libs/binder/include/binder/Parcel.h

/*
 * Copyright (C) 2005 The Android Open Source Project
 *
 * 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.
 */

#pragma once

#include <map> // for legacy reasons
#include <string>
#include <type_traits>
#include <vector>

#include <android-base/unique_fd.h>
#include <cutils/native_handle.h>
#include <utils/Errors.h>
#include <utils/RefBase.h>
#include <utils/String16.h>
#include <utils/Vector.h>
#include <utils/Flattenable.h>

#include <binder/IInterface.h>
#include <binder/Parcelable.h>

#ifdef BINDER_IPC_32BIT
//NOLINTNEXTLINE(google-runtime-int) b/173188702
typedef unsigned int binder_size_t;
#else
//NOLINTNEXTLINE(google-runtime-int) b/173188702
typedef unsigned long long binder_size_t;
#endif

struct flat_binder_object;

// ---------------------------------------------------------------------------
namespace android {

template <typename T> class Flattenable;
template <typename T> class LightFlattenable;
class IBinder;
class IPCThreadState;
class ProcessState;
class RpcSession;
class String8;
class TextOutput;

class Parcel {
    friend class IPCThreadState;
    friend class RpcState;

public:
    class ReadableBlob;
    class WritableBlob;

                        Parcel();
                        ~Parcel();
    
    const uint8_t*      data() const;
    size_t              dataSize() const;
    size_t              dataAvail() const;
    size_t              dataPosition() const;
    size_t              dataCapacity() const;

    status_t            setDataSize(size_t size);
    void                setDataPosition(size_t pos) const;
    status_t            setDataCapacity(size_t size);

    status_t            setData(const uint8_t* buffer, size_t len);

    status_t            appendFrom(const Parcel *parcel,
                                   size_t start, size_t len);

    int                 compareData(const Parcel& other);

    bool                allowFds() const;
    bool                pushAllowFds(bool allowFds);
    void                restoreAllowFds(bool lastValue);

    bool                hasFileDescriptors() const;

    // Zeros data when reallocating. Other mitigations may be added
    // in the future.
    //
    // WARNING: some read methods may make additional copies of data.
    // In order to verify this, heap dumps should be used.
    void                markSensitive() const;

    // For a 'data' Parcel, this should mark the Parcel as being prepared for a
    // transaction on this specific binder object. Based on this, the format of
    // the wire binder protocol may change (data is written differently when it
    // is for an RPC transaction).
    void markForBinder(const sp<IBinder>& binder);

    // Whenever possible, markForBinder should be preferred. This method is
    // called automatically on reply Parcels for RPC transactions.
    void markForRpc(const sp<RpcSession>& session);

    // Whether this Parcel is written for RPC transactions (after calls to
    // markForBinder or markForRpc).
    bool isForRpc() const;

    // Writes the IPC/RPC header.
    status_t            writeInterfaceToken(const String16& interface);
    status_t            writeInterfaceToken(const char16_t* str, size_t len);

    // Parses the RPC header, returning true if the interface name
    // in the header matches the expected interface from the caller.
    //
    // Additionally, enforceInterface does part of the work of
    // propagating the StrictMode policy mask, populating the current
    // IPCThreadState, which as an optimization may optionally be
    // passed in.
    bool                enforceInterface(const String16& interface,
                                         IPCThreadState* threadState = nullptr) const;
    bool                enforceInterface(const char16_t* interface,
                                         size_t len,
                                         IPCThreadState* threadState = nullptr) const;
    bool                checkInterface(IBinder*) const;

    void                freeData();

    size_t              objectsCount() const;
    
    status_t            errorCheck() const;
    void                setError(status_t err);
    
    status_t            write(const void* data, size_t len);
    void*               writeInplace(size_t len);
    status_t            writeUnpadded(const void* data, size_t len);
    status_t            writeInt32(int32_t val);
    status_t            writeUint32(uint32_t val);
    status_t            writeInt64(int64_t val);
    status_t            writeUint64(uint64_t val);
    status_t            writeFloat(float val);
    status_t            writeDouble(double val);
    status_t            writeCString(const char* str);
    status_t            writeString8(const String8& str);
    status_t            writeString8(const char* str, size_t len);
    status_t            writeString16(const String16& str);
    status_t            writeString16(const std::optional<String16>& str);
    status_t            writeString16(const std::unique_ptr<String16>& str) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeString16(const char16_t* str, size_t len);
    status_t            writeStrongBinder(const sp<IBinder>& val);
    status_t            writeInt32Array(size_t len, const int32_t *val);
    status_t            writeByteArray(size_t len, const uint8_t *val);
    status_t            writeBool(bool val);
    status_t            writeChar(char16_t val);
    status_t            writeByte(int8_t val);

    // Take a UTF8 encoded string, convert to UTF16, write it to the parcel.
    status_t            writeUtf8AsUtf16(const std::string& str);
    status_t            writeUtf8AsUtf16(const std::optional<std::string>& str);
    status_t            writeUtf8AsUtf16(const std::unique_ptr<std::string>& str) __attribute__((deprecated("use std::optional version instead")));

    status_t            writeByteVector(const std::optional<std::vector<int8_t>>& val);
    status_t            writeByteVector(const std::unique_ptr<std::vector<int8_t>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeByteVector(const std::vector<int8_t>& val);
    status_t            writeByteVector(const std::optional<std::vector<uint8_t>>& val);
    status_t            writeByteVector(const std::unique_ptr<std::vector<uint8_t>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeByteVector(const std::vector<uint8_t>& val);
    status_t            writeInt32Vector(const std::optional<std::vector<int32_t>>& val);
    status_t            writeInt32Vector(const std::unique_ptr<std::vector<int32_t>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeInt32Vector(const std::vector<int32_t>& val);
    status_t            writeInt64Vector(const std::optional<std::vector<int64_t>>& val);
    status_t            writeInt64Vector(const std::unique_ptr<std::vector<int64_t>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeInt64Vector(const std::vector<int64_t>& val);
    status_t            writeUint64Vector(const std::optional<std::vector<uint64_t>>& val);
    status_t            writeUint64Vector(const std::unique_ptr<std::vector<uint64_t>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeUint64Vector(const std::vector<uint64_t>& val);
    status_t            writeFloatVector(const std::optional<std::vector<float>>& val);
    status_t            writeFloatVector(const std::unique_ptr<std::vector<float>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeFloatVector(const std::vector<float>& val);
    status_t            writeDoubleVector(const std::optional<std::vector<double>>& val);
    status_t            writeDoubleVector(const std::unique_ptr<std::vector<double>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeDoubleVector(const std::vector<double>& val);
    status_t            writeBoolVector(const std::optional<std::vector<bool>>& val);
    status_t            writeBoolVector(const std::unique_ptr<std::vector<bool>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeBoolVector(const std::vector<bool>& val);
    status_t            writeCharVector(const std::optional<std::vector<char16_t>>& val);
    status_t            writeCharVector(const std::unique_ptr<std::vector<char16_t>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeCharVector(const std::vector<char16_t>& val);
    status_t            writeString16Vector(
                            const std::optional<std::vector<std::optional<String16>>>& val);
    status_t            writeString16Vector(
                            const std::unique_ptr<std::vector<std::unique_ptr<String16>>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeString16Vector(const std::vector<String16>& val);
    status_t            writeUtf8VectorAsUtf16Vector(
                            const std::optional<std::vector<std::optional<std::string>>>& val);
    status_t            writeUtf8VectorAsUtf16Vector(
                            const std::unique_ptr<std::vector<std::unique_ptr<std::string>>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeUtf8VectorAsUtf16Vector(const std::vector<std::string>& val);

