c如何结束套接字读取

Question

I am trying to read in the server until client sends done msg. which is myVar.id==-1. I read with an infinite loop in the server until it reads done flag from the client. It reads until it gets done flag from client but it is not ending it is hanging there. any idea?

//server

sockdesc = socket(AF_INET, SOCK_STREAM, 0);
if ( sockdesc < 0 )
{
  cout << "Error creating socket" << endl;
  exit(0);
}
else{
   if ( getaddrinfo("0.0.0.0", portnum, NULL, &myinfo) != 0 )
   {
      cout << "Error getting address" << endl;
      exit(0);
   }
}
if (bind(sockdesc, myinfo->ai_addr, myinfo->ai_addrlen) < 0 ){
  cout << "Error binding to socket" << endl;
  exit(0);
}
if ( listen(sockdesc, 1) < 0 ){
  cout << "Error in listen" << endl;
  exit(0);
}
connection = accept(sockdesc, NULL, NULL);
if ( connection < 0 ){
  cout << "Error in accept" << endl;
  exit(0);
}
while(true){
    value = read(connection, (char*)&myVar, sizeof(procd));
    if (value < 0) {
      perror("ERROR reading from socket");
      exit(1);
    }
    if(myVar.id==-1){
        close(connection);
        exit(0);
    }//if
    else{
        //display what received

    }           
}

//client
while ( getline (inputFile,line) )//read a line till EOF
{       
    write(sockdesc, (char*)&myVar, sizeof(procd));  
}
myVar.id=-1;
write(sockdesc, (char*)&myVar, sizeof(procd));

Answer 1

You must also handle the condition that your client can die unexpectedly... ... In which case READ would return a zero...

Although you don't state what platform you are using, but the manual page on Linux says: If fildes refers to a socket, read() shall be equivalent to recv() with no flags set.

And the manual page for recv() says:

Return Value

Upon successful completion, recv() shall return the length of the message in bytes. If no messages are available to be received and the peer has performed an orderly shutdown, recv() shall return 0. Otherwise, -1 shall be returned and errno set to indicate the error.

Your code doesn't handle the special condition where read returns zero.

Answer 2

Your code doesn't really show enough... Note, sending structs over a socket is tricky, see this

passing a struct over TCP (SOCK_STREAM) socket in C

Here are some thoughts that might help...

while ( getline (inputFile,line) ) {       
  write(sockdesc, (char*)&myVar, sizeof(procd));  
}
myVar.id=-1;
write(sockdesc, (char*)&myVar, sizeof(procd));

I'm assuming that myVar is declared as follows procd myVar; on the stack?

I don't know what getline is doing, getline in stdio takes three arguments?What getline function are you using, if this is C this is likely a problem?

Where is getline putting the data, are one of the args to getline a pointer into myVar ?

I also have to assume that these are on the same machine using the same compiler because sending a struct in binary won't work in some cases ie if you send it from x86 to a big endian machine or to a machine who packs the struct differently things will not work. See the link I posted to earlier.

With all that said and you really need to do more error checking. I'd try the following to see if it works then work from there...

struct test {
  ssize_t id;
};
struct test payload;
payload.id=-1;  
write(sockdesc, (char*)&payload, sizeof(test));