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// oid.h
/* Copyright 2009 10gen Inc.
* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#pragma once
#include "../util/hex.h"
namespace mongo {
#pragma pack(1)
/** Object ID type.
BSON objects typically have an _id field for the object id. This field should be the first
member of the object when present. class OID is a special type that is a 12 byte id which
is likely to be unique to the system. You may also use other types for _id's.
When _id field is missing from a BSON object, on an insert the database may insert one
automatically in certain circumstances.
Warning: You must call OID::newState() after a fork().
Typical contents of the BSON ObjectID is a 12-byte value consisting of a 4-byte timestamp (seconds since epoch),
a 3-byte machine id, a 2-byte process id, and a 3-byte counter. Note that the timestamp and counter fields must
be stored big endian unlike the rest of BSON. This is because they are compared byte-by-byte and we want to ensure
a mostly increasing order.
class OID {
OID() : a(0), b(0) { }
/** init from a 24 char hex string */
explicit OID(const string &s) { init(s); }
/** initialize to 'null' */
void clear() { a = 0; b = 0; }
const unsigned char *getData() const { return data; }
bool operator==(const OID& r) const { return a==r.a && b==r.b; }
bool operator!=(const OID& r) const { return a!=r.a || b!=r.b; }
int compare( const OID& other ) const { return memcmp( data , , 12 ); }
bool operator<( const OID& other ) const { return compare( other ) < 0; }
bool operator<=( const OID& other ) const { return compare( other ) <= 0; }
/** @return the object ID output as 24 hex digits */
string str() const { return toHexLower(data, 12); }
string toString() const { return str(); }
static OID gen() { OID o; o.init(); return o; }
/** sets the contents to a new oid / randomized value */
void init();
/** init from a 24 char hex string */
void init( string s );
/** Set to the min/max OID that could be generated at given timestamp. */
void init( Date_t date, bool max=false );
time_t asTimeT();
Date_t asDateT() { return asTimeT() * (long long)1000; }
bool isSet() const { return a || b; }
/** call this after a fork to update the process id */
static void justForked();
static unsigned getMachineId(); // features command uses
static void regenMachineId(); // used by unit tests
struct MachineAndPid {
unsigned char _machineNumber[3];
unsigned short _pid;
bool operator!=(const OID::MachineAndPid& rhs) const;
static MachineAndPid ourMachine, ourMachineAndPid;
union {
struct {
// 12 bytes total
unsigned char _time[4];
MachineAndPid _machineAndPid;
unsigned char _inc[3];
struct {
long long a;
unsigned b;
unsigned char data[12];
static unsigned ourPid();
static void foldInPid(MachineAndPid& x);
static MachineAndPid genMachineAndPid();
#pragma pack()
ostream& operator<<( ostream &s, const OID &o );
inline StringBuilder& operator<< (StringBuilder& s, const OID& o) { return (s << o.str()); }
/** Formatting mode for generating JSON from BSON.
See <>
for details.
enum JsonStringFormat {
/** strict RFC format */
/** 10gen format, which is close to JS format. This form is understandable by
javascript running inside the Mongo server via eval() */
/** Javascript JSON compatible */
inline ostream& operator<<( ostream &s, const OID &o ) {
s << o.str();
return s;
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