Calling Sage from Other Applications

Sage can be started and controlled via a pseudo-tty in the same way Sage calls and makes use of many of it's components. However, an even easier way to use Sage as a backend computational engine is to use the builtin simple server. This simple server can be called from any program that can make HTTP requests. There is self-contained example at the top of the file, and an example using PHP is below.

Start the Server

First we need to start up a Sage notebook server process. There are many ways to do this, but for a self-contained server (that doesn't interfere with your personal notebook, cleans itself up on disposal, and has a single randomly-crated account) create the file serve.py 

import time, os, random

from sage.server.misc import find_next_available_port
from sage.server.notebook.notebook_object import test_notebook
port = find_next_available_port(9000, verbose=False)
passwd = hex(random.randint(1,1<<128))

f = open('notebook_info.txt', 'w')

# create a new, empty notebook with a single user
nb = test_notebook(passwd, secure=False, address='localhost', port=port, verbose=True)

f.write("%s\n%s\n" % (port, passwd))
f.close()

print "Press control-C to stop."

try:
    # wait until a ^C
    while True:
        time.sleep(10)
except KeyboardInterrupt:
    pass

print "Killing notebook."
nb.dispose()

And the server can be started with 

$ sage -python serve.py

Upon running this command, the configuration (port and temporary password) will be written to notebook_info.txt. Change the address flag to something other than localhost if you wish to use it from a separate computer.

Use the Server

Sage is now ready to be used from another process, either locally or remotely. The following is a very simple PHP script to interface with Sage. 

<?php

$sage_divider = "___S_A_G_E___";

if (isset($_REQUEST['sage_session']) and $_REQUEST['sage_session']) {
    $sage_session = $_REQUEST['sage_session'];
}


if (!isset($json_decode)) {
    
    function _unwrap($s) {
        $s = trim($s);
        if ($s[0] == '"') {
            return substr($s, 1, -1);
        }
        else if ($s[0] == '[') {
            // assumes no comma in items
            $s = trim(substr($s, 1,-1));
            if ($s == "") {
                return array();
            }
            else if (strpos($s, ',') === FALSE) {
                return array(_unwrap($s));
            }
            $all = explode(',', substr($s, 1,-1));
            for($i=0; $i<count($all); $i++) {
                $all[$i] = _unwrap($all[$i]);
            }
            return $all;
        }
        else {
            return intval($s);
        }
    }
    
    function json_decode($s, $assoc=1) {
        // just enough to parse the sage return results...
        $res = array();
        $s = trim($s);
        $s = substr($s, 1, -1); // the outside {}'s
        $all = explode(':', $s);  // can't split on ,'s
        $key = $all[0];
        for($i=1; $i < count($all)-1; $i++) {
            $comma = strrpos($all[$i], ',');
            $val = substr($all[$i], 0, $comma);
            $res[$key] = $val;
            $key = substr($all[$i], $comma+1);
        }
        $res[$key] = $all[count($all)-1];
        // now process the items
        $res2 = array();
        foreach($res as $key => $val) {
            $res2[_unwrap($key)] = _unwrap($val);
        }
        return $res2;
    }
}


function sage_login($server, $username, $password, $renew=0) {
    global $sage_session, $sage_url, $sage_divider;
    $sage_url = $server;
    $page = file_get_contents("$sage_url/simple/login?username=$username&password=$password");
    $res_array = explode($sage_divider, $page);
    $res = json_decode($res_array[0]);
    $sage_session = $res['session'];
    return $sage_session;
}

function sage_eval($line) {
    global $sage_session, $sage_url, $sage_divider;
    $page = file_get_contents("$sage_url/simple/compute?session=$sage_session&code=".urlencode($line));
    $res_array = explode($sage_divider, $page);
    $res = json_decode($res_array[0]);
    $res['result'] = $res_array[1];
    return $res;
}

function sage_readfile($cell, $file) {
    global $sage_session, $sage_url;
    readfile("$sage_url/simple/file?session=$sage_session&cell=$cell&file=$file");
}

function sage_logout() {
    global $sage_session, $sage_url;
    file_get_contents("$sage_url/simple/logout?session=$sage_session");
}

function sage_create_integer($val, $name=NULL) {
    return sage_create_generic("ZZ", $val, $name);
}

function sage_create_rational($val, $name=NULL) {
    return sage_create_generic("QQ", $val, $name);
}

function sage_create_real($val, $name=NULL) {
    return sage_create_generic("RealNumber", $val, $name);
}

function sage_create_expression($val, $name=NULL) {
    return sage_create_generic("SR", $val, $name);
}

$sage_name_counter = 0;

function sage_create_generic($parent, $val, $name=NULL) {
    global $sage_name_counter;
    if ($name == NULL) {
        $sage_name_counter += 1;
        $name = "_php_sage_$sage_name_counter";
    }
    sage_eval("$name = $parent('''" . addslashes($val) . "''')");
    return $name;
}

?>

Now for a simple example which takes a function and plots and differentiates it. 

<?php

include "sage.php";

// You could hard-code these...
$data = explode("\n", file_get_contents("notebook_info.txt", "r"));
$pass = $data[1];
$port = $data[0];
$server = "http://localhost:$port";

if (!isset($sage_session) || !$sage_session) {
    sage_login($server, "admin", $pass);
}
else {
    $sage_url = $server;
}



if (isset($_REQUEST['file'])) {
    sage_readfile($_REQUEST['cell'], $_REQUEST['file']);
}
else {
    
?>

<html>
<body>
<?php

if (isset($_REQUEST['expr'])) {

    $f = sage_create_expression($_REQUEST['expr']);
    $res = sage_eval("$f.diff(x)");
    $df = $res['result'];
    $res = sage_eval("plot($f, (x, -5, 5))");
    $plot = $res['files'][0];
    $cell = $res['cell_id'];

//    sage_logout();
    
    echo "f(x) = $_REQUEST[expr]<br>\n";
    echo "df/dx = $df\n<br><br>\n";
    echo "<img src='diff.php?cell=$cell&file=$plot&sage_session=$sage_session'>\n";

    $f_str = $_REQUEST['expr'];
    
    echo "<hr>";
    
}
else {
    $f_str = "";
}


echo "<form>\n";
if (isset($sage_session)) {
    echo "<input type='hidden' name='sage_session' value='$sage_session'>\n";
}
echo "f(x) = <input type='text' name='expr' value='$f_str'>\n";
echo "<input type='submit'>";
echo "</form>\n";

?>
</html>


<?php } ?>

Put these two files into your web directory, and hard code the password and/or path to notebook_info.txt from above, and it is ready to use. (It takes a bit to start up a new sage session the first time it is accessed.) Note that the user input is not directly passed to Sage, as this would be a huge security risk. In contrast sage_create_* functions above are safe, as they do not use Python's eval.

This is just the tip of the iceburg, and can easily be translated to other languages such as Java, C, etc. If timeout it set to values other than -1 long-running computations can be started and later queried/interrupted. Images and other files can be served up directly, and all of Sage is at your disposal.

simple_server (last edited 2009-05-25 18:48:55 by robertwb)