I am writing a program that takes an .epub file, unzips it, edits the content.opt file to add custom metadata, then zip the contents to create a new .epub file. I am using calibre as both my e-reader and my .epub editor, since calibre makes it very easy to edit both the metadata for an .epub as well as the contents of an .epub file.
I am able to successfully create a new .epub file. I have tested this new file can be read both with calibre and my Kobo e-reader.
However, none of the metadata from the original .epub file transfers over to the new .epub file. Additionally I am unable to edit the .epub file in calibre. When I try I get the error "No META-INF/container.xml in epub". I have tried using multiple .epub files and I get the same results and errors.
Unzipped, the contents of the original .epub file is as follows:
META/INF
↳container.xml
content.opf
mimetype
pages_styles.css
[title]_split_000.xhtml
[title]_split_001.xhtml
.....
[title]_split_012.xhtml
[title]_split_013.xhtml
stylesheet.css
toc.ncx
The unzipped directory for the newly created .epub file is identical to the original. Running diff -r -q /[title]_original /[title]_recreated produces no output, which would indicate they are in fact identical. So I am unsure how calibre can read one file and not read another. The error seems to indicate that calibre is somehow unable to find the META-INF/container.xml file, which is used to tell an e-reader where metadata is being stored in the directory.
Note: I am not editing any content for the original .epub during the unzipping or zipping process until I am able to figure out what is happening.
I am running the command go run main.go zip.go in the directory with the two go files and the .epub file [title]:
main.go
package main
import (
// "log"
// "strings"
)
type FileLocations struct {
src string
ext string
dest string
}
func main() {
fileName := "[title]"
temp := FileLocations{
src: fileName,
ext: ".epub",
dest: fileName,
}
// Unzip the zip/epub file
UnzipHelper(temp.src, temp.ext, temp.dest)
// Zip the modified directory
ZipHelper(temp.src, temp.ext)
}
func UnzipHelper(src string, ext string, dest string) error {
_, err := Unzip(src, ext, dest)
if err != nil {
return err
}
return nil
}
func ZipHelper(src string, ext string) error {
err := Zip(src, ext)
if err != nil {
return err
}
return nil
}
zip.go
package main
import (
"archive/zip"
"fmt"
"io"
"log"
"os"
"path/filepath"
"strings"
)
func Unzip(src string, ext string, dest string) ([]string, error) {
file := src + ext
var filenames []string
r, err := zip.OpenReader(file)
if err != nil {
return filenames, err
}
defer r.Close()
for _, f := range r.File {
// Store filename/path for returning and using later on
fpath := filepath.Join(dest, f.Name)
// Check for ZipSlip
if !strings.HasPrefix(fpath, filepath.Clean(dest)+string(os.PathSeparator)) {
return filenames, fmt.Errorf("%s: illegal file path", fpath)
}
filenames = append(filenames, fpath)
if f.FileInfo().IsDir() {
// Make Folder
os.MkdirAll(fpath, os.ModePerm)
continue
}
// Make File
if err = os.MkdirAll(filepath.Dir(fpath), os.ModePerm); err != nil {
return filenames, err
}
outFile, err := os.OpenFile(fpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
if err != nil {
return filenames, err
}
rc, err := f.Open()
if err != nil {
return filenames, err
}
_, err = io.Copy(outFile, rc)
// Close the file without defer to close before next iteration of loop
outFile.Close()
rc.Close()
if err != nil {
return filenames, err
}
}
// Remove zip file so it can be recreated later
os.Remove(file)
return filenames, nil
}
func Zip(filename string, ext string) error {
// Creates .epub file
file, err := os.Create(filename + ext)
if err != nil {
log.Fatal("os.Create(filename) error: ", err)
}
defer file.Close()
w := zip.NewWriter(file)
defer w.Close()
walker := func(path string, info os.FileInfo, err error) error {
fmt.Println("Crawling: " + path)
if err != nil {
return err
}
if info.IsDir() {
return nil
}
file, err := os.Open(path)
if err != nil {
return err
}
defer file.Close()
f, err := w.Create(path)
if err != nil {
return err
}
_, err = io.Copy(f, file)
if err != nil {
return err
}
return nil
}
err = filepath.Walk(filename, walker)
if err != nil {
log.Fatal("filepath.Walk error: ", err)
}
return err
}
