bundle2: support unbundling empty part

We augment the unbundler to make it able to unbundle the empty part we are now
able to bundle.

mercurial/bundle2.py

@@ -240,9 +240,31 class unbundle20(object):
 
     def _readpart(self):
         """return None when an end of stream markers is reach"""
-        headersize = self._readexact(2)
-        assert headersize == '\0\0'
+
+        headersize = self._unpack(_fpartheadersize)[0]
+        self.ui.debug('part header size: %i\n' % headersize)
+        if not headersize:
         return None
+        headerblock = self._readexact(headersize)
+        # some utility to help reading from the header block
+        self._offset = 0 # layer violation to have something easy to understand
+        def fromheader(size):
+            """return the next <size> byte from the header"""
+            offset = self._offset
+            data = headerblock[offset:(offset + size)]
+            self._offset = offset + size
+            return data
+        typesize = _unpack(_fparttypesize, fromheader(1))[0]
+        parttype = fromheader(typesize)
+        self.ui.debug('part type: "%s"\n' % parttype)
+        current = part(parttype)
+        assert fromheader(2) == '\0\0' # no option for now
+        del self._offset # clean up layer, nobody saw anything.
+        self.ui.debug('part parameters: 0\n')
+        assert self._readexact(4) == '\0\0\0\0' #empty payload
+        self.ui.debug('payload chunk size: 0\n')
+        return current
+
 
 class part(object):
     """A bundle2 part contains application level payload
@@ -251,8 +273,9 class part(object):
     handler.
     """
 
-    def __init__(self, parttype):
+    def __init__(self, parttype, data=''):
         self.type = parttype
+        self.data = data
 
     def getchunks(self):
         ### header

tests/test-bundle2.t

@@ -60,6 +60,8 Create an extension to test bundle2 API
   >             ui.write('    %s\n' % value)
   >     parts = list(unbundler)
   >     ui.write('parts count:   %i\n' % len(parts))
+  >     for p in parts:
+  >         ui.write('  :%s:\n' % p.type)
   > EOF
   $ cat >> $HGRCPATH << EOF
   > [extensions]
@@ -206,6 +208,7 unbundling debug
       babar%#==tutu
   - simple
   start extraction of bundle2 parts
+  part header size: 0
   end of bundle2 stream
   parts count:   0
 
@@ -243,3 +246,27 Test part
   test:empty\x00\x00\x00\x00\x00\x00\x00\x00 (no-eol) (esc)
 
 
+  $ hg unbundle2 < ../parts.hg2
+  options count: 0
+  parts count:   2
+    :test:empty:
+    :test:empty:
+
+  $ hg unbundle2 --debug < ../parts.hg2
+  start processing of HG20 stream
+  reading bundle2 stream parameters
+  options count: 0
+  start extraction of bundle2 parts
+  part header size: 13
+  part type: "test:empty"
+  part parameters: 0
+  payload chunk size: 0
+  part header size: 13
+  part type: "test:empty"
+  part parameters: 0
+  payload chunk size: 0
+  part header size: 0
+  end of bundle2 stream
+  parts count:   2
+    :test:empty:
+    :test:empty: