RetroShare/libresapi/src/api/Pagination.h
2017-04-03 19:21:54 +02:00

111 lines
3.8 KiB
C++

#pragma once
/*
* libresapi
* Copyright (C) 2015 electron128 <electron128@yahoo.com>
* Copyright (C) 2017 Gioacchino Mazzurco <gio@eigenlab.org>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "ApiTypes.h"
namespace resource_api
{
// C must be a type with STL like iterator, a begin() and an end() method
// additionally a function id() which gives a unique value for every container element
// the type of the id should be string
// the type returned by dereferencing the iterator should have a stream operator for StreamBase
// the stream operator must not add an element "id", this is done by the pagination handler
template<class C>
void handlePaginationRequest(Request& req, Response& resp, C& data)
{
if(data.begin() == data.end()){
// set result type to list
resp.mDataStream.getStreamToMember();
resp.mDebug << "note: list is empty" << std::endl;
resp.setOk();
return;
}
std::string begin_after;
std::string last;
req.mStream << makeKeyValueReference("begin_after", begin_after)
<< makeKeyValueReference("last", last);
typename C::iterator it_first = data.begin();
if(begin_after != "begin" && begin_after != "")
{
while(it_first != data.end() && id(*it_first) != begin_after)
it_first++;
it_first++; // get after the specified element
if(it_first == data.end())
{
resp.setFail("Error: first id did not match any element");
return;
}
}
typename C::iterator it_last = data.begin();
if(last == "end" || last == "")
{
it_last = data.end();
}
else
{
while(it_last != data.end() && id(*it_last) != last)
it_last++;
if(it_last == data.end())
{
resp.setFail("Error: last id did not match any element");
return;
}
++it_last; // increment to get iterator to element after the last wanted element
}
/* G10h4ck: Guarded message count limitation with
* JSON_API_LIMIT_CHAT_MSG_COUNT_BY_DEFAULT as ATM it seems that handling a
* big bunch of messages hasn't been a problem for client apps, and even in
* that case the client can specify +begin_after+ and +last+ in the request,
* this way we don't make more difficult the life of those who just want get
* the whole list of chat messages that seems to be a common usecase
*/
#ifdef JSON_API_LIMIT_CHAT_MSG_COUNT_BY_DEFAULT
int count = 0;
#endif
for(typename C::iterator it = it_first; it != it_last; ++it)
{
StreamBase& stream = resp.mDataStream.getStreamToMember();
stream << *it;
stream << makeKeyValue("id", id(*it));
// todo: also handle the case when the last element is specified and the first element is begin
// then want to return the elements near the specified element
// G10h4ck: @see first comment about JSON_API_LIMIT_CHAT_MSG_COUNT_BY_DEFAULT
#ifdef JSON_API_LIMIT_CHAT_MSG_COUNT_BY_DEFAULT
++count;
if(count > 20)
{
resp.mDebug << "limited the number of returned items to 20";
break;
}
#endif
}
resp.setOk();
}
} // namespace resource_api