一.包头结构体
- //包头
- struct PackageHeader
- {
- //包头大小(sizeof(PackageHeader))
- unsigned int uTransPackageHdrSize;
- //当前包头的大小(sizeof(PackageHeader)+当前数据包长度)
- unsigned int uTransPackageSize;
- //数据的总大小
- unsigned int uDataSize;
- //数据被分成包的个数
- unsigned int uDataPackageNum;
- //数据包当前的帧号
- unsigned int uDataPackageCurrIndex;
- //数据包在整个数据中的偏移
- unsigned int uDataPackageOffset;
- };
每包数据由包头和包体组成，包头用于标记每包数据的特征，包体是图片根据指定大小分出的每段数据，这里指定大小为const int UDP_MAX_SIZE=1200。
为何要分包可参考：TCP、UDP数据包大小的限制
二.分包与组包
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++;
- }
- }
先将图片转换为QBuffer，这样就可以获取图片的数据和长度，然后根据指定大小UDP_MAX_SIZE分包。在包头中设置每包数据的特征，然后将包体加到包头后面发送出去。
2.组包
- 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));
- }
组包是分包的逆过程，根据包头中“数据的总大小”和“数据被分成包的个数”两个字段可以判断组包是否完整，如果完整就在接收端显示出来。
三.示例
界面包括发送端和接收端，接收端的IP地址是自动获取的本机IP地址，上图将发送端的IP地址设置为与接收端IP地址相同，可实现自发自收。
每秒帧数可实时设置每秒发送图片的张数，发送帧数表示一共发送了多少张，接收帧数表示一共接收了多少张，图片大小表示每张图片多少Byte。
可将示例运行于两台计算机，实现双向收发。
源码链接：见http://blog.****.net/caoshangpa/article/details/52681572的评论
http://blog.****.net/caoshangpa/article/details/52681572