Question

我有一个服务器 - 客户端java代码，服务器部分必须用c编写。代码的第一部分（服务器端）是从客户端接收多播消息，然后通过tcp连接连接到客户端并发送一些消息。使用我的c代码，我可以从客户端收到多播消息，但是当我尝试建立tcp连接时，我收到错误。 c服务器无法与java客户端建立TCP连接。我发布以下代码。如果您能找到问题，请告诉我。谢谢。 IPMulticastDiscoveryClient.java客户端代码

package org.postgresql.discovery;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import org.postgresql.discovery.ClientTCPResponseProvider;
/**

* A feature for detecting remote service addresses (IPs) via IP Multicast.

* 

* Each service must first bind itself with the help of the IPMulticastDiscovery Server

* and is identified with a unique name.

* 
* 

*

*/

 public class IPMulticastDiscoveryClient {
private static String myIp = null;

public IPMulticastDiscoveryClient(){

}

/**

 * Locates a bound service with a unique name via IPMulticast

 * 

 * @param service unique name of the service

 * @return the IP address of the service as String

 * @throws Exception

 */

public String getIpForService(String service, String host) throws Exception{

    //CloudCacheLogger.info("Looking for service: " + service);

    // 1. open a response channel

    ClientTCPResponseProvider response = new ClientTCPResponseProvider(service);

    // 2. multicast request

    sendJoinCluster(service, host);

    // 3. collect response

    //if(response.getFinalResult() == null){



    //}

    try {

        Thread.sleep(1000);

    } catch (InterruptedException e) {

        e.printStackTrace();

    }



    String result = response.getFinalResult();

    //myIp = result.split(";")[1];

    //result = result.split(";")[0];



    // 4. close the response channel

    response.destroy();

    // 5. check

    if(result == null){

        throw new Exception("Could not discover service: " + service);

    } else {

        //CloudCacheLogger.info("found service: " + service + " at " + result);

        return result;

    }

}



/**

 * Uses a remote service to discover the local, external IP address

 * 

 * @param service unique name of a remote service

 * @return the local, external ip address

 * @throws Exception

 */

public String getMyIpFromService(String service) throws Exception{

    if(myIp != null)

        return myIp;

    else throw new Exception("could not determine local ip");

}



private static void sendJoinCluster(String message, String host){

    try {

        System.out.println("\nIn sendJoinCluster");

        InetAddress group = InetAddress.getByName(host);

        MulticastSocket s = new MulticastSocket(9876);

        s.joinGroup(group);

        DatagramPacket hi = new DatagramPacket(message.getBytes(), message.length(),group, 6789);

        s.send(hi);

        s.leaveGroup(group);

        s.close();



    } catch (Exception e){

        e.printStackTrace();

    }

}



public static void main (String args[]) throws Exception {

    IPMulticastDiscoveryClient client = new IPMulticastDiscoveryClient();

    String result = client.getIpForService("FindIP", "228.5.6.7");

    System.out.println(result);

}

}

ClientTCPResponseProvider.java

package org.postgresql.discovery;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

/**
* Offers a socket for receiving repsonses from remote services. Once the client 
sent  a location
* request, it waits for messages to arrive on this Socket.
* 
* 
*
*/
public class ClientTCPResponseProvider {

private ServerSocket providerSocket;
private Socket connection = null;
private ObjectOutputStream out;
private ObjectInputStream in;

private boolean endConnection = false;

private String keyword = null;
private String finalResult = "";

public ClientTCPResponseProvider(String keyword){
    System.out.println("\nIn ClientTCPResponseProvider");
    this.keyword = keyword;
    Thread t = new Thread(new ThreadedProvider());
    t.start();
}

public void destroy(){
    endConnection = true;
    try {
        providerSocket.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

void goConnect(){
    try{
        System.out.println("\nIn goConnect.");
        //1. creating a server socket
        providerSocket = new ServerSocket(8888);
        //2. Wait for connection

