Split down into multiple functions

.devcontainer/devcontainer.json

@@ -13,6 +13,9 @@
             "extensions": ["golang.go"]
         }
     },
+    "containerEnv": {
+        "TMPDIR": "/workspaces/pdfsign/tmp"
+    },
     "forwardPorts": [],
     "postCreateCommand": "go mod download",
     "remoteUser": "root"

.gitignore

@@ -6,3 +6,4 @@ testfiles/*_signed.pdf
 testfiles/failed/*
 pdfsign
 certs/*
+tmp/

sign/appearance.go

@@ -8,12 +8,127 @@ import (
 )
 
 func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
-	if len(context.SignData.Signature.Info.Image) > 0 {
+	if len(context.SignData.Appearance.Image) > 0 {
 		return context.createImageAppearance(rect)
 	}
 	return context.createTextAppearance(rect)
 }
 
+// Helper functions for PDF resource components
+
+// writeAppearanceHeader writes the header for the appearance stream.
+//
+// Should be closed by writeFormTypeAndLength.
+func writeAppearanceHeader(buffer *bytes.Buffer, rectWidth, rectHeight float64) {
+	buffer.WriteString("<<\n")
+	buffer.WriteString("  /Type /XObject\n")
+	buffer.WriteString("  /Subtype /Form\n")
+	buffer.WriteString(fmt.Sprintf("  /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
+	buffer.WriteString("  /Matrix [1 0 0 1 0 0]\n") // No scaling or translation
+}
+
+func createFontResource(buffer *bytes.Buffer) {
+	buffer.WriteString("   /Font <<\n")
+	buffer.WriteString("     /F1 <<\n")
+	buffer.WriteString("       /Type /Font\n")
+	buffer.WriteString("       /Subtype /Type1\n")
+	buffer.WriteString("       /BaseFont /Times-Roman\n")
+	buffer.WriteString("     >>\n")
+	buffer.WriteString("   >>\n")
+}
+
+func createImageResource(buffer *bytes.Buffer, imageObjectId uint32) {
+	buffer.WriteString("   /XObject <<\n")
+	buffer.WriteString(fmt.Sprintf("     /Im1 %d 0 R\n", imageObjectId))
+	buffer.WriteString("   >>\n")
+}
+
+func writeFormTypeAndLength(buffer *bytes.Buffer, streamLength int) {
+	buffer.WriteString("  /FormType 1\n")
+	buffer.WriteString(fmt.Sprintf("  /Length %d\n", streamLength))
+	buffer.WriteString(">>\n")
+}
+
+func writeBufferStream(buffer *bytes.Buffer, stream []byte) {
+	buffer.WriteString("stream\n")
+	buffer.Write(stream)
+	buffer.WriteString("endstream\n")
+}
+
+func (context *SignContext) createImageXObject() ([]byte, error) {
+	imageData := context.SignData.Appearance.Image
+
+	// Read image configuration to get original dimensions
+	img, _, err := image.DecodeConfig(bytes.NewReader(imageData))
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode image configuration: %w", err)
+	}
+
+	// Use original image dimensions
+	width := float64(img.Width)
+	height := float64(img.Height)
+
+	// Create basic PDF Image XObject
+	var imageObject bytes.Buffer
+
+	imageObject.WriteString("<<\n")
+	imageObject.WriteString("  /Type /XObject\n")
+	imageObject.WriteString("  /Subtype /Image\n")
+	imageObject.WriteString(fmt.Sprintf("  /Width %.0f\n", width))
+	imageObject.WriteString(fmt.Sprintf("  /Height %.0f\n", height))
+	imageObject.WriteString("  /ColorSpace /DeviceRGB\n")
+	imageObject.WriteString("  /BitsPerComponent 8\n")
+	imageObject.WriteString("  /Filter /DCTDecode\n")
+	imageObject.WriteString(fmt.Sprintf("  /Length %d\n", len(imageData)))
+	imageObject.WriteString(">>\n")
+
+	imageObject.WriteString("stream\n")
+	imageObject.Write(imageData)
+	imageObject.WriteString("\nendstream\n")
+
+	return imageObject.Bytes(), nil
+}
+
+func computeTextSizeAndPosition(text string, rectWidth, rectHeight float64) (float64, float64, float64) {
+	// Calculate font size
+	fontSize := rectHeight * 0.8                     // Use most of the height for the font
+	textWidth := float64(len(text)) * fontSize * 0.5 // Approximate text width
+	if textWidth > rectWidth {
+		fontSize = rectWidth / (float64(len(text)) * 0.5) // Adjust font size to fit text within rect width
+	}
+
+	// Center text horizontally and vertically
+	textWidth = float64(len(text)) * fontSize * 0.5
+	textX := (rectWidth - textWidth) / 2
+	if textX < 0 {
+		textX = 0
+	}
+	textY := (rectHeight-fontSize)/2 + fontSize/3 // Approximate vertical centering
+
+	return fontSize, textX, textY
+}
+
+func drawText(buffer *bytes.Buffer, text string, fontSize float64, x, y float64) {
+	buffer.WriteString("q\n")                                   // Save graphics state
+	buffer.WriteString("BT\n")                                  // Begin text
+	buffer.WriteString(fmt.Sprintf("/F1 %.2f Tf\n", fontSize))  // Set font and size
+	buffer.WriteString(fmt.Sprintf("%.2f %.2f Td\n", x, y))     // Set text position
+	buffer.WriteString("0.2 0.2 0.6 rg\n")                      // Set font color to ballpoint-like color (RGB)
+	buffer.WriteString(fmt.Sprintf("%s Tj\n", pdfString(text))) // Show text
+	buffer.WriteString("ET\n")                                  // End text
+	buffer.WriteString("Q\n")                                   // Restore graphics state
+}
+
+func drawImage(buffer *bytes.Buffer, rectWidth, rectHeight float64) {
+	// We save state twice on purpose due to the cm operation
+	buffer.WriteString("q\n") // Save graphics state
+	buffer.WriteString("q\n") // Save before image transformation
+	buffer.WriteString(fmt.Sprintf("%.2f 0 0 %.2f 0 0 cm\n", rectWidth, rectHeight))
+	buffer.WriteString("/Im1 Do\n") // Draw image
+	buffer.WriteString("Q\n")       // Restore after transformation
+	buffer.WriteString("Q\n")       // Restore graphics state
+}
+
 func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error) {
 	rectWidth := rect[2] - rect[0]
 	rectHeight := rect[3] - rect[1]
@@ -22,61 +137,26 @@ func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error
 		return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
 	}
 
