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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
#ifndef mozilla_dom_GeneratePlaceholderCanvasData_h
#define mozilla_dom_GeneratePlaceholderCanvasData_h
#include "mozilla/StaticPrefs_privacy.h"
#include "nsCOMPtr.h"
#include "nsIRandomGenerator.h"
#include "nsServiceManagerUtils.h"
#define RANDOM_BYTES_TO_SAMPLE 32
namespace mozilla::dom {
/**
* When privacy.resistFingerprinting.randomDataOnCanvasExtract is true, tries
* to generate random data for placeholder canvas by sampling
* RANDOM_BYTES_TO_SAMPLE bytes and then returning it. If this fails or if
* privacy.resistFingerprinting.randomDataOnCanvasExtract is false, returns
* nullptr.
*
* @return uint8_t* output buffer
*/
inline uint8_t* TryToGenerateRandomDataForPlaceholderCanvasData() {
if (!StaticPrefs::privacy_resistFingerprinting_randomDataOnCanvasExtract()) {
return nullptr;
}
nsresult rv;
nsCOMPtr<nsIRandomGenerator> rg =
do_GetService("@mozilla.org/security/random-generator;1", &rv);
if (NS_FAILED(rv)) {
return nullptr;
}
uint8_t* randomData;
rv = rg->GenerateRandomBytes(RANDOM_BYTES_TO_SAMPLE, &randomData);
if (NS_FAILED(rv)) {
return nullptr;
}
return randomData;
}
/**
* If randomData not nullptr, repeats those bytes many times to fill buffer. If
* randomData is nullptr, returns all-white pixel data.
*
* @param[in] randomData Buffer of RANDOM_BYTES_TO_SAMPLE bytes of random
* data, or nullptr
* @param[in] size Size of output buffer
* @param[out] buffer Output buffer
*/
inline void FillPlaceholderCanvas(uint8_t* randomData, uint32_t size,
uint8_t* buffer) {
if (!randomData) {
memset(buffer, 0xFF, size);
return;
}
auto remaining_to_fill = size;
auto index = 0;
while (remaining_to_fill > 0) {
auto bytes_to_write = (remaining_to_fill > RANDOM_BYTES_TO_SAMPLE)
? RANDOM_BYTES_TO_SAMPLE
: remaining_to_fill;
memcpy(buffer + (index * RANDOM_BYTES_TO_SAMPLE), randomData,
bytes_to_write);
remaining_to_fill -= bytes_to_write;
index++;
}
free(randomData);
}
/**
* When privacy.resistFingerprinting.randomDataOnCanvasExtract is true, tries
* to generate random canvas data by sampling RANDOM_BYTES_TO_SAMPLE bytes and
* then repeating those bytes many times to fill the buffer. If this fails or
* if privacy.resistFingerprinting.randomDataOnCanvasExtract is false, returns
* all-white, opaque pixel data.
*
* It is recommended that callers call this function instead of individually
* calling TryToGenerateRandomDataForPlaceholderCanvasData and
* FillPlaceholderCanvas unless there are requirements, like NoGC, that prevent
* them from calling the RNG service inside this function.
*
* @param[in] size Size of output buffer
* @param[out] buffer Output buffer
*/
inline void GeneratePlaceholderCanvasData(uint32_t size, uint8_t* buffer) {
uint8_t* randomData = TryToGenerateRandomDataForPlaceholderCanvasData();
FillPlaceholderCanvas(randomData, size, buffer);
}
} // namespace mozilla::dom
#endif // mozilla_dom_GeneratePlaceholderCanvasData_h