Introduction to Socket Programming Advisor: Quincy Wu Speaker: Kuan-Ta Lu Date: Nov. 25, 2010

Socket Interface  是一種應用程式介面 (API) ，介於 application 層與 transport 層之間，並且提供標準的函式以符合不同的網 路傳輸規格。  最早的 Socket Interface 於 1982 年由柏克萊大學為支援 UNIX 作業系統上的 TCP/IP 應用所開發的 Socket 介面， 稱為 Berkeley Socket Interface ，而其軟體則稱為 Berkeley Software Distribution(BSD) 。  Windows Sockets ，簡稱 Winsock ，是以 UNIX 系統上 Berkeley Sockets 的函式為基礎，並加上了一些符合視 窗環境特性的函式。 2

Socket Interface (con.) 3

Connection-oriented socket (TCP) 4

socket()  Create an endpoint for communication  int socket( int domain, int type, int protocol );  domain PF_INET for IPv4 PF_INET6 for IPv6  type SOCK_STREAM for reliable TCP sockets SOCK_DGRAM for unreliable fast UDP sockets  protocol default: 0 5

bind()  Bind a name to a socket  int bind( int s, const struct sockaddr * name, socklen_t namelen );  s The file descriptor to be bound.  name A pointer to the sockaddr structure that holds the address to be bound to the socket.  namelen The length of the sockaddr structure pointed to by name. 6

bind() (con.)  struct sockaddr { sa_family_t sa_family; // address family, AF_xxx char sa_data[14]; // 14 bytes of protocol address };  sa_family represents address family  sa_data contains data about address 7

bind() (con.)  struct in_addr { uint32_t s_addr; // 32bit IPv4 address (4 bytes) // network byte ordered }; struct sockaddr_in { sa_family_t sin_family; // Address family (2 bytes) in_port_t sin_port; // Port number (2 bytes) struct in_addr sin_addr; // Internet address (4 bytes) char sin_zero[8]; // Empty (for padding) (8 bytes) } 8

bind() (con.)  Example: struct sockaddr_in servaddr; servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY);htonl servaddr.sin_port = htons(13); Bind (sockfd, (struct sockaddr *) & servaddr, sizeof(servaddr) ); 9

listen()  Listen for connections on a socket  int listen( int s, int backlog );  s The descriptor for the socket that you want to listen on.  backlog The maximum length that the queue of pending connections may grow to. 10

connect()  Initiate a connection on a socket  int connect( int s, const struct sockaddr * name, socklen_t namelen );  s The descriptor of the socket on which to initiate the connection.  name The name of the socket to connect to for a SOCK_STREAM connection.  namelen The length of the name, in bytes. 11

accept()  Accept a connection on a socket  int accept( int s, struct sockaddr * addr, socklen_t * addrlen );  s The listen()ing socket descriptor.  addr This is filled in with the address of the site that's connecting to you.  addrlen This is filled in with the sizeof() the structure returned in the addr parameter. You can safely ignore it if you assume you're getting a struct sockaddr_in back, which you know you are, because that's the type you passed in for addr. 12

send()  Send a message to a connected socket  ssize_t send( int s, const void * msg, size_t len, int flags );  msg A pointer to the message that you want to send.  len The length of the message.  flags Set flags to zero if you want it to be "normal" data. 13

recv()  Receive a message from a socket  ssize_t recv( int s, void * buf, size_t len, int flags );  buf A pointer to a buffer where the function can store the message.  len The size of the buffer.  flags Set flags to 0 if you want it to be a regular vanilla recv(). 14

close()  Close a socket descriptor  int close(int s);  Windows users: the function you need to use is called closesocket(), not close(). 15

Connectionless socket (UDP) 16

sendto()  Send a message to a socket at a specific address  ssize_t sendto( int s, const void * msg, size_t len, int flags, const struct sockaddr * to, socklen_t tolen );  to A pointer to a sockaddr object that specifies the address of the target.  tolen A socklen_t object that specifies the size of the to address. 17

recvfrom()  Receive a message from the socket at a specified address  ssize_t recvfrom( int s, void * buff, size_t len, int flags, struct sockaddr * from, socklen_t * fromlen );  from NULL, or a pointer to a sockaddr object where the function can store the source address of the message.  fromlen A pointer to a socklen_t object that specifies the size of the from buffer. The function stores the actual size of the address in this object. 18

inet_ntop() inet_pton()  Convert IP addresses to human-readable form and back  const char *inet_ntop(int af, const void *src, char *dst, socklen_t size); int inet_pton(int af, const char *src, void *dst);  The "n" stands for "network", and "p" for "presentation".  These functions are for dealing with human-readable IP addresses and converting them to their binary representation for use with various functions and system calls. 19

IPv4 v.s IPv6 Socket 20

Demo  Environment  OS: Fedora 14  Client(homer): :e10:6840:21:4a5b:39ff:fed6:1b73  Server(sinbad): :e10:6840:21:21a:92ff:fe02:3495  Socket TCP (IPv4): tcp4_client.c, tcp4_server.ctcp4_client.ctcp4_server.c  Socket UDP (IPv4): udp4_client.c, udp4_server.cudp4_client.cudp4_server.c  Socket TCP (IPv6): tcp6_client.c, tcp6_server.ctcp6_client.ctcp6_server.c 21

Reference h/tcpip.htmlhttp:// h/tcpip.html 3. socket_programming.ppthttp://ms11.voip.edu.tw/~jryan/ref/ chenglin- socket_programming.ppt mming.pdfhttp://ms11.voip.edu.tw/~jryan/ref/Introduction_to_IPv6_progra mming.pdf 6. Programming_&_IPv6_Translation Middleware.pdfhttp://ms11.voip.edu.tw/~jryan/ref/Windows_Socket Programming_&_IPv6_Translation Middleware.pdf 7. tw/%E4%BC%AF%E5%85%8B%E5%88%A9%E5%A5%97%E6% 8E%A5%E5%AD%97http://zh.wikipedia.org/zh- tw/%E4%BC%AF%E5%85%8B%E5%88%A9%E5%A5%97%E6% 8E%A5%E5%AD% thttp://ms11.voip.edu.tw/~jryan/ref/ipv6_socket_programming.pp t 22

Thanks for listening~ 23

htons() htonl() ntohs() ntohl()  Convert multi-byte integer types from host byte order to network byte order  uint32_t htonl(uint32_t hostlong); uint16_t htons(uint16_t hostshort); uint32_t ntohl(uint32_t netlong); uint16_t ntohs(uint16_t netshort);  htons()host to network short  htonl()host to network long  ntohs()network to host short  ntohl()network to host long 24