-	var appearance_stream_buffer bytes.Buffer
-
 	text := context.SignData.Signature.Info.Name
 
-	// Calculate font size
+	fontSize, textX, textY := computeTextSizeAndPosition(text, rectWidth, rectHeight)
-	fontSize := rectHeight * 0.8                     // Use most of the height for the font
-	textWidth := float64(len(text)) * fontSize * 0.5 // Approximate text width
-	if textWidth > rectWidth {
-		fontSize = rectWidth / (float64(len(text)) * 0.5) // Adjust font size to fit text within rect width
-	}
 
-	appearance_stream_buffer.WriteString("q\n")                                  // Save graphics state
+	var appearance_stream_buffer bytes.Buffer
-	appearance_stream_buffer.WriteString("BT\n")                                 // Begin text
-	appearance_stream_buffer.WriteString(fmt.Sprintf("/F1 %.2f Tf\n", fontSize)) // Font and size
 
-	// Center text horizontally and vertically
+	drawText(&appearance_stream_buffer, text, fontSize, textX, textY)
-	textWidth = float64(len(text)) * fontSize * 0.5
-	textX := (rectWidth - textWidth) / 2
-	if textX < 0 {
-		textX = 0
-	}
-	textY := (rectHeight-fontSize)/2 + fontSize/3 // Approximate vertical centering
-
-	appearance_stream_buffer.WriteString(fmt.Sprintf("%.2f %.2f Td\n", textX, textY)) // Position text
-	appearance_stream_buffer.WriteString("0.2 0.2 0.6 rg\n")                          // Set font color to ballpoint-like color (RGB)
-	appearance_stream_buffer.WriteString(fmt.Sprintf("%s Tj\n", pdfString(text)))     // Show text
-	appearance_stream_buffer.WriteString("ET\n")                                      // End text
-	appearance_stream_buffer.WriteString("Q\n")                                       // Restore graphics state
 
