asked on

receiving

My code is unstable. Sometimes it works, sometimes it doesn't. I guess it depends on network speed or something else.

So please help to improve it. tks a lot.

If run debug, I can see some thing weird:
+ BlockLength always equa 0 after read( newsockfd,&BlockLength, sizeof(int))
+ result is alway equal 1 after read(newsockfd,buffer,BUFFER_SEND)

however, result equal 2048 after fwrite (buffer,1,BUFFER_SEND,fp);
I need your explanation here.
Server crashes because of strncpy().

client.c
server.c

sarabande

i don't know whether it is the only problem but the

strcpy(buffer2,buffer);

is bad cause it requires a terminating zero char at end of buffer.

you only were reading BUFFER_SEND bytes from socket what is 2048 bytes. that doesn't include the '\0' you were needing for strcpy.

i still think it would be better you would send size of message (and perhaps message identifier) prior to sending the message.

then your receiver could read first the size of message:

int n;
     unsigned int size_to_read = 0;

     n = read(newsockfd, (char*)&size_to_read,sizeof(unsigned int));
    
     if (n != (int)sizeof(unsigned int))
         return error();

     unsigned int message_id = 0;

     n = read(newsockfd, (char*)&message_id,sizeof(unsigned int));
    
     if (n != (int)sizeof(unsigned int))
         return error();
    
     // if we were here we have total size of message and message id
     // first we check if message_id is the expected

    if (message_id != 3 || size_to_read == 0 || size_to_read >= BUFFER_SEND)   // assuming file 
         return error();

    unsigned int nread = 0;
    
    while (nread < size_to_read)
    {
          n = read(newsockfd, &buffer[nread], size_to_read - nread);
          if (n <= 0)
               return error();
          nread += n;
    }
    // we add the terminating zero here
    buffer[size_to_read] = '\0';

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the last while loop is needed cause tcpip may not transfer the whole send buffer but only parts of it.

Sara

phoffric

The client is sending a message (Total Number Of Files), a short message, and the server is trying to read BUFFER_SEND bytes (a long message). If there are timing differences such that the server wasn't running for awhile after the connection was accepted and if the client subsequently sent multiple messages, then the server code below might pick up part of the subsequent messages. And your code, as written, would lose part of those subsequent messages.

client:

void sendFileAllFiles ( SOCKET sock,  list<string>& myList)
{
        std::stringstream totalfile;

        cout<<" in sendFile myList size: "<<myList.size()<<endl;       
        totalfile << myList.size();
        string a = totalfile.str();
        char *tf = (char*)malloc(sizeof(char) *a.length() +1);
        memset(tf,'\0',sizeof(char)*a.length()+1);
        strcpy(tf,a.c_str());
        send(sock, tf,a.size(),0);

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server:

int GetTotalFile (SOCKET sock)
{
        char buffer[BUFFER_LEN]="\0";
        int n;
	n = read(sock,buffer,BUFFER_SEND);