    status_t            writeStrongBinderVector(const std::optional<std::vector<sp<IBinder>>>& val);
    status_t            writeStrongBinderVector(const std::unique_ptr<std::vector<sp<IBinder>>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeStrongBinderVector(const std::vector<sp<IBinder>>& val);

    // Write an Enum vector with underlying type int8_t.
    // Does not use padding; each byte is contiguous.
    template<typename T, std::enable_if_t<std::is_enum_v<T> && std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            writeEnumVector(const std::vector<T>& val)
            { return writeData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            writeEnumVector(const std::optional<std::vector<T>>& val)
            { return writeData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            writeEnumVector(const std::unique_ptr<std::vector<T>>& val) __attribute__((deprecated("use std::optional version instead")))
            { return writeData(val); }
    // Write an Enum vector with underlying type != int8_t.
    template<typename T, std::enable_if_t<std::is_enum_v<T> && !std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            writeEnumVector(const std::vector<T>& val)
            { return writeData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && !std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            writeEnumVector(const std::optional<std::vector<T>>& val)
            { return writeData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && !std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            writeEnumVector(const std::unique_ptr<std::vector<T>>& val) __attribute__((deprecated("use std::optional version instead")))
            { return writeData(val); }

    template<typename T>
    status_t            writeParcelableVector(const std::optional<std::vector<std::optional<T>>>& val)
            { return writeData(val); }
    template<typename T>
    status_t            writeParcelableVector(const std::unique_ptr<std::vector<std::unique_ptr<T>>>& val) __attribute__((deprecated("use std::optional version instead")))
            { return writeData(val); }
    template<typename T>
    status_t            writeParcelableVector(const std::shared_ptr<std::vector<std::unique_ptr<T>>>& val) __attribute__((deprecated("use std::optional version instead")))
            { return writeData(val); }
    template<typename T>
    status_t            writeParcelableVector(const std::shared_ptr<std::vector<std::optional<T>>>& val)
            { return writeData(val); }
    template<typename T>
    status_t            writeParcelableVector(const std::vector<T>& val)
            { return writeData(val); }

    template<typename T>
    status_t            writeNullableParcelable(const std::optional<T>& parcelable)
            { return writeData(parcelable); }
    template<typename T>
    status_t            writeNullableParcelable(const std::unique_ptr<T>& parcelable) __attribute__((deprecated("use std::optional version instead")))
            { return writeData(parcelable); }

    status_t            writeParcelable(const Parcelable& parcelable);

    template<typename T>
    status_t            write(const Flattenable<T>& val);

    template<typename T>
    status_t            write(const LightFlattenable<T>& val);

    template<typename T>
    status_t            writeVectorSize(const std::vector<T>& val);
    template<typename T>
    status_t            writeVectorSize(const std::optional<std::vector<T>>& val);
    template<typename T>
    status_t            writeVectorSize(const std::unique_ptr<std::vector<T>>& val) __attribute__((deprecated("use std::optional version instead")));

    // Place a native_handle into the parcel (the native_handle's file-
    // descriptors are dup'ed, so it is safe to delete the native_handle
    // when this function returns).
    // Doesn't take ownership of the native_handle.
    status_t            writeNativeHandle(const native_handle* handle);

    // Place a file descriptor into the parcel.  The given fd must remain
    // valid for the lifetime of the parcel.
    // The Parcel does not take ownership of the given fd unless you ask it to.
    status_t            writeFileDescriptor(int fd, bool takeOwnership = false);

    // Place a file descriptor into the parcel.  A dup of the fd is made, which
    // will be closed once the parcel is destroyed.
    status_t            writeDupFileDescriptor(int fd);

    // Place a Java "parcel file descriptor" into the parcel.  The given fd must remain
    // valid for the lifetime of the parcel.
    // The Parcel does not take ownership of the given fd unless you ask it to.
    status_t            writeParcelFileDescriptor(int fd, bool takeOwnership = false);

    // Place a Java "parcel file descriptor" into the parcel.  A dup of the fd is made, which will
    // be closed once the parcel is destroyed.
    status_t            writeDupParcelFileDescriptor(int fd);

    // Place a file descriptor into the parcel.  This will not affect the
    // semantics of the smart file descriptor. A new descriptor will be
    // created, and will be closed when the parcel is destroyed.
    status_t            writeUniqueFileDescriptor(
                            const base::unique_fd& fd);

    // Place a vector of file desciptors into the parcel. Each descriptor is
    // dup'd as in writeDupFileDescriptor
    status_t            writeUniqueFileDescriptorVector(
                            const std::optional<std::vector<base::unique_fd>>& val);
    status_t            writeUniqueFileDescriptorVector(
                            const std::unique_ptr<std::vector<base::unique_fd>>& val) __attribute__((deprecated("use std::optional version instead")));
    status_t            writeUniqueFileDescriptorVector(
                            const std::vector<base::unique_fd>& val);

    // Writes a blob to the parcel.
    // If the blob is small, then it is stored in-place, otherwise it is
    // transferred by way of an anonymous shared memory region.  Prefer sending
    // immutable blobs if possible since they may be subsequently transferred between
    // processes without further copying whereas mutable blobs always need to be copied.
    // The caller should call release() on the blob after writing its contents.
    status_t            writeBlob(size_t len, bool mutableCopy, WritableBlob* outBlob);

    // Write an existing immutable blob file descriptor to the parcel.
    // This allows the client to send the same blob to multiple processes
    // as long as it keeps a dup of the blob file descriptor handy for later.
    status_t            writeDupImmutableBlobFileDescriptor(int fd);

    status_t            writeObject(const flat_binder_object& val, bool nullMetaData);

