UDP 데이터그램 통신에서 서버가 recvfrom 부터 계속 대기상태가 됩니다.

#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>
#include <cstdio>
#include <iostream>
using namespace std;
#include <cstring>
#include <signal.h>
#include <cstdlib>
 
 
 
#define BUFFER_SIZE 5
#define RESULT_BUFFER_SIZE 1024
#define RESULTFILE  "resultfile"
 
//#define TEST
 
static int socketfd;
static int acceptfd;
static int resultfd;
static char buffer[BUFFER_SIZE];
static char resultbuffer[RESULT_BUFFER_SIZE];
 
static void handleSIGINT(int sig) {
  //close(acceptfd);
  close(resultfd);
  string rm("rm -f ");
  rm+=RESULTFILE;
  system(rm.c_str());
  close(acceptfd);
  close(socketfd);
  kill(0,SIGKILL);
}
 
int main() {
  if(socketfd>=0) {
    close(socketfd);
  }
  if((socketfd=socket(AF_INET,SOCK_STREAM,0))==-1) {
    perror("socket error message : ");
    exit(0);
  }
  #ifdef TEST
    printf("socket success\n");
  #endif
  struct sigaction actionplan;
  sigemptyset(&actionplan.sa_mask);
  actionplan.sa_flags=0x0;
  actionplan.sa_handler=handleSIGINT;
  while(sigaction(SIGINT,&actionplan,0)==-1) {
    printf("Registerring handleSIGINT handler\n");
  }
  struct sockaddr_in iserver;
  iserver.sin_family=AF_INET;
  iserver.sin_addr.s_addr=inet_addr("112.145.252.108");
  iserver.sin_port=htons(60000);
  memset(iserver.sin_zero,0,8);
  while(bind(socketfd,(struct sockaddr*)&iserver,sizeof(struct sockaddr))==-1) {
    perror("bind error message : ");
    sleep(2);
  }
  #ifdef TEST
    printf("bind success\n");
  #endif
  if(listen(socketfd,10)==-1) {
    perror("listen error message : ");
  }
  #ifdef TEST
    printf("listen success\n");
  #endif
  struct sockaddr_in client;
  socklen_t size;
 
  if((acceptfd=accept(socketfd,(struct sockaddr*)&client,&size))==-1) {
    perror("accept Error message : ");
    exit(0);
  }
  #ifdef TEST
    printf("accept success\n");
    printf("The connected client ip is %s\n",inet_ntoa(client.sin_addr));
  #endif
 
  memset(buffer,0,sizeof(buffer));
  int length,llength;
    #ifdef TEST
      printf("ee\n");//test
      int loop=0;
    #endif
  string command("");
 
  string rm("rm -f ");
  rm+=RESULTFILE;
 
while(1) {
  command="";
  while((length=recv(acceptfd,buffer,sizeof(buffer),0))>0) {
    #ifdef TEST
      loop++;
      printf("%s\n",buffer);
      printf("The loop is %d\n",loop);
      printf("The length is %d\n",length);
    #endif
    if(buffer[strlen(buffer)-1]=='\n') {
      buffer[strlen(buffer)-1]=0;
      command+=buffer;
      break;
    }
    command+=buffer;
    memset(buffer,0,sizeof(buffer));
  }
  system(rm.c_str());
  command+=">"+string("")+RESULTFILE;
  #ifdef TEST
    printf("The executed command is : %s\n",command.c_str());
  #endif
 
  memset(resultbuffer,0,sizeof(resultbuffer));
  int is_executed=system(command.c_str());
  command+="";
  #ifdef TEST
    printf("The returned value is %d after system function was called.\n",is_executed);
  #endif
 
  char tmp[1];tmp[0]=EOF;
  if(is_executed!=0) {
    sprintf(resultbuffer,"system error %d",is_executed);
    send(acceptfd,resultbuffer,sizeof(resultbuffer),0);
    send(acceptfd,tmp,sizeof(tmp),0);
  }
 
 
  if((resultfd=open(RESULTFILE,O_RDONLY))==-1) {
    perror("open error message : ");
  }
  else {
    printf("The file is opened.\n");
  }
 
  while((length=read(resultfd,resultbuffer,sizeof(resultbuffer)))>0) {//\uba85\ub839 \uc2e4\ud589\uc758 \uacb0\uacfc\ub97c \uc0c1\ub300\ud3b8\uc5d0\uac8c \ub0b4\ubcf4\ub0b8\ub2e4.
    while((llength=send(acceptfd,resultbuffer,strlen(resultbuffer),0))>0) {
//printf("sending...\n");//test
      printf("%s",resultbuffer);//test
      memset(resultbuffer,0,sizeof(resultbuffer));
    }
  }
  //if(length==0) {
    printf("finishing...\n");//test
    printf("00000\n");//test
    memset(resultbuffer,0,sizeof(resultbuffer));
    //resultbuffer[0]=EOF;
    llength=send(acceptfd,tmp,sizeof(tmp),0);
    printf("llength is %d\n",llength);//test
    memset(resultbuffer,0,sizeof(resultbuffer));
  //}
  close(resultfd);
}
 
 
  close(acceptfd);
  close(resultfd);
  system(rm.c_str());
  close(socketfd);
  return 0;
}

#include <sys/socket.h>
#include <cstdio>
#include <cstdlib>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <unistd.h>
#include <cstring>
 
#define TEST
 
static int socketfd;
static void handleSIGINT(int sig) {
  close(socketfd);
  kill(0,SIGKILL);  
 
}
 
int main() {
  char buffer[10];
  if((socketfd=socket(AF_INET,SOCK_DGRAM,0))==-1) {
    perror("socket error message : ");
    exit(0);
  }
  struct sigaction actionplan;
  sigemptyset(&actionplan.sa_mask);
  actionplan.sa_flags=0x0;
  actionplan.sa_handler=handleSIGINT;
  while(sigaction(SIGINT,&actionplan,0)==-1) {
    printf("Registerring sigaction\n");
  }
 
  struct sockaddr_in server;
  server.sin_family=AF_INET;
  server.sin_addr.s_addr=inet_addr("112.145.252.108");
  server.sin_port=htons(60000);
  memset(server.sin_zero,0,8);
 
  if(bind(socketfd,(struct sockaddr*)&server,sizeof(struct sockaddr))==-1) {
    perror("bind error message : ");close(socketfd);exit(0);
  }
  /*if(listen(socketfd,5)==-1) {
    perror("listen error message : ");close(socketfd);exit(0);
  }*/
 
 
 
 
  struct sockaddr_in client;
  socklen_t size=(socklen_t)sizeof(client);
  int length;
  #ifdef TEST
    printf("Before recvfrom\n");
  #endif
  while((length=recvfrom(socketfd,buffer,sizeof(buffer),0,(struct sockaddr*)&client,&size))>0) {
    printf("%s\n",buffer);
  }
  /*while((length=read(socketfd,buffer,sizeof(buffer)))>0) {
    printf("%s\n",buffer);
  }*/
  if(length==-1) {
    perror("recvfrom error message : ");close(socketfd);exit(0);
  }
  else if(length==0) {
    printf("no message\n");
  }
  #ifdef TEST
    printf("After recvfrom\n"); 
  #endif
 
  close(socketfd);
  return 0;
}