Using multiple keywords in xattr via _kMDItemUserTags or kMDItemOMUserTags

Question

While reorganizing my images, in anticipation of OSX Mavericks I am writing a script to insert tags into the xattr fields of my image files, so I can search them with Spotlight. (I am also editing the EXIF just to be safe.)

My questions are:

1. Which attribute is the best to use? _kMDItemUserTags seems to be the OSX version, but kMDItemOMUserTags is already in use by OpenMeta. I would ideally like something that will be Linux and OSX forward compatible.

2. How do I set multiple tags? Are the comma- or space-delimited or something else?

As an example, using the python xattr module, I am issuing these commands:

xattr.setxattr(FileName, "_kMDItemUserTags", "Name - Sample")
xattr.setxattr(FileName, "kMDItemOMUserTags", "Name,Institution,Sample")

I have also seen mention of these tags: kOMUserTags and kMDItemkeywords but don't know if they are likely to be implemented...

EDIT: Further investigation has shown that for things to be searchable in 10.8,

• You need to preface the kMD with com.apple.metadata:
• You have to either hex-encode or wrap in a plist.

This python code will generate the tag for kMDItemFinderComment which is searchable in spotlight...

def writexattrs(F,TagList):

    """ writexattrs(F,TagList):
    writes the list of tags to three xattr field:
    'kMDItemFinderComment','_kMDItemUserTags','kMDItemOMUserTags'
       This version uses the xattr library """

    plistFront = '<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0"><array>'
    plistEnd = '</array></plist>'
    plistTagString = ''
    for Tag in TagList:
        plistTagString = plistTagString + '<string>{}</string>'.format(Tag)
    TagText = plistFront + plistTagString + plistEnd

    OptionalTag = "com.apple.metadata:"
    XattrList = ["kMDItemFinderComment","_kMDItemUserTags","kMDItemOMUserTags"]
    for Field in XattrList:
        xattr.setxattr (F,OptionalTag+Field,TagText.encode('utf8'))
            # Equivalent shell command is xattr -w com.apple.metadata:kMDItemFinderComment [PLIST value] [File name]

I could not get it to work recursively on a folder with reliable results.

Answer 1

1. If you are worried about compatibility you have to set both of the attributes _kMDItemUserTags and kMDItemOMUserTags. I don't think there's a different solution since all the new OS X apps will use the former attribute, while the old apps still use the latter. This is just my speculation, but I guess OpenMeta will eventually be discontinued in favor of the new native API. Looking to the future you can use the _kMDItemUserTags attribute for your new apps/scripts even in Linux environment.

2. The tags are set as a property list-encoded array of strings as you have figured out. I don't know if it is a requirement but the OS X encodes the property list in the binary format and not in XML as you did.

I adapted your code to use binary property list as attribute values and everything worked. Here's my code. I am using biplist library which you can get with easy_install biplist.

import xattr
import biplist

def write_xattr_tags(file_path, tags):
    bpl_tags = biplist.writePlistToString(tags)
    optional_tag = "com.apple.metadata:"
    map(lambda a: xattr.setxattr(file_path, optional_tag + a, bpl_tags),
        ["kMDItemFinderComment", "_kMDItemUserTags", "kMDItemOMUserTags"])

Tested with files and directories using tag:<some_tag> in Spotlight.

Hope this helps.

• Note: I am using OS X Lion in this answer but it should work on Mavericks without any problems.
• Edit: If you want to apply the tags to the contents of a directory it has to be done individually for every file since the xattr python module doesn't have the recursive option.