 	// Create the appearance XObject
 	var appearance_buffer bytes.Buffer
-	appearance_buffer.WriteString("<<\n")
+	writeAppearanceHeader(&appearance_buffer, rectWidth, rectHeight)
-	appearance_buffer.WriteString("  /Type /XObject\n")
-	appearance_buffer.WriteString("  /Subtype /Form\n")
-	appearance_buffer.WriteString(fmt.Sprintf("  /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
-	appearance_buffer.WriteString("  /Matrix [1 0 0 1 0 0]\n") // No scaling or translation
 
 	// Resources dictionary with font
 	appearance_buffer.WriteString("  /Resources <<\n")
-	appearance_buffer.WriteString("   /Font <<\n")
+	createFontResource(&appearance_buffer)
-	appearance_buffer.WriteString("     /F1 <<\n")
-	appearance_buffer.WriteString("       /Type /Font\n")
-	appearance_buffer.WriteString("       /Subtype /Type1\n")
-	appearance_buffer.WriteString("       /BaseFont /Times-Roman\n")
-	appearance_buffer.WriteString("     >>\n")
-	appearance_buffer.WriteString("   >>\n")
 	appearance_buffer.WriteString("  >>\n")
 
-	appearance_buffer.WriteString("  /FormType 1\n")
+	writeFormTypeAndLength(&appearance_buffer, appearance_stream_buffer.Len())
-	appearance_buffer.WriteString(fmt.Sprintf("  /Length %d\n", appearance_stream_buffer.Len()))
-	appearance_buffer.WriteString(">>\n")
 
-	appearance_buffer.WriteString("stream\n")
+	writeBufferStream(&appearance_buffer, appearance_stream_buffer.Bytes())
-	appearance_buffer.Write(appearance_stream_buffer.Bytes())
-	appearance_buffer.WriteString("endstream\n")
 
 	return appearance_buffer.Bytes(), nil
 }
@@ -102,71 +182,20 @@ func (context *SignContext) createImageAppearance(rect [4]float64) ([]byte, erro
 
 	var appearance_stream_buffer bytes.Buffer
 
-	// We save state twice on purpose due to the cm operation
+	drawImage(&appearance_stream_buffer, rectWidth, rectHeight)
-	appearance_stream_buffer.WriteString("q\n") // Save graphics state
-	appearance_stream_buffer.WriteString("q\n") // Save before image transformation
-	appearance_stream_buffer.WriteString(fmt.Sprintf("%.2f 0 0 %.2f 0 0 cm\n", rectWidth, rectHeight))
-	appearance_stream_buffer.WriteString("/Im1 Do\n")
-	appearance_stream_buffer.WriteString("Q\n") // Restore after transformation
-	appearance_stream_buffer.WriteString("Q\n") // Restore graphics state
 
 	// Create the appearance XObject
 	var appearance_buffer bytes.Buffer
-	appearance_buffer.WriteString("<<\n")
+	writeAppearanceHeader(&appearance_buffer, rectWidth, rectHeight)
-	appearance_buffer.WriteString("  /Type /XObject\n")
-
-	appearance_buffer.WriteString("  /Subtype /Form\n")
-	appearance_buffer.WriteString(fmt.Sprintf("  /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
 
 	// Resources dictionary with XObject
 	appearance_buffer.WriteString("  /Resources <<\n")
-
+	createImageResource(&appearance_buffer, imageObjectId)
-	appearance_buffer.WriteString("   /XObject <<\n")
-	appearance_buffer.WriteString(fmt.Sprintf("     /Im1 %d 0 R\n", imageObjectId))
-	appearance_buffer.WriteString("   >>\n")
 	appearance_buffer.WriteString("  >>\n")
 
