HELP! Very Strange escape sequence problem

[tsa45]

To make things simple: My program as a server recieves message from client using recv call. I use C++, GNU socket APIs under Ubuntu.

I let recv() recieve 1 charactor in the incoming message per iteration, in the recv loop. And if the recieved byte is an escape sequence such as "\n" and "\r", the server should detect it.
The problem is, sometimes it works and sometimes it fails....

following simplified code is what I did. Sometimes it works perfect, when "\n" or "\r" are recieved, the program will correctly output "n" or "r". However, sometimes it fails to detect the current recieved buffer equals to "\n" or "\r", while mbuffer IS "\n" or "\r".

The correct output is like:
---mbuffer: '
---'
---n

The failure output is like:
---mbuffer:'
---'


mbuffer must be an line break sequance such as "\n", because the second " ' " is in a new line each time the "mbuffer" is outputted. In the failure output, mbuffer is "\n" or "\r", but the program dose not output "n" or "r"

Is that because the strcmp() is not stable?????????

while(recv(clientSoket, mbuffer,1,0)>0)
{
.......
.......
cout<<"mbuffer:"<<"'"<<*mbuffer<<"'"<<endl;


if(strcmp(mbuffer,"\r"))
 {        
    cout<<"r"<<endl;
 }
else if(strcmp(mbuffer,"\n"))                     
{       
    cout<<"n"<<endl;
                        
}

............
............
}

[kbw]

Can you post a bit more code please. We'll need to see the declaration of mbuffer and if/how it's initialised before entering the loop.

[tsa45]

The following is the way I declare mbuffer. I did not initialize it before go into recv loop

char *mbuffer=(char *)malloc(sizeof(char));

why I let size of mbuffer = 1*sizeof(char), is because everytime the recv is putting 1 charactor into mbuffer.

There is another detail. Within the loop, every time after recv puts one character it recieved into mbuffer, I append mbuffer's content into another buffer, which should be the main buffer holding all the content of the message from client. I use strcat(buffer, mbuffer); to to this task.

following is my program code so far. The thread entry function is threadEntry(void *).

/*
The Server Entry
*/
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>

#include <time.h>
#include <string.h>
#include <vector>
#include <unistd.h>
#include <iostream>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <pthread.h>
#include "MessageContext.h"
#include "Server.h"
#include <stdlib.h>
#include <errno.h>
#define MAX_BUFFER        1
#define MAX_BUFFER_TO_HOLD 256
#define SERVER_PORT        37454

using namespace std;



pthread_t listenerT;
int serverFd;
Server server;
typedef struct threadParameter
{
        int index;
        int clientSoket;
        pthread_t thread;

}PARA;

int numT; //number of thread
bool continue_;

bool mystrcmp(char *s1, const char *s2)
{
	int i=0;
	do{

		if(s1[i]!=s2[i])
			return false;



	}while(s1[i++]!='\0');
	return true;
}


void threadEntry_(void *ptr)
{

                PARA* para=(PARA *)ptr;
                ptr=NULL;
                //int index=para->index;

                int *clientSoket=(int*)malloc(sizeof(int));
                *clientSoket=para->clientSoket;
                int *numr=(int*)malloc(sizeof(int));
                    int *numn=(int*)malloc(sizeof(int));
                    int *byteRcved=(int*)malloc(sizeof(int));
                    *numr=0;
                    *numn=0;
                    *byteRcved=0;
                    int *cont=(int*)malloc(sizeof(int));
                    *cont=1;


                   pthread_t tid=para->thread;
                char *buffer=(char *)malloc(MAX_BUFFER_TO_HOLD*sizeof(char));
                char *mbuffer=(char *)malloc(MAX_BUFFER*sizeof(char));

                 memset((void *)buffer, 0, MAX_BUFFER_TO_HOLD);


                pthread_detach(tid);


cout<<"--------"<<endl;

                while(int tmp=recv(*clientSoket, mbuffer,MAX_BUFFER,0)>0&&continue_)
                {
cout<<"----"<<endl;
cout<<"mbuffer:"<<"'"<<*mbuffer<<"'"<<endl;
cout<<"numr:"<<*numr<<"numn:"<<*numn<<endl;
cout<<"cont"<<*cont<<endl;
if(mystrcmp(mbuffer,"\\"))
	cout<<"ASD"<<endl;


