add PDF export

cmd/qrbill-api/api.go

@@ -103,11 +103,12 @@ func logic() error {
 
 		if format != "png" &&
 			format != "svg" &&
+			format != "pdf" &&
 			format != "txt" &&
 			format != "html" &&
 			format != "wv" &&
 			format != "eps" {
-			msg := fmt.Sprintf("format (%q) must be one of png, svg, txt or html", format)
+			msg := fmt.Sprintf("format (%q) must be one of png, svg, pdf, eps, txt or html", format)
 			log.Printf("%s %s", prefix, msg)
 			http.Error(w, msg, http.StatusBadRequest)
 			return
@@ -158,6 +159,17 @@ func logic() error {
 
 			w.Header().Add("Content-Type", "image/svg+xml")
 
+		case "pdf":
+			var err error
+			b, err = bill.EncodeToPDF()
+			if err != nil {
+				log.Printf("%s %s", prefix, err)
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+
+			w.Header().Add("Content-Type", "application/pdf")
+
 		case "eps":
 			var err error
 			b, err = bill.EncodeToEPS()

internal/pdf/pdf.go

@@ -0,0 +1,334 @@
+// 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
+//
+//     http://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 pdf implements a minimal PDF 1.7 writer, just functional enough to
+// create a PDF file containing a QR code encoded as rectangles.
+//
+// It follows the standard “PDF 32000-1:2008 PDF 1.7”:
+// https://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/PDF32000_2008.pdf
+package pdf
+
+import (
+	"fmt"
+	"io"
+	"strings"
+	"time"
+)
+
+func dateString(t time.Time) string {
+	return "D:" + t.Format("20060102150405-07'00'")
+}
+
+// ObjectID is a PDF object id.
+type ObjectID int
+
+// String implements fmt.Stringer.
+func (o ObjectID) String() string {
+	return fmt.Sprintf("%d 0 R", int(o))
+}
+
+// Object is implemented by all PDF objects.
+type Object interface {
+	// Objects returns all Objects which should be encoded into the
+	// PDF file.
+	Objects() []Object
+
+	// Encode encodes the object into the PDF file w.
+	Encode(w io.Writer, ids map[string]ObjectID) error
+
+	// SetID updates the object id.
+	SetID(id ObjectID)
+
+	// Name returns the human-readable object name.
+	Name() string
+
+	fmt.Stringer
+}
+
+// Common represents a PDF object.
+type Common struct {
+	ObjectName string
+	ID         ObjectID
+	Stream     []byte
+}
+
+// String implements fmt.Stringer.
+func (c *Common) String() string {
+	return c.ID.String()
+}
+
+// SetID implements Object.
+func (c *Common) SetID(id ObjectID) {
+	c.ID = id
+}
+
+// Name implements Object.
+func (c *Common) Name() string {
+	return c.ObjectName
+}
+
+// Objects implements Object.
+func (c *Common) Objects() []Object {
+	return []Object{c}
+}
+
+// Encode implements Object.
+func (c *Common) Encode(w io.Writer, ids map[string]ObjectID) error {
+	_, err := fmt.Fprintf(w, `
+%d 0 obj
+<<
+  /Length %d
+>>
+stream
+%s
+endstream
+endobj`, c.ID, len(c.Stream), c.Stream)
