1RECV(2)                       System Calls Manual                      RECV(2)
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NAME

6       recv, recvfrom, recvmsg - receive a message from a socket
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SYNOPSIS

9       #include <sys/types.h>
10       #include <sys/socket.h>
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12       cc = recv(s, buf, len, flags)
13       int cc, s;
14       char *buf;
15       int len, flags;
16
17       cc = recvfrom(s, buf, len, flags, from, fromlen)
18       int cc, s;
19       char *buf;
20       int len, flags;
21       struct sockaddr *from;
22       int *fromlen;
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24       cc = recvmsg(s, msg, flags)
25       int cc, s;
26       struct msghdr msg[];
27       int flags;
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DESCRIPTION

30       Recv, recvfrom, and recvmsg are used to receive messages from a socket.
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32       The  recv  call  is  normally used only on a connected socket (see con‐
33       nect(2)), while recvfrom and recvmsg may be used to receive data  on  a
34       socket whether it is in a connected state or not.
35
36       If  from  is  non-zero, the source address of the message is filled in.
37       Fromlen is a value-result parameter, initialized to  the  size  of  the
38       buffer  associated  with  from,  and modified on return to indicate the
39       actual size of the address stored there.  The length of the message  is
40       returned  in  cc.  If a message is too long to fit in the supplied buf‐
41       fer, excess bytes may be discarded depending on the type of socket  the
42       message is received from (see socket(2)).
43
44       If  no messages are available at the socket, the receive call waits for
45       a message to arrive, unless the socket is nonblocking (see ioctl(2)) in
46       which  case a cc of -1 is returned with the external variable errno set
47       to EWOULDBLOCK.
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49       The select(2) call may be used to determine when more data arrives.
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51       The flags argument to a recv call is formed by or'ing one  or  more  of
52       the values,
53
54              #define  MSG_OOB         0x1    /* process out-of-band data */
55              #define  MSG_PEEK        0x2    /* peek at incoming message */
56
57       The  recvmsg  call  uses  a  msghdr structure to minimize the number of
58       directly supplied parameters.  This structure has the  following  form,
59       as defined in <sys/socket.h>:
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61              struct msghdr {
62                   caddr_t   msg_name;      /* optional address */
63                   int  msg_namelen;        /* size of address */
64                   struct    iovec *msg_iov;          /* scatter/gather array */
65                   int  msg_iovlen;         /* # elements in msg_iov */
66                   caddr_t   msg_accrights;      /* access rights sent/received */
67                   int  msg_accrightslen;
68              };
69
70       Here  msg_name  and  msg_namelen specify the destination address if the
71       socket is unconnected; msg_name may be given as a null  pointer  if  no
72       names are desired or required.  The msg_iov and msg_iovlen describe the
73       scatter gather locations, as described in read(2).  A buffer to receive
74       any  access  rights  sent  along  with  the  message  is  specified  in
75       msg_accrights, which has length msg_accrightslen.   Access  rights  are
76       currently limited to file descriptors, which each occupy the size of an
77       int.
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RETURN VALUE

80       These calls return the number of bytes received,  or  -1  if  an  error
81       occurred.
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ERRORS

84       The calls fail if:
85
86       [EBADF]             The argument s is an invalid descriptor.
87
88       [ENOTSOCK]          The argument s is not a socket.
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90       [EWOULDBLOCK]       The  socket  is marked non-blocking and the receive
91                           operation would block.
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93       [EINTR]             The receive was interrupted by delivery of a signal
94                           before any data was available for the receive.
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96       [EFAULT]            The  data  was specified to be received into a non-
97                           existent or protected part of the  process  address
98                           space.
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SEE ALSO

101       fcntl(2), read(2), send(2), select(2), getsockopt(2), socket(2)
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1054.2 Berkeley Distribution        May 23, 1986                          RECV(2)
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