bundle2: enforce parttype as alphanumerical

The binary format description has always stated that the parttype should be simple,
but it was never really enforced. Recent discussions have convinced me we want to
keep the part type simple and easy to debug. There is enough extensibility in
the rest of the format.

mercurial/bundle2.py

@@ -85,7 +85,7 b' Binary format is as follow'
 
     :typesize: (one byte)
 
-    :parttype: alphanumerical part name
+    :parttype: alphanumerical part name (restricted to ^a-zA-Z0-9_:-])
 
     :partid: A 32bits integer (unique in the bundle) that can be used to refer
              to this part.
@@ -153,6 +153,7 b' import string'
 import obsolete
 import pushkey
 import url
+import re
 
 import changegroup, error
 from i18n import _
@@ -171,6 +172,13 b' from i18n import _'
 
 preferedchunksize = 4096
 
+_parttypeforbidden = re.compile('[^a-zA-Z0-9_:-]')
+
+def validateparttype(parttype):
+    """raise ValueError if a parttype contains invalid character"""
+    if _parttypeforbidden.match(parttype):
+        raise ValueError(parttype)
+
 def _makefpartparamsizes(nbparams):
     """return a struct format to read part parameter sizes
 
@@ -191,6 +199,7 b' def parthandler(parttype, params=()):'
             '''process a part of type "my part".'''
             ...
     """
+    validateparttype(parttype)
     def _decorator(func):
         lparttype = parttype.lower() # enforce lower case matching.
         assert lparttype not in parthandlermapping
@@ -590,6 +599,7 b' class bundlepart(object):'
 
     def __init__(self, parttype, mandatoryparams=(), advisoryparams=(),
                  data='', mandatory=True):
+        validateparttype(parttype)
         self.id = None
         self.type = parttype
         self._data = data