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/* hasher.cpp
*
* Defines a simple hash function class
*/
/**
* Copyright (C) 2012 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
* 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/>.
*
* 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.
*/
#include "mongo/db/hasher.h"
#include "mongo/db/jsobj.h"
#include "mongo/util/md5.hpp"
#include "mongo/util/startup_test.h"
namespace mongo {
using std::unique_ptr;
namespace {
typedef unsigned char HashDigest[16];
class Hasher {
MONGO_DISALLOW_COPYING(Hasher);
public:
explicit Hasher(HashSeed seed);
~Hasher(){};
// pointer to next part of input key, length in bytes to read
void addData(const void* keyData, size_t numBytes);
// finish computing the hash, put the result in the digest
// only call this once per Hasher
void finish(HashDigest out);
private:
md5_state_t _md5State;
HashSeed _seed;
};
Hasher::Hasher(HashSeed seed) : _seed(seed) {
md5_init(&_md5State);
md5_append(&_md5State, reinterpret_cast<const md5_byte_t*>(&_seed), sizeof(_seed));
}
void Hasher::addData(const void* keyData, size_t numBytes) {
md5_append(&_md5State, static_cast<const md5_byte_t*>(keyData), numBytes);
}
void Hasher::finish(HashDigest out) {
md5_finish(&_md5State, out);
}
void recursiveHash(Hasher* h, const BSONElement& e, bool includeFieldName) {
int canonicalType = endian::nativeToLittle(e.canonicalType());
h->addData(&canonicalType, sizeof(canonicalType));
if (includeFieldName) {
h->addData(e.fieldName(), e.fieldNameSize());
}
if (!e.mayEncapsulate()) {
// if there are no embedded objects (subobjects or arrays),
// compute the hash, squashing numeric types to 64-bit ints
if (e.isNumber()) {
// Use safeNumberLong, it is well-defined for troublesome doubles.
const auto i = endian::nativeToLittle(e.safeNumberLong());
h->addData(&i, sizeof(i));
} else {
h->addData(e.value(), e.valuesize());
}
} else {
// else identify the subobject.
// hash any preceding stuff (in the case of codeWscope)
// then each sub-element
// then finish with the EOO element.
BSONObj b;
if (e.type() == CodeWScope) {
h->addData(e.codeWScopeCode(), e.codeWScopeCodeLen());
b = e.codeWScopeObject();
} else {
b = e.embeddedObject();
}
BSONObjIterator i(b);
while (i.moreWithEOO()) {
BSONElement el = i.next();
recursiveHash(h, el, true);
}
}
}
struct HasherUnitTest : public StartupTest {
void run() {
// Hard-coded check to ensure the hash function is consistent across platforms
BSONObj o = BSON("check" << 42);
verify(BSONElementHasher::hash64(o.firstElement(), 0) == -944302157085130861LL);
}
} hasherUnitTest;
} // namespace
long long int BSONElementHasher::hash64(const BSONElement& e, HashSeed seed) {
Hasher h(seed);
recursiveHash(&h, e, false);
HashDigest d;
h.finish(d);
// HashDigest is actually 16 bytes, but we just read 8 bytes
ConstDataView digestView(reinterpret_cast<const char*>(d));
return digestView.read<LittleEndian<long long int>>();
}
} // namespace mongo
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