TCP_ECHO_APP 분석

1. TCP_ECHO_APP 분석 JSYOON 2010. 1. 6

2. Buffer for send/recv in TCP • Packets are not discrete data in TCP.They are flow ! recv ( socket, app_buff, sizeof(app_buff), flags) returns recv_length Server side Flow Control by TCP Client side APP Recv_Buffer Send_Buffer APP Send_Buffer Recv_Buffer send ( socket, app_buff, sizeof(app_buff), flags) returns send_length

3. Example • APP_Buff size: 5 send ( socket, app_buff, sizeof(app_buff), flags) returns send_length Server side Flow Control by TCP Client side abcde APP Recv_Buffer Send_Buffer APP APP_Buff APP_Buff Send_Buffer Recv_Buffer recv ( socket, app_buff, sizeof(app_buff), flags) returns recv_length

4. recvn( ) • recvn(socket ID, stored buffer, buffer size, flags) • Loop until (left buffer size > 0) • take amount of left buffer size from TCP_RECV_BUFFERthen return recv_size • if recv_size is zero, it doesn’t do anything • left buffer size is reduced by recv_size • pointer has to increase as recv_size • int • recvn(SOCKET s, char *buf, int len, int flags) • { • int received; • char *ptr = buf; • int left = len; • while (left > 0) • { • received = recv(s, ptr, left, flags); • if (received == SOCKET_ERROR) • { • return SOCKET_ERROR; • } • else if (received == 0) • { • break; • } • left -= received; • ptr += received; • } • return (len - left); • }

5. Modified recvn( ) • while (1) • {r_len=recv(sock, r_buf, BUFSIZE, 0); • if (r_len==0 || r_len==s_len) • { • break; • } • } • Do Loop • Take data from TCP_RECV_BUFFER as much as sizeof(r_buf) • If recv_data size is zero or recv_data is the same as sent data size, then the loop is finished