        Object message = null;

        long timeout = 1000;
        long initTime = System.currentTimeMillis();

        do{
            //System.out.println("Waiting for connection...");
            connection = providerSocket.accept();
            //System.out.println("Connection received from " + connection.getInetAddress().getHostName());
            //3. get Input and Output streams
            out = new ObjectOutputStream(connection.getOutputStream());
            out.flush();
            in = new ObjectInputStream(connection.getInputStream());
            //4. The two parts communicate via the input and output streams
            try{
                message = in.readObject();
                String response = (String)message;
                //System.out.println("received: " + response);
                if(response.startsWith(keyword) && response.split(":")[0].equals(keyword)){
                    finalResult += connection.getInetAddress().getHostAddress()+";";
                    System.out.println(" IVAN " +finalResult);
                    //finalResult += connection.getLocalAddress().getHostAddress()+ ";";
                    //endConnection = true;
                }
            }
            catch(ClassNotFoundException classnot){
                System.err.println("Data received in unknown format");
            }
            in.close();
            out.close();
            connection.close();
        } while(System.currentTimeMillis()-initTime < timeout);
        providerSocket.close();
    }
    catch(IOException ioException){
        ioException.printStackTrace();
    }
}

private class ThreadedProvider implements Runnable{
    //@Override
    public void run() {
        goConnect();    
    }
}

public String getFinalResult() {
    return finalResult;
}

}

C中的服务器代码

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>
#include <pthread.h>

void *listenToClient();
char *trim(char *str);
void sendMessageToClient(char *ip, int *port, char *message);

#define HELLO_PORT 6789
#define HELLO_GROUP "228.5.6.7"
#define MSGBUFSIZE 256
char *ClientIP = "localhost";
char *HostIP = "192.168.164.138";
int isRunning = 1;
main(int argc, char *argv[])
{   
pthread_t thread;
int th;
th = pthread_create( &thread, NULL, listenToClient, NULL);
pthread_join( thread, NULL);    
exit(0);
}

 void *listenToClient(){
 struct sockaddr_in addr;
 int fd, nbytes,addrlen;
 struct ip_mreq mreq;
 char msgbuf[MSGBUFSIZE];

 u_int yes=1;                

 /* create what looks like an ordinary UDP socket */
 if ((fd=socket(AF_INET,SOCK_DGRAM,0)) < 0) {
  perror("socket");
  exit(1);
 }

/* allow multiple sockets to use the same PORT number */
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) < 0) {
   perror("Reusing ADDR failed");
   exit(1);
   }

 /* set up destination address */
 memset(&addr,0,sizeof(addr));
 addr.sin_family=AF_INET;
 addr.sin_addr.s_addr=htonl(INADDR_ANY); 
 addr.sin_port=htons(HELLO_PORT);

 /* bind to receive address */
 if (bind(fd,(struct sockaddr *) &addr,sizeof(addr)) < 0) {
  perror("bind");
  exit(1);
 }

 /* use setsockopt() to request that the kernel join a multicast group */
 mreq.imr_multiaddr.s_addr=inet_addr(HELLO_GROUP);
 mreq.imr_interface.s_addr=htonl(INADDR_ANY);

 if (setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0) {
  perror("setsockopt");
  exit(1);
     }

do {     
  addrlen=sizeof(addr);
  if ((nbytes=recvfrom(fd,msgbuf,MSGBUFSIZE,0,(struct sockaddr *) &addr,&addrlen)) < 0) {
       perror("recvfrom");
       exit(1);
  }
  puts(msgbuf);
      char message[] = "FindIP:192.168.164.138 (Some IP)\n");    
  printf("\nSending Message To Client: %s\n", message);
      sendMessageToClient(ClientIP, 8888, message);
}while(isRunning==1);
close(fd);
}

  /**Sends the messages to the remote machine
  * ip = Address of the machine where message has to sent
  * port = port used for sending the message
  * message= string message
  *
  */
  void sendMessageToClient(char *ip, int *port, char *message) {
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;

char buffer[256];

portno = port;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
    error("ERROR opening socket");
server = gethostbyname(ip);
if (server == NULL) {
    fprintf(stderr, "ERROR, no such host\n");
    exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *) server->h_addr, (char *) &serv_addr.sin_addr.s_addr,
        server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
    error("ERROR connecting");
bzero(buffer, 256);
strcpy(buffer,message);

n = send(sockfd, buffer, strlen(buffer), 0);
if (n < 0)
    error("ERROR writing to socket");
bzero(buffer, 256);
close(sockfd);
return 0;
    }

Answer 1

portno = port;

我怀疑你想要

portno = *port;

Answer 2

此功能的声明不正确：

void sendMessageToClient(char *ip, int *port, char *message)

port的类型应为int，而不是int *。无论客户端消息来自何处，代码始终连接到localhost:8888;那是你的意图吗？

顺便说一句，您在C代码中使用了许多过时的函数（例如bcopy()，bzero()和gethostbyname()）。

C服务器代码 - Java客户端代码TCP连接问题

2 个答案: