send() and sendto() blocking in a file transfer program - c

Question

it seems that when i use send() function (in a TCP file transfer program) like this
while((count = recv(socketConnection, buff, 100000, 0))>0)
myfile.write(buff,count);
the function recv() just waits untill the whole data comes and exits the loop when it is no more receiving any data but in a similar program for a UDP program
while((n = recvfrom(sockfd,mesg,1024,0,(struct sockaddr *)&cliaddr,&len))>0)
myfile.write(mesg,n);
the recvfrom() function just blocks and does not exit the loop for some reason, as far as i know both recv() and recvfrom() are blocking right?? Then why the difference. Does it have something to do with the functions or just the nature of TCP,UDP(which i guess is not a reason)??
P.S. Please help me understand this guys, I'm a newbie to socket programming and networking.
EDIT: full server program for both TCP and UDP
UDP server (with recvfrom() )
int i=0;
int sockfd,n;
struct sockaddr_in servaddr,cliaddr;
socklen_t len;
char mesg[1024];
sockfd=socket(AF_INET,SOCK_DGRAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
servaddr.sin_port=htons(32000);
bind(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
ofstream myfile;
// fcntl(sockfd,F_SETFL,O_NONBLOCK);
myfile.open("2gb",ios::out);
while((n = recvfrom(sockfd,mesg,1024,0,(struct sockaddr *)&cliaddr,&len))>0)
myfile.write(mesg,n);
TCP (recv() ) server program
struct sockaddr_in socketInfo;
char sysHost[MAXHOSTNAME+1]; // Hostname of this computer we are running on
struct hostent *hPtr;
int socketHandle;
int portNumber = 8070;
//queue<char*> my_queue;
bzero(&socketInfo, sizeof(sockaddr_in)); // Clear structure memory
gethostname(sysHost, MAXHOSTNAME); // Get the name of this computer we are running on
if((hPtr = gethostbyname(sysHost)) == NULL)
{
cerr << "System hostname misconfigured." << endl;
exit(EXIT_FAILURE);
}
if((socketHandle = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
close(socketHandle);
exit(EXIT_FAILURE);
}
// std::cout<<"hi starting server";
socklen_t optlen;
int rcvbuff=262144;
optlen = sizeof(rcvbuff);
socketInfo.sin_family = AF_INET;
socketInfo.sin_addr.s_addr = htonl(INADDR_ANY);
socketInfo.sin_port = htons(portNumber); // Set port number
if( bind(socketHandle, (struct sockaddr *) &socketInfo, sizeof(socketInfo)) < 0)
{
close(socketHandle);
perror("bind");
exit(EXIT_FAILURE);
}
listen(socketHandle, 1);
int socketConnection;
if( (socketConnection = accept(socketHandle, NULL, NULL)) < 0)
{
exit(EXIT_FAILURE);
}
close(socketHandle);
time_start(boost::posix_time::microsec_clock::local_time());
int rc = 0; // Actual number of bytes read
int count=0;
char *buff;
int a=100000;
buff=new char[a];
ofstream myfile;
myfile.open("345kb.doc",ios::out|ios::app);
if(myfile.is_open())
{
long i=0;
while((count = recv(socketConnection, buff, 100000, 0))>0)
{
myfile.write(buff,count);
}}

Answer 1

the function recv() just waits untill the whole data comes and exits the loop when it is no more receiving any data
recv() on a TCP connection returns 0 when the sending side has closed the connection and this is the condition for your loop to terminate.
for a UDP program the recvfrom() function just blocks and does not exit the loop for some reason,
Because UDP is a connection-less protocol hence there is no special return code from recv() for a closed UDP connection. Unless someone sends you a 0-length datagram.

Answer 2

recv() will end the loop because at the other side the socket is closed, so recv() will return 0 (socket gracefully closed) whereas, recvfrom that does not have that signal, it does not know about closing, because it's an unconnected socket. It's stay there until it receives a packet or timeout, with UDP you need a way to tell that the communication is over (finish).