Merge pull request #544 from vidartf/fix-merge-empty-base

Fix error with empty base in merge

nbdime/nbmergeapp.py

@@ -44,7 +44,8 @@ def main_merge(args):
         # Agreed on deletion = no conflics = return 0
         return 0
 
-    b = read_notebook(bfn, on_null='minimal')
+    # Git seems to give empty base file for double insertions
+    b = read_notebook(bfn, on_null='minimal', on_empty='minimal')
     l = read_notebook(lfn, on_null='minimal')
     r = read_notebook(rfn, on_null='minimal')
 

nbdime/utils.py

@@ -6,6 +6,7 @@
 import codecs
 from collections import defaultdict
 import errno
+import io
 import locale
 import os
 import re
@@ -22,7 +23,7 @@
     EXPLICIT_MISSING_FILE = '/dev/null'
 
 
-def read_notebook(f, on_null):
+def read_notebook(f, on_null, on_empty=None):
     """Read and return notebook json from filename
 
     Parameters:
@@ -32,6 +33,10 @@ def read_notebook(f, on_null):
         on_null: What to return when filename null
             "empty": return empty dict
             "minimal": return miminal valid notebook
+        on_empty: What to return when the file is completely empty (0 size)
+            None: Raise an error
+            "empty": return empty dict
+            "minimal: return minimal valid notebook
     """
     if f == EXPLICIT_MISSING_FILE:
         if on_null == 'empty':
@@ -43,7 +48,24 @@ def read_notebook(f, on_null):
                 'Not valid value for `on_null`: %r. Valid values '
                 'are "empty" or "minimal"' % (on_null,))
     else:
-        return nbformat.read(f, as_version=4)
+        try:
+            return nbformat.read(f, as_version=4)
+        except nbformat.reader.NotJSONError:
+            if on_empty is None:
+                raise
+            # Reraise if file is not empty
+            if isinstance(f, string_types):
+                with io.open(f, encoding='utf-8') as fo:
+                    if len(fo.read(10)) != 0:
+                        raise
+            if on_empty == 'empty':
+                return {}
+            elif on_empty == 'minimal':
+                return nbformat.v4.new_notebook()
+            else:
+                raise ValueError(
+                    'Not valid value for `on_empty`: %r. Valid values '
+                    'are None, "empty" or "minimal"' % (on_empty,))
 
 
 def as_text(text):

nbdime/webapp/nbdimeserver.py

@@ -72,7 +72,7 @@ def write_error(self, status_code, **kwargs):
                 return self.finish(str(value))
         return super(NbdimeHandler, self).write_error(status_code, **kwargs)
 
-    def read_notebook(self, arg):
+    def read_notebook(self, arg, fail_on_empty=True):
         # Currently assuming arg is a filename relative to
         # where the server was started from, later we may
         # want to accept urls or full notebooks as well.
@@ -96,7 +96,17 @@ def read_notebook(self, arg):
             if path == EXPLICIT_MISSING_FILE:
                 nb = nbformat.v4.new_notebook()
             elif os.path.exists(path):
-                nb = nbformat.read(path, as_version=4)
+                try:
+                    nb = nbformat.read(path, as_version=4)
+                except nbformat.reader.NotJSONError:
+                    if fail_on_empty:
+                        raise
+                    # Handle empty notebook file
+                    if isinstance(path, string_types):
+                        with io.open(path, encoding='utf-8') as fo:
+                            if len(fo.read(10)) != 0:
+                                raise
+                    nb = nbformat.v4.new_notebook()
             else:
                 nb = nbformat.reads(r.text, as_version=4)
         except requests.exceptions.HTTPError as e:
@@ -261,7 +271,7 @@ def post(self):
     def get_notebook_argument(self, argname):
         if 'mergetool_args' in self.params:
             arg = self.params['mergetool_args'][argname]
-            return self.read_notebook(arg)
+            return self.read_notebook(arg, fail_on_empty=False)
         return super(ApiMergeHandler, self).get_notebook_argument(argname)