+	return err
+}
+
+// DocumentInfo represents a PDF document information object.
+type DocumentInfo struct {
+	Common
+
+	CreationDate time.Time
+	Producer     string
+	Title        string
+}
+
+// Objects implements Object.
+func (d *DocumentInfo) Objects() []Object {
+	return []Object{d}
+}
+
+// Encode implements Object.
+func (d *DocumentInfo) Encode(w io.Writer, ids map[string]ObjectID) error {
+	_, err := fmt.Fprintf(w, `
+%d 0 obj
+<<
+  /Title (%s)
+  /CreationDate (%s)
+  /ModDate (%s)
+  /Producer (%s)
+>>
+endobj`,
+		int(d.ID),
+		d.Title,
+		dateString(d.CreationDate),
+		dateString(d.CreationDate),
+		d.Producer)
+	return err
+}
+
+// Catalog represents a PDF catalog object.
+type Catalog struct {
+	Common
+	Pages Object // Pages
+}
+
+// Objects implements Object.
+func (r *Catalog) Objects() []Object {
+	return append([]Object{r}, r.Pages.Objects()...)
+}
+
+// Encode implements Object.
+func (r *Catalog) Encode(w io.Writer, ids map[string]ObjectID) error {
+	_, err := fmt.Fprintf(w, `
+%d 0 obj
+<<
+  /Type /Catalog
+  /Pages %v
+>>
+endobj`, int(r.ID), r.Pages)
+	return err
+}
+
+// Pages represents a PDF pages object
+type Pages struct {
+	Common
+	Kids []Object // Page
+}
+
+// Objects implements Object.
+func (p *Pages) Objects() []Object {
+	result := []Object{p}
+	for _, o := range p.Kids {
+		result = append(result, o.Objects()...)
+	}
+	return result
+}
+
+// Encode implements Object.
+func (p *Pages) Encode(w io.Writer, ids map[string]ObjectID) error {
+	_, err := fmt.Fprintf(w, `
+%d 0 obj
+<<
+  /Kids %v
+  /Type /Pages
+  /Count %d
+>>
+endobj`, int(p.ID), p.Kids, len(p.Kids))
+	return err
+}
+
+// Page represents a PDF page object with size DIN A4
+type Page struct {
+	Common
+
+	Resources []Object // Image
+	Contents  []Object // Common (streams)
+
+	// Parent contains the human-readable name of the parent object,
+	// which will be translated into an object ID when encoding.
+	Parent string
+}
+
+// Objects implements Object.
+func (p *Page) Objects() []Object {
+	result := []Object{p}
+	for _, o := range p.Resources {
+		result = append(result, o.Objects()...)
+	}
+	for _, o := range p.Contents {
+		result = append(result, o.Objects()...)
+	}
+	return result
+}
+
+// Encode implements Object.
+func (p *Page) Encode(w io.Writer, ids map[string]ObjectID) error {
+	xObjects := make([]string, len(p.Resources))
+	for idx, o := range p.Resources {
+		xObjects[idx] = fmt.Sprintf("/%s %v", o.Name(), ids[o.Name()])
+	}
+	_, err := fmt.Fprintf(w, `
+%d 0 obj
+<<
+  /Resources <<
+    /XObject <<
+%s
+    >>
+  >>
+  /Contents %v
+  /Parent %v
+  /Type /Page
+  /MediaBox [ 0 0 152 152 ]
+>>
+endobj`, int(p.ID), strings.Join(xObjects, "\n"), p.Contents, ids[p.Parent])
+	return err
+}
+
+type countingWriter struct {
+	cnt int
+	w   io.Writer
