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/*
* Copyright (C) 2025 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <WebCore/SharedMemory.h>
#include <limits>
#include <wtf/text/WTFString.h>
namespace IPC {
// String type for efficient holding of read-only strings that are transfered multiple times,
// possibly to different processes.
// Originators are able to optionally create from custom memory mappings.
// A small string is held without copy and transferred inline.
// A large string is held as single shared memory object.
// Receive side, release()d Strings refer to the possible shared memory object.
class TransferString {
public:
struct SharedSpan8 {
WebCore::SharedMemoryHandle dataHandle;
};
struct SharedSpan16 {
WebCore::SharedMemoryHandle dataHandle;
};
using IPCData = Variant<std::monostate, std::span<const Latin1Character>, std::span<const char16_t>, SharedSpan8, SharedSpan16>;
static std::optional<TransferString> create(const String&);
static std::optional<TransferString> create(StringView);
#if USE(CF)
static std::optional<TransferString> create(CFStringRef);
#endif
#if USE(FOUNDATION) && defined(__OBJC__)
static std::optional<TransferString> create(NSString *);
#endif
TransferString() = default;
// Constructor for custom memory mapping of Latin1 (String::span8()) string.
TransferString(SharedSpan8&&);
// Constructor for custom memory mapping of char16_t (String::span16()) string.
TransferString(SharedSpan16&&);
TransferString(IPCData&&);
TransferString(TransferString&&) = default;
TransferString& operator=(TransferString&&) = default;
static constexpr size_t transferAsMappingSize = 16384 * 5;
// Release the string.
// Pass maxCopySizeInBytes = transferAsMappingSize - 1 to release without copy, possibly holding the underlying virtual memory mapping.
// Pass maxCopySizeInBytes = std::numeric_limits<size_t>::max() to release with copy always, avoiding potential virtual memory fragmentation.
// Fails on out-of-memory (if mapping fails).
std::optional<String> release(size_t maxCopySizeInBytes = transferAsMappingSize - 1) &&;
// Release the string via copy.
std::optional<String> releaseToCopy() && { return WTFMove(*this).release(std::numeric_limits<size_t>::max()); };
IPCData toIPCData() const LIFETIME_BOUND;
private:
static std::optional<TransferString> createCopy(std::span<const Latin1Character>);
static std::optional<TransferString> createCopy(std::span<const char16_t>);
TransferString(String&&);
#if USE(CF)
TransferString(CFStringRef);
#endif
#if USE(CF)
using Storage = Variant<String, RetainPtr<CFStringRef>, SharedSpan8, SharedSpan16>;
#else
using Storage = Variant<String, SharedSpan8, SharedSpan16>;
#endif
Storage m_storage;
};
inline std::optional<TransferString> TransferString::create(const String& string)
{
if (string.sizeInBytes() >= transferAsMappingSize) {
if (string.is8Bit())
return createCopy(string.span8());
return createCopy(string.span16());
}
return TransferString { String { string } };
}
inline std::optional<TransferString> TransferString::create(StringView string)
{
if (string.sizeInBytes() >= transferAsMappingSize) {
if (string.is8Bit())
return createCopy(string.span8());
return createCopy(string.span16());
}
return TransferString { string.toString() };
}
inline TransferString::TransferString(String&& string)
: m_storage(WTFMove(string))
{
}
#if USE(FOUNDATION) && defined(__OBJC__)
inline std::optional<TransferString> TransferString::create(NSString *string)
{
return create((__bridge CFStringRef)string);
}
#endif
inline TransferString::TransferString(SharedSpan8&& handle)
: m_storage(WTFMove(handle))
{
}
inline TransferString::TransferString(SharedSpan16&& handle)
: m_storage(WTFMove(handle))
{
}
inline TransferString::TransferString(IPCData&& data)
{
WTF::switchOn(WTFMove(data),
[&](std::monostate) {
m_storage = String { };
},
[&](std::span<const Latin1Character> characters) {
m_storage = String { characters };
},
[&](std::span<const char16_t> characters) {
m_storage = String { characters };
},
[&](SharedSpan8 handle) {
m_storage = WTFMove(handle);
},
[&](SharedSpan16 handle) {
m_storage = WTFMove(handle);
}
);
}
}
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