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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/browser/interest_group/interest_group_real_time_report_util.h"
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <map>
#include <optional>
#include "base/check_op.h"
#include "base/notreached.h"
#include "base/rand_util.h"
#include "content/services/auction_worklet/public/cpp/real_time_reporting.h"
#include "content/services/auction_worklet/public/mojom/real_time_reporting.mojom.h"
#include "third_party/blink/public/common/features.h"
#include "url/gurl.h"
#include "url/origin.h"
namespace content {
namespace {
// The URL path for sending real time reporting histograms.
constexpr char kRealTimeReportPath[] =
"/.well-known/interest-group/real-time-report";
} // namespace
double CalculateFlipProbability(double epsilon) {
double f = 2.0 / (1 + std::exp(epsilon / 2.0));
return f / 2.0;
}
std::vector<uint8_t> Rappor(std::optional<int32_t> maybe_bucket,
double flip_probability,
int num_buckets) {
std::vector<uint8_t> histogram(num_buckets, 0);
if (maybe_bucket.has_value()) {
// Browser side that receives contributions from worklets should have
// guaranteed this.
CHECK_GE(*maybe_bucket, 0);
CHECK_LT(*maybe_bucket, num_buckets);
histogram[*maybe_bucket] = 1;
}
if (flip_probability > 0) {
for (size_t i = 0; i < static_cast<size_t>(num_buckets); i++) {
if (base::RandDouble() < flip_probability) {
histogram[i] = 1 - histogram[i];
}
}
}
return histogram;
}
std::optional<int32_t> SampleContributions(
const std::vector<auction_worklet::mojom::RealTimeReportingContributionPtr>&
contributions) {
if (contributions.empty()) {
return std::nullopt;
}
double priority_weight_sum = 0.0;
for (const auto& contribution : contributions) {
// Browser side that receives contributions from worklets should have
// guaranteed this.
CHECK(contribution->priority_weight > 0);
priority_weight_sum += contribution->priority_weight;
}
// `random` is always smaller than `priority_weight_sum`, since RandDouble()
// produces output in the range [0, 1).
double random = base::RandDouble() * priority_weight_sum;
priority_weight_sum = 0.0;
for (const auto& contribution : contributions) {
priority_weight_sum += contribution->priority_weight;
if (priority_weight_sum >= random) {
return contribution->bucket;
}
}
// If `contributions` is not empty, one should have be chosen and returned.
NOTREACHED();
}
std::map<url::Origin, std::vector<uint8_t>>
CalculateRealTimeReportingHistograms(
std::map<
url::Origin,
std::vector<auction_worklet::mojom::RealTimeReportingContributionPtr>>
contributions,
double flip_probability) {
std::map<url::Origin, std::vector<uint8_t>> histograms;
for (const auto& [origin, single_origin_contributions] : contributions) {
std::optional<int32_t> maybe_bucket =
SampleContributions(single_origin_contributions);
// If an origin did not make any contributions, it will contribute an array
// of zeros by default, which will still require the input going through the
// noising mechanism to satisfy the privacy requirements.
histograms.emplace(
origin,
Rappor(
maybe_bucket, flip_probability,
blink::features::kFledgeRealTimeReportingNumBuckets.Get() +
auction_worklet::RealTimeReportingPlatformError::kNumValues));
}
return histograms;
}
GURL GetRealTimeReportDestination(const url::Origin& origin) {
return origin.GetURL().Resolve(kRealTimeReportPath);
}
bool HasValidRealTimeBucket(
const auction_worklet::mojom::RealTimeReportingContributionPtr&
contribution) {
return contribution->bucket >= 0 &&
contribution->bucket <
blink::features::kFledgeRealTimeReportingNumBuckets.Get() +
auction_worklet::RealTimeReportingPlatformError::kNumValues;
}
bool HasValidRealTimePriorityWeight(
const auction_worklet::mojom::RealTimeReportingContributionPtr&
contribution) {
// WebIDL of priority weight was (restricted) double, which does not allow
// NaN or infinite. But a compromised worklet can still send these values.
return contribution->priority_weight > 0 &&
std::isfinite(contribution->priority_weight);
}
std::vector<uint8_t> BitPacking(std::vector<uint8_t> data) {
std::vector<uint8_t> packed;
packed.reserve((data.size() + 7) / 8);
uint8_t current_byte = 0;
for (size_t i = 0; i < data.size(); i++) {
current_byte = (current_byte << 1) | data[i];
if ((i + 1) % 8 == 0) {
packed.push_back(current_byte);
current_byte = 0;
} else if (i == data.size() - 1) {
current_byte <<= 8 - (i + 1) % 8;
packed.push_back(current_byte);
}
}
return packed;
}
} // namespace content
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