Working with Sockets and Web Services

Lianja App Builder has built-in support for TCPIP sockets. These provide the ability for you to produce and consume data to/from remote servers written in your favorite language e.g. Visual FoxPro, Python, PHP, and/or JavaScript (node.js).

Tip: Use these functions in timer delegates to handle user notifications and/or data broadcasting

SOCKET_SERVER()

socket_server(expN, expC)

Argument	Description
expN	The TCPIP port number to listen on
expC	The procedure to call to handle the connection

Example

proc myhandler(skt as numeric)
    private m_running = .t.
    do while m_running
        if socket_peek(skt) <= 0
            sleep 1
            loop
        endif
        data = socket_read(skt)
        // do what you want to do with the data
    enddo
endproc

// create a server listening on port 9000
skt = socket_server(9000, "myhandler")
if skt < 0
    // error
endif

SOCKET_OPEN()

socket_open(expC, expN1 [,expn2])

Argument	Description
expC	The IP address or nodename
expN1	The TCPIP port number
expN2	The (optional) timeout in seconds

Example

// connect to a remote server e.g. node.js listening on port 9000
skt = socket_open("mydomain.com", 9000)
if skt < 0
    // error
endif

SOCKET_PEEK()

socket_peek(expN)

Argument	Description
expN	The socket number returned from socket_open() or socket_server()

Example

if socket_peek(skt) > 0 
    // we have some data to read...
endif

SOCKET_READ()

socket_read(expN)

Argument	Description
expN	The socket number returned from socket_open() or socket_server()

Example

// read the JSON encoded object from the socket
data = socket_read(skt)

// assume we are connected to node.js (as an example) 
// and decode the JSON string
myobj = json_decode(data)

// now myobj is a VFP object with all the properties 
// (and subobjects/arrays etc)

SOCKET_WRITE()

socket_write(expN, expC)

Argument	Description
expN	The socket number returned from socket_open() or socket_server()
expC	The data we want to send to the remote server

Example

// assume we are connected to node.js (as an example) then 
// send the data in JSON format
data = json_encode(myobj)

// write the JSON encoded object to the socket
m_count = socket_write(skt, data)
if m_count != len(data)
    // error sending data
endif

SOCKET_CLOSE()

socket_close(expN)

Argument	Description
expN	The socket number returned from socket_open() or socket_server()

Example

// close the socket connection
m_skt = socket_close(skt)
if m_skt != skt
    // error closing socket
endif
socket_lasterror()	None	
// check the socket operation
if socket_lasterror() != 0
    // remote server connection failed, try reconnecting
endif