Category Archives: Coding

epub cover extractor

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Another quick little utility I wrote recently. This extracts covers from your epub files and can change the size, greyscale etc. By default it will greyscale and resize them, to work as screensavers for ebook readers.

Sample image from an epub:
sample image

No more WIndows – linux only

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I’ve been using Linux Mint as my main home desktop for 11 years now and as of about a month ago I finally got rid of Windows. The two things that were holding me back were gaming and Overdrive ebooks.

Linux gaming has come a LONG way and it now works good enough for me to ditch Windows. I successfully got most games working:

  • Steam – most games work
  • Epic Games, Ubisoft, GOG, via Lutris
  • Amazon Gaming via Nile – not elegant, but it works

As for Overdrive, I found Knock on github – it will take the downloaded .acsm file and download the epub file. I originally got Adobe Digital Editions installed and it worked, but Knock is much easier. I just put the knock executable into my ~/bin and once I download the .acsm file I run knock on it.

Using Active Directory for authentication in Spring with custom permissions (roles)

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Recently at work, I had to work on setting up a Spring application to do Active Directory authentication and use our internal permissions service. After much googling and playing around I finally figured out how to get it all working. I suspect this may not be the best way to do this, but it works.

Set this up in your config XML

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<!-- Connect to AD -->
<bean id="activeDirectoryAuthenticationProvider" class="org.springframework.security.ldap.authentication.ad.ActiveDirectoryLdapAuthenticationProvider">
<constructor -arg value="YOURDOMAIN"></constructor>
<constructor -arg value="ldap://YOURSERVER"></constructor>
<property name="userDetailsContextMapper" ref="customDetailsMapper"></property>
<property name="convertSubErrorCodesToExceptions" value="true"></property>
</bean>
 
<!-- add in your permissions -->
<bean id="customDetailsMapper" class="Full path to CustomDetailsMapper class"></bean>

Now, the CustomDetailsMapper

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package mypackage;
 
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
 
import org.apache.log4j.Logger;
import org.springframework.ldap.core.DirContextOperations;
import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.authority.SimpleGrantedAuthority;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.ldap.userdetails.LdapUserDetailsMapper;
 
public class CustomUserDetailsMapper extends LdapUserDetailsMapper {
 
    protected static Logger logger = Logger.getLogger("CustomUserDetailsMapper");
    private static final Collection<string> DEFAULT_PERMS = Arrays.asList("login");
 
 
    @Override
    public UserDetails mapUserFromContext(DirContextOperations ctx, String username, Collection< ? extends GrantedAuthority> authorities) {
        /**
         * at this point, the user has permissions based on groups in LDAP/AD. If
         * we used AD for permissions, this would be sufficient, but we want permissions
         * from elsewhere so we need to modify the permissions/authorities
         */
        logger.info(" old authorities: "+authorities);
        UserDetails user = super.mapUserFromContext( ctx, username, getPermissions(username));
        logger.info(" adjusted user: "+user);
 
        return user;
    }
 
    /**
     * gets permissions
     *
     * @param username the username to get permissions for
     * @return a Set of permissions for the user
     */
    private Set<grantedauthority> getPermissions(String username) {
        Set</grantedauthority><grantedauthority> permissions = new HashSet</grantedauthority><grantedauthority>();
 
        /**
         * get your permissions here - however you need to
         * then convert them to SimpleGrantedAuthority
         */
 
        for (String perm : permissionsFromOtherSource) {
            permissions.add(new SimpleGrantedAuthority(perm));
        }
        return permissions;
    }
}
</grantedauthority></string>

NOTE: the blog’s java code formatter is messing this code up a bit (specifically the GrantedAuthority parts), but you should be able to get the gist of it. Basically, after the user is filled out from AD, we get a handle to it and we change the permissions on it.