    // Like Parcel.java's writeNoException().  Just writes a zero int32.
    // Currently the native implementation doesn't do any of the StrictMode
    // stack gathering and serialization that the Java implementation does.
    status_t            writeNoException();
    
    status_t            read(void* outData, size_t len) const;
    const void*         readInplace(size_t len) const;
    int32_t             readInt32() const;
    status_t            readInt32(int32_t *pArg) const;
    uint32_t            readUint32() const;
    status_t            readUint32(uint32_t *pArg) const;
    int64_t             readInt64() const;
    status_t            readInt64(int64_t *pArg) const;
    uint64_t            readUint64() const;
    status_t            readUint64(uint64_t *pArg) const;
    float               readFloat() const;
    status_t            readFloat(float *pArg) const;
    double              readDouble() const;
    status_t            readDouble(double *pArg) const;
    bool                readBool() const;
    status_t            readBool(bool *pArg) const;
    char16_t            readChar() const;
    status_t            readChar(char16_t *pArg) const;
    int8_t              readByte() const;
    status_t            readByte(int8_t *pArg) const;

    // Read a UTF16 encoded string, convert to UTF8
    status_t            readUtf8FromUtf16(std::string* str) const;
    status_t            readUtf8FromUtf16(std::optional<std::string>* str) const;
    status_t            readUtf8FromUtf16(std::unique_ptr<std::string>* str) const __attribute__((deprecated("use std::optional version instead")));

    const char*         readCString() const;
    String8             readString8() const;
    status_t            readString8(String8* pArg) const;
    const char*         readString8Inplace(size_t* outLen) const;
    String16            readString16() const;
    status_t            readString16(String16* pArg) const;
    status_t            readString16(std::optional<String16>* pArg) const;
    status_t            readString16(std::unique_ptr<String16>* pArg) const __attribute__((deprecated("use std::optional version instead")));
    const char16_t*     readString16Inplace(size_t* outLen) const;
    sp<IBinder>         readStrongBinder() const;
    status_t            readStrongBinder(sp<IBinder>* val) const;
    status_t            readNullableStrongBinder(sp<IBinder>* val) const;

    // Read an Enum vector with underlying type int8_t.
    // Does not use padding; each byte is contiguous.
    template<typename T, std::enable_if_t<std::is_enum_v<T> && std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            readEnumVector(std::vector<T>* val) const
            { return readData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            readEnumVector(std::unique_ptr<std::vector<T>>* val) const __attribute__((deprecated("use std::optional version instead")))
            { return readData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            readEnumVector(std::optional<std::vector<T>>* val) const
            { return readData(val); }
    // Read an Enum vector with underlying type != int8_t.
    template<typename T, std::enable_if_t<std::is_enum_v<T> && !std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            readEnumVector(std::vector<T>* val) const
            { return readData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && !std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            readEnumVector(std::unique_ptr<std::vector<T>>* val) const __attribute__((deprecated("use std::optional version instead")))
            { return readData(val); }
    template<typename T, std::enable_if_t<std::is_enum_v<T> && !std::is_same_v<typename std::underlying_type_t<T>,int8_t>, bool> = 0>
    status_t            readEnumVector(std::optional<std::vector<T>>* val) const
            { return readData(val); }

    template<typename T>
    status_t            readParcelableVector(
                            std::optional<std::vector<std::optional<T>>>* val) const
            { return readData(val); }
    template<typename T>
    status_t            readParcelableVector(
                            std::unique_ptr<std::vector<std::unique_ptr<T>>>* val) const __attribute__((deprecated("use std::optional version instead")))
            { return readData(val); }
    template<typename T>
    status_t            readParcelableVector(std::vector<T>* val) const
            { return readData(val); }

    status_t            readParcelable(Parcelable* parcelable) const;

    template<typename T>
    status_t            readParcelable(std::optional<T>* parcelable) const
            { return readData(parcelable); }
    template<typename T>
    status_t            readParcelable(std::unique_ptr<T>* parcelable) const __attribute__((deprecated("use std::optional version instead")))
            { return readData(parcelable); }

    // If strong binder would be nullptr, readStrongBinder() returns an error.
    // TODO: T must be derived from IInterface, fix for clarity.
    template<typename T>
    status_t            readStrongBinder(sp<T>* val) const;

    template<typename T>
    status_t            readNullableStrongBinder(sp<T>* val) const;

    status_t            readStrongBinderVector(std::optional<std::vector<sp<IBinder>>>* val) const;
    status_t            readStrongBinderVector(std::unique_ptr<std::vector<sp<IBinder>>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readStrongBinderVector(std::vector<sp<IBinder>>* val) const;

    status_t            readByteVector(std::optional<std::vector<int8_t>>* val) const;
    status_t            readByteVector(std::unique_ptr<std::vector<int8_t>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readByteVector(std::vector<int8_t>* val) const;
    status_t            readByteVector(std::optional<std::vector<uint8_t>>* val) const;
    status_t            readByteVector(std::unique_ptr<std::vector<uint8_t>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readByteVector(std::vector<uint8_t>* val) const;
    status_t            readInt32Vector(std::optional<std::vector<int32_t>>* val) const;
    status_t            readInt32Vector(std::unique_ptr<std::vector<int32_t>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readInt32Vector(std::vector<int32_t>* val) const;
    status_t            readInt64Vector(std::optional<std::vector<int64_t>>* val) const;
    status_t            readInt64Vector(std::unique_ptr<std::vector<int64_t>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readInt64Vector(std::vector<int64_t>* val) const;
    status_t            readUint64Vector(std::optional<std::vector<uint64_t>>* val) const;
    status_t            readUint64Vector(std::unique_ptr<std::vector<uint64_t>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readUint64Vector(std::vector<uint64_t>* val) const;
    status_t            readFloatVector(std::optional<std::vector<float>>* val) const;
    status_t            readFloatVector(std::unique_ptr<std::vector<float>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readFloatVector(std::vector<float>* val) const;
    status_t            readDoubleVector(std::optional<std::vector<double>>* val) const;
    status_t            readDoubleVector(std::unique_ptr<std::vector<double>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readDoubleVector(std::vector<double>* val) const;
    status_t            readBoolVector(std::optional<std::vector<bool>>* val) const;
    status_t            readBoolVector(std::unique_ptr<std::vector<bool>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readBoolVector(std::vector<bool>* val) const;
    status_t            readCharVector(std::optional<std::vector<char16_t>>* val) const;
    status_t            readCharVector(std::unique_ptr<std::vector<char16_t>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readCharVector(std::vector<char16_t>* val) const;
    status_t            readString16Vector(
                            std::optional<std::vector<std::optional<String16>>>* val) const;
    status_t            readString16Vector(
                            std::unique_ptr<std::vector<std::unique_ptr<String16>>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readString16Vector(std::vector<String16>* val) const;
    status_t            readUtf8VectorFromUtf16Vector(
                            std::optional<std::vector<std::optional<std::string>>>* val) const;
    status_t            readUtf8VectorFromUtf16Vector(
                            std::unique_ptr<std::vector<std::unique_ptr<std::string>>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readUtf8VectorFromUtf16Vector(std::vector<std::string>* val) const;

    template<typename T>
    status_t            read(Flattenable<T>& val) const;

    template<typename T>
    status_t            read(LightFlattenable<T>& val) const;

