Office 2010 Serial accept(2) accept connection on
 

accept(two) - Linux guy page Name
accept - accept a connection on a socket
Synopsis
#include <systypes.h>
#include <syssocket.h>
int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
Description The accept() system call is used with connection-based socket types (SOCK_STREAM, SOCK_SEQPACKET). It extracts the first connection
request about the queue of pending connections, creates a new connected socket, and returns a new file descriptor referring to that socket. The newly created
socket is not in the listening state. The original socket sockfd is unaffected by this call.
The argument sockfd is a socket that has been created with socket(two), bound to a local address with bind(two), and is
listening for connections after a listen(two).
The argument addr is a pointer to a sockaddr structure. This structure is filled in with the address of the peer socket, as known to the
communications layer. The exact format of the address returned addr is determined by the socket's address family (see socket(2) and the
respective protocol guy pages). The addrlen argument is a value-result argument: it should initially contain the size of the structure pointed to by
addr; on return it will contain the actual length (in bytes) of the address returned. When addr is NULL nothing is filled in.
If no pending connections are present about the queue, and the socket is not marked as non-blocking, accept() blocks the caller until a connection is
present. If the socket is marked non-blocking and no pending connections are present about the queue, accept() fails with the error EAGAIN.
In order to be notified of incoming connections on a socket, you can use select(2) or poll(two). A readable event will be
delivered when a new connection is attempted and you may then call accept() to get a socket for that connection. Alternatively, you can set the socket
to deliver SIGIO when activity occurs on a socket; see socket(7) for details.
For certain protocols which require an explicit confirmation, such as DECNet, accept() can be thought of as merely dequeuing the next connection
request and not implying confirmation. Confirmation can be implied by a normal read or write on the new file descriptor, and rejection can be implied by
closing the new socket. Currently only DECNet has these semantics on Linux.
Notes
There may not always be a connection waiting after a SIGIO is delivered or
select(2) or poll(two) return a readability event because the connection might have been removed by an asynchronous network error or
another thread before accept() is called. If this happens then the call will block waiting for the next connection to arrive. To ensure that
accept() never blocks, the passed socket sockfd needs to have the O_NONBLOCK flag set (see socket(7)).
Return Value
On success, accept() returns a non-negative integer that is a descriptor for the
accepted socket. On error, -1 is returned, and errno is set appropriately.
Error Handling
Linux accept() passes already-pending network errors around the new socket as an error
code from accept(). This behaviour differs from other BSD socket implementations. For reliable operation the application should detect the network
errors defined for the protocol after accept() and treat them like EAGAIN by retrying. In case of TCPIP these are ENETDOWN,
EPROTO, ENOPROTOOPT, EHOSTDOWN, ENONET, EHOSTUNREACH, EOPNOTSUPP, and ENETUNREACH.
Errors
accept() shall fail if: EAGAIN or EWOULDBLOCK
The socket is marked non-blocking and no connections are present to be accepted.
EBADF
The descriptor is invalid.
ECONNABORTED
A connection has been aborted.
EINTR
The system call was interrupted by a signal that was caught before a valid connection arrived.
EINVAL
Socket is not listening for connections, or addrlen is invalid (e.g., is negative).
EMFILE
The per-process limit of open file descriptors has been reached.
ENFILE
The system limit around the total number of open files has been reached.
ENOTSOCK
The descriptor references a file, not a socket.
EOPNOTSUPP
The referenced socket is not of type SOCK_STREAM.
accept() may fail if: EFAULT
The addr argument is not in a writable part of the user address space.
ENOBUFS, ENOMEM
Not enough free memory. This often means that the memory allocation is limited by the socket buffer limits, not by the system memory.
EPROTO
Protocol error.
Linux accept() may fail if: EPERM
Firewall rules forbid connection.
In addition, network errors for the new socket and as defined for the protocol may be returned. Various Linux kernels can return other errors such as
ENOSR, ESOCKTNOSUPPORT, EPROTONOSUPPORT, ETIMEDOUT. The value ERESTARTSYS may be seen during a trace.
Conforming to
SVr4,Genuine Office 2007, 4.4BSD (accept() first appeared in 4.2BSD).
On Linux, the new socket returned by accept() does not inherit file status flags such as O_NONBLOCK and O_ASYNC from the
listening socket. This behaviour differs from the canonical BSD sockets implementation. Portable programs should not rely on inheritance or non-inheritance of
file status flags and always explicitly set all required flags about the socket returned from accept().
Note
The third argument of accept() was originally declared as an 'int *' (and is that under libc4
and libc5 and on many other systems like 4.x BSD, SunOS 4, SGI); a POSIX.1g draft standard wanted to change it into a 'size_t *', and that is what it is for
SunOS 5. Later POSIX drafts have 'socklen_t *', and so do the Single Unix Specification and glibc2. Quoting Linus Torvalds:
"_Any_ sane library _must_ have "socklen_t" be the same size as int. Anything else breaks any BSD socket layer stuff. POSIX initially did make it a
size_t, and I (and hopefully others, but obviously not too many) complained to them very loudly indeed. Making it a size_t is completely broken, exactly
because size_t very seldom is the same size as "int" on 64-bit architectures,Office 2010 Serial, for example. And it has to be the same size as "int" because that's what
the BSD socket interface is. Anyway, the POSIX people eventually got a clue, and created "socklen_t". They shouldn't have touched it in the first place, but
once they did they felt it had to have a named type for some unfathomable reason (probably somebody didn't like losing face over having done the original
stupid thing, so they silently just renamed their blunder)."
See Also
bind(two), connect(two),Office Pro Plus 2010 Key, listen(two), select(2),
socket(2) Referenced By
capabilities(7),
ddp(7),Office 2007 Professional Plus Key,
getpeername(2),Office 2010 Pro Plus,
getsockname(two),
getsockopt(2),
ip(7),
perlfunc(1),
pth(3),
recv(two),
sctp(7),
select_tut(two),
send(2),
socketcall(2),
syscalls(2),
tcp(7)