Use the READ command to read data
on the specified socket. The maximum amount of data to be read is
specified by the maxlength parameter. If the socket
is in blocking mode and data is not available on the socket, the command
blocks until data arrives.
Consider the following additional information:
- If the socket is a stream socket and the length of the data returned is 0, the remote peer has closed its side of the connection.
- If the socket is a connected datagram socket, the command returns data up to the length specified by the maxlength parameter. The remainder of the datagram is discarded. To ensure that the entire datagram is received, set the maxlength parameter to 65535 or greater.
Guidelines: - For stream sockets, data is processed
as streams of information with no boundaries separating the data. The application provides record management. Applications should
place the command in a loop until all the data has been received.
- For nonblocking sockets, use the SELECT command to determine whether
there is data to be read on the socket.
Tip: If the SO_ASCII socket option is enabled,
then the data received is translated from EBCDIC to ASCII.
Format
.-,--10 000----.
>>-SOCKET--(--"READ"--,--socketid--+--------------+--)---------><
'-,--maxlength-'
Parameters
- socketid
- The socket descriptor.
- maxlength
- The maximum amount of data (in bytes) to be returned. The maxlength parameter can be a number in the range 0-100
000. By default, this parameter is set to 10 000.
Returned value
The command returns a string that contains the return
code, the maximum length of the data returned, and the data, for example, 0 19 This is sample data. The return code can be 0, a REXX socket API error number, or the REXX TCP/IP error number that is set by the socket command. The return code 0 indicates that the requested socket command was completed successfully. The data length 0 indicates that the connection was closed
by the remote peer.
See Socket call error return codes for additional information about the numeric error codes that are returned by this command.
The following REXX TCP/IP error numbers can be returned: - 4 EITNR
- 5 EIO
- 9 EBADF
- 22 EINVAL
- 35 EWOULDBLOCK
- 38 ENOTSOCK
- 45 EOPNOTSUPP
- 54 ECONNRESET
- 57 ENOTCONN
- 60 ETIMEDOUT
The following REXX socket API error numbers can be returned:- 2001 EINVALIDRXSOCKETCALL
- 2005 ESUBTASKNOTACTIVE
- 2009 ESOCKETNOTDEFINED
LE C/C++ equivalent
ssize_t read(int fs, void *buf, size_t N);
Code example
/* REXX EZARXR21 */
/*
* This sample demonstrates the use of the READ and RECV
* socket commands.
*
* To use the READ command, set the variable g_RECVCMD equal to "READ"
* to use the RECV command, set the variable g_RECVCMD equal to "RECV"
*
* The program creates a listening socket and then goes into a
* loop and blocks on the accept command. When a new connection is
* ACCEPTED the program will issue the READ or RECV command until
* the connection is terminated.
*
* If the data received is the string "DONE", then the
* program will close the accepted socket and wait for a new
* connection request.
*/
g_RECVCMD = "READ"
src = socket("INITIALIZE","MYSET01",10);
if perror(src,"INITIALIZE") = 0 then do
src = socket("SOCKET","AF_INET6","STREAM");
if perror(src,"SOCKET") = 0 then do
parse var src . l_sockid
l_name6 = "AF_INET6 54004 0 ::0 0";
src = socket("BIND", l_sockid, l_name6);
if perror(src,"BIND") = 0 then do
src = socket("LISTEN", l_sockid);
if perror(src,"LISTEN") = 0 then do
say "Listening on socket "l_sockid;
do forever
src = socket("ACCEPT", l_sockid );
if perror(src,"ACCEPT") = 0 then do
parse var src . l_newsockid . ;
l_datalen = -1;
l_Done = "FALSE";
l_totallen = 0;
l_packet = "";
/* **********************************************
* Loop around RECV|READ command until all data has
* has been received and the client closes the
* connection.
* **********************************************/
do until l_datalen = 0 | l_done = "TRUE"
src = socket(g_RECVCMD,l_newsockid,512);
if perror(src,g_RECVCMD) = 0 then do
parse var src l_retcode l_datalen l_data
if l_datalen > 0 then do
l_totallen = l_totallen + l_datalen;
if l_packet = "" then do
l_packet = l_data;
if l_packet = "DONE" then
l_done = "TRUE";
end;
else l_packet = l_packet||l_data;
end;
else do
/* ***************************************
* A data length of zero indicates the
* connection has been closed by the
* remote side
* ***************************************/
Say "Connection has been closed",
"received "l_totallen" bytes";
l_done = "TRUE";
end;
end;
else do
l_done = "TRUE";
end;
end; /* DO READ */
src = socket("CLOSE",l_newsockid);
src = perror(src,"CLOSE");
end; /* ACCEPT */
end; /* DO FOREVER */
end;
end;
end;
end; /* INITIALIZE */
src = perror(socket("TERMINATE","MYSET01"),"TERMINATE");
exit 0;
/* This routine returns -1 if the first word if arg 1 is not zero */
perror: if word(arg(1),1) = 0 then return 0; else
Say arg(2) "Error : "arg(1);
return -1;
Figure 2. READ command example