    // resizeOutVector is used to resize AIDL out vector parameters.
    template<typename T>
    status_t            resizeOutVector(std::vector<T>* val) const;
    template<typename T>
    status_t            resizeOutVector(std::optional<std::vector<T>>* val) const;
    template<typename T>
    status_t            resizeOutVector(std::unique_ptr<std::vector<T>>* val) const __attribute__((deprecated("use std::optional version instead")));

    // Like Parcel.java's readExceptionCode().  Reads the first int32
    // off of a Parcel's header, returning 0 or the negative error
    // code on exceptions, but also deals with skipping over rich
    // response headers.  Callers should use this to read & parse the
    // response headers rather than doing it by hand.
    int32_t             readExceptionCode() const;

    // Retrieve native_handle from the parcel. This returns a copy of the
    // parcel's native_handle (the caller takes ownership). The caller
    // must free the native_handle with native_handle_close() and 
    // native_handle_delete().
    native_handle*     readNativeHandle() const;

    
    // Retrieve a file descriptor from the parcel.  This returns the raw fd
    // in the parcel, which you do not own -- use dup() to get your own copy.
    int                 readFileDescriptor() const;

    // Retrieve a Java "parcel file descriptor" from the parcel.  This returns the raw fd
    // in the parcel, which you do not own -- use dup() to get your own copy.
    int                 readParcelFileDescriptor() const;

    // Retrieve a smart file descriptor from the parcel.
    status_t            readUniqueFileDescriptor(
                            base::unique_fd* val) const;

    // Retrieve a Java "parcel file descriptor" from the parcel.
    status_t            readUniqueParcelFileDescriptor(base::unique_fd* val) const;


    // Retrieve a vector of smart file descriptors from the parcel.
    status_t            readUniqueFileDescriptorVector(
                            std::optional<std::vector<base::unique_fd>>* val) const;
    status_t            readUniqueFileDescriptorVector(
                            std::unique_ptr<std::vector<base::unique_fd>>* val) const __attribute__((deprecated("use std::optional version instead")));
    status_t            readUniqueFileDescriptorVector(
                            std::vector<base::unique_fd>* val) const;

    // Reads a blob from the parcel.
    // The caller should call release() on the blob after reading its contents.
    status_t            readBlob(size_t len, ReadableBlob* outBlob) const;

    const flat_binder_object* readObject(bool nullMetaData) const;

    // Explicitly close all file descriptors in the parcel.
    void                closeFileDescriptors();

    // Debugging: get metrics on current allocations.
    static size_t       getGlobalAllocSize();
    static size_t       getGlobalAllocCount();

    bool                replaceCallingWorkSourceUid(uid_t uid);
    // Returns the work source provided by the caller. This can only be trusted for trusted calling
    // uid.
    uid_t               readCallingWorkSourceUid() const;

    void                print(TextOutput& to, uint32_t flags = 0) const;

private:
    typedef void        (*release_func)(Parcel* parcel,
                                        const uint8_t* data, size_t dataSize,
                                        const binder_size_t* objects, size_t objectsSize);

    uintptr_t           ipcData() const;
    size_t              ipcDataSize() const;
    uintptr_t           ipcObjects() const;
    size_t              ipcObjectsCount() const;
    void                ipcSetDataReference(const uint8_t* data, size_t dataSize,
                                            const binder_size_t* objects, size_t objectsCount,
                                            release_func relFunc);

    status_t            finishWrite(size_t len);
    void                releaseObjects();
    void                acquireObjects();
    status_t            growData(size_t len);
    status_t            restartWrite(size_t desired);
    status_t            continueWrite(size_t desired);
    status_t            writePointer(uintptr_t val);
    status_t            readPointer(uintptr_t *pArg) const;
    uintptr_t           readPointer() const;
    void                freeDataNoInit();
    void                initState();
    void                scanForFds() const;
    status_t            validateReadData(size_t len) const;

    void                updateWorkSourceRequestHeaderPosition() const;

    status_t            finishFlattenBinder(const sp<IBinder>& binder);
    status_t            finishUnflattenBinder(const sp<IBinder>& binder, sp<IBinder>* out) const;
    status_t            flattenBinder(const sp<IBinder>& binder);
    status_t            unflattenBinder(sp<IBinder>* out) const;

    template<class T>
    status_t            readAligned(T *pArg) const;

    template<class T>   T readAligned() const;

    template<class T>
    status_t            writeAligned(T val);

    status_t            writeRawNullableParcelable(const Parcelable*
                                                   parcelable);