                        if(*cont==1)
                        {
                        *byteRcved=*byteRcved+1;
                        if(*byteRcved>=MAX_BUFFER_TO_HOLD)
                        {cout<<"out of band"<<endl;
                        break;}

                        if(mystrcmp(mbuffer,"\r"))
                        {        *numr=*numr+1;
cout<<"numr++:  "<<*numr<<endl;


                        }
                        else if(mystrcmp(mbuffer,"\n"))
                        {        *numn=*numn+1;
cout<<"numn++:  "<<*numn<<endl;
                        }
                        else
                        {        strcat(buffer, mbuffer);

                        }
                        if((*numr)>=3||(*numn)>=3)
                        {
cout<<"sent:"<<endl;
cout<<"'";
for(int i=0;i<strlen(buffer);i++)
        cout<<buffer[i];
cout<<"'"<<endl;
                                send(*clientSoket,(void *)buffer, strlen(buffer),0);
                                *cont=2;

                                if(errno!=0)
                                        cout<<"error "<<errno<<endl;


                        }

                        }

                        memset((void *)mbuffer, 0, MAX_BUFFER);
cout<<"----"<<endl;
                }




                memset(cont,0,1);
                memset((void *)mbuffer, 0, MAX_BUFFER);
                memset((void *)buffer, 0, MAX_BUFFER_TO_HOLD);
                cout<<"client exited"<<endl;

                if(buffer!=NULL)
                {        free(buffer);
                        buffer=NULL;
                }
                if(mbuffer!=NULL)
                {       free(mbuffer);
                        mbuffer=NULL;
                }

                close (*clientSoket);
                free(para);

        //        cout<<"cli"<<endl;
                free(clientSoket);
        //        cout<<"numr"<<endl;
                free(numr);
        //        cout<<"numn"<<endl;
                free(numn);
        //        cout<<"byteRcved"<<endl;
                free(byteRcved);
        //        cout<<"cont"<<endl;
                free(cont);
        //        cout<<"finish"<<endl;
//cout<<"------------"<<endl;
                pthread_exit(NULL);

}

void *threadEntry(void *ptr)
{
        threadEntry_(ptr);


}

void *listenerEntry(void *ptr)
{
        pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, (int*)0);
        pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS,(int*)0);


        numT=0;//initially,it contains a thread for detecting user EOF on server side
        int connectionFd;
        struct sockaddr_in servaddr;
        char timebuffer[MAX_BUFFER+1];
        time_t currentTime;

        serverFd=socket(AF_INET,SOCK_STREAM,0);
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family=AF_INET;
        servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
        servaddr.sin_port=htons(SERVER_PORT);

        bind(serverFd, (struct sockaddr *)&servaddr, sizeof(servaddr));

        listen(serverFd, 100);


        while(1){

                //struct sockaddr Caddr;
                connectionFd=accept(serverFd,(struct sockaddr*)NULL, NULL);

                //cout<<Caddr;
                numT++;

                PARA *para=(PARA*)malloc(sizeof(PARA));
                para->index=numT-1;
                para->clientSoket=connectionFd;


                pthread_create(&para->thread,NULL,threadEntry,(void *)para);


                cout<<"client "<<numT<<" connected"<<endl;




        }

        pthread_exit(NULL);

}


bool inputAvailable()  
{
  struct timeval tv={0L,0L};
  fd_set fds;
  FD_ZERO(&fds);
  FD_SET(0, &fds);
  return select(1, &fds, NULL, NULL, &tv);
}



int main()
{
        cout<<"**************************************"<<endl;
        cout<<"press Enter to exit"<<endl;
        cout<<"**************************************"<<endl;
        pthread_create(&listenerT,NULL,listenerEntry,(void *)NULL);
        continue_=true;
        while(!inputAvailable())
        {
        }
        continue_=false;
        if(pthread_cancel(listenerT)!=0)
                cout<<"failed to kill listener thread"<<endl;


        pthread_join(listenerT,NULL);

        cout<<"server ended"<<endl;
        close (serverFd);
}

[krjeev]

your mystrcmp() method is wrong, need to modify.
Use some existing string compare method, if you are not sure.......