ui: add a configbytes method, for space configuration

ui: add a configbytes method, for space configuration

This accepts a floating point number, followed by optional whitespace,
followed by an optional one- or two-letter unit specifier (for
bytes, kilobytes, megabytes, or gigabytes).

--- a/mercurial/ui.py	Thu Apr 18 23:53:39 2013 +0200
+++ b/mercurial/ui.py	Thu Apr 18 12:58:28 2013 -0700
@@ -6,7 +6,7 @@
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
-import errno, getpass, os, socket, sys, tempfile, traceback
+import errno, getpass, os, re, socket, sys, tempfile, traceback
 import config, scmutil, util, error, formatter
 
 class ui(object):
@@ -262,6 +262,45 @@
             raise error.ConfigError(_("%s.%s is not an integer ('%s')")
                                     % (section, name, v))
 
+    def configbytes(self, section, name, default=0, untrusted=False):
+        """parse a configuration element as a quantity in bytes
+
+        Units can be specified as b (bytes), k or kb (kilobytes), m or
+        mb (megabytes), g or gb (gigabytes).
+
+        >>> u = ui(); s = 'foo'
+        >>> u.setconfig(s, 'val1', '42')
+        >>> u.configbytes(s, 'val1')
+        42
+        >>> u.setconfig(s, 'val2', '42.5 kb')
+        >>> u.configbytes(s, 'val2')
+        43520
+        >>> u.configbytes(s, 'unknown', '7 MB')
+        7340032
+        >>> u.setconfig(s, 'invalid', 'somevalue')
+        >>> u.configbytes(s, 'invalid')
+        Traceback (most recent call last):
+            ...
+        ConfigError: foo.invalid is not a byte quantity ('somevalue')
+        """
+
+        orig = string = self.config(section, name)
+        if orig is None:
+            if not isinstance(default, str):
+                return default
+            orig = string = default
+        multiple = 1
+        m = re.match(r'([^kmbg]+?)\s*([kmg]?)b?$', string, re.I)
+        if m:
+            string, key = m.groups()
+            key = key.lower()
+            multiple = dict(k=1024, m=1048576, g=1073741824).get(key, 1)
+        try:
+            return int(float(string) * multiple)
+        except ValueError:
+            raise error.ConfigError(_("%s.%s is not a byte quantity ('%s')")
+                                    % (section, name, orig))
+
     def configlist(self, section, name, default=None, untrusted=False):
         """parse a configuration element as a list of comma/space separated
         strings