base/Stream.h

// Copyright 2019 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 "msvc.h"

#include <string>

#include <inttypes.h>
#include <sys/types.h>

namespace android {
namespace base {

// Abstract interface to byte streams of all kind.
// This is mainly used to implement disk serialization.
class Stream {
public:
    // Default constructor.
    Stream() = default;

    // Destructor.
    virtual ~Stream() = default;

    // Read up to |size| bytes and copy them to |buffer|. Return the number
    // of bytes that were actually transferred, or -errno value on error.
    virtual ssize_t read(void* buffer, size_t size) = 0;

    // Write up to |size| bytes from |buffer| into the stream. Return the
    // number of bytes that were actually transferred, or -errno value on
    // error.
    virtual ssize_t write(const void* buffer, size_t size) = 0;

    // Write a single byte |value| into the stream. Ignore errors.
    void putByte(uint8_t value);

    // Write a 16-bit |value| as big-endian into the stream. Ignore errors.
    void putBe16(uint16_t value);

    // Write a 32-bit |value| as big-endian into the stream. Ignore errors.
    void putBe32(uint32_t value);

    // Write a 64-bit |value| as big-endian into the stream. Ignore errors.
    void putBe64(uint64_t value);

    // Read a single byte from the stream. Return 0 on error.
    uint8_t getByte();

    // Read a single big-endian 16-bit value from the stream.
    // Return 0 on error.
    uint16_t getBe16();

    // Read a single big-endian 32-bit value from the stream.
    // Return 0 on error.
    uint32_t getBe32();

    // Read a single big-endian 64-bit value from the stream.
    // Return 0 on error.
    uint64_t getBe64();

    // Write a 32-bit float |value| to the stream.
    void putFloat(float value);

    // Read a single 32-bit float value from the stream.
    float getFloat();

    // Write a 0-terminated C string |str| into the stream. Ignore error.
    void putString(const char* str);
    void putString(const std::string& str);

    // Write a string |str| of |strlen| bytes into the stream.
    // Ignore errors.
    void putString(const char* str, size_t strlen);

    // Read a string from the stream. Return a new string instance,
    // which will be empty on error. Note that this can only be used
    // to read strings that were written with putString().
    std::string getString();

    // Put/gen an integer number into the stream, making it use as little space
    // there as possible.
    // It uses a simple byte-by-byte encoding scheme, putting 7 bits of the
    // number with the 8th bit set when there's more data to read, until the
    // whole number is read.
    // The compression is efficient if the number range is small, but it starts
    // wasting space when values approach 14 bits for int16 (16K), 28 bits for
    // int32 (268M) or 56 bits for int64 (still a lot).
    void putPackedNum(uint64_t num);
    uint64_t getPackedNum();

    // Same thing, but encode negative numbers efficiently as well (single sign
    // bit + packed unsigned representation)
    void putPackedSignedNum(int64_t num);
    int64_t getPackedSignedNum();
};

}  // namespace base
}  // namespace android