I am experimenting with ePUB and need to be able to write the mimetype file without compression and the other files as standard Deflate compressed files. I am having trouble figuring out how to set the compression level option to 0. Could you please provide an example of how to pass the parameters to this method? Can I write the uncompressed file and then switch to Deflate for the remaining files on-the-fly or do I need to close the zip and then append files? Any help would be much appreciated.

Hello Richard!

Zip.deflateOutStream() wraps an existing OutStream and is used like this:

outStream := ... // where ever your standard OutStream comes from
deflateStream := Zip.deflateOutStream(out, ["level":0])
deflateStream.write(...)
deflateStream.flush.close

Don't forget to flush the stream before closing, as this writes out any final meta.

I don't know anything about EPUB files, but from your description it sounds like you're trying to deflate single file in a Zip. That can be accomplished like this:

file    := `wotever.pub`.toFile
fout    := file.out
zip     := Zip.write(fout)

out     := zip.writeNext(`/file1`)
deflate := Zip.deflateOutStream(out, ["level":0])
deflate.write(...)  // write file contents
deflate.flush.close

zip.finish
fout.flush.close

Note how the Zip is written as normal, but the content of the /file is deflated.

Thanks for the prompt reply. I now see how to set the level parameter, but still can not get an uncompressed file to be added. I had to move the zip.finish to before the deflate.flush.close to prevent Java IOException: Stream closed.

I am using deflate.writeChars(...) to write the ePUB "mimetype" content of "application/epub+zip". Do I need to use the "nowrap" parameter to achieve what is referred to as a STORED file?

I had to move the zip.finish to before the deflate.flush.close

That doesn't sound right. I was thinking that a safer way to accomplish the same would be to not to wrap Zip streams, but to write file contents to a separate Buf instead. Should be conceptually easier to follow if nothing else. Something like:

// open zip stream
zipOut  := `wotever.pub`.toFile.out
zip     := Zip.write(zipOut)

// deflate contents to a Buf
fileBuf := Buf()
deflate := Zip.deflateOutStream(fileBuf.out, ["level":0])
deflate.write(...)  // write file contents for /file1
deflate.flush.close

// write buf to the zip stream
out     := zip.writeNext(`/file1`)
out.writeBuf(fileBuf.flip)
out.close

// close zip stream
zip.finish
zipOut.flush.close

Do I need to use the "nowrap" parameter to achieve what is referred to as a STORED file?

I have no idea. Do you have any links to the ePUB specification?

Back to look at this again after a long break. An ePUB has the mimetype with content "application/epub+zip" as the first file in the zip archive. It needs to be stored as-in without deflate compression (this is referred to as STORED). The remaining files are stored using Deflate as the compression method. So is there a way to add the first file without any compression and just use compression on the ePUB content files? Sorry if this is confusing.

Hi Richard,

Looking around (as I confess to not fully understanding your predicament), it seems EPUB files adhere to the Open Container Format which is described by Wikipedia as

The mimetype file must be a text document in ASCII that contains the string application/epub+zip. It must also be uncompressed, unencrypted, and the first file in the ZIP archive. This file provides a more reliable way for applications to identify the mimetype of the file than just the .epub extension.

I don't know if Brian or others can shed light on some kind of ->trap backdoor but I don't think this is supported by the current Fantom API.

This StackOverflow post shows how to achieve it in Java though:

private void writeMimeType(ZipOutputStream zip) throws IOException {
    byte[] content = "application/epub+zip".getBytes("UTF-8");
    ZipEntry entry = new ZipEntry("mimetype");
    entry.setMethod(ZipEntry.STORED);
    entry.setSize(20);
    entry.setCompressedSize(20);
    entry.setCrc(0x2CAB616F); // pre-computed
    zip.putNextEntry(entry);
    zip.write(content);
    zip.closeEntry();
}

Being nosey, in general, what does / will your EPUB library do?

Again, thanks for the prompt reply. I am developing an application to store Configuration Management data for systems in a simpler way. I prototyped bits in Lua but have been looking for alternative languages. I played with Fanton some time ago and liked it - hence the return visit.

I have decided to use ePub as an open way to share the "reports" from the database for easy distribution. I was going to use PDF but then came across ePub and thought that would be better.