.TH socket_fastopen_connect4 3
.SH NAME
socket_fastopen_connect4 \- make a TCP connection and send some data
.SH SYNTAX
.B #include <libowfat/socket.h>

ssize_t \fBsocket_fastopen_connect4\fP(int \fIs\fR,const char \fIip\fR[4],uint16 \fIport\fR,
                                 const char* \fIbuf\fR,size_t \fIlen\fR);
.SH DESCRIPTION
socket_fastopen_connect4 attempts to make a connection from TCP socket \fIs\fR to
TCP port \fIport\fR on IP address \fIip\fR.  If that succeeds, it
attempts to send \fIlen\fR bytes from \fIbuf\fR.

The difference to calling socket_connect4 followed by write is that, on
platforms supporting TCP Fast Open, socket_fastopen_connect4 will send
the first data packet in the third packet of the TCP handshake, saving
one useless ACK packet in network traffic.

This is only useful for protocols where the client sends the first
bytes.

socket_connect4 may return
.sp 1
.IP \(bu
>=0, to indicate that the connection succeeded and this many bytes were
sent.
.IP \(bu
-1, setting errno to error_inprogress or error_wouldblock, to indicate
that the socket is non-blocking
.IP \(bu
-1, setting errno to something else, to indicate that the connection
failed (and failed immediately, if the socket is non-blocking).
.PP

When a background connection succeeds or fails, \fIs\fR becomes
writable; you can use socket_connected to see whether the connection
succeeded.  If the connection failed, socket_connected returns 0,
setting errno appropriately.

Once a TCP socket is connected, you can use the read and write
system calls to transmit data.

You can call socket_connect4 without calling socket_bind4.  This has the
effect as first calling socket_bind4 with IP address 0.0.0.0 and port 0.

.SH EXAMPLE
  #include <libowfat/socket.h>

  int \fIs\fR;
  char \fIip\fR[4];
  uint16 \fIp\fR;

  \fIs\fR = socket_tcp4();
  socket_bind4(s,ip,p);
  socket_fastopen_connect4(s,ip,p,"hello",5);

.SH "SEE ALSO"
socket_connect4(3), socket_fastopen_connect6(3), socket_fastopen(3)