--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -6,8 +6,92 @@
 # of the GNU General Public License, incorporated herein by reference.
 
 from demandload import demandload
+from i18n import gettext as _
 demandload(globals(), "util")
-demandload(globals(), "os re shutil tempfile")
+demandload(globals(), "cStringIO email.Parser os re shutil tempfile")
+
+def extract(ui, fileobj):
+    '''extract patch from data read from fileobj.
+
+    patch can be normal patch or contained in email message.
+
+    return tuple (filename, message, user, date). any item in returned
+    tuple can be None.  if filename is None, fileobj did not contain
+    patch. caller must unlink filename when done.'''
+
+    # attempt to detect the start of a patch
+    # (this heuristic is borrowed from quilt)
+    diffre = re.compile(r'^(?:Index:[ \t]|diff[ \t]|RCS file: |' +
+                        'retrieving revision [0-9]+(\.[0-9]+)*$|' +
+                        '(---|\*\*\*)[ \t])', re.MULTILINE)
+
+    fd, tmpname = tempfile.mkstemp(prefix='hg-patch-')
+    tmpfp = os.fdopen(fd, 'w')
+    try:
+        hgpatch = False
+
+        msg = email.Parser.Parser().parse(fileobj)
+
+        message = msg['Subject']
+        user = msg['From']
+        # should try to parse msg['Date']
+        date = None
+
+        if message:
+            message = message.replace('\n\t', ' ')
+            ui.debug('Subject: %s\n' % message)
+        if user:
+            ui.debug('From: %s\n' % user)
+        diffs_seen = 0
+        ok_types = ('text/plain', 'text/x-diff', 'text/x-patch')
+
+        for part in msg.walk():
+            content_type = part.get_content_type()
+            ui.debug('Content-Type: %s\n' % content_type)
+            if content_type not in ok_types:
+                continue
+            payload = part.get_payload(decode=True)
+            m = diffre.search(payload)
+            if m:
+                ui.debug(_('found patch at byte %d\n') % m.start(0))
+                diffs_seen += 1
+                cfp = cStringIO.StringIO()
+                if message:
+                    cfp.write(message)
+                    cfp.write('\n')
+                for line in payload[:m.start(0)].splitlines():
+                    if line.startswith('# HG changeset patch'):
+                        ui.debug(_('patch generated by hg export\n'))
+                        hgpatch = True
+                        # drop earlier commit message content
+                        cfp.seek(0)
+                        cfp.truncate()
+                    elif hgpatch:
+                        if line.startswith('# User '):
+                            user = line[7:]
+                            ui.debug('From: %s\n' % user)
+                        elif line.startswith("# Date "):
+                            date = line[7:]
+                    if not line.startswith('# '):
+                        cfp.write(line)
+                        cfp.write('\n')
+                message = cfp.getvalue()
+                if tmpfp:
+                    tmpfp.write(payload)
+                    if not payload.endswith('\n'):
+                        tmpfp.write('\n')
+            elif not diffs_seen and message and content_type == 'text/plain':
+                message += '\n' + payload
+    except:
+        tmpfp.close()
+        os.unlink(tmpname)
+        raise
+
+    tmpfp.close()
+    if not diffs_seen:
+        os.unlink(tmpname)
+        return None, message, user, date
+    return tmpname, message, user, date
 
 def readgitpatch(patchname):
     """extract git-style metadata about patches from <patchname>"""