diff -r d0425225ce52 -r 6e1ef32fbd82 VirtualMailManager/__init__.py
--- a/VirtualMailManager/__init__.py	Thu Feb 04 19:08:01 2010 +0000
+++ b/VirtualMailManager/__init__.py	Fri Feb 05 20:13:32 2010 +0000
@@ -8,8 +8,25 @@
 import re
 import locale
 
-from constants.VERSION import *
-import constants.ERROR as ERR
+from encodings.idna import ToASCII, ToUnicode
+
+from VirtualMailManager.constants.ERROR import \
+     DOMAIN_INVALID, DOMAIN_TOO_LONG, NOT_EXECUTABLE, NO_SUCH_BINARY, \
+     NO_SUCH_DIRECTORY
+from VirtualMailManager.constants.VERSION import *
+from VirtualMailManager.Exceptions import VMMException
+
+
+__all__ = [
+    # imported modules
+    'os', 're', 'locale',
+    # version information from VERSION
+    '__author__', '__date__', '__version__',
+    # error codes
+    'ENCODING', 'ace2idna', 'chk_domainname', 'exec_ok', 'expand_path',
+    'get_unicode', 'idn2ascii', 'is_dir',
+]
+
 
 # Try to set all of the locales according to the current
 # environment variables and get the character encoding.
@@ -19,24 +36,9 @@
     locale.setlocale(locale.LC_ALL, 'C')
 ENCODING = locale.nl_langinfo(locale.CODESET)
 
-def w_std(*args):
-    """Writes each arg of args, encoded in the current ENCODING, to stdout and
-    appends a newline."""
-    _write = os.sys.stdout.write
-    for arg in args:
-        _write(arg.encode(ENCODING, 'replace'))
-        _write('\n')
+RE_ASCII_CHARS = """^[\x20-\x7E]*$"""
+RE_DOMAIN = """^(?:[a-z0-9-]{1,63}\.){1,}[a-z]{2,6}$"""
 
-def w_err(code, *args):
-    """Writes each arg of args, encoded in the current ENCODING, to stderr and
-    appends a newline.
-    This function additional interrupts the program execution and uses 'code'
-    system exit status."""
-    _write = os.sys.stderr.write
-    for arg in args:
-        _write(arg.encode(ENCODING, 'replace'))
-        _write('\n')
-    os.sys.exit(code)
 
 def get_unicode(string):
     """Converts `string` to `unicode`, if necessary."""
@@ -44,14 +46,61 @@
         return string
     return unicode(string, ENCODING, 'replace')
 
-__all__ = [
-        # imported modules
-        'os', 're', 'locale',
-        # version information from VERSION
-        '__author__', '__date__', '__version__',
-        # error codes
-        'ERR',
-        # defined stuff
-        'ENCODING', 'get_unicode', 'w_std', 'w_err'
-        ]
-# EOF
+def expand_path(path):
+    """Expands paths, starting with ``.`` or ``~``, to an absolute path."""
+    if path.startswith('.'):
+        return os.path.abspath(path)
+    if path.startswith('~'):
+        return os.path.expanduser(path)
+    return path
+
+def is_dir(path):
+    """Checks if ``path`` is a directory.
+
+    Throws a `VMMException` if ``path`` is not a directory.
+    """
+    path = expand_path(path)
+    if not os.path.isdir(path):
+        raise VMMException(_(u'“%s” is not a directory') % get_unicode(path),
+                           NO_SUCH_DIRECTORY)
+    return path
+
+def exec_ok(binary):
+    """Checks if the ``binary`` exists and if it is executable.
+
+    Throws a `VMMException` if the ``binary`` isn't a file or is not
+    executable.
+    """
+    binary = expand_path(binary)
+    if not os.path.isfile(binary):
+        raise VMMException(_(u'“%s” is not a file') % get_unicode(binary),
+                           NO_SUCH_BINARY)
+    if not os.access(binary, os.X_OK):
+        raise VMMException(_(u'File is not executable: “%s”') % \
+                           get_unicode(binary), NOT_EXECUTABLE)
+    return binary
+
+def idn2ascii(domainname):
+    """Converts the idn domain name `domainname` into punycode."""
+    return '.'.join([ToASCII(lbl) for lbl in domainname.split('.') if lbl])
+
+def ace2idna(domainname):
+    """Converts the domain name `domainname` from ACE according to IDNA."""
+    return u'.'.join([ToUnicode(lbl) for lbl in domainname.split('.') if lbl])
+
+def chk_domainname(domainname):
+    """Returns the validated domain name `domainname`.
+
+    It also converts the name of the domain from IDN to ASCII, if necessary.
+
+    Throws an VMMException, if the domain name is too long or doesn't look
+    like a valid domain name (label.label.label).
+    """
+    if not re.match(RE_ASCII_CHARS, domainname):
+        domainname = idn2ascii(domainname)
+    if len(domainname) > 255:
+        raise VMMException(_(u'The domain name is too long.'), DOMAIN_TOO_LONG)
+    if not re.match(RE_DOMAIN, domainname):
+        raise VMMException(_(u'The domain name “%s” is invalid.') % domainname,
+                           DOMAIN_INVALID)
+    return domainname