.Unmarshal(jsonstr, &zplTests); err != nil {
+		log.Fatalf("Failed to unmarshal test cases: %s", err)
+	}
 }
 
 func Test_CompressASCII(t *testing.T) {
 	if str := CompressASCII("FFFFFFFF000000"); str != "NFL0" {
-		t.Fatalf("CompressASCII failed")
+		t.Fatalf("CompressASCII failed: got %s, want NFL0", str)
 	}
 }
 
 func Test_ConvertToZPL(t *testing.T) {
-	var graphicType GraphicType
 	for i, testcase := range zplTests {
-		filename, zplstring, graphictype := testcase.Filename, testcase.Zplstring, testcase.Graphictype
-		// open file
-		file, err := os.Open(filename)
-		if err != nil {
-			log.Printf("Warning: could not open the file \"%s\": %s\n", filename, err)
-			return
-		}
-
-		defer file.Close()
-
-		// load image head information
-		config, format, err := image.DecodeConfig(file)
-		if err != nil {
-			log.Printf("Warning: image not compatible, format: %s, config: %v, error: %s\n", format, config, err)
-		}
-
-		// reset file pointer to the beginning of the file
-		file.Seek(0, 0)
-
-		// load and decode image
-		img, _, err := image.Decode(file)
-		if err != nil {
-			log.Printf("Warning: could not decode the file, %s\n", err)
-			return
-		}
-
-		// flatten image
-		flat := FlattenImage(img)
-
-		// convert image to zpl compatible type
-		switch graphictype {
-		case "ASCII":
-			graphicType = ASCII
-		case "Binary":
-			graphicType = Binary
-		case "CompressedASCII":
-			graphicType = CompressedASCII
-		default:
-			graphicType = CompressedASCII
-		}
-
-		gfimg := ConvertToZPL(flat, graphicType)
-
-		if graphictype == "Binary" {
-			gfimg = base64.StdEncoding.EncodeToString([]byte(gfimg))
-		} else {
-			// remove whitespace - only for the test
-			gfimg = strings.Replace(gfimg, " ", "", -1)
-			gfimg = strings.Replace(gfimg, "\n", "", -1)
-		}
-
-		if gfimg != zplstring {
-			log.Printf("ConvertToZPL Test for file \"%s\" failed, wanted: \n%s\ngot: \n%s\n", filename, zplstring, gfimg)
-			t.Fatalf("Testcase %d ConvertToZPL failed", i)
-		}
+		t.Run(testcase.Filename, func(t *testing.T) {
+			testConvertToZPL(t, testcase, i)
+		})
 	}
 }
+
+func testConvertToZPL(t *testing.T, testcase zplTest, index int) {
+	file, err := os.Open(testcase.Filename)
+	if err != nil {
+		t.Fatalf("Failed to open file %s: %s", testcase.Filename, err)
+	}
+	defer file.Close()
+
+	_, _, err = image.DecodeConfig(file)
+	if err != nil {
+		t.Fatalf("Failed to decode config for file %s: %s", testcase.Filename, err)
+	}
+
+	if _, err := file.Seek(0, 0); err != nil {
+		t.Fatalf("Failed to reset file pointer for %s: %s", testcase.Filename, err)
+	}
+
+	img, _, err := image.Decode(file)
+	if err != nil {
+		t.Fatalf("Failed to decode image for file %s: %s", testcase.Filename, err)
+	}
+
+	flat := FlattenImage(img)
+	graphicType := parseGraphicType(testcase.Graphictype)
+	gfimg := ConvertToZPL(flat, graphicType)
+
+	if graphicType == Binary {
+		gfimg = base64.StdEncoding.EncodeToString([]byte(gfimg))
+	} else {
+		gfimg = cleanZPLString(gfimg)
+	}
+
+	if gfimg != testcase.Zplstring {
+		t.Fatalf("Testcase %d ConvertToZPL failed for file %s: \nExpected: \n%s\nGot: \n%s\n", index, testcase.Filename, testcase.Zplstring, gfimg)
+	}
+}
+
+func parseGraphicType(graphicTypeStr string) GraphicType {
+	switch graphicTypeStr {
+	case "ASCII":
+		return ASCII
+	case "Binary":
+		return Binary
+	case "CompressedASCII":
+		return CompressedASCII
+	default:
+		return CompressedASCII
+	}
+}
+
+func cleanZPLString(zpl string) string {
+	zpl = strings.ReplaceAll(zpl, " ", "")
+	zpl = strings.ReplaceAll(zpl, "\n", "")
+	return zpl
+}