    //-----------------------------------------------------------------------------
    // Generic type read and write methods for Parcel:
    //
    // readData(T *value) will read a value from the Parcel.
    // writeData(const T& value) will write a value to the Parcel.
    //
    // Our approach to parceling is based on two overloaded functions
    // readData() and writeData() that generate parceling code for an
    // object automatically based on its type. The code from templates are generated at
    // compile time (if constexpr), and decomposes an object through a call graph matching
    // recursive descent of the template typename.
    //
    // This approach unifies handling of complex objects,
    // resulting in fewer lines of code, greater consistency,
    // extensibility to nested types, efficiency (decisions made at compile time),
    // and better code maintainability and optimization.
    //
    // Design decision: Incorporate the read and write code into Parcel rather than
    // as a non-intrusive serializer that emits a byte stream, as we have
    // active objects, alignment, legacy code, and historical idiosyncrasies.
    //
    // --- Overview
    //
    // Parceling is a way of serializing objects into a sequence of bytes for communication
    // between processes, as part of marshaling data for remote procedure calls.
    //
    // The Parcel instance contains objects serialized as bytes, such as the following:
    //
    // 1) Ordinary primitive data such as int, float.
    // 2) Established structured data such as String16, std::string.
    // 3) Parcelables, which are C++ objects that derive from Parcelable (and thus have a
    //    readFromParcel and writeToParcel method).  (Similar for Java)
    // 4) A std::vector<> of such data.
    // 5) Nullable objects contained in std::optional, std::unique_ptr, or std::shared_ptr.
    //
    // And active objects from the Android ecosystem such as:
    // 6) File descriptors, base::unique_fd (kernel object handles)
    // 7) Binder objects, sp<IBinder> (active Android RPC handles)
    //
    // Objects from (1) through (5) serialize into the mData buffer.
    // Active objects (6) and (7) serialize into both mData and mObjects buffers.
    //
    // --- Data layout details
    //
    // Data is read or written to the parcel by recursively decomposing the type of the parameter
    // type T through readData() and writeData() methods.
    //
    // We focus on writeData() here in our explanation of the data layout.
    //
    // 1) Alignment
    // Implementation detail: Regardless of the parameter type, writeData() calls are designed
    // to finish at a multiple of 4 bytes, the default alignment of the Parcel.
    //
    // Writes of single uint8_t, int8_t, enums based on types of size 1, char16_t, etc
    // will result in 4 bytes being written.  The data is widened to int32 and then written;
    // hence the position of the nonzero bytes depend on the native endianness of the CPU.
    //
    // Writes of primitive values with 8 byte size, double, int64_t, uint64_t,
    // are stored with 4 byte alignment.  The ARM and x86/x64 permit unaligned reads
    // and writes (albeit with potential latency/throughput penalty) which may or may
    // not be observable unless the process is IO bound.
    //
    // 2) Parcelables
    // Parcelables are detected by the type's base class, and implemented through calling
    // into the Parcelable type's readFromParcel() or writeToParcel() methods.
    // Historically, due to null object detection, a (int32_t) 1 is prepended to the data written.
    // Parcelables must have a default constructor (i.e. one that takes no arguments).
    //
    // 3) Arrays
    // Arrays of uint8_t and int8_t, and enums based on size 1 are written as
    // a contiguous packed byte stream.  Hidden zero padding is applied at the end of the byte
    // stream to make a multiple of 4 bytes (and prevent info leakage when writing).
    //
    // All other array writes can be conceptually thought of as recursively calling
    // writeData on the individual elements (though may be implemented differently for speed).
    // As discussed in (1), alignment rules are therefore applied for each element
    // write (not as an aggregate whole), so the wire representation of data can be
    // substantially larger.
    //
    // Historical Note:
    // Because of element-wise alignment, CharVector and BoolVector are expanded
    // element-wise into integers even though they could have been optimized to be packed
    // just like uint8_t, int8_t (size 1 data).
    //
    // 3.1) Arrays accessed by the std::vector type.  This is the default for AIDL.
    //
    // 4) Nullables
    // std::optional, std::unique_ptr, std::shared_ptr are all parceled identically
    // (i.e. result in identical byte layout).
    // The target of the std::optional, std::unique_ptr, or std::shared_ptr
    // can either be a std::vector, String16, std::string, or a Parcelable.
    //
    // Detection of null relies on peeking the first int32 data and checking if the
    // the peeked value is considered invalid for the object:
    // (-1 for vectors, String16, std::string) (0 for Parcelables).  If the peeked value
    // is invalid, then a null is returned.
    //
    // Application Note: When to use each nullable type:
    //
    // std::optional: Embeds the object T by value rather than creating a new instance
    // by managed pointer as std::unique_ptr or std::shared_ptr.  This will save a malloc
    // when creating an optional instance.
    //
    // Use of std::optionals by value can result in copies of the underlying value stored in it,
    // so a std::move may be used to move in and move out (for example) a vector value into
    // the std::optional or for the std::optional itself.
    //
    // std::unique_ptr, std::shared_ptr: These are preferred when the lifetime of the object is
    // already managed by the application.  This reduces unnecessary copying of data
    // especially when the calls are local in-proc (rather than via binder rpc).
    //
    // 5) StrongBinder (sp<IBinder>)
    // StrongBinder objects are written regardless of null. When read, null StrongBinder values
    // will be interpreted as UNKNOWN_ERROR if the type is a single argument <sp<T>>
    // or in a vector argument <std::vector<sp<T>>. However, they will be read without an error
    // if present in a std::optional, std::unique_ptr, or std::shared_ptr vector, e.g.
    // <std::optional<std::vector<sp<T>>>.
    //
    // See AIDL annotation @Nullable, readStrongBinder(), and readNullableStrongBinder().
    //
    // Historical Note: writing a vector of StrongBinder objects <std::vector<sp<T>>
    // containing a null will not cause an error. However reading such a vector will cause
    // an error _and_ early termination of the read.

    //  --- Examples
    //
    // Using recursive parceling, we can parcel complex data types so long
    // as they obey the rules described above.
    //
    // Example #1
    // Parceling of a 3D vector
    //
    // std::vector<std::vector<std::vector<int32_t>>> v1 {
    //     { {1}, {2, 3}, {4} },
    //     {},
    //     { {10}, {20}, {30, 40} },
    // };
    // Parcel p1;
    // p1.writeData(v1);
    // decltype(v1) v2;
    // p1.setDataPosition(0);
    // p1.readData(&v2);
    // ASSERT_EQ(v1, v2);
    //
    // Example #2
    // Parceling of mixed shared pointers
    //
    // Parcel p1;
    // auto sp1 = std::make_shared<std::vector<std::shared_ptr<std::vector<int>>>>(3);
    // (*sp1)[2] = std::make_shared<std::vector<int>>(3);
    // (*(*sp1)[2])[2] = 2;
    // p1.writeData(sp1);
    // decltype(sp1) sp2;
    // p1.setDataPosition(0);
    // p1.readData(&sp2);
    // ASSERT_EQ((*sp1)[0], (*sp2)[0]); // nullptr
    // ASSERT_EQ((*sp1)[1], (*sp2)[1]); // nullptr
    // ASSERT_EQ(*(*sp1)[2], *(*sp2)[2]); // { 0, 0, 2}

    //  --- Helper Methods
    // TODO: move this to a utils header.
    //
    // Determine if a type is a specialization of a templated type
    // Example: is_specialization_v<T, std::vector>

    template <typename Test, template <typename...> class Ref>
    struct is_specialization : std::false_type {};

    template <template <typename...> class Ref, typename... Args>
    struct is_specialization<Ref<Args...>, Ref>: std::true_type {};

    template <typename Test, template <typename...> class Ref>
    static inline constexpr bool is_specialization_v = is_specialization<Test, Ref>::value;

    // Get the first template type from a container, the T from MyClass<T, ...>.
    template<typename T> struct first_template_type;

    template <template <typename ...> class V, typename T, typename... Args>
    struct first_template_type<V<T, Args...>> {
        using type_t = T;
    };

    template <typename T>
    using first_template_type_t = typename first_template_type<T>::type_t;

    // For static assert(false) we need a template version to avoid early failure.
    template <typename T>
    static inline constexpr bool dependent_false_v = false;

