Question

我需要从C / C ++的linux套接字中读取VarInts。任何图书馆，想法或什么？

我尝试阅读并将char转换为bool [8]尝试未成功阅读VarInt ...

此外，这是为了兼容新的Minecraft 1.7.2通信协议，因此，the documentation of the protocol也可能有所帮助。

让我解释一下我的项目：我正在制作一个Minecraft服务器软件，以便在我的VPS中运行（因为java太慢了......）而且我对这个协议感到困惑。一个线程等待连接，当它有新连接时，它会创建一个新的Client对象并启动客户端线程，开始与客户端通信。

我认为没有必要显示代码。如果我错了，请告诉我，我会用一些代码进行编辑。

Answer 1

首先请注意，varints是作为实际字节发送的，而不是字符1和0的字符串。

对于unsigned varint，我相信以下内容将为您解码，假设您已在data指向的缓冲区中获取varint数据。此示例函数返回在引用参数int decoded_bytes中解码的字节数。

uint64_t decode_unsigned_varint( const uint8_t *const data, int &decoded_bytes )
{
    int i = 0;
    uint64_t decoded_value = 0;
    int shift_amount = 0;

    do 
    {
        decoded_value |= (uint64_t)(data[i] & 0x7F) << shift_amount;     
        shift_amount += 7;
    } while ( (data[i++] & 0x80) != 0 );

    decoded_bytes = i;
    return decoded_value;
}

要对已签名的varint进行解码，可以使用第二个调用第一个函数的函数：

int64_t decode_signed_varint( const uint8_t *const data, int &decoded_bytes )
{
    uint64_t unsigned_value = decode_unsigned_varint(data, decoded_bytes);
    return (int64_t)( unsigned_value & 1 ? ~(unsigned_value >> 1) 
                                         :  (unsigned_value >> 1) );
}

我相信这两个功能都是正确的。我使用下面的代码进行了一些基本测试，以验证Google页面中的几个数据点。输出正确。

#include <stdint.h>
#include <iostream>


uint64_t decode_unsigned_varint( const uint8_t *const data, int &decoded_bytes )
{
    int i = 0;
    uint64_t decoded_value = 0;
    int shift_amount = 0;

    do 
    {
        decoded_value |= (uint64_t)(data[i] & 0x7F) << shift_amount;     
        shift_amount += 7;
    } while ( (data[i++] & 0x80) != 0 );

    decoded_bytes = i;
    return decoded_value;
}

int64_t decode_signed_varint( const uint8_t *const data, int &decoded_bytes )
{
    uint64_t unsigned_value = decode_unsigned_varint(data, decoded_bytes);
    return (int64_t)( unsigned_value & 1 ? ~(unsigned_value >> 1) 
                                         :  (unsigned_value >> 1) );
}



uint8_t ex_p300[] = { 0xAC, 0x02 };
uint8_t ex_n1  [] = { 0x01 };

using namespace std;

int main()
{
    int decoded_bytes_p300;
    uint64_t p300;

    p300 = decode_unsigned_varint( ex_p300, decoded_bytes_p300 );

    int decoded_bytes_n1;
    int64_t  n1;

    n1 = decode_signed_varint( ex_n1, decoded_bytes_n1 );

    cout << "p300 = " << p300 
         << "   decoded_bytes_p300 = " << decoded_bytes_p300 << endl;

    cout << "n1 = " << n1 
         << "   decoded_bytes_n1 = " << decoded_bytes_n1 << endl;

    return 0;
}

要对varints进行编码，您可以使用以下函数。请注意，缓冲区uint8_t *const data应该有至少10个字节的空间，因为最大的varint是10个字节长 #include

// Encode an unsigned 64-bit varint.  Returns number of encoded bytes.
// 'buffer' must have room for up to 10 bytes.
int encode_unsigned_varint(uint8_t *const buffer, uint64_t value)
{
    int encoded = 0;

    do
    {
        uint8_t next_byte = value & 0x7F;
        value >>= 7;

        if (value)
            next_byte |= 0x80;

        buffer[encoded++] = next_byte;

    } while (value);


    return encoded;
}

// Encode a signed 64-bit varint.  Works by first zig-zag transforming
// signed value into an unsigned value, and then reusing the unsigned
// encoder.  'buffer' must have room for up to 10 bytes.
int encode_signed_varint(uint8_t *const buffer, int64_t value)
{
    uint64_t uvalue;

    uvalue = uint64_t( value < 0 ? ~(value << 1) : (value << 1) );

    return encode_unsigned_varint( buffer, uvalue );
}

从linux套接字读取“varint”

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