PHP socket_write works first time, but

Question

I am tying to write several messages (each message created dynamically) to a device through one socket created with PHP. The first message always goes through; but, subsequent messages do not go through. To help me debug, please let me know if there is a problem with this example:

        $socket= socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
        socket_connect($socket, $ip, $port); 
        socket_write($socket, "message 1\r");
        socket_write($socket, "message 2\r");

@pduersteler placed immediately after socket_write gives a '0' or socket_strerror(socket_last_error()) gives "Unknown error: 0" — John R
– John R, Commented May 11, 2012 at 22:42

Elias Van Ootegem · Accepted Answer · 2012-05-11 23:00:25Z

3

Have you tried adding carriage returns to the socket_write($socket, "message 1\r\n"); to the end of the message? In many cases, when working with buffers and streams, that seems to do the trick.

Something else worth giving a shot:

//all suggestions rolled into one (including Chris' chr(0) - thanks for that one)
socket_write($socket, 'message 1'."\r\n".chr(0));
usleep(5);
socket_write($socket, 'Foobar'."\r\n".chr(0));

just giving that little bit of extra time to clear the buffer can do wonders.

EDIT

Just had another brain wave: have you tried using the optional length parameter, too?

socket_write($socket, 'message 1'."\r\n".chr(0),strlen('message 1'."\r\n".chr(0)));

edited May 11, 2012 at 23:00

answered May 11, 2012 at 21:26

Elias Van Ootegem

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14 Comments

John R Over a year ago

I will try messing with usleep(5). I am currently ending the messages with '\r'. (I will edit to reflect the '\r')

Elias Van Ootegem Over a year ago

@JohnR: ending with \r won't do, best to use either \n (UNIX) or \r\n (windows). \r is sort of windows-y but not quite there... so I strongly advise you to use \r\n :P

goat Over a year ago

In addition to the line ending suggestion, the program on the other end might be waiting for a null byte terminated chunk. $nullByte = chr(0); That had me scratching my own head last week...

John R Over a year ago

@chris , I'm not clear; should that be placed after the socket write line?

John R Over a year ago

@EliasVanOotegem , Thanks! What worked for me was usleep(500000) . usleep is in microseconds, so that is half a second. I will shorten the duration some, but it fixed the problem.

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