-	appearance_buffer.WriteString("  /FormType 1\n")
+	writeFormTypeAndLength(&appearance_buffer, appearance_stream_buffer.Len())
-	appearance_buffer.WriteString(fmt.Sprintf("  /Length %d\n", appearance_stream_buffer.Len()))
-	appearance_buffer.WriteString(">>\n")
 
-	appearance_buffer.WriteString("stream\n")
+	writeBufferStream(&appearance_buffer, appearance_stream_buffer.Bytes())
-	appearance_buffer.Write(appearance_stream_buffer.Bytes())
-	appearance_buffer.WriteString("endstream\n")
 
 	return appearance_buffer.Bytes(), nil
 }
-
-func (context *SignContext) createImageXObject() ([]byte, error) {
-	imageData := context.SignData.Signature.Info.Image
-
-	// Read image configuration to get original dimensions
-	img, _, err := image.DecodeConfig(bytes.NewReader(imageData))
-	if err != nil {
-		return nil, fmt.Errorf("failed to decode image configuration: %w", err)
-	}
-
-	// Use original image dimensions
-	width := float64(img.Width)
-	height := float64(img.Height)
-
-	// Create basic PDF Image XObject
-	var imageObject bytes.Buffer
-
-	imageObject.WriteString("<<\n")
-	imageObject.WriteString("  /Type /XObject\n")
-	imageObject.WriteString("  /Subtype /Image\n")
-	imageObject.WriteString(fmt.Sprintf("  /Width %.0f\n", width))
-	imageObject.WriteString(fmt.Sprintf("  /Height %.0f\n", height))
-	imageObject.WriteString("  /ColorSpace /DeviceRGB\n")
-	imageObject.WriteString("  /BitsPerComponent 8\n")
-	imageObject.WriteString("  /Filter /DCTDecode\n") // JPEG compression
-	imageObject.WriteString(fmt.Sprintf("  /Length %d\n", len(imageData)))
-	imageObject.WriteString(">>\n")
-
-	imageObject.WriteString("stream\n")
-	imageObject.Write(imageData)
-	imageObject.WriteString("\nendstream\n")
-
-	return imageObject.Bytes(), nil
-}

sign/helpers.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"os"
 	"strings"
 	"time"
 
@@ -196,35 +195,3 @@ func isASCII(s string) bool {
 	}
 	return true
 }
-
-// CopyFile copies a file from src to dst.
-// It's a replacement for os.Rename that works across filesystems.
-func CopyFile(src, dst string) error {
-	// Open the source file
-	srcFile, err := os.Open(src)
-	if err != nil {
-		return fmt.Errorf("failed to open source file: %w", err)
-	}
-	defer srcFile.Close()
-
-	// Create the destination directory if it doesn't exist
-	dstDir := dst[:strings.LastIndex(dst, "/")]
-	if err := os.MkdirAll(dstDir, 0o755); err != nil {
-		return fmt.Errorf("failed to create destination directory: %w", err)
-	}
-
-	// Create the destination file
-	dstFile, err := os.Create(dst)
-	if err != nil {
-		return fmt.Errorf("failed to create destination file: %w", err)
-	}
-	defer dstFile.Close()
-
-	// Copy the contents
-	_, err = io.Copy(dstFile, srcFile)
-	if err != nil {
-		return fmt.Errorf("failed to copy file contents: %w", err)
-	}
-
-	return nil
-}

sign/sign.go

@@ -45,12 +45,16 @@ type SignData struct {
 
 // Appearance represents the appearance of the signature
 type Appearance struct {
-	Visible     bool
+	Visible bool
+
 	Page        uint32
 	LowerLeftX  float64
 	LowerLeftY  float64
 	UpperRightX float64
 	UpperRightY float64
+
+	Image            []byte // Image data to use as signature appearance
+	ImageAsWatermark bool   // If true, the text will be drawn over the image
 }
 
 type VisualSignData struct {
@@ -93,7 +97,6 @@ type SignDataSignatureInfo struct {
 	Reason      string
 	ContactInfo string
 	Date        time.Time
-	Image       []byte // Image data to use in signature appearance
 }
 
 type SignContext struct {

sign/sign_test.go

@@ -80,9 +80,9 @@ func verifySignedFile(t *testing.T, tmpfile *os.File, originalFileName string) {
 	if err != nil {
 		t.Fatalf("%s: %s", tmpfile.Name(), err.Error())
 
