C语言socket connect()函数（未完）

Posted 2022-03-28 Dontla

参考文章：C网络编程socket之connect函数

需研究下这个函数超时多久才返回。。。

文章目录

• • man 2 文档解释

man 2 文档解释

CONNECT(2)                                                           Linux Programmer's Manual                                                          CONNECT(2)

NAME
       connect - initiate a connection on a socket	//初始化套接字上的连接

SYNOPSIS
       #include <sys/types.h>          /* See NOTES */
       #include <sys/socket.h>

       int connect(int sockfd, const struct sockaddr *addr,
                   socklen_t addrlen);

DESCRIPTION
       The  connect()  system call connects the socket referred to by the file descriptor sockfd to the address specified by addr.  The addrlen argument specifies the size of addr.  The format of the address in addr is determined by the address space of the socket sockfd; see socket(2) for further details.
       //connect（）系统调用将文件描述符sockfd引用的套接字连接到addr指定的地址。addrlen参数指定addr的大小。addr中地址的格式由socket sockfd的地址空间决定；详见插座（2）。

       If the socket sockfd is of type SOCK_DGRAM, then addr is the address to which datagrams are sent by default, and the only address from which datagrams  are received.  If the socket is of type SOCK_STREAM or SOCK_SEQPACKET, this call attempts to make a connection to the socket that is bound to the address spec‐ ified by addr.

       Generally, connection-based protocol sockets may successfully connect() only once; connectionless protocol sockets may  use  connect()  multiple  times  to change  their  association.   Connectionless  sockets may dissolve the association by connecting to an address with the sa_family member of sockaddr set to AF_UNSPEC (supported on Linux since kernel 2.2).

RETURN VALUE
       If the connection or binding succeeds, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       The following are general socket errors only.  There may be other domain-specific error codes.

       EACCES For UNIX domain sockets, which are identified by pathname: Write permission is denied on the socket file, or search permission is denied for one  of the directories in the path prefix.  (See also path_resolution(7).)

       EACCES, EPERM
              The  user  tried  to  connect  to a broadcast address without having the socket broadcast flag enabled or the connection request failed because of a local firewall rule.

       EADDRINUSE
              Local address is already in use.

       EADDRNOTAVAIL
              (Internet domain sockets) The socket referred to by sockfd had not previously been bound to an address  and,  upon  attempting  to  bind  it  to  an ephemeral  port,  it  was  determined  that  all  port  numbers  in  the  ephemeral  port  range  are  currently  in  use.   See  the  discussion of /proc/sys/net/ipv4/ip_local_port_range in ip(7).

       EAFNOSUPPORT
              The passed address didn't have the correct address family in its sa_family field.

       EAGAIN Insufficient entries in the routing cache.

       EALREADY
              The socket is nonblocking and a previous connection attempt has not yet been completed.

       EBADF  The file descriptor is not a valid index in the descriptor table.

       ECONNREFUSED
              No-one listening on the remote address.

       EFAULT The socket structure address is outside the user's address space.

       EINPROGRESS
              The socket is nonblocking and the connection cannot be completed immediately.  It is possible to select(2) or poll(2) for  completion  by  selecting the  socket  for  writing.   After  select(2)  indicates writability, use getsockopt(2) to read the SO_ERROR option at level SOL_SOCKET to determine whether connect() completed successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is one of the usual error codes listed here, explaining  the reason for the failure).

       EINTR  The system call was interrupted by a signal that was caught; see signal(7).

       EISCONN
              The socket is already connected.

       ENETUNREACH
              Network is unreachable.

       ENOTSOCK
              The file descriptor sockfd does not refer to a socket.

       EPROTOTYPE
              The  socket  type does not support the requested communications protocol.  This error can occur, for example, on an attempt to connect a UNIX domain datagram socket to a stream socket.

       ETIMEDOUT
              Timeout while attempting connection.  The server may be too busy to accept new connections.  Note that for IP sockets the timeout may be  very  long when syncookies are enabled on the server.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD, (the connect() function first appeared in 4.2BSD).

NOTES
       POSIX.1  does  not  require  the inclusion of <sys/types.h>, and this header file is not required on Linux.  However, some historical (BSD) implementations required this header file, and portable applications are probably wise to include it.

       The third argument of connect() is in reality an int (and this is what 4.x BSD and libc4 and libc5 have).  Some POSIX confusion  resulted  in  the  present socklen_t, also used by glibc.  See also accept(2).

       If connect() fails, consider the state of the socket as unspecified.  Portable applications should close the socket and create a new one for reconnecting.

EXAMPLE
       An example of the use of connect() is shown in getaddrinfo(3).

SEE ALSO
       accept(2), bind(2), getsockname(2), listen(2), socket(2), path_resolution(7)

COLOPHON
       This  page  is part of release 4.04 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the latest version
       of this page, can be found at http://www.kernel.org/doc/man-pages/.

Linux                                                                       2015-12-28                                                                  CONNECT(2)