125 lines
4.5 KiB
Go
125 lines
4.5 KiB
Go
package sign
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import (
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"fmt"
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"strconv"
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"github.com/digitorus/pdf"
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)
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// Define annotation flag constants
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const (
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AnnotationFlagInvisible = 1 << 0
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AnnotationFlagHidden = 1 << 1
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AnnotationFlagPrint = 1 << 2
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AnnotationFlagNoZoom = 1 << 3
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AnnotationFlagNoRotate = 1 << 4
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AnnotationFlagNoView = 1 << 5
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AnnotationFlagReadOnly = 1 << 6
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AnnotationFlagLocked = 1 << 7
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AnnotationFlagToggleNoView = 1 << 8
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AnnotationFlagLockedContents = 1 << 9
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)
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// createVisualSignature creates a visual signature field in a PDF document.
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// visible: determines if the signature field should be visible or not.
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// pageNumber: the page number where the signature should be placed.
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// rect: the rectangle defining the position and size of the signature field.
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// Returns the visual signature string and an error if any.
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func (context *SignContext) createVisualSignature(visible bool, pageNumber int, rect [4]float64) (visual_signature string, err error) {
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// Initialize the visual signature object with its ID.
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visual_signature = strconv.Itoa(int(context.VisualSignData.ObjectId)) + " 0 obj\n"
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// Define the object as an annotation.
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visual_signature += "<< /Type /Annot"
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// Specify the annotation subtype as a widget.
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visual_signature += " /Subtype /Widget"
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if visible {
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// Set the position and size of the signature field if visible.
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visual_signature += fmt.Sprintf(" /Rect [%f %f %f %f]", rect[0], rect[1], rect[2], rect[3])
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} else {
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// Set the rectangle to zero if the signature is invisible.
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visual_signature += " /Rect [0 0 0 0]"
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}
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// Retrieve the root object from the PDF trailer.
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root := context.PDFReader.Trailer().Key("Root")
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// Get all keys from the root object.
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root_keys := root.Keys()
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found_pages := false
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for _, key := range root_keys {
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if key == "Pages" {
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// Check if the root object contains the "Pages" key.
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found_pages = true
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break
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}
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}
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// Get the pointer to the root object.
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rootPtr := root.GetPtr()
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// Store the root object reference in the catalog data.
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context.CatalogData.RootString = strconv.Itoa(int(rootPtr.GetID())) + " " + strconv.Itoa(int(rootPtr.GetGen())) + " R"
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if found_pages {
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// Find the page object by its number.
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page, err := findPageByNumber(root.Key("Pages"), pageNumber)
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if err != nil {
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return "", err
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}
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// Get the pointer to the page object.
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page_ptr := page.GetPtr()
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// Store the page ID in the visual signature context so that we can add it to xref table later.
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context.VisualSignData.PageId = page_ptr.GetID()
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// Add the page reference to the visual signature.
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visual_signature += " /P " + strconv.Itoa(int(page_ptr.GetID())) + " " + strconv.Itoa(int(page_ptr.GetGen())) + " R"
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}
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// Define the annotation flags for the signature field (132)
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//annotationFlags := AnnotationFlagPrint | AnnotationFlagNoZoom | AnnotationFlagNoRotate | AnnotationFlagReadOnly | AnnotationFlagLockedContents
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visual_signature += fmt.Sprintf(" /F %d", 132)
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// Define the field type as a signature.
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visual_signature += " /FT /Sig"
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// Set a unique title for the signature field.
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visual_signature += " /T " + pdfString("Signature "+strconv.Itoa(len(context.SignData.ExistingSignatures)+1))
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// (Optional) A set of bit flags specifying the interpretation of specific entries
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// in this dictionary. A value of 1 for the flag indicates that the associated entry
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// is a required constraint. A value of 0 indicates that the associated entry is
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// an optional constraint. Bit positions are 1 (Filter); 2 (SubFilter); 3 (V); 4
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// (Reasons); 5 (LegalAttestation); 6 (AddRevInfo); and 7 (DigestMethod).
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// For PDF 2.0 the following bit flags are added: 8 (Lockdocument); and 9
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// (AppearanceFilter). Default value: 0.
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visual_signature += " /Ff 0"
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// Reference the signature dictionary.
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visual_signature += " /V " + strconv.Itoa(int(context.SignData.ObjectId)) + " 0 R"
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// Close the dictionary and end the object.
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visual_signature += " >>"
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visual_signature += "\nendobj\n"
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return visual_signature, nil
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}
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// Helper function to find a page by its number
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func findPageByNumber(pages pdf.Value, pageNumber int) (pdf.Value, error) {
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if pages.Key("Type").Name() == "Pages" {
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kids := pages.Key("Kids")
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for i := 0; i < kids.Len(); i++ {
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page, err := findPageByNumber(kids.Index(i), pageNumber)
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if err == nil {
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return page, nil
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}
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}
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} else if pages.Key("Type").Name() == "Page" {
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if pageNumber == 1 {
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return pages, nil
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}
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pageNumber--
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}
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return pdf.Value{}, fmt.Errorf("page number %d not found", pageNumber)
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}
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