implement a native EPS writer

cmd/qrbill-api/api.go

@@ -105,7 +105,8 @@ func logic() error {
 			format != "svg" &&
 			format != "txt" &&
 			format != "html" &&
-			format != "wv" {
+			format != "wv" &&
+			format != "eps" {
 			msg := fmt.Sprintf("format (%q) must be one of png, svg, txt or html", format)
 			log.Printf("%s %s", prefix, msg)
 			http.Error(w, msg, http.StatusBadRequest)
@@ -157,6 +158,18 @@ func logic() error {
 
 			w.Header().Add("Content-Type", "image/svg+xml")
 
+		case "eps":
+			var err error
+			b, err = bill.EncodeToEPS()
+			if err != nil {
+				log.Printf("%s %s", prefix, err)
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+
+			w.Header().Add("Content-Type", "image/eps")
+			w.Header().Add("Content-Disposition", `attachment; filename="qr.eps"`)
+
 		case "txt":
 			w.Header().Add("Content-Type", "text/plain; charset=utf-8")
 			spew.Fdump(w, qrch.Validate())

go.mod

@@ -3,10 +3,11 @@ module github.com/stapelberg/qrbill
 go 1.14
 
 require (
-	github.com/ajstarks/svgo v0.0.0-20200320125537-f189e35d30ca
+	github.com/ajstarks/svgo v0.0.0-20200725142600-7a3c8b57fecb
 	github.com/davecgh/go-spew v1.1.1
 	github.com/makiuchi-d/gozxing v0.0.0-20200903113411-25f730ed83da
 	github.com/mattn/go-isatty v0.0.12
+	golang.org/x/sys v0.0.0-20200724161237-0e2f3a69832c // indirect
 	golang.org/x/text v0.3.4 // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 )

go.sum

@@ -1,5 +1,5 @@
-github.com/ajstarks/svgo v0.0.0-20200320125537-f189e35d30ca h1:kWzLcty5V2rzOqJM7Tp/MfSX0RMSI1x4IOLApEefYxA=
+github.com/ajstarks/svgo v0.0.0-20200725142600-7a3c8b57fecb h1:EVl3FJLQCzSbgBezKo/1A4ADnJ4mtJZ0RvnNzDJ44nY=
-github.com/ajstarks/svgo v0.0.0-20200320125537-f189e35d30ca/go.mod h1:K08gAheRH3/J6wwsYMMT4xOr94bZjxIelGM0+d/wbFw=
+github.com/ajstarks/svgo v0.0.0-20200725142600-7a3c8b57fecb/go.mod h1:K08gAheRH3/J6wwsYMMT4xOr94bZjxIelGM0+d/wbFw=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/makiuchi-d/gozxing v0.0.0-20200903113411-25f730ed83da h1:OgNu1PPD9EvZckyKDAc8DA4KymNXuc6vaCLsdOGyjOE=
@@ -8,6 +8,8 @@ github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHX
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42 h1:vEOn+mP2zCOVzKckCZy6YsCtDblrpj/w7B9nxGNELpg=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200724161237-0e2f3a69832c h1:UIcGWL6/wpCfyGuJnRFJRurA+yj8RrW7Q6x2YMCXt6c=
+golang.org/x/sys v0.0.0-20200724161237-0e2f3a69832c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.4 h1:0YWbFKbhXG/wIiuHDSKpS0Iy7FSA+u45VtBMfQcFTTc=
 golang.org/x/text v0.3.4/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=

qrbill.go

@@ -287,6 +287,21 @@ func (b *Bill) EncodeToSVG() ([]byte, error) {
 	return bytes.ReplaceAll(qrCodeSVG, []byte(`</g>`), append(cross, []byte("</g>")...)), nil
 }
 
+func (b *Bill) EncodeToEPS() ([]byte, error) {
+	var err error
+	code, err := encoder.Encoder_encode(b.qrcontents, decoder.ErrorCorrectionLevel_M, qrEncodeHints())
+	if err != nil {
+		return nil, err
+	}
+
+	const quietzone = 4
+	qrCodeEPS, err := renderResultEPS(code, qrCodeEdgeSidePx, qrCodeEdgeSidePx, quietzone)
+	if err != nil {
+		return nil, err
+	}
+	return qrCodeEPS, nil
+}
+
 func (b *Bill) EncodeToImage() (image.Image, error) {
 	return generateSwissQrCode(b.qrcontents)
 }

