On the fly unzipping for dl-repo

_README.md

This is an example of how to modify dl-repo so it can serve a entry from a zip file on the fly without creating temporary files. It compiles but I haven't tested it. It also obviously needs error handling added, for when an entry with the given path doesn't exist.

The idea is you can make requests like:

GET /dl-repo/unzip/copy/nla.obj-12345/OEBPS/chapter-001-chapter-i.html

Note: The JVM's builtin ZipFile class kinda sucks because it can only take a file path not a channel so can only be used on local files not files in the repository. I suggest using an alternative implementation that abstracts the I/O calls through an interface. TrueZip is one such implementation, I'm sure there's others.

ItemNodesController.java

import de.schlichtherle.truezip.rof.AbstractReadOnlyFile;
import de.schlichtherle.truezip.zip.ZipEntry;
import de.schlichtherle.truezip.zip.ZipFile;

// ...

    @RequestMapping(value = "/Repository/unzip/copy/{copyId:nla\\.obj-[^/]+}/{path:.+}", method = {RequestMethod.GET})
    @ResponseBody
    public void unzipCopy(@PathVariable String copyId,
                          @PathVariable String path,
                          HttpServletResponse response) throws IOException {
        try (AmberSession session = amberDbService.get()) {
            Copy copy = session.findModelObjectById(copyId, Copy.class);
            try (SeekableByteChannel channel = copy.getFile().openChannel();
                ZipFile zip = new ZipFile(new ChannelReadOnlyFile(channel))) {
                ZipEntry entry = zip.getEntry(path);

                response.addHeader("Content-Length", Long.toString(entry.getSize()));

                // XXX; check that this map has the right content type mappings for your epub stuff
                String contentType = MimetypesFileTypeMap.getDefaultFileTypeMap().getContentType(path);
                response.setContentType(contentType);

                IOUtils.copy(zip.getInputStream(entry), response.getOutputStream());
            }
        }
    }

    static class ChannelReadOnlyFile extends AbstractReadOnlyFile {
        final SeekableByteChannel channel;

        ChannelReadOnlyFile(SeekableByteChannel channel) {
            this.channel = channel;
        }

        @Override
        public long length() throws IOException {
            return channel.size();
        }

        @Override
        public long getFilePointer() throws IOException {
            return channel.position();
        }

        @Override
        public void seek(long position) throws IOException {
            channel.position(position);
        }

        @Override
        public int read() throws IOException {
            ByteBuffer buf = ByteBuffer.allocate(1);
            int nread = channel.read(buf);
            return nread > 0 ? buf.get(0) : nread;
        }

        @Override
        public int read(byte[] bytes, int off, int len) throws IOException {
            ByteBuffer buf = ByteBuffer.wrap(bytes, off, len);
            return channel.read(buf);
        }


        @Override
        public void close() throws IOException {
            channel.close();
        }
    }

pom.xml

    <dependency>
      <groupId>de.schlichtherle.truezip</groupId>
      <artifactId>truezip-driver-zip</artifactId>
      <version>7.7.10</version>
    </dependency>