如果你还不是很明白所有的步骤，不用着急，在看到下面的具体实现时你会更加清楚。
Echo Server
下面我会展示服务器的具体实现。我假定您已经安装好Wangle。需要注意的是截至目前Wangle还不能在Mac OS上安装，我建议您可以安装虚拟机，使用Ubuntu来安装Wangle。
这就是echo handler：接收一个string，打印到stdout中，再发送回pipeline。要注意write语句中的定界符不可以省略，因为pipeline会按照字节解码。
// the main logic of our echo server; receives a string and writes it straight
// back
class EchoHandler : public HandlerAdapter {
public:
virtual void read(Context* ctx, std::string msg) override {
std::cout << "handling " << msg << std::endl;
write(ctx, msg + "rn");
}
};
Echohandler其实是我们pipeline的最后一个handler，现在我们需要创建一个PipelineFactory来控制所有的request和response。
// where we define the chain of handlers for each messeage received
class EchoPipelineFactory : public PipelineFactory {
public:
EchoPipeline::Ptr newPipeline(std::shared_ptr sock) {
auto pipeline = EchoPipeline::create();
pipeline->addBack(AsyncSocketHandler(sock));
pipeline->addBack(LineBasedFrameDecoder(8192));
pipeline->addBack(StringCodec());
pipeline->addBack(EchoHandler());
pipeline->finalize();
return pipeline;
}
};
pipeline中每一个handler的插入顺序都需要严格注意，因为它们是按照先后排序的，此处我们有4个handler
1.AsyncSocketHandler: 上游：读取scoket中的二进制流转换成零拷贝字节缓存 下游：将字节缓存内容写入底层socket
2. LineBasedFrameDecoder: 上游：接收字节缓存，按行分割数据 下游：将字节缓存发送给AsyncSocketHandler
3. StringCodec: 上游：接收字节缓存，解码为std:string传递给EchoHandler 下游：接收std:string, 编码为字节缓存,传递给LineBasedFrameDecoder
4. EchoHandler: 上游：接收std:string对象，将其写入pipeline－将消息返回给Echohandler。 下游：接收一个std:string对象，转发给StringCodec Handler。 现在我们所需要做的就是将pipeline factory关联到ServerBootstrap，绑定一个端口，这样我们已经完成了 基本上所有的工作。
#include <gflags/gflags.h>
#include <wangle/bootstrap/ServerBootstrap.h>
#include <wangle/channel/AsyncSocketHandler.h>
#include <wangle/codec/LineBasedFrameDecoder.h>
#include <wangle/codec/StringCodec.h>
using namespace folly;
using namespace wangle;
DEFINE_int32(port, 8080, "echo server port");
typedef Pipeline<IOBufQueue&, std::string> EchoPipeline;
// the main logic of our echo server; receives a string and writes it straight
// back
class EchoHandler : public HandlerAdapter<std::string> {
public:
virtual void read(Context* ctx, std::string msg) override {
std::cout << "handling " << msg << std::endl;
write(ctx, msg + "rn");
}
};
// where we define the chain of handlers for each messeage received
class EchoPipelineFactory : public PipelineFactory<EchoPipeline> {
public:
EchoPipeline::Ptr newPipeline(std::shared_ptr<AsyncTransportWrapper> sock) {
auto pipeline = EchoPipeline::create();
pipeline->addBack(AsyncSocketHandler(sock));
pipeline->addBack(LineBasedFrameDecoder(8192));
pipeline->addBack(StringCodec());
pipeline->addBack(EchoHandler());
pipeline->finalize();
return pipeline;
}
};
int main(int argc, char** argv) {
google::ParseCommandLineFlags(&argc, &argv, true);
ServerBootstrap<EchoPipeline> server;
server.childPipeline(std::make_shared<EchoPipelineFactory>());
server.bind(FLAGS_port);
server.waitForStop();
return 0;
}
