Diff3: Added diff3 wrapper

r2/example.ini

@@ -477,6 +477,10 @@ feedback_email = reddit@gmail.com
 # Special case sensitive domains
 case_sensitive_domains = i.imgur.com, youtube.com
 
+# Location (directory) for temp files for diff3 merging
+# Empty will use python default for temp files
+diff3_temp_location = /dev/shm
+
 [server:main]
 use = egg:Paste#http
 host = 0.0.0.0

r2/r2/lib/merge.py

@@ -0,0 +1,56 @@
+import subprocess
+import tempfile
+import difflib
+from pylons.i18n import _
+from pylons import g
+
+class ConflictException(Exception):
+    def __init__(self, new, your, original):
+        self.your = your
+        self.new = new
+        self.original = original
+        self.htmldiff = make_htmldiff(new, your, _("current edit"), _("your edit"))
+        Exception.__init__(self)
+
+
+def make_htmldiff(a, b, adesc, bdesc):
+    diffcontent = difflib.HtmlDiff(wrapcolumn=60)
+    return diffcontent.make_table(a.splitlines(),
+                                  b.splitlines(),
+                                  fromdesc=adesc,
+                                  todesc=bdesc)
+
+def threeWayMerge(original, a, b):
+    try:
+        temp_dir = g.diff3_temp_location if g.diff3_temp_location else None
+        data = [a, original, b]
+        files = []
+        for d in data:
+            f = tempfile.NamedTemporaryFile(dir=temp_dir)
+            f.write(d.encode('utf-8'))
+            f.flush()
+            files.append(f)
+        try:
+            final = subprocess.check_output(["diff3", "-a", "--merge"] + [f.name for f in files])
+        except subprocess.CalledProcessError:
+            raise ConflictException(b, a, original)
+    finally:
+        for f in files:
+            f.close()
+    return final.decode('utf-8')
+
+if __name__ == "__main__":
+    class test_globals:
+        diff3_temp_location = None
+
+    g = test_globals()
+
+    original = "Hello people of the human rance\n\nHow are you tday"
+    a = "Hello people of the human rance\n\nHow are you today"
+    b = "Hello people of the human race\n\nHow are you tday"
+
+    print threeWayMerge(original, a, b)
+
+    g.diff3_temp_location = '/dev/shm'
+
+    print threeWayMerge(original, a, b)