-		destinationPath := "../testfiles/failed/" + originalFileName
+		err2 := os.Rename(tmpfile.Name(), "../testfiles/failed/"+originalFileName)
-		if copyErr := CopyFile(tmpfile.Name(), destinationPath); copyErr != nil {
+		if err2 != nil {
-			t.Errorf("Failed to copy failed test file: %s", copyErr)
+			t.Error(err2)
 		}
 	}
 }
@@ -214,7 +214,8 @@ func TestSignPDFFileUTF8(t *testing.T) {
 	info, err := verify.File(tmpfile)
 	if err != nil {
 		t.Fatalf("%s: %s", tmpfile.Name(), err.Error())
-		if err := CopyFile(tmpfile.Name(), "../testfiles/failed/"+originalFileName); err != nil {
+		err := os.Rename(tmpfile.Name(), "../testfiles/failed/"+originalFileName)
+		if err != nil {
 			t.Error(err)
 		}
 	} else if len(info.Signers) == 0 {
@@ -271,7 +272,8 @@ func TestSignPDFVisible(t *testing.T) {
 	_, err = verify.File(tmpfile)
 	if err != nil {
 		t.Fatalf("%s: %s", tmpfile.Name(), err.Error())
-		if err := CopyFile(tmpfile.Name(), "../testfiles/failed/"+originalFileName); err != nil {
+		err := os.Rename(tmpfile.Name(), "../testfiles/failed/"+originalFileName)
+		if err != nil {
 			t.Error(err)
 		}
 	}
@@ -504,7 +506,6 @@ func TestSignPDFWithImage(t *testing.T) {
 				Reason:      "Test with visible signature and image",
 				ContactInfo: "None",
 				Date:        time.Now().Local(),
-				Image:       signatureImage, // Use the signature image
 			},
 			CertType:   ApprovalSignature,
 			DocMDPPerm: AllowFillingExistingFormFieldsAndSignaturesPerms,
@@ -515,6 +516,7 @@ func TestSignPDFWithImage(t *testing.T) {
 			LowerLeftY:  50,
 			UpperRightX: 600,
 			UpperRightY: 125,
+			Image:       signatureImage, // Use the signature image
 		},
 		DigestAlgorithm: crypto.SHA512,
 		Signer:          pkey,
@@ -555,7 +557,6 @@ func TestSignPDFWithTwoImages(t *testing.T) {
 				Reason:      "First signature with image",
 				ContactInfo: "None",
 				Date:        time.Now().Local(),
-				Image:       signatureImage,
 			},
 			CertType:   ApprovalSignature,
 			DocMDPPerm: AllowFillingExistingFormFieldsAndSignaturesPerms,
@@ -566,6 +567,7 @@ func TestSignPDFWithTwoImages(t *testing.T) {
 			LowerLeftY:  50,
 			UpperRightX: 250,
 			UpperRightY: 125,
+			Image:       signatureImage,
 		},
 		DigestAlgorithm: crypto.SHA512,
 		Signer:          pkey,
@@ -594,7 +596,6 @@ func TestSignPDFWithTwoImages(t *testing.T) {
 				Reason:      "Second signature with image",
 				ContactInfo: "None",
 				Date:        time.Now().Local(),
-				Image:       signatureImage,
 			},
 			CertType:   ApprovalSignature,
 			DocMDPPerm: AllowFillingExistingFormFieldsAndSignaturesPerms,
@@ -605,6 +606,7 @@ func TestSignPDFWithTwoImages(t *testing.T) {
 			LowerLeftY:  50,
 			UpperRightX: 500,
 			UpperRightY: 125,
+			Image:       signatureImage,
 		},
 		DigestAlgorithm: crypto.SHA512,
 		Signer:          pkey,