Add file to zip archive without compression

Question

In Go, how do we add a file to a zip archive without compression?

For context, I'm following along with an IBM tutorial to create an epub zip file. It shows the following Python code:

import zipfile, os

def create_archive(path='/path/to/our/epub/directory'):
    '''Create the ZIP archive.  The mimetype must be the first file in the archive 
    and it must not be compressed.'''

    epub_name = '%s.epub' % os.path.basename(path)

    # The EPUB must contain the META-INF and mimetype files at the root, so 
    # we'll create the archive in the working directory first and move it later
    os.chdir(path)    

    # Open a new zipfile for writing
    epub = zipfile.ZipFile(epub_name, 'w')

    # Add the mimetype file first and set it to be uncompressed
    epub.write(MIMETYPE, compress_type=zipfile.ZIP_STORED)

    # For the remaining paths in the EPUB, add all of their files
    # using normal ZIP compression
    for p in os.listdir('.'):
        for f in os.listdir(p):
            epub.write(os.path.join(p, f)), compress_type=zipfile.ZIP_DEFLATED)
    epub.close()

In this example, the file mimetype (which has content application/epub+zip only) must not be compressed.

The Go documentation does provide one example of writing to a zip archive, but all files are compressed.

Answer 1

There are two methods to add a file to file to a zip.Writer: the Create method and the CreateHeader. While Create only lets you specify a filename, the CreateHeader method gives more flexibility including the ability to set the compression method.

For example:

w, err := zipwriter.CreateHeader(&zip.FileHeader{
    Name:   filename,
    Method: zip.Store,
})

You can now write data to w the same as in the example code from the Go documentation and it will be stored in the zip file without compression.