+}
+
+func (cw *countingWriter) Write(p []byte) (n int, err error) {
+	n, err = cw.w.Write(p)
+	cw.cnt += n
+	return n, err
+}
+
+// Encoder is a PDF writer.
+type Encoder struct {
+	w *countingWriter
+}
+
+// NewEncoder returns a ready-to-use Encoder writing to w.
+func NewEncoder(w io.Writer) *Encoder {
+	return &Encoder{
+		w: &countingWriter{w: w},
+	}
+}
+
+// writeXrefTable writes a cross-reference table to e.w. See also “PDF
+// 32000-1:2008 PDF 1.7” section “7.5.4 Cross-Reference Table”
+func (e *Encoder) writeXrefTable(Objects []Object, xrefOffsets []int) error {
+	if _, err := fmt.Fprintf(e.w, "\nxref\n0 %d\n", len(Objects)+1); err != nil {
+		return err
+	}
+
+	// index 0 can never point to a valid Object, so print an invalid entry:
+	if _, err := fmt.Fprintf(e.w, "%010d %05d %s \n", 0, 65535, "f"); err != nil {
+		return err
+	}
+
+	const generation = 0
+	for _, offset := range xrefOffsets {
+		if _, err := fmt.Fprintf(e.w, "%010d %05d %s \n", offset, generation, "n"); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Encode writes the PDF file represented by the specified catalog.
+func (e *Encoder) Encode(r *Catalog, info *DocumentInfo) error {
+	// As per “PDF Explained: How a PDF File is Written”:
+	// https://www.geekbooks.me/book/view/pdf-explained
+
+	// (1.) Output the header.
+
+	// Byte sequence 0xE2E3CFD3 as per the recommendation from
+	// “Developing with PDF”. See “Chapter 1. PDF Syntax”:
+	// https://www.safaribooksonline.com/library/view/developing-with-pdf/9781449327903/ch01.html#_header
+	if _, err := e.w.Write(append([]byte("%PDF-1.4\n%"), 0xe2, 0xe3, 0xcf, 0xd3)); err != nil {
+		return err
+	}
+
+	// Flatten the Object graph into a slice
+	objects := append(r.Objects(), info.Objects()...)
+
+	// (3.) Assign ids from 1 to n and store them in a lookup table
+	// (some Objects need to resolve name references when encoding).
+	ids := make(map[string]ObjectID, len(objects))
+	for idx, obj := range objects {
+		id := ObjectID(idx + 1)
+		obj.SetID(id)
+		ids[obj.Name()] = id
+	}
+
+	// (4.) Output the Objects one by one, starting with Object number
+	// one, recording the byte offset of each for the cross-reference
+	// table.
+	xrefOffsets := make([]int, len(objects))
+	for idx, obj := range objects {
+		xrefOffsets[idx] = e.w.cnt + 1
+		if err := obj.Encode(e.w, ids); err != nil {
+			return err
+		}
+	}
+
+	// (5.) Write the cross-reference table.
+	xrefOffset := e.w.cnt
+
+	if err := e.writeXrefTable(objects, xrefOffsets); err != nil {
+		return err
+	}
+
+	// (6.) Write the trailer, trailer dictionary, and end-of-file marker.
+	if _, err := fmt.Fprintf(e.w, `trailer
+<<
+  /Root %v
+  /Size %d
+  /Info %v
+>>
+startxref
+%d
+%%%%EOF
+`, ids["catalog"], len(objects)+1, ids["info"], xrefOffset); err != nil {
+		return err
+	}
+
+	return nil
+}