qrcodegeneratoreps.go

@@ -0,0 +1,127 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package qrbill
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/makiuchi-d/gozxing"
+	"github.com/makiuchi-d/gozxing/qrcode/encoder"
+)
+
+// renderResultEPS is a copy of renderResult from
+// gozxing/qrcode/qrcode_writer.go, adapted to output to SVG.
+func renderResultEPS(code *encoder.QRCode, width, height, quietZone int) ([]byte, error) {
+	input := code.GetMatrix()
+	if input == nil {
+		return nil, gozxing.NewWriterException("IllegalStateException")
+	}
+	inputWidth := input.GetWidth()
+	inputHeight := input.GetHeight()
+	qrWidth := inputWidth + (quietZone * 2)
+	qrHeight := inputHeight + (quietZone * 2)
+	outputWidth := qrWidth
+	if outputWidth < width {
+		outputWidth = width
+	}
+	outputHeight := qrHeight
+	if outputHeight < height {
+		outputHeight = height
+	}
+
+	multiple := outputWidth / qrWidth
+	if h := outputHeight / qrHeight; multiple > h {
+		multiple = h
+	}
+	// Padding includes both the quiet zone and the extra white pixels to accommodate the requested
+	// dimensions. For example, if input is 25x25 the QR will be 33x33 including the quiet zone.
+	// If the requested size is 200x160, the multiple will be 4, for a QR of 132x132. These will
+	// handle all the padding from 100x100 (the actual QR) up to 200x160.
+	leftPadding := (outputWidth - (inputWidth * multiple)) / 2
+	topPadding := (outputHeight - (inputHeight * multiple)) / 2
+
+	// --------------------------------------------------------------------------------
+
+	var eps strings.Builder
+	// See postscript language document structuring conventions specification version 3.0
+	// https://www-cdf.fnal.gov/offline/PostScript/5001.PDF
+
+	// See Encapsulated PostScript File Format Specification
+	// https://www.adobe.com/content/dam/acom/en/devnet/actionscript/articles/5002.EPSF_Spec.pdf
+
+	// EPS files must not have lines of ASCII text that exceed 255 characters,
+	// excluding line-termination characters.
+
+	// Lines must be terminated with one of the following combinations:
+	// - CR (carriage return, ASCII decimal 13)
+	// - LF (line feed, ASCII decimal 10)
+	// - CR LF
+	// - LF CR
+
+	// BoundingBox parameters are lower-left (llx, lly) and upper-right (urx, ury)
+	eps.WriteString("%!PS-Adobe-3.0 EPSF-3.0\n")
+	eps.WriteString("%%Creator: https://github.com/stapelberg/qrbill\n")
+	// TODO: summarize message and recipient in title
+	// TODO: is there a max length for the title?
+	eps.WriteString("%%Title: QR-Bill\n")
+	eps.WriteString("%%CreationDate: " + time.Now().Format("2006-01-02") + "\n")
+	eps.WriteString("%%BoundingBox: 0 0 1265 1265\n")
+	eps.WriteString("%%EndComments\n")
+	eps.WriteString("/F { rectfill } def\n")
+
+	// Change the application coordinate system to work like the SVG one does,
+	// for consistency between the different code paths. See also General
+	// Coordinate System Transformation, Page 18, Encapsulated PostScript File
+	// Format Specification:
+	// https://www.adobe.com/content/dam/acom/en/devnet/actionscript/articles/5002.EPSF_Spec.pdf
+	eps.WriteString("0 1265 translate\n")
+	eps.WriteString("1 -1 scale\n")
+
+	// Explicitly fill the background with white:
+	eps.WriteString("1 1 1 setrgbcolor\n")
+	// or 1 setgray?
+	eps.WriteString("0 0 1265 1265 F\n")
+
+	// Explicitly set color to black:
+	eps.WriteString("0 0 0 setrgbcolor\n")
+	// or 0 setgray?
+
+	for inputY, outputY := 0, topPadding; inputY < inputHeight; inputY, outputY = inputY+1, outputY+multiple {
+		// Write the contents of this row of the barcode
+		for inputX, outputX := 0, leftPadding; inputX < inputWidth; inputX, outputX = inputX+1, outputX+multiple {
+			if input.Get(inputX, inputY) == 1 {
+				eps.WriteString(fmt.Sprintf("%d %d %d %d F\n", outputX, outputY, multiple, multiple))
+			}
+		}
+	}
+
+	eps.WriteString("549 549 translate\n")
+
+	// overlay an EPS version of the swiss cross
+	eps.WriteString("1 1 1 setrgbcolor\n")
+	eps.WriteString("0 0 166 166 F\n")
+
+	eps.WriteString("0 0 0 setrgbcolor\n")
+	eps.WriteString("12 12 142 142 F\n")
+
+	eps.WriteString("1 1 1 setrgbcolor\n")
+	eps.WriteString("36 66 94 28 F\n")
+	eps.WriteString("68 34 30 92 F\n")
+
+	eps.WriteString("%%EOF")
+	return []byte(eps.String()), nil
+}