    // primitive types that we consider packed and trivially copyable as an array
    template <typename T>
    static inline constexpr bool is_pointer_equivalent_array_v =
            std::is_same_v<T, int8_t>
            || std::is_same_v<T, uint8_t>
            // We could support int16_t and uint16_t, but those aren't currently AIDL types.
            || std::is_same_v<T, int32_t>
            || std::is_same_v<T, uint32_t>
            || std::is_same_v<T, float>
            // are unaligned reads and write support is assumed.
            || std::is_same_v<T, uint64_t>
            || std::is_same_v<T, int64_t>
            || std::is_same_v<T, double>
            || (std::is_enum_v<T> && (sizeof(T) == 1 || sizeof(T) == 4)); // size check not type

    // allowed "nullable" types
    // These are nonintrusive containers std::optional, std::unique_ptr, std::shared_ptr.
    template <typename T>
    static inline constexpr bool is_parcel_nullable_type_v =
            is_specialization_v<T, std::optional>
            || is_specialization_v<T, std::unique_ptr>
            || is_specialization_v<T, std::shared_ptr>;

    // special int32 value to indicate NonNull or Null parcelables
    // This is fixed to be only 0 or 1 by contract, do not change.
    static constexpr int32_t kNonNullParcelableFlag = 1;
    static constexpr int32_t kNullParcelableFlag = 0;

    // special int32 size representing a null vector, when applicable in Nullable data.
    // This fixed as -1 by contract, do not change.
    static constexpr int32_t kNullVectorSize = -1;

    // --- readData and writeData methods.
    // We choose a mixture of function and template overloads to improve code readability.
    // TODO: Consider C++20 concepts when they become available.

    // writeData function overloads.
    // Implementation detail: Function overloading improves code readability over
    // template overloading, but prevents writeData<T> from being used for those types.

    status_t writeData(bool t) {
        return writeBool(t);  // this writes as int32_t
    }

    status_t writeData(int8_t t) {
        return writeByte(t);  // this writes as int32_t
    }

    status_t writeData(uint8_t t) {
        return writeByte(static_cast<int8_t>(t));  // this writes as int32_t
    }

    status_t writeData(char16_t t) {
        return writeChar(t);  // this writes as int32_t
    }

    status_t writeData(int32_t t) {
        return writeInt32(t);
    }

    status_t writeData(uint32_t t) {
        return writeUint32(t);
    }

    status_t writeData(int64_t t) {
        return writeInt64(t);
    }

    status_t writeData(uint64_t t) {
        return writeUint64(t);
    }

    status_t writeData(float t) {
        return writeFloat(t);
    }

    status_t writeData(double t) {
        return writeDouble(t);
    }

    status_t writeData(const String16& t) {
        return writeString16(t);
    }

    status_t writeData(const std::string& t) {
        return writeUtf8AsUtf16(t);
    }

    status_t writeData(const base::unique_fd& t) {
        return writeUniqueFileDescriptor(t);
    }

    status_t writeData(const Parcelable& t) {  // std::is_base_of_v<Parcelable, T>
        // implemented here. writeParcelable() calls this.
        status_t status = writeData(static_cast<int32_t>(kNonNullParcelableFlag));
        if (status != OK) return status;
        return t.writeToParcel(this);
    }

    // writeData<T> template overloads.
    // Written such that the first template type parameter is the complete type
    // of the first function parameter.
    template <typename T,
            typename std::enable_if_t<std::is_enum_v<T>, bool> = true>
    status_t writeData(const T& t) {
        // implemented here. writeEnum() calls this.
        using UT = std::underlying_type_t<T>;
        return writeData(static_cast<UT>(t)); // recurse
    }

    template <typename T,
            typename std::enable_if_t<is_specialization_v<T, sp>, bool> = true>
    status_t writeData(const T& t) {
        return writeStrongBinder(t);
    }

    // std::optional, std::unique_ptr, std::shared_ptr special case.
    template <typename CT,
            typename std::enable_if_t<is_parcel_nullable_type_v<CT>, bool> = true>
    status_t writeData(const CT& c) {
        using T = first_template_type_t<CT>;  // The T in CT == C<T, ...>
        if constexpr (is_specialization_v<T, std::vector>
                || std::is_same_v<T, String16>
                || std::is_same_v<T, std::string>) {
            if (!c) return writeData(static_cast<int32_t>(kNullVectorSize));
        } else if constexpr (std::is_base_of_v<Parcelable, T>) {
            if (!c) return writeData(static_cast<int32_t>(kNullParcelableFlag));
        } else /* constexpr */ {  // could define this, but raise as error.
            static_assert(dependent_false_v<CT>);
        }
        return writeData(*c);
    }

    template <typename CT,
            typename std::enable_if_t<is_specialization_v<CT, std::vector>, bool> = true>
    status_t writeData(const CT& c) {
        using T = first_template_type_t<CT>;  // The T in CT == C<T, ...>
        if (c.size() >  std::numeric_limits<int32_t>::max()) return BAD_VALUE;
        const auto size = static_cast<int32_t>(c.size());
        writeData(size);
        if constexpr (is_pointer_equivalent_array_v<T>) {
            constexpr size_t limit = std::numeric_limits<size_t>::max() / sizeof(T);
            if (c.size() > limit) return BAD_VALUE;
            // is_pointer_equivalent types do not have gaps which could leak info,
            // which is only a concern when writing through binder.

            // TODO: Padding of the write is suboptimal when the length of the
            // data is not a multiple of 4.  Consider improving the write() method.
            return write(c.data(), c.size() * sizeof(T));
        } else if constexpr (std::is_same_v<T, bool>
                || std::is_same_v<T, char16_t>) {
            // reserve data space to write to
            auto data = reinterpret_cast<int32_t*>(writeInplace(c.size() * sizeof(int32_t)));
            if (data == nullptr) return BAD_VALUE;
            for (const auto t: c) {
                *data++ = static_cast<int32_t>(t);
            }
        } else /* constexpr */ {
            for (const auto &t : c) {
                const status_t status = writeData(t);
                if (status != OK) return status;
            }
        }
        return OK;
    }

    // readData function overloads.
    // Implementation detail: Function overloading improves code readability over
    // template overloading, but prevents readData<T> from being used for those types.

