Socket Back

• socket represents the end of a channel, which is used to communicate. Thus, each end like the server or a client should have its own socket
  • UDP Socket Coding
  • Original Socket Coding
• supports different protocols
  • UNIX
  • INET
  • IPX

1. Create a socket

method

int socket(int family, int type, int protocol)

parameters

• family: 協議簇
  • AF_INET
  • AF_UNIX
• type: 服務類型
  • SOCK_STREAM
  • SOCK_DGRAM
  • SOCK_RAW
• protocol: 0(default)

return value

• >0: socket descriptor
• -1: failure
• errno: wrong code

2. Socket address

data structure

/* common format */
struct sockaddr
{
    /* types of addr, usually AF_XXX */
    u_short sa_family;
    /* addr */
    char sa_data[14];
}

/* TCP/IP */
struct sockaddr_in
{
    short sin_family;    // AF_INET 
    u_short sin_port;    //port number
    struct in_addr sin_addr;    //IP addr
    char sin_zero[8];    //pending byte
}

struct in_addr
{
    union
    {
        struct{ u_char s_b1, s_b2, s_b3, s_b4;} S_un_b;
        struct{ u_short s_w1,s_w2;} S_un_w;
        u_long S_addr;
    }S_un;
}

method to convert addr between string and network format

struct sockaddr_in addr;
/* convert string to network format */
inet_aton("219.245.78.159", &addr.sin_addr);
/* convert network format to string */
cout << inet_ntoa(addr.sin_addr) << endl;

method to get socket address and port

• getsockname()
• getpeername()

3. Socket options

method

/* get options of sockets */
int getsockopt(int sockfd, int level, int optname, void* optval, sock_len *optlen)
/* set options of sockets */
int setsockopt(int sockfd, int level, int optname, void* optval, sock_len optlen)
/* set socket to blocked/non-blocked mode, set/get owners of the socket */
int fcntl(int fd, int cmd, ...)

parameters

• sockfd: socket描述符
• level: 選項級別
  • SOL_SOCKET: 通用socket選項
    • SO_KEEPALIVE: 2小時內若無數據交換, TCP協議將自動發送探測數據包來檢測網絡連接
    • SO_RCVBUF/SO_SNDBUF: 設置發送或接受緩衝區大小
    • SO_RCVTIMEO/SO_SNDTIMEO: 設置發送或接受函數的時間閾值上界
    • SO_REUSEADDR:
      • 重用處於TIME_WAIT狀態, 具有相同本地地址和端口的socket;
      • 允許同一個端口啟動同一個服務器多個實例(多個進程), 但IP不能相同;
      • 允許單個進程綁定相同的端口到多個socket上, 但IP不能相同;
      • 允許完全相同的地址和端口重複綁定, 只用於UDP的多播, 而不用於TCP;
  • IPPROTO_IP: IP選項
    • IP_HDRINCL: 是否自己建立IP數據包頭
  • IPPROTO_TCP: TCP選項
    • TCP_MAXSEG: TCP協議最大數據段長度
    • TCP_NODELAY: 小數據包是否延遲發送
• optname: 選項名字
• optval: 選項值

• optlen: 选项值長度(存放選項值長度的指針)

• fd: 文件(socket)描述符

• cmd: 執行的操作

  • F_GETFL: 獲得描述符標誌

  • F_SETFL: 參數O_NONBLOCK, 設置socket為非阻塞模式

    /* set to non-blocked mode */
    flags = fcntl(fd, F_GETFL, 0);
    flags |= O_NONBLOCK;
    fcntl(fd, F_SETFL, flags);
    /* set to blocked mode */
    flags = fcntl(fd, F_GETFL, 0);
    flags &= ^O_NONBLOCK;
    fcntl(fd, F_SETFL, flags);
    

  • F_GETOWN: 參數int*, 獲得socket的擁有者
  • F_SETOWN: 參數int, 設置socket的擁有者

return value

• 0: success
• -1: failure