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// Copyright (C) 2013 Google 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
//
// 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.
//
// ValidatingUtil wraps data with checksum and timestamp. Format:
//
// timestamp=<timestamp>
// checksum=<checksum>
// <data>
//
// The timestamp is the time_t that was returned from time() function. The
// timestamp does not need to be portable because it is written and read only by
// ValidatingUtil. The value is somewhat human-readable: it is the number of
// seconds since the epoch.
//
// The checksum is the 32-character hexadecimal MD5 checksum of <data>. It is
// meant to protect from random file changes on disk.
#include "validating_util.h"
#include <cassert>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <string>
#include "util/md5.h"
namespace i18n {
namespace addressinput {
namespace {
const char kTimestampPrefix[] = "timestamp=";
const size_t kTimestampPrefixLength = sizeof kTimestampPrefix - 1;
const char kChecksumPrefix[] = "checksum=";
const size_t kChecksumPrefixLength = sizeof kChecksumPrefix - 1;
const char kSeparator = '\n';
// Places the header value into |header_value| parameter and erases the header
// from |data|. Returns |true| if the header format is valid.
bool UnwrapHeader(const char* header_prefix,
size_t header_prefix_length,
std::string* data,
std::string* header_value) {
assert(header_prefix != NULL);
assert(data != NULL);
assert(header_value != NULL);
if (data->compare(
0, header_prefix_length, header_prefix, header_prefix_length) != 0) {
return false;
}
std::string::size_type separator_position =
data->find(kSeparator, header_prefix_length);
if (separator_position == std::string::npos) {
return false;
}
header_value->assign(
*data, header_prefix_length, separator_position - header_prefix_length);
data->erase(0, separator_position + 1);
return true;
}
} // namespace
// static
void ValidatingUtil::Wrap(time_t timestamp, std::string* data) {
assert(data != NULL);
char timestamp_string[2 + 3 * sizeof timestamp];
int size = std::sprintf(timestamp_string, "%ld", timestamp);
assert(size > 0);
assert(size < sizeof timestamp_string);
(void)size;
std::string header;
header.append(kTimestampPrefix, kTimestampPrefixLength);
header.append(timestamp_string);
header.push_back(kSeparator);
header.append(kChecksumPrefix, kChecksumPrefixLength);
header.append(MD5String(*data));
header.push_back(kSeparator);
data->reserve(header.size() + data->size());
data->insert(0, header);
}
// static
bool ValidatingUtil::UnwrapTimestamp(std::string* data, time_t now) {
assert(data != NULL);
if (now < 0) {
return false;
}
std::string timestamp_string;
if (!UnwrapHeader(
kTimestampPrefix, kTimestampPrefixLength, data, ×tamp_string)) {
return false;
}
time_t timestamp = atol(timestamp_string.c_str());
if (timestamp < 0) {
return false;
}
// One month contains:
// 30 days *
// 24 hours per day *
// 60 minutes per hour *
// 60 seconds per minute.
static const double kOneMonthInSeconds = 30.0 * 24.0 * 60.0 * 60.0;
double age_in_seconds = difftime(now, timestamp);
return !(age_in_seconds < 0.0) && age_in_seconds < kOneMonthInSeconds;
}
// static
bool ValidatingUtil::UnwrapChecksum(std::string* data) {
assert(data != NULL);
std::string checksum;
if (!UnwrapHeader(kChecksumPrefix, kChecksumPrefixLength, data, &checksum)) {
return false;
}
return checksum == MD5String(*data);
}
} // namespace addressinput
} // namespace i18n
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