Qt通過UDP傳圖片，實現自定義分包和組包

一.包頭結構體

 

//包頭
struct PackageHeader
{
    //包頭大小(sizeof(PackageHeader))
    unsigned int uTransPackageHdrSize;
    //當前包頭的大小(sizeof(PackageHeader)+當前數據包長度)
    unsigned int uTransPackageSize;
    //數據的總大小
    unsigned int uDataSize;
    //數據被分成包的個數
    unsigned int uDataPackageNum;
    //數據包當前的幀號
    unsigned int uDataPackageCurrIndex;
    //數據包在整個數據中的偏移
    unsigned int uDataPackageOffset;
};

每包數據由包頭和包體組成，包頭用於標記每包數據的特征，包體是圖片根據指定大小分出的每段數據，這里指定大小為const int UDP_MAX_SIZE=1200。

 

為何要分包可參考：TCP、UDP數據包大小的限制

二.分包與組包

1.分包

 

int dataLength=buffer.data().size();

unsigned char *dataBuffer=(unsigned char *)buffer.data().data();

int packetNum = 0;
int lastPaketSize = 0;
packetNum = dataLength / UDP_MAX_SIZE;
lastPaketSize = dataLength % UDP_MAX_SIZE;
int currentPacketIndex = 0;
if (lastPaketSize != 0)
{
    packetNum = packetNum + 1;
}

PackageHeader packageHead;

packageHead.uTransPackageHdrSize=sizeof(packageHead);
packageHead.uDataSize = dataLength;
packageHead.uDataPackageNum = packetNum;

unsigned char frameBuffer[1024*1000];
memset(frameBuffer,0,1024*1000);
while (currentPacketIndex < packetNum)
{
    if (currentPacketIndex < (packetNum-1))
    {
        packageHead.uTransPackageSize = sizeof(PackageHeader)+UDP_MAX_SIZE;
        packageHead.uDataPackageCurrIndex = currentPacketIndex+1;
        packageHead.uDataPackageOffset = currentPacketIndex*UDP_MAX_SIZE;
        memcpy(frameBuffer, &packageHead, sizeof(PackageHeader));
        memcpy(frameBuffer+sizeof(PackageHeader), dataBuffer+packageHead.uDataPackageOffset, UDP_MAX_SIZE);

        int length=udpsocketSend->writeDatagram(
                    (const char*)frameBuffer, packageHead.uTransPackageSize,
                    QHostAddress(ui->lineEditIP->text()), ui->lineEditPort->text().toInt());

        if(length!=packageHead.uTransPackageSize)
        {
          qDebug()<<"Failed to send image";
        }

        currentPacketIndex++;
    }
    else
    {
        packageHead.uTransPackageSize = sizeof(PackageHeader)+(dataLength-currentPacketIndex*UDP_MAX_SIZE);
        packageHead.uDataPackageCurrIndex = currentPacketIndex+1;
        packageHead.uDataPackageOffset = currentPacketIndex*UDP_MAX_SIZE;
        memcpy(frameBuffer, &packageHead, sizeof(PackageHeader));
        memcpy(frameBuffer+sizeof(PackageHeader), dataBuffer+packageHead.uDataPackageOffset, dataLength-currentPacketIndex*UDP_MAX_SIZE);
        int length=udpsocketSend->writeDatagram(
                    (const char*)frameBuffer, packageHead.uTransPackageSize,
                    QHostAddress(ui->lineEditIP->text()), ui->lineEditPort->text().toInt());

        if(length!=packageHead.uTransPackageSize)
        {
          qDebug()<<"Failed to send image";
        }

        currentPacketIndex++;
    }
}

先將圖片轉換為QBuffer，這樣就可以獲取圖片的數據和長度，然后根據指定大小UDP_MAX_SIZE分包。在包頭中設置每包數據的特征，然后將包體加到包頭后面發送出去。

 

2.組包

 

static int num = 1;
static uint size = 0;

PackageHeader *packageHead = (PackageHeader *)datagram.data();
if (packageHead->uDataPackageCurrIndex == num)
{
    num++;
    size += packageHead->uTransPackageSize-packageHead->uTransPackageHdrSize;
    if (size > 1024*1000)
    {
        qDebug()<<"image too big";
        num = 1;
        size = 0;
        return;
    }
    if (packageHead->uDataPackageOffset > 1024*1000)
    {
        qDebug()<<"image too big";
        packageHead->uDataPackageOffset = 0;
        num = 1;
        size = 0;
        return;
    }

    memcpy(imageData.data+packageHead->uDataPackageOffset, datagram.data()+packageHead->uTransPackageHdrSize,
           packageHead->uTransPackageSize-packageHead->uTransPackageHdrSize);
    if ((packageHead->uDataPackageNum == packageHead->uDataPackageCurrIndex)
            && (size == packageHead->uDataSize))
    {
        imageData.length = packageHead->uDataSize;

        QImage image;
        image.loadFromData((uchar *)imageData.data,imageData.length,"JPG");
        QPixmap pixmap=QPixmap::fromImage(image);
        ui->labelImage_2->setPixmap(pixmap);
        recvImageNum++;
        ui->lineEditRevFrame->setText(QString::number(recvImageNum));
        ui->lineEditRevSize->setText(QString::number(imageData.length));
        memset(&imageData,0,sizeof(UdpUnpackData));
        num = 1;
        size = 0;
    }
}
else
{
    num = 1;
    size = 0;
    memset(&imageData,0,sizeof(UdpUnpackData));
}

組包是分包的逆過程，根據包頭中“數據的總大小”和“數據被分成包的個數”兩個字段可以判斷組包是否完整，如果完整就在接收端顯示出來。
三.示例

 

界面包括發送端和接收端，接收端的IP地址是自動獲取的本機IP地址，上圖將發送端的IP地址設置為與接收端IP地址相同，可實現自發自收。

每秒幀數可實時設置每秒發送圖片的張數，發送幀數表示一共發送了多少張，接收幀數表示一共接收了多少張，圖片大小表示每張圖片多少Byte。

可將示例運行於兩台計算機，實現雙向收發。

源碼鏈接：見http://blog.csdn.net/caoshangpa/article/details/52681572的評論

 

http://blog.csdn.net/caoshangpa/article/details/52681572