'Analyze the contents of the Git index and extract filenames.
:param body: The contents of the file to analyze.
:return: A list of filenames found.'

def git_index(self, body):

    filenames = set()
    signature = 'DIRC'
    offset = 12
    if (body[:4] != signature):
        return set()
    (version,) = struct.unpack('>I', body[4:8])
    (index_entries,) = struct.unpack('>I', body[8:12])
    if (version == 2):
        filename_offset = 62
    elif (version == 3):
        filename_offset = 63
    else:
        return set()
    for _ in range(0, index_entries):
        offset += (filename_offset - 1)
        (length,) = struct.unpack('>B', body[offset:(offset + 1)])
        if (length > (len(body) - offset)):
            return set()
        filename = body[(offset + 1):((offset + 1) + length)]
        padding = (8 - ((filename_offset + length) % 8))
        filenames.add(filename)
        offset += ((length + 1) + padding)
    return filenames
