tonysun83 commented on a change in pull request #740: Add Bookmark support for 
mango json queries
URL: https://github.com/apache/couchdb/pull/740#discussion_r132597476
 
 

 ##########
 File path: src/mango/src/mango_json_bookmark.erl
 ##########
 @@ -0,0 +1,68 @@
+% Licensed under the Apache License, Version 2.0 (the "License"); you may not
+% use this file except in compliance with the License. You may obtain a copy of
+% the License at
+%
+%   http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+% License for the specific language governing permissions and limitations under
+% the License.
+
+
+-module(mango_json_bookmark).
+
+-export([
+    update_args/2,
+    create/1
+]).
+
+
+-include_lib("couch_mrview/include/couch_mrview.hrl").
+-include("mango_cursor.hrl").
+-include("mango.hrl").
+
+update_args(EncodedBookmark, Args) ->
+    Bookmark = unpack(EncodedBookmark),
+    update_args2(Bookmark, Args).
+
+
+update_args2(Bookmark, #mrargs{skip = Skip} = Args) when is_list(Bookmark) ->
+    case lists:keymember(startkey, 1, Bookmark) andalso 
lists:keymember(startkey_docid, 1, Bookmark) of
+        true -> 
+            {startkey, Startkey} = lists:keyfind(startkey, 1, Bookmark),
+            {startkey_docid, StartkeyDocId} = lists:keyfind(startkey_docid, 1, 
Bookmark),
+            Args2 = Args#mrargs{
+                start_key = Startkey,
+                start_key_docid = StartkeyDocId,
+                skip = 1 + Skip
+            },
+            Args2;
+        false ->
+            Args
+    end;
+update_args2(_Bookmark, Args) ->
+    Args.
+    
+
+create(#cursor{bookmark_docid = BookmarkDocId, bookmark_key = BookmarkKey}) 
when BookmarkKey =/= undefined ->
+    QueryArgs = [
+        {startkey_docid, BookmarkDocId},
+        {startkey, BookmarkKey}
+    ],
+    Bin = term_to_binary(QueryArgs, [compressed, {minor_version,1}]),
+    couch_util:encodeBase64Url(Bin);
+create(#cursor{bookmark = Bookmark}) ->
+    Bookmark.
+
+
+unpack(nil) ->
+    nil;
+unpack(Packed) ->
+    try
+        binary_to_term(couch_util:decodeBase64Url(Packed))
 
 Review comment:
   This part got me thinking a bit. What is a valid vs invalid bookmark? So 
when unpacked, a json bookmark is a start_key and end_key range, and a text 
bookmark is a node+shard range. So the composition is slightly different. So a 
text index bookmark should be considered invalid for a json index bookmark 
right? When I tried that particular scenario, the bookmark passed correctly ``` 
Here's a sample text bookmark: 
"g2wAAAACaAJkAA5zdGFydGtleV9kb2NpZG0AAAAkZTkwMDAwMWQtYmM0OC00OGE2LTliMWEtYWM5YTFmNWQxYTAzaAJkAAhzdGFydGtleWsAAStq"```
 . 
   
   If you did it the other way around...substitute a json index bookmark into a 
text index bookmark, it fails with invalid_bookmark.
   
   Wondering if we should be more consistent/strict and and verify both types 
of bookmarks?
 
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