Merge pull request #20 from zigg/master

add in-place patching and patch read from stdin.  enables use of

Author: stefankoegl

bin/jsonpatch

@@ -1,12 +1,11 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-from __future__ import print_function
-
 import sys
 import os.path
 import json
 import jsonpatch
+import tempfile
 import argparse
 
 
@@ -15,9 +14,14 @@ parser = argparse.ArgumentParser(
 parser.add_argument('ORIGINAL', type=argparse.FileType('r'),
                     help='Original file')
 parser.add_argument('PATCH', type=argparse.FileType('r'),
-                    help='Patch file')
+                    nargs='?', default=sys.stdin,
+                    help='Patch file (read from stdin if omitted)')
 parser.add_argument('--indent', type=int, default=None,
                     help='Indent output by n spaces')
+parser.add_argument('-b', '--backup', action='store_true',
+                    help='Back up ORIGINAL if modifying in-place')
+parser.add_argument('-i', '--in-place', action='store_true',
+                    help='Modify ORIGINAL in-place instead of to stdout')
 parser.add_argument('-v', '--version', action='version',
                     version='%(prog)s ' + jsonpatch.__version__)
 
@@ -35,7 +39,67 @@ def patch_files():
     doc = json.load(args.ORIGINAL)
     patch = json.load(args.PATCH)
     result = jsonpatch.apply_patch(doc, patch)
-    print(json.dumps(result, indent=args.indent))
+
+    if args.in_place:
+        dirname = os.path.abspath(os.path.dirname(args.ORIGINAL.name))
+
+        try:
+            # Attempt to replace the file atomically.  We do this by
+            # creating a temporary file in the same directory as the
+            # original file so we can atomically move the new file over
+            # the original later.  (This is done in the same directory
+	    # because atomic renames do not work across mount points.)
+
+            fd, pathname = tempfile.mkstemp(dir=dirname)
+            fp = os.fdopen(fd, 'w')
+            atomic = True
+
+        except OSError:
+            # We failed to create the temporary file for an atomic
+            # replace, so fall back to non-atomic mode by backing up
+            # the original (if desired) and writing a new file.
+
+            if args.backup:
+                os.rename(args.ORIGINAL.name, args.ORIGINAL.name + '.orig')
+            fp = open(args.ORIGINAL.name, 'w')
+            atomic = False
+
+    else:
+        # Since we're not replacing the original file in-place, write
+        # the modified JSON to stdout instead.
+
+        fp = sys.stdout
+
+    # By this point we have some sort of file object we can write the 
+    # modified JSON to.
+
+    json.dump(result, fp, indent=args.indent)
+    fp.write('\n')
+
+    if args.in_place:
+        # Close the new file.  If we aren't replacing atomically, this
+        # is our last step, since everything else is already in place.
+
+        fp.close()
+
+        if atomic:
+            try:
+                # Complete the atomic replace by linking the original
+                # to a backup (if desired), fixing up the permissions
+                # on the temporary file, and moving it into place.
+
+                if args.backup:
+                    os.link(args.ORIGINAL.name, args.ORIGINAL.name + '.orig')
+                os.chmod(pathname, os.stat(args.ORIGINAL.name).st_mode)
+                os.rename(pathname, args.ORIGINAL.name)
+
+            except OSError:
+                # In the event we could not actually do the atomic
+                # replace, unlink the original to move it out of the
+                # way and finally move the temporary file into place.
+                
+                os.unlink(args.ORIGINAL.name)
+                os.rename(pathname, args.ORIGINAL.name)
 
 
 if __name__ == "__main__":