    status_t readData(bool* t) const {
        return readBool(t);  // this reads as int32_t
    }

    status_t readData(int8_t* t) const {
        return readByte(t);  // this reads as int32_t
    }

    status_t readData(uint8_t* t) const {
        return readByte(reinterpret_cast<int8_t*>(t));  // NOTE: this reads as int32_t
    }

    status_t readData(char16_t* t) const {
        return readChar(t);  // this reads as int32_t
    }

    status_t readData(int32_t* t) const {
        return readInt32(t);
    }

    status_t readData(uint32_t* t) const {
        return readUint32(t);
    }

    status_t readData(int64_t* t) const {
        return readInt64(t);
    }

    status_t readData(uint64_t* t) const {
        return readUint64(t);
    }

    status_t readData(float* t) const {
        return readFloat(t);
    }

    status_t readData(double* t) const {
        return readDouble(t);
    }

    status_t readData(String16* t) const {
        return readString16(t);
    }

    status_t readData(std::string* t) const {
        return readUtf8FromUtf16(t);
    }

    status_t readData(base::unique_fd* t) const {
        return readUniqueFileDescriptor(t);
    }

    status_t readData(Parcelable* t) const { // std::is_base_of_v<Parcelable, T>
        // implemented here. readParcelable() calls this.
        int32_t present;
        status_t status = readData(&present);
        if (status != OK) return status;
        if (present != kNonNullParcelableFlag) return UNEXPECTED_NULL;
        return t->readFromParcel(this);
    }

    // readData<T> template overloads.
    // Written such that the first template type parameter is the complete type
    // of the first function parameter.

    template <typename T,
            typename std::enable_if_t<std::is_enum_v<T>, bool> = true>
    status_t readData(T* t) const {
        // implemented here. readEnum() calls this.
        using UT = std::underlying_type_t<T>;
        return readData(reinterpret_cast<UT*>(t));
    }

    template <typename T,
            typename std::enable_if_t<is_specialization_v<T, sp>, bool> = true>
    status_t readData(T* t) const {
        return readStrongBinder(t);  // Note: on null, returns failure
    }


    template <typename CT,
            typename std::enable_if_t<is_parcel_nullable_type_v<CT>, bool> = true>
    status_t readData(CT* c) const {
        using T = first_template_type_t<CT>;  // The T in CT == C<T, ...>
        const size_t startPos = dataPosition();
        int32_t peek;
        status_t status = readData(&peek);
        if (status != OK) return status;
        if constexpr (is_specialization_v<T, std::vector>
                || std::is_same_v<T, String16>
                || std::is_same_v<T, std::string>) {
            if (peek == kNullVectorSize) {
                c->reset();
                return OK;
            }
        } else if constexpr (std::is_base_of_v<Parcelable, T>) {
            if (peek == kNullParcelableFlag) {
                c->reset();
                return OK;
            }
        } else /* constexpr */ {  // could define this, but raise as error.
            static_assert(dependent_false_v<CT>);
        }
        // create a new object.
        if constexpr (is_specialization_v<CT, std::optional>) {
            c->emplace();
        } else /* constexpr */ {
            T* const t = new (std::nothrow) T;  // contents read from Parcel below.
            if (t == nullptr) return NO_MEMORY;
            c->reset(t);
        }
        // rewind data ptr to reread (this is pretty quick), otherwise we could
        // pass an optional argument to readData to indicate a peeked value.
        setDataPosition(startPos);
        if constexpr (is_specialization_v<T, std::vector>) {
            return readData(&**c, READ_FLAG_SP_NULLABLE);  // nullable sp<> allowed now
        } else {
            return readData(&**c);
        }
    }

    // std::vector special case, incorporating flags whether the vector
    // accepts nullable sp<> to be read.
    enum ReadFlags {
        READ_FLAG_NONE = 0,
        READ_FLAG_SP_NULLABLE = 1 << 0,
    };

    template <typename CT,
            typename std::enable_if_t<is_specialization_v<CT, std::vector>, bool> = true>
    status_t readData(CT* c, ReadFlags readFlags = READ_FLAG_NONE) const {
        using T = first_template_type_t<CT>;  // The T in CT == C<T, ...>
        int32_t size;
        status_t status = readInt32(&size);
        if (status != OK) return status;
        if (size < 0) return UNEXPECTED_NULL;
        const size_t availableBytes = dataAvail();  // coarse bound on vector size.
        if (static_cast<size_t>(size) > availableBytes) return BAD_VALUE;
        c->clear(); // must clear before resizing/reserving otherwise move ctors may be called.
        if constexpr (is_pointer_equivalent_array_v<T>) {
            // could consider POD without gaps and alignment of 4.
            auto data = reinterpret_cast<const T*>(
                    readInplace(static_cast<size_t>(size) * sizeof(T)));
            if (data == nullptr) return BAD_VALUE;
            c->insert(c->begin(), data, data + size); // insert should do a reserve().
        } else if constexpr (std::is_same_v<T, bool>
                || std::is_same_v<T, char16_t>) {
            c->reserve(size); // avoids default initialization
            auto data = reinterpret_cast<const int32_t*>(
                    readInplace(static_cast<size_t>(size) * sizeof(int32_t)));
            if (data == nullptr) return BAD_VALUE;
            for (int32_t i = 0; i < size; ++i) {
                c->emplace_back(static_cast<T>(*data++));
            }
        } else if constexpr (is_specialization_v<T, sp>) {
            c->resize(size); // calls ctor
            if (readFlags & READ_FLAG_SP_NULLABLE) {
                for (auto &t : *c) {
                    status = readNullableStrongBinder(&t);  // allow nullable
                    if (status != OK) return status;
                }
            } else {
                for (auto &t : *c) {
                    status = readStrongBinder(&t);
                    if (status != OK) return status;
                }
            }
        } else /* constexpr */ {
            c->resize(size); // calls ctor
            for (auto &t : *c) {
                status = readData(&t);
                if (status != OK) return status;
            }
        }
        return OK;
    }

    //-----------------------------------------------------------------------------
    private:

    status_t            mError;
    uint8_t*            mData;
    size_t              mDataSize;
    size_t              mDataCapacity;
    mutable size_t      mDataPos;
    binder_size_t*      mObjects;
    size_t              mObjectsSize;
    size_t              mObjectsCapacity;
    mutable size_t      mNextObjectHint;
    mutable bool        mObjectsSorted;

    mutable bool        mRequestHeaderPresent;

    mutable size_t      mWorkSourceRequestHeaderPosition;

    mutable bool        mFdsKnown;
    mutable bool        mHasFds;
    bool                mAllowFds;

    // if this parcelable is involved in a secure transaction, force the
    // data to be overridden with zero when deallocated
    mutable bool        mDeallocZero;

    release_func        mOwner;

    sp<RpcSession> mSession;

    class Blob {
    public:
        Blob();
        ~Blob();

        void clear();
        void release();
        inline size_t size() const { return mSize; }
        inline int fd() const { return mFd; }
        inline bool isMutable() const { return mMutable; }

    protected:
        void init(int fd, void* data, size_t size, bool isMutable);

        int mFd; // owned by parcel so not closed when released
        void* mData;
        size_t mSize;
        bool mMutable;
    };

