#!/bin/sh
 
# Find the mails you want to compress in a single maildir.
#
#     Skip files that don't have ,S=<size> in the filename. 
#
# Compress the mails to tmp/
#
#     Update the compressed files' mtimes to be the same as they were in the original files (e.g. touch command) 
#
# Run maildirlock <path> <timeout>. It writes PID to stdout, save it.
#
#     <path> is path to the directory containing Maildir's dovecot-uidlist (the control directory, if it's separate)
# 
#     <timeout> specifies how long to wait for the lock before failing. 
#
# If maildirlock grabbed the lock successfully (exit code 0) you can continue.
# For each mail you compressed:
#
#     Verify that it still exists where you last saw it.
#     If it doesn't exist, delete the compressed file. Its flags may have been changed or it may have been expunged. This happens rarely, so just let the next run handle it.
#
#     If the file does exist, rename() (mv) the compressed file over the original file.
#
#         Dovecot can now read the file, but to avoid compressing it again on the next run, you'll probably want to rename it again to include e.g. a "Z" flag in the file name to mark that it was compressed (e.g. 1223212411.M907959P17184.host,S=3271:2,SZ). Remember that the Maildir specifications require that the flags are sorted by their ASCII value, although Dovecot itself doesn't care about that. 
#
# Unlock the maildir by sending a TERM signal to the maildirlock process (killing the PID it wrote to stdout). 
 
##
## <http://ivaldi.nl/blog/2011/12/06/compressed-mail-in-dovecot/>
##
 
store=/home/
compress=gzip
#compress=bzip2
 
find "$store" -type d -name "cur" | while read maildir;
do
        tmpdir=$(cd "$maildir/../tmp" &>/dev/null && pwd) || exit 1
 
        find=$(find "$maildir" -type f -name "*,S=*" ! -name "*,*:2,*,*Z*" -printf "%f\n")
 
        if [ -z "$find" ];
        then
                continue
        fi
 
        echo "$find" | while read filename;
        do
                srcfile="$maildir/$filename"
                tmpfile="$tmpdir/$filename"
 
                $compress --best --stdout "$srcfile" > "$tmpfile" &&
 
                # Copy over some things
                chown --reference="$srcfile" "$tmpfile" &&
                chmod --reference="$srcfile" "$tmpfile" &&
                touch --reference="$srcfile" "$tmpfile"
        done
 
        # Should really check dovecot-uidlist is in $maildir/..
        if lock=$(/usr/libexec/dovecot/maildirlock "$maildir/.." 10);
        then
                # The directory is locked now
                echo "Processing $maildir/..."
 
                echo "$find" | while read filename;
        do
                srcfile="$maildir/$filename"
                tmpfile="$tmpdir/$filename"
 
                $compress --best --stdout "$srcfile" > "$tmpfile" &&
 
                # Copy over some things
                chown --reference="$srcfile" "$tmpfile" &&
                chmod --reference="$srcfile" "$tmpfile" &&
                touch --reference="$srcfile" "$tmpfile"
        done
 
        # Should really check dovecot-uidlist is in $maildir/..
        if lock=$(/usr/libexec/dovecot/maildirlock "$maildir/.." 10);
        then
                # The directory is locked now
                echo "Processing $maildir/..."
 
                echo "$find" | while read filename;
                do
                        flags=$(echo $filename | awk -F:2, '{print $2}')
 
                        if echo $flags | grep ',';
                        then
                                newname=$filename"Z"
                        else
                                newname=$filename",Z"
                        fi
 
                        srcfile=$maildir/$filename
                        tmpfile=$tmpdir/$filename
                        dstfile=$maildir/$newname
 
                        if [ -f "$srcfile" ] && [ -f "$tmpfile" ];
                        then
                                #echo "$srcfile -> $dstfile"
 
                                mv "$tmpfile" "$srcfile" &&
                                mv "$srcfile" "$dstfile"
                        else
                                rm -f "$tmpfile"
                        fi
                done
 
                kill $lock
        else
                echo "Failed to lock: $maildir" >&2
 
                echo "$find" | while read filename;
                do
                        rm -f "$tmpdir/$filename"
                done
        fi
done