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// file dbclientcursor.h
/* Copyright 2009 10gen Inc.
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* 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 <>.
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
#pragma once
#include <boost/noncopyable.hpp>
#include <stack>
#include "mongo/client/dbclientinterface.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/json.h"
#include "mongo/util/net/message.h"
namespace mongo {
class AScopedConnection;
/** for mock purposes only -- do not create variants of DBClientCursor, nor hang code here
@see DBClientMockCursor
class DBClientCursorInterface : boost::noncopyable {
virtual ~DBClientCursorInterface() {}
virtual bool more() = 0;
virtual BSONObj next() = 0;
// TODO bring more of the DBClientCursor interface to here
DBClientCursorInterface() {}
/** Queries return a cursor object */
class DBClientCursor : public DBClientCursorInterface {
/** If true, safe to call next(). Requests more from server if necessary. */
bool more();
/** If true, there is more in our local buffers to be fetched via next(). Returns
false when a getMore request back to server would be required. You can use this
if you want to exhaust whatever data has been fetched to the client already but
then perhaps stop.
int objsLeftInBatch() const { _assertIfNull(); return _putBack.size() + batch.nReturned - batch.pos; }
bool moreInCurrentBatch() { return objsLeftInBatch() > 0; }
/** next
@return next object in the result cursor.
on an error at the remote server, you will get back:
{ $err: <std::string> }
if you do not want to handle that yourself, call nextSafe().
Warning: The returned BSONObj will become invalid after the next batch
is fetched or when this cursor is destroyed.
BSONObj next();
restore an object previously returned by next() to the cursor
void putBack( const BSONObj &o ) { _putBack.push( o.getOwned() ); }
/** throws AssertionException if get back { $err : ... } */
BSONObj nextSafe();
/** peek ahead at items buffered for future next() calls.
never requests new data from the server. so peek only effective
with what is already buffered.
WARNING: no support for _putBack yet!
void peek(std::vector<BSONObj>&, int atMost);
// Peeks at first element, if exists
BSONObj peekFirst();
* peek ahead and see if an error occurred, and get the error if so.
bool peekError(BSONObj* error = NULL);
iterate the rest of the cursor and return the number if items
int itcount() {
int c = 0;
while ( more() ) {
return c;
/** cursor no longer valid -- use with tailable cursors.
note you should only rely on this once more() returns false;
'dead' may be preset yet some data still queued and locally
available from the dbclientcursor.
bool isDead() const { return cursorId == 0; }
bool tailable() const { return (opts & QueryOption_CursorTailable) != 0; }
/** see ResultFlagType (constants.h) for flag values
mostly these flags are for internal purposes -
ResultFlag_ErrSet is the possible exception to that
bool hasResultFlag( int flag ) {
return (resultFlags & flag) != 0;
/// Change batchSize after construction. Can change after requesting first batch.
void setBatchSize(int newBatchSize) { batchSize = newBatchSize; }
DBClientCursor( DBClientBase* client, const std::string &_ns, BSONObj _query, int _nToReturn,
int _nToSkip, const BSONObj *_fieldsToReturn, int queryOptions , int bs ) :
haveLimit( _nToReturn > 0 && !(queryOptions & QueryOption_CursorTailable)),
_ownCursor( true ),
wasError( false ) {
DBClientCursor( DBClientBase* client, const std::string &_ns, long long _cursorId, int _nToReturn, int options ) :
nToReturn( _nToReturn ),
haveLimit( _nToReturn > 0 && !(options & QueryOption_CursorTailable)),
opts( options ),
wasError(false) {
virtual ~DBClientCursor();
long long getCursorId() const { return cursorId; }
/** by default we "own" the cursor and will send the server a KillCursor
message when ~DBClientCursor() is called. This function overrides that.
void decouple() { _ownCursor = false; }
void attach( AScopedConnection * conn );
std::string originalHost() const { return _originalHost; }
std::string getns() const { return ns; }
Message* getMessage(){ return batch.m.get(); }
* Used mainly to run commands on connections that doesn't support lazy initialization and
* does not support commands through the call interface.
* @param cmd The BSON representation of the command to send.
* @return true if command was sent successfully
bool initCommand();
* actually does the query
bool init();
void initLazy( bool isRetry = false );
bool initLazyFinish( bool& retry );
class Batch : boost::noncopyable {
friend class DBClientCursor;
std::auto_ptr<Message> m;
int nReturned;
int pos;
const char *data;
Batch() : m( new Message() ), nReturned(), pos(), data() { }
friend class DBClientBase;
friend class DBClientConnection;
int nextBatchSize();
void _finishConsInit();
Batch batch;
DBClientBase* _client;
std::string _originalHost;
std::string ns;
BSONObj query;
int nToReturn;
bool haveLimit;
int nToSkip;
const BSONObj *fieldsToReturn;
int opts;
int batchSize;
std::stack< BSONObj > _putBack;
int resultFlags;
long long cursorId;
bool _ownCursor; // see decouple()
std::string _scopedHost;
std::string _lazyHost;
bool wasError;
void dataReceived() { bool retry; std::string lazyHost; dataReceived( retry, lazyHost ); }
void dataReceived( bool& retry, std::string& lazyHost );
void requestMore();
void exhaustReceiveMore(); // for exhaust
// Don't call from a virtual function
void _assertIfNull() const { uassert(13348, "connection died", this); }
// non-copyable , non-assignable
DBClientCursor( const DBClientCursor& );
DBClientCursor& operator=( const DBClientCursor& );
// init pieces
void _assembleInit( Message& toSend );
/** iterate over objects in current batch only - will not cause a network call
class DBClientCursorBatchIterator {
DBClientCursorBatchIterator( DBClientCursor &c ) : _c( c ), _n() {}
bool moreInCurrentBatch() { return _c.moreInCurrentBatch(); }
BSONObj nextSafe() {
massert( 13383, "BatchIterator empty", moreInCurrentBatch() );
return _c.nextSafe();
int n() const { return _n; }
DBClientCursor &_c;
int _n;
} // namespace mongo
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