    #if defined(__clang__)
    #pragma clang diagnostic push
    #pragma clang diagnostic ignored "-Wweak-vtables"
    #endif

    // FlattenableHelperInterface and FlattenableHelper avoid generating a vtable entry in objects
    // following Flattenable template/protocol.
    class FlattenableHelperInterface {
    protected:
        ~FlattenableHelperInterface() { }
    public:
        virtual size_t getFlattenedSize() const = 0;
        virtual size_t getFdCount() const = 0;
        virtual status_t flatten(void* buffer, size_t size, int* fds, size_t count) const = 0;
        virtual status_t unflatten(void const* buffer, size_t size, int const* fds, size_t count) = 0;
    };

    #if defined(__clang__)
    #pragma clang diagnostic pop
    #endif

    // Concrete implementation of FlattenableHelperInterface that delegates virtual calls to the
    // specified class T implementing the Flattenable protocol. It "virtualizes" a compile-time
    // protocol.
    template<typename T>
    class FlattenableHelper : public FlattenableHelperInterface {
        friend class Parcel;
        const Flattenable<T>& val;
        explicit FlattenableHelper(const Flattenable<T>& _val) : val(_val) { }

    protected:
        ~FlattenableHelper() = default;
    public:
        virtual size_t getFlattenedSize() const {
            return val.getFlattenedSize();
        }
        virtual size_t getFdCount() const {
            return val.getFdCount();
        }
        virtual status_t flatten(void* buffer, size_t size, int* fds, size_t count) const {
            return val.flatten(buffer, size, fds, count);
        }
        virtual status_t unflatten(void const* buffer, size_t size, int const* fds, size_t count) {
            return const_cast<Flattenable<T>&>(val).unflatten(buffer, size, fds, count);
        }
    };
    status_t write(const FlattenableHelperInterface& val);
    status_t read(FlattenableHelperInterface& val) const;

public:
    class ReadableBlob : public Blob {
        friend class Parcel;
    public:
        inline const void* data() const { return mData; }
        inline void* mutableData() { return isMutable() ? mData : nullptr; }
    };

    class WritableBlob : public Blob {
        friend class Parcel;
    public:
        inline void* data() { return mData; }
    };

private:
    size_t mOpenAshmemSize;

public:
    // TODO: Remove once ABI can be changed.
    size_t getBlobAshmemSize() const;
    size_t getOpenAshmemSize() const;
};

// ---------------------------------------------------------------------------

template<typename T>
status_t Parcel::write(const Flattenable<T>& val) {
    const FlattenableHelper<T> helper(val);
    return write(helper);
}

template<typename T>
status_t Parcel::write(const LightFlattenable<T>& val) {
    size_t size(val.getFlattenedSize());
    if (!val.isFixedSize()) {
        if (size > INT32_MAX) {
            return BAD_VALUE;
        }
        status_t err = writeInt32(static_cast<int32_t>(size));
        if (err != NO_ERROR) {
            return err;
        }
    }
    if (size) {
        void* buffer = writeInplace(size);
        if (buffer == nullptr)
            return NO_MEMORY;
        return val.flatten(buffer, size);
    }
    return NO_ERROR;
}

template<typename T>
status_t Parcel::read(Flattenable<T>& val) const {
    FlattenableHelper<T> helper(val);
    return read(helper);
}

template<typename T>
status_t Parcel::read(LightFlattenable<T>& val) const {
    size_t size;
    if (val.isFixedSize()) {
        size = val.getFlattenedSize();
    } else {
        int32_t s;
        status_t err = readInt32(&s);
        if (err != NO_ERROR) {
            return err;
        }
        size = static_cast<size_t>(s);
    }
    if (size) {
        void const* buffer = readInplace(size);
        return buffer == nullptr ? NO_MEMORY :
                val.unflatten(buffer, size);
    }
    return NO_ERROR;
}

template<typename T>
status_t Parcel::writeVectorSize(const std::vector<T>& val) {
    if (val.size() > INT32_MAX) {
        return BAD_VALUE;
    }
    return writeInt32(static_cast<int32_t>(val.size()));
}

template<typename T>
status_t Parcel::writeVectorSize(const std::optional<std::vector<T>>& val) {
    if (!val) {
        return writeInt32(-1);
    }

    return writeVectorSize(*val);
}

template<typename T>
status_t Parcel::writeVectorSize(const std::unique_ptr<std::vector<T>>& val) {
    if (!val) {
        return writeInt32(-1);
    }

    return writeVectorSize(*val);
}

template<typename T>
status_t Parcel::resizeOutVector(std::vector<T>* val) const {
    int32_t size;
    status_t err = readInt32(&size);
    if (err != NO_ERROR) {
        return err;
    }

    if (size < 0) {
        return UNEXPECTED_NULL;
    }
    val->resize(size_t(size));
    return OK;
}

template<typename T>
status_t Parcel::resizeOutVector(std::optional<std::vector<T>>* val) const {
    int32_t size;
    status_t err = readInt32(&size);
    if (err != NO_ERROR) {
        return err;
    }

    val->reset();
    if (size >= 0) {
        val->emplace(size_t(size));
    }

    return OK;
}

template<typename T>
status_t Parcel::resizeOutVector(std::unique_ptr<std::vector<T>>* val) const {
    int32_t size;
    status_t err = readInt32(&size);
    if (err != NO_ERROR) {
        return err;
    }

    val->reset();
    if (size >= 0) {
        val->reset(new std::vector<T>(size_t(size)));
    }

    return OK;
}

template<typename T>
status_t Parcel::readStrongBinder(sp<T>* val) const {
    sp<IBinder> tmp;
    status_t ret = readStrongBinder(&tmp);

    if (ret == OK) {
        *val = interface_cast<T>(tmp);

        if (val->get() == nullptr) {
            return UNKNOWN_ERROR;
        }
    }

    return ret;
}

template<typename T>
status_t Parcel::readNullableStrongBinder(sp<T>* val) const {
    sp<IBinder> tmp;
    status_t ret = readNullableStrongBinder(&tmp);

    if (ret == OK) {
        *val = interface_cast<T>(tmp);

        if (val->get() == nullptr && tmp.get() != nullptr) {
            ret = UNKNOWN_ERROR;
        }
    }

    return ret;
}

// ---------------------------------------------------------------------------

inline TextOutput& operator<<(TextOutput& to, const Parcel& parcel)
{
    parcel.print(to);
    return to;
}

} // namespace android

// ---------------------------------------------------------------------------