RECV(3)                    POSIX Programmer's Manual                   RECV(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.


NNAAMMEE
       recv -- receive a message from a connected socket

SSYYNNOOPPSSIISS
       #include <sys/socket.h>

       ssize_t recv(int _s_o_c_k_e_t, void *_b_u_f_f_e_r, size_t _l_e_n_g_t_h, int _f_l_a_g_s);

DDEESSCCRRIIPPTTIIOONN
       The _r_e_c_v() function shall receive a message from a connection-mode or
       connectionless-mode socket. It is normally used with connected sockets
       because it does not permit the application to retrieve the source
       address of received data.

       The _r_e_c_v() function takes the following arguments:

       _s_o_c_k_e_t    Specifies the socket file descriptor.

       _b_u_f_f_e_r    Points to a buffer where the message should be stored.

       _l_e_n_g_t_h    Specifies the length in bytes of the buffer pointed to by the
                 _b_u_f_f_e_r argument.

       _f_l_a_g_s     Specifies the type of message reception. Values of this
                 argument are formed by logically OR'ing zero or more of the
                 following values:

                 MSG_PEEK    Peeks at an incoming message. The data is treated
                             as unread and the next _r_e_c_v() or similar function
                             shall still return this data.

                 MSG_OOB     Requests out-of-band data. The significance and
                             semantics of out-of-band data are protocol-
                             specific.

                 MSG_WAITALL On SOCK_STREAM sockets this requests that the
                             function block until the full amount of data can
                             be returned. The function may return the smaller
                             amount of data if the socket is a message-based
                             socket, if a signal is caught, if the connection
                             is terminated, if MSG_PEEK was specified, or if
                             an error is pending for the socket.

       The _r_e_c_v() function shall return the length of the message written to
       the buffer pointed to by the _b_u_f_f_e_r argument. For message-based
       sockets, such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message
       shall be read in a single operation.  If a message is too long to fit
       in the supplied buffer, and MSG_PEEK is not set in the _f_l_a_g_s argument,
       the excess bytes shall be discarded. For stream-based sockets, such as
       SOCK_STREAM, message boundaries shall be ignored. In this case, data
       shall be returned to the user as soon as it becomes available, and no
       data shall be discarded.

       If the MSG_WAITALL flag is not set, data shall be returned only up to
       the end of the first message.

       If no messages are available at the socket and O_NONBLOCK is not set on
       the socket's file descriptor, _r_e_c_v() shall block until a message
       arrives. If no messages are available at the socket and O_NONBLOCK is
       set on the socket's file descriptor, _r_e_c_v() shall fail and set _e_r_r_n_o to
       [[EEAAGGAAIINN]] or [[EEWWOOUULLDDBBLLOOCCKK]].

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _r_e_c_v() shall return the length of the
       message in bytes. If no messages are available to be received and the
       peer has performed an orderly shutdown, _r_e_c_v() shall return 0.
       Otherwise, -1 shall be returned and _e_r_r_n_o set to indicate the error.

EERRRROORRSS
       The _r_e_c_v() function shall fail if:

       EEAAGGAAIINN or EEWWOOUULLDDBBLLOOCCKK
              The socket's file descriptor is marked O_NONBLOCK and no data is
              waiting to be received; or MSG_OOB is set and no out-of-band
              data is available and either the socket's file descriptor is
              marked O_NONBLOCK or the socket does not support blocking to
              await out-of-band data.

       EEBBAADDFF  The _s_o_c_k_e_t argument is not a valid file descriptor.

       EECCOONNNNRREESSEETT
              A connection was forcibly closed by a peer.

       EEIINNTTRR  The _r_e_c_v() function was interrupted by a signal that was caught,
              before any data was available.

       EEIINNVVAALL The MSG_OOB flag is set and no out-of-band data is available.

       EENNOOTTCCOONNNN
              A receive is attempted on a connection-mode socket that is not
              connected.

       EENNOOTTSSOOCCKK
              The _s_o_c_k_e_t argument does not refer to a socket.

       EEOOPPNNOOTTSSUUPPPP
              The specified flags are not supported for this socket type or
              protocol.

       EETTIIMMEEDDOOUUTT
              The connection timed out during connection establishment, or due
              to a transmission timeout on active connection.

       The _r_e_c_v() function may fail if:

       EEIIOO    An I/O error occurred while reading from or writing to the file
              system.

       EENNOOBBUUFFSS
              Insufficient resources were available in the system to perform
              the operation.

       EENNOOMMEEMM Insufficient memory was available to fulfill the request.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The _r_e_c_v() function is equivalent to _r_e_c_v_f_r_o_m() with null pointer
       _a_d_d_r_e_s_s and _a_d_d_r_e_s_s___l_e_n arguments, and to _r_e_a_d() if the _s_o_c_k_e_t argument
       refers to a socket and the _f_l_a_g_s argument is 0.

       The _s_e_l_e_c_t() and _p_o_l_l() functions can be used to determine when data is
       available to be received.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _p_o_l_l(), _p_s_e_l_e_c_t(), _r_e_a_d(), _r_e_c_v_m_s_g(), _r_e_c_v_f_r_o_m(), _s_e_n_d(), _s_e_n_d_m_s_g(),
       _s_e_n_d_t_o(), _s_h_u_t_d_o_w_n(), _s_o_c_k_e_t(), _w_r_i_t_e()

       The Base Definitions volume of POSIX.1-2008, <<ssyyss__ssoocckkeett..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be obtained online
       at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                              RECV(3)