qrbill.go

@@ -302,6 +302,21 @@ func (b *Bill) EncodeToEPS() ([]byte, error) {
 	return qrCodeEPS, nil
 }
 
+func (b *Bill) EncodeToPDF() ([]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 := renderResultPDF(code, qrCodeEdgeSidePx, qrCodeEdgeSidePx, quietzone)
+	if err != nil {
+		return nil, err
+	}
+	return qrCodeEPS, nil
+}
+
 func (b *Bill) EncodeToImage() (image.Image, error) {
 	return generateSwissQrCode(b.qrcontents)
 }

qrcodegeneratorpdf.go

@@ -0,0 +1,194 @@
+// 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 (
+	"bytes"
+	"fmt"
+	"image"
+	"io"
+	"strings"
+	"time"
+
+	"github.com/makiuchi-d/gozxing"
+	"github.com/makiuchi-d/gozxing/qrcode/encoder"
+	"github.com/stapelberg/qrbill/internal/pdf"
+)
+
+// Image represents a PDF image object containing a DIN A4-sized page
+// scanned with 600dpi (i.e. into 4960x7016 pixels).
+type Image struct {
+	pdf.Common
+
+	Bounds image.Rectangle
+}
+
+// Objects implements Object.
+func (i *Image) Objects() []pdf.Object { return []pdf.Object{i} }
+
+// Encode implements Object.
+func (i *Image) Encode(w io.Writer, ids map[string]pdf.ObjectID) error {
+	_, err := fmt.Fprintf(w, `
+%d 0 obj
+<<
+  /Subtype /Form
+  /FormType 1
+  /Type /XObject
+  /ColorSpace /DeviceGray
+  /BBox [0 0 %d %d]
+  /Matrix [1 0 0 1 0 0]
+  /Resources << /ProcSet [/PDF] >>
+  /Length %d
+>>
+stream
+%s
+endstream
+endobj`,
+		int(i.Common.ID),
+		i.Bounds.Max.X,
+		i.Bounds.Max.Y,
+		len(i.Common.Stream),
+		i.Common.Stream)
+	return err
+}
+
+// renderResultPDF is a copy of renderResult from
+// gozxing/qrcode/qrcode_writer.go, adapted to output to PDF.
+func renderResultPDF(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
+
+	_, _ = leftPadding, topPadding
+
+	var codePath strings.Builder
+	codePath.WriteString("q\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
+	codePath.WriteString("1 0 0 -1 0 1265 cm\n")
+
+	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 {
+				codePath.WriteString(fmt.Sprintf("%d %d %d %d re\n",
+					outputX, outputY, multiple, multiple))
+				//eps.WriteString(fmt.Sprintf("%d %d %d %d F\n", outputX, outputY, multiple, multiple))
+			}
+		}
+	}
+	// Fill the whole path at once.
+	// This step is crucial:
+	// filling individual rectangles results in rendering artifacts
+	// in some PDF viewers at some zoom levels.
+	// Filling the whole path seems to prevent that entirely.
+	codePath.WriteString("0 g\n")
+	codePath.WriteString("f\n")
+
+	// overlay a PDF version of the swiss cross
+	codePath.WriteString("1 0 0 1 549 549 cm\n")
+
+	codePath.WriteString("1 g\n") // white
+	codePath.WriteString("0 0 166 166 re\n")
+	codePath.WriteString("f\n")
+
+	codePath.WriteString("0 g\n") // black
+	codePath.WriteString("12 12 142 142 re\n")
+	codePath.WriteString("f\n")
+
+	codePath.WriteString("1 g\n") // white
+	codePath.WriteString("36 66 94 28 re\n")
+	codePath.WriteString("f\n")
+	codePath.WriteString("68 34 30 92 re\n")
+	codePath.WriteString("f\n")
+
+	codePath.WriteString("Q\n")
+
+	kids := []pdf.Object{
+		&pdf.Page{
+			Common: pdf.Common{ObjectName: "page0"},
+			Resources: []pdf.Object{
+				&Image{
+					Common: pdf.Common{
+						ObjectName: "qr",
+						Stream:     []byte(codePath.String()),
+					},
+					Bounds: image.Rect(0, 0, 1265, 1265),
+				},
+			},
+			Parent: "pages",
+			Contents: []pdf.Object{
+				&pdf.Common{
+					ObjectName: "content0",
+					//[]byte("q 595.28 0 0 841.89 0.00 0.00 cm /code0 Do Q\n"),
+					Stream: []byte(`q
+0.12 0 0 0.12 0 0 cm
+/qr Do
+Q
+`),
+				},
+			},
+		},
+	}
+
+	doc := &pdf.Catalog{
+		Common: pdf.Common{ObjectName: "catalog"},
+		Pages: &pdf.Pages{
+			Common: pdf.Common{ObjectName: "pages"},
+			Kids:   kids,
+		},
+	}
+	info := &pdf.DocumentInfo{
+		Common:       pdf.Common{ObjectName: "info"},
+		CreationDate: time.Now(),
+		Producer:     "https://github.com/stapelberg/qrbill",
+		Title:        "QR-Bill",
+		// TODO: summarize the qr code in the subject
+	}
+	var buf bytes.Buffer
+	pdfEnc := pdf.NewEncoder(&buf)
+	if err := pdfEnc.Encode(doc, info); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}