The design and implementation of tcp-ip. 07 Lwip Interface (RAW API)

Transcription

1 The design and implementation of tcp-ip 07 Lwip Interface (RAW API)

2 Lwip API 3 RAW API Netconn / Socket API RTOS No need Need (need IPC) Control based on PCB socket Calling methods Callback Close to the windows or Linux socket APIs Structure Core APIs Higher level APIs Application Lower memory devices Application without RTOS Developers has more control Higher memory devices Porting of protocols or application coming from Linux/windows complexity ++ + Memory -- + IPC: Inter process communication Presentation Title 13/08/2014

3 The application using RAW API 4 Operation Not in a sequential manner. The callback function is associated with a particular connection. When a packet arrives in the connection, the callback function is called by the stack. For any long running computations, it use splitting the application into two parts(communication and computation) to overcome. Presentation Title 13/08/2014

4 How to build TCP server (RAW API) 6 Initialization Create socket(ip and Port) Register the accept callback Processing Register processing callback for new connection Programming processing code Close Active close Passive close Note: Need processing both connection and data transfer. Data can be transferred only when connection is established. Presentation Title 13/08/2014

5 Client lwip Action lwip Server RAW TCP state Description for RAW API <= tcp_new() CLOSED Create new tcp pcb <= tcp_bind() Bind port number <= tcp_listen() LISTEN Create listening endpoint(new lpcb) <=tcp_accept() Set accept callback connect SYN <= tcp_arg() Set callback arg(ptr to lpcb) Client connects to server, send SYN SYN + ACK allocate new pcb SYN RCVD lwip creates new pcb lwip responds SYN+ACK ACK Client responds ACK ESTABLISH ED Server receive the expected ACK, complete 3-way handshake. Invoke accept callback <=tcp_accepted() lwip notifies app(pcb) Server accepts connection <=tcp_arg() Set callback arg(ptr to pcb) <=tcp_recv() Server sets recv callback <=tcp_err() Server sets err/abort callback mark PCB active <=tcp_sent() Register in the accept callback Server sets sent callback Data can be Tx/Rx

6 Connection Establishment(Remote Server/lwIP local client) Server lwip Action lwip Server RAW TCP state Description for RAW API listen <= tcp_new() Closed Create new tcp pcb [<= tcp_bind()] Bind port number, optionally <= tcp_arg() Set callback arg(ptr to pcb) <= tcp_recv() Client sets recv callback <= tcp_sent() <= tcp_err() <= tcp_connect() May done in the connected callback Client sets sent callback Client sets err/abort callback Connect, register callback SYN SYN_SENT lwip sends SYN SYN+ACK Server responds SYN+ACK ACK ESTABLISH ED lwip sends ACK, complete 3-way handshake. Invoke connected callback mark PCB active 8

7 Data Transfer Side lwip Action lwip Side TCP state Description for RAW API Send Data Established Data can be Tx/Rx Invoke recv callback LwIP notices the app Application through callback Side lwip Action lwip Side TCP state Description for RAW API Data <= tcp_write() Established Data can be Tx/Rx Invoke sent callback LwIP notices the app Application through callback 9

8 Connection Termination (Active Close) Passive Side lwip Action lwip Active Side TCP state Description for RAW API Established <= tcp_close Active close FIN FIN WAIT1 Active side sent FIN. ACK FIN WAIT2 Passive side responds ACK. [send=>] Close Passive side sent data(if any). FIN Passive side sent FIN ACK TIME WAIT Active side responds ACK Invoke recv callback (NULL) LwIP frees private data structures TIME_WAIT timer expires CLOSED LwIP frees PCB 10

9 Active Side Close => Connection Termination (Passive Close) lwip Action lwip Passive Side TCP state Established Description for RAW API Active side close connection FIN ACK FIN ACK Invoke callback [<= tcp_write()] <= tcp_close() CLOSE WAIT LAST ACK CLOSED Active side send FIN lwip Passive Side responds ACK (Active side has been closed) LwIP frees private data structures Passive side send data(if any) Passive side close connection Passive side send FIN Active side responds ACK (Passive side enter closed) 11

10 Initialization 12 /* The initialization function. */ void tcp_server_init(void) { struct tcp_pcb *pcb; pcb = tcp_new(); / * Create a new TCP PCB. */ tcp_bind(pcb, IP_ADDR_ANY, 5000); /* Bind the PCB to TCP port */ Create socket (IP and port) IP: local IP Port: 5000 tcp_listen(pcb); /* Change TCP state to LISTEN. */ Add this pcb to tcp_pcb_listen_list } /* Set up tcp_server_accet() function to be called when a new connection arrives. */ tcp_accept(pcb, tcp_server_accept, NULL); Important! We know new connection has been established. Code optimization Any error may occur! So the better writing is adding some code like this: if(pcb!= NULL) { } Presentation Title 13/08/2014

11 Processing 13 /* This is the callback function that is called when a connection has been accepted. */ arg Additional argument to pass to the callback function according to tcp_arg */ newpcb The new connection pcb */ err An error code if there has been an error accepting. */ err_t tcp_server_accept (void *arg, struct tcp_pcb *newpcb, err_t err); { tcp_arg(newpcb, arg); tcp_recv(newpcb, tcp_server_recv); tcp_sent(newpcb, tcp_server_sent) tcp_err(newpcb, tcp_server_error); tcp_poll(newpcb, tcp_server_poll, 1); Registering processing function for new connection. Always tcp_recv is used. } return ERR_OK; Presentation Title 13/08/2014

12 Processing 14 /* This is the callback function that is called when a connection recevies data. */ arg Additional argument to pass to the callback function according to tcp_arg */ newpcb The connection pcb which received data */ p The received data (or NULL when the connection has been closed!) */ err An error code if there has been an error accepting. */ err_t tcp_server_recv(void *arg, struct tcp_pcb *tpcb, struct pbuf *p, err_t err) { /* Add your processing code, you have already have */ /* 1. the information about connect(pcb) */ /* 2. the pointer to data */ } Think! When does the other callback functions are called? Presentation Title 13/08/2014

13 Close 15 Active close err_t tcp_close(struct tcp_pcb *pcb) Passive close Note you can trigger receive callback once a time! Presentation Title 13/08/2014

14 The design and implementation of tcp-ip 07 Lwip Interface (RAW API)