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content.go
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content.go
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package extract
import (
"fmt"
"io/ioutil"
"os"
"github.com/hhrutter/pdflib/filter"
"github.com/hhrutter/pdflib/types"
"github.com/pkg/errors"
)
func writeContent(ctx *types.PDFContext, streamDict *types.PDFStreamDict, pageNumber, section int) (err error) {
var fileName string
if section >= 0 {
fileName = fmt.Sprintf("%s/content_p%d_%d.txt", ctx.Write.DirName, pageNumber, section)
} else {
fileName = fmt.Sprintf("%s/content_p%d.txt", ctx.Write.DirName, pageNumber)
}
// Decode streamDict if used filter is supported only.
err = filter.DecodeStream(streamDict)
if err == filter.ErrUnsupportedFilter {
err = nil
return
}
if err != nil {
return
}
// Dump decoded chunk to file.
err = ioutil.WriteFile(fileName, streamDict.Content, os.ModePerm)
return
}
// Process the content of a page which is a stream dict or an array of stream dicts.
func processPageDict(ctx *types.PDFContext, objNumber, genNumber int, dict *types.PDFDict, pageNumber int) (err error) {
logDebugExtract.Printf("processPageDict begin: page=%d\n", pageNumber)
obj, found := dict.Find("Contents")
if !found {
return
}
if obj == nil {
return
}
obj, err = ctx.Dereference(obj)
if err != nil {
return
}
switch obj := obj.(type) {
case types.PDFStreamDict:
err = writeContent(ctx, &obj, pageNumber, -1)
if err != nil {
return
}
case types.PDFArray:
// process array of content stream dicts.
for i, obj := range obj {
streamDict, err := ctx.DereferenceStreamDict(obj)
if err != nil {
return err
}
err = writeContent(ctx, streamDict, pageNumber, i)
if err != nil {
return err
}
}
default:
err = errors.Errorf("writePageContents: page content must be stream dict or array")
return
}
return
}
func needsPage(selectedPages types.IntSet, pageCount int) bool {
return selectedPages == nil || len(selectedPages) == 0 || selectedPages[pageCount]
}
func processPagesDict(ctx *types.PDFContext, indRef *types.PDFIndirectRef, pageCount *int, selectedPages types.IntSet) (err error) {
logDebugExtract.Printf("processPagesDict begin: pageCount=%d\n", *pageCount)
dict, err := ctx.DereferenceDict(*indRef)
if err != nil {
return
}
// Iterate over page tree.
kidsArray := dict.PDFArrayEntry("Kids")
if kidsArray == nil {
return errors.New("writePagesDict: corrupt \"Kids\" entry")
}
for _, obj := range *kidsArray {
if obj == nil {
continue
}
// Dereference next page node dict.
indRef, ok := obj.(types.PDFIndirectRef)
if !ok {
return errors.New("writePagesDict: missing indirect reference for kid")
}
objNumber := int(indRef.ObjectNumber)
genNumber := int(indRef.GenerationNumber)
pageNodeDict, err := ctx.DereferenceDict(indRef)
if err != nil {
return errors.New("writePagesDict: cannot dereference pageNodeDict")
}
if pageNodeDict == nil {
return errors.New("validatePagesDict: pageNodeDict is null")
}
dictType := pageNodeDict.Type()
if dictType == nil {
return errors.New("writePagesDict: missing pageNodeDict type")
}
switch *dictType {
case "Pages":
// Recurse over pagetree
err = processPagesDict(ctx, &indRef, pageCount, selectedPages)
if err != nil {
return err
}
case "Page":
*pageCount++
// extractContent of a page if no pages selected or if page is selected.
if needsPage(selectedPages, *pageCount) {
err = processPageDict(ctx, objNumber, genNumber, pageNodeDict, *pageCount)
if err != nil {
return err
}
}
default:
return errors.Errorf("writePagesDict: Unexpected dict type: %s", *dictType)
}
}
logDebugExtract.Printf("processPagesDict end: pageCount=%d\n", *pageCount)
return
}
// Content writes content streams for selected pages to dirOut.
// Each content stream results in a separate text file.
func Content(ctx *types.PDFContext, selectedPages types.IntSet) (err error) {
logDebugExtract.Printf("Content begin: dirOut=%s\n", ctx.Write.DirName)
// Get an indirect reference to the root page dict.
indRefRootPageDict, err := ctx.Pages()
if err != nil {
return err
}
pageCount := 0
err = processPagesDict(ctx, indRefRootPageDict, &pageCount, selectedPages)
if err != nil {
return err
}
logDebugExtract.Println("Content end")
return
}