Question

我有以下代码迭代Buffer寻找数据包结束标记。此Buffer对象中可能有多个数据包，因此我使用数据包标记来查找数据，处理数据然后通过切片缓冲区移动到下一个数据包。但是我丢失了数据包，因为我在for循环上的条件是buffer.length并且缓冲区长度正在变化（变短）但是i值总是在增加！关于如何解决这个问题的任何想法？

bufferFragment用于捕获部分数据包并将它们附加到下一个数据包的开头。这部分有效。

for (var i = 0; i < buffer.length; i++) 
{
    if (buffer[i] == 16 && buffer[i + 1] == 3)
    {
        dataPacket = buffer.slice(0,i+4);
        parseData(dataPacket);
        buffer = buffer.slice(i+4);
    }
    else
    {
        bufferFragment = buffer;
    }
}

更新

似乎在某些情况下，当循环越来越长时，贪婪并捕获的数据应该超出预期。

这是一个完整的测试脚本（http://runnable.com/U75ce4esNHFj7028）

var testBufferText = "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";

var testBuffer = new Buffer(testBufferText,'hex');

var bufferFragment;

extractPackets(testBuffer);

function extractPackets(data) 
{
    var buffer = new Buffer(data);
    var origBuffer = buffer;
    var findCount = 0;

    var startFlag = false;
    var shortenedFlag = 0;
    var appendedData = false;

    if (bufferFragment) 
    {   
        buffer = Buffer.concat([bufferFragment, buffer]);
        concatBuffer = new Buffer(buffer.length);
        buffer.copy(concatBuffer);
        appendedData = bufferFragment;
        bufferFragment = undefined;
    }

    for (var i = 0; i < buffer.length; i++) {
        if (buffer[i] == 16 && buffer[i + 1] == 16) 
        {
            shortenedFlag += 1;
            buffer = Buffer.concat([buffer.slice(0, i), buffer.slice(i + 1)]);
        }
    }

    for (var i = 0; i < buffer.length; i++) {
        //Look for a DLE Packet
        if (buffer[i] == 16)
        {
            if (buffer[i + 1] != 16 && buffer[i + 1] != 3)
            {
                startFlag = true;
                break;
            }
        }
        else
        {
            buffer = buffer.slice(i + 1);
        }
    }

    var sameAsTempBuffer = new Buffer(buffer.length);
    buffer.copy(sameAsTempBuffer);

    // if we detected a start, look for end of packet 10 03
    if(startFlag == true)
    {
        for (var i = 0; i < buffer.length; i++) 
        {
            if (buffer[i] == 16 && buffer[i + 1] == 3)
            {
                var dataPacket = buffer.slice(0,i+4);

                buffer = buffer.slice(i+4);
                i -= 4;

                console.log("Data Packet to Process",dataPacket);
            }

        }
    }

    if (buffer.length)
    {
        bufferFragment = buffer;
    }

    return;
}

输出

Data Packet to Process <Buffer 10 02 07 b0 97 a5 08 5d a1 20 f3 00 00 46 10 03 e3 94>
Data Packet to Process <Buffer 10 02 07 36 e7 bb 08 5d 49 52 89 00 00 01 10 03 a9 40>
Data Packet to Process <Buffer 10 02 07 0c 8a 1f 09 4c a1 20 f3 94 74 3e 10 03 89 07>
Data Packet to Process <Buffer 10 02 07 a4 1c 22 09 5d 40 08 de 00 00 01 10 03 43 7e>
Data Packet to Process <Buffer 10 02 05 8e 53 51 09 a0 00 0a 1a 9b 58 00 00 00 00 00 a9 63 bf 10 03 5c 45>
Data Packet to Process <Buffer 10 02 07 d4 96 81 09 5d 49 52 89 00 00 01 10 03 82 7b 10 02 0b 01 24 47 50 56 54 47 2c 2c 54 2c 2c 4d 2c 30 2e 31 30 39 2c 4e 2c 30 2e 32 30 31 2c 4b 2c ...>
Data Packet to Process <Buffer 10 02 07 3e 36 c3 09 5d a1 20 f3 00 00 46 10 03 6e 46 10 02 07 22 97 e7 09 5d 49 52 89 00 00 01 10 03 8c 5f 10 02 01 78 66 35 0a 8d 40 62 2d 58 81 35 b0 ...>

前5个是好的然后循环变得贪婪并试图捕获更多的数据包！

Answer 1

其实找到了答案！关键是将i添加到偏移量中！

var testBufferText = "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";

var testBuffer = new Buffer(testBufferText,'hex');

var bufferFragment;

extractPackets(testBuffer);

function extractPackets(data) 
{
    var buffer = new Buffer(data);
    var origBuffer = buffer;
    var findCount = 0;

    var startFlag = false;
    var shortenedFlag = 0;
    var appendedData = false;

    if (bufferFragment) 
    {   
        buffer = Buffer.concat([bufferFragment, buffer]);
        concatBuffer = new Buffer(buffer.length);
        buffer.copy(concatBuffer);
        appendedData = bufferFragment;
        bufferFragment = undefined;
    }

    for (var i = 0; i < buffer.length; i++) {
        if (buffer[i] == 16 && buffer[i + 1] == 16) 
        {
            shortenedFlag += 1;
            buffer = Buffer.concat([buffer.slice(0, i), buffer.slice(i + 1)]);
        }
    }

    for (var i = 0; i < buffer.length; i++) {
        //Look for a DLE Packet
        if (buffer[i] == 16)
        {
            if (buffer[i + 1] != 16 && buffer[i + 1] != 3)
            {
                startFlag = true;
                break;
            }
        }
        else
        {
            buffer = buffer.slice(i + 1);
        }
    }

    var sameAsTempBuffer = new Buffer(buffer.length);
    buffer.copy(sameAsTempBuffer);

    // if we detected a start, look for end of packet 10 03
    if(startFlag == true)
    {
        for (var i = 0; i < buffer.length; i++) 
        {
            if (buffer[i] == 16 && buffer[i + 1] == 3)
            {
                var dataPacket = buffer.slice(0,i+4);

                buffer = buffer.slice(i+4);
                i -= i + 4;

                console.log("Data Packet to Process",dataPacket);
            }

        }
    }

    if (buffer.length)
    {
        bufferFragment = buffer;
    }

    return;
}

NodeJS Javascript用于循环更改内容

1 个答案: