PL/php

= PL/php - PHP Procedural Language for PostgreSQL =

PageOutline(2-3,Contents,inline)

What is PL/php?

PL/php is a procedural language with hooks into the PostgreSQL
database sytem. It was written by Command Prompt, Inc. and has since
been open sourced and licensed under the PHP and PostgreSQL (BSD)
licenses.

Download and Installation 1. Download the following files from their respective sites. {{{
PL/php
--------------------
http://www.commandprompt.com/files/plphp-7.4.x.tar.bz2
http://www.commandprompt.com/files/plphp-8.x.tar.bz2

PHP
--------------------
Supported versions are 4.3.8+ or 5.0.2+.
See http://www.php.net/downloads/

PostgreSQL
----------
Supported versions are 8.0.x and 8.1.x.
See http://www.postgresql.org/download/
}}}
1. Unpack the tarballs for PHP and PostgreSQL (leave the plphp tarball alone for now; we'll use it later!).
1. If you downloaded a GZIP file, {{{
tar -xvzf filename.tar.gz
}}}
1. If you downloaded a BZIP2 file, {{{
tar -xvjf filename.tar.bz2
}}}
1. Build your PHP library with everything disabled. {{{
cd php-X.Y.Z/
./configure --with-php=/path/to/php.so
}}}
1. Apply the plphp patch to your PostgreSQL source {{{
tar xvjf plphp-<version>.x.tar.bz2 plphp.patch
patch -p1 < ../plphp.patch
autoconf
}}}
1. Configure PostgreSQL with your PHP source (use an absolute path). {{{
./configure --with-php=/path/to/php-<version> <your typical configure args>
}}}
1. Build and install your plphp.so library. {{{
cd src/pl/plphp
make
make install
}}}
1. Start postmaster and execute following sql to create the plphp language: {{{
CREATE FUNCTION plphp_call_handler() RETURNS language_handler
AS 'plphp' LANGUAGE C;
CREATE TRUSTED LANGUAGE plphp HANDLER plphp_call_handler;
}}}

Functions and Arguments

To create a function, use the standard syntax:

{{{
CREATE FUNCTION funcname (argument-types) RETURNS return-type AS $$ # plphp function body here
$$ LANGUAGE 'plphp';
}}}

Arguments are passed in the $args array and the result value is returned
with the 'return' statement.

{{{
CREATE FUNCTION plphp_max(integer, integer) RETURNS integer AS $$
if ($args⁰ > $args¹) {
return $args⁰;
} else {
return $args¹;
}
$$ STRICT LANGUAGE 'plphp'
}}}

NOTE: The use of the STRICT clause saves us from having to
think about NULL input values to our function. If a NULL value is
passed, the function will not be run at all, but will rather just
return a NULL result automatically.

In a non-strict function, if the actual value of an argument is NULL,
the corresponding $args[n-1] variable will be set to an empty string
(unset).

Data Types and Returns

The arguments passed into your pl/PHP function are converted to text
so you can manipulate them with the loose typing enjoyed in typical
PHP scripts. Conversely, the return command will accept any string
that is acceptable input format for the function's declared return
type.

Global Shared Variable

There is a global variable that can be used to store data between
function calls, called $_SHARED.

{{{
CREATE FUNCTION set_var(text) RETURNS text AS $$
global $_SHARED;
$_SHARED['first']=$args⁰;
return 'ok';
$$ LANGUAGE 'plphp';

CREATE FUNCTION get_var() RETURNS text AS $$
global $_SHARED;
return $_SHARED['first'];
$$ LANGUAGE 'plphp';

SELECT set_var('hello plphp');
SELECT get_var(); -- will return 'hello plphp'

}}}

NOTE: The shared global variable is connection-specific. This is
useful for passing information around a single script execution,
but it is wiped when the connection is closed.

PostgreSQL Array Support

There is support for multi-dimensional arrays.

For example:

{{{
CREATE FUNCTION php_array() RETURNS text[][] AS $$
$return = array(array("Steven", "Klassen"),
array("Jonathan", "Daugherty"));

return $return;
$$ LANGUAGE 'plphp';
}}}

{{{
sklassen=# select php_array();
php_array
----------------------------------------- {{Steven,Klassen},{Jonathan,Daugherty}}
(1 row)
}}}

Polymorphic Arguments and Return Types

Functions may be declared to accept and return the polymorphic types
'anyelement', 'anyarray', and 'anyrecord'. See the PostgreSQL
documentation section 33.2.5 for a more detailed explanation of
polymorphic functions.

For example,

{{{
CREATE FUNCTION array_three_values(anyelement, anyelement, anyelement) RETURNS anyarray AS '
$ret⁰ = $args⁰;
$ret¹ = $args¹;
$ret² = $args²;
return $ret;
' LANGUAGE 'plphp';

SELECT array_three_values(3,2,1);
array_three_values
-------------------- {3,2,1}
(1 row)

CREATE OR REPLACE FUNCTION php_row(integer) RETURNS record AS '
$ret[f1]=$args⁰;
$ret[f2]="hello";
$ret[f3]="world";
return $ret;
' LANGUAGE 'plphp';

select * FROM php_row(1) AS (f1 integer, f2 text, f3 text);

}}}

Database Access (SPI)

Two functions are provided for database access. {{{
resource spi_exec_query(string query[, int limit])
}}}
1. spi_fetch_row - Return an associative array of the row's results. {{{
array spi_fetch_row(resource result)
}}}

1. spi_exec_query - Execute a query with optional limit.

For example:

This isn't a particularly useful function, but it will illustrate the
above-described access functions. You provide an integer id and it
returns the username text field.

{{{
CREATE FUNCTION get_username(integer) RETURNS text AS ' # Assign the query to a variable.
$query = "SELECT username FROM users WHERE id = " .$args⁰;

1. Run the query and get the $result object.
   $result = spi_exec_query($query);

1. Fetch the row from the $result.
   $row = spi_fetch_row($result);

return $row[''username''];
' LANGUAGE 'plphp';

sklassen=# select get_username(1);
get_username
--------------
sklassen
(1 row)

}}}

Triggers

When a function is being used to return a trigger, the associative
array $_TD contains trigger-related values.

$_TD["new"]::
   An associative array containing the values of the new table row for
   INSERT/UPDATE actions, or empty for DELETE.  The array is indexed
   by field name.  Important note: Fields that are NULL will not
   appear in the array!

$_TD["old"]::
   An associative array containing the values of the old table row for
   UPDATE/DELETE actions, or empty for INSERT.  The array is indexed
   by field name.  Important note: Fields that are NULL will not
   appear in the array!

$_TD["name"]::
   Contains the trigger name itself.

$_TD["event"]::
   Contains one of the values: "INSERT", "UPDATE", "DELETE", or
   "UNKNOWN". /note to offshore re: unknown/

$_TD["when"]::
   Contains one of the values: "BEFORE", "AFTER", or "UNKNOWN".

$_TD["level"]::
   Contains one of the values: "ROW", "STATEMENT", or "UNKNOWN".

$_TD["relid"]::
   Contains the relation ID of the table on which the trigger occured.

$_TD["relname"]::
   Contains the relation name.

$_TD["args"]::
   An array of arguments passed to the trigger, if any.  They can be
   accessed as $_TD["args"][idx].  Example, $_TD["args"][0].

$_TD["argc"]::
  The number of arguments passed to the trigger, if any.

=== Example of an AFTER INSERT trigger ===

Suppose you have a users table with the typical columns and an
activity table that you're using to track page accesses. On row

INSERT to the activity table, you want to update the last_seen field
of the appropriate user's record.

Consider the following table definitions:

{{{
CREATE TABLE users (
id serial PRIMARY KEY NOT NULL,
username text NOT NULL,
email text,
last_seen timestamp without time zone,
active boolean DEFAULT true NOT NULL
);

CREATE TABLE activity (
id serial PRIMARY KEY NOT NULL,
users_id integer NOT NULL,
file_accessed text NOT NULL,
stamp timestamp without time zone DEFAULT now() NOT NULL,
CONSTRAINT users_id_exists FOREIGN KEY (users_id) REFERENCES users(id)
);

CREATE FUNCTION update_lastseen() RETURNS trigger AS '
$new =& $_TD[''new''];

if (isset($new[''users_id'']) && isset($new[''stamp''])) {
        $query = "UPDATE users SET last_seen = ''" .$new[''stamp''].
                 "'' WHERE id = " .$new[''users_id''];

$rv = spi_exec_query($query);
    }

return;
' LANGUAGE 'plphp';

CREATE TRIGGER after_update_lastseen_trigger
AFTER INSERT ON activity FOR EACH ROW EXECUTE PROCEDURE update_lastseen();

}}}

'''1. We'll insert a new user row.'''

{{{
sklassen=# insert into users (username, email) values ('sklassen','sklassen@commandprompt.com');
INSERT 1

sklassen=# select * from users where username = 'sklassen';

id | username |           email            | last_seen | active 
----+----------+----------------------------+-----------+--------
  1 | sklassen | sklassen@commandprompt.com |           | t
(1 row)
}}}

'''2. Insert a new row into the activity table.'''

{{{
sklassen=# insert into activity (users_id, file_accessed) values (1,'index.html');
INSERT 1

'''3. Check and make sure our trigger fired as expected.'''

sklassen=# select * from users where username = 'sklassen';
id | username | email | last_seen | active
----+----------+----------------------------+----------------------------+--------
1 | sklassen | sklassen@commandprompt.com | 2005-01-10 09:48:57.191595 | t
(1 row)

}}}

=== Example of a BEFORE INSERT OR UPDATE trigger ===

Let's say we have a user named admin that we want to prevent the
pplication from modifying. We'll create a BEFORE DELETE trigger that
prevents them from deleting the row and a BEFORE UPDATE trigger that
prevents them modifying the username on which the previous trigger
depends.

{{{
CREATE OR REPLACE FUNCTION immortal() RETURNS trigger AS ' # The record may not be deleted if the username is "admin".
echo "You cannot delete the admin user.\n";
return ($_TD[''old''][''username''] == ''admin'') ? "SKIP" :
"MODIFY";
' LANGUAGE 'plphp';

CREATE TRIGGER before_delete_immortal_trigger BEFORE DELETE ON users
FOR EACH ROW EXECUTE PROCEDURE immortal();

CREATE OR REPLACE FUNCTION protect_admin() RETURNS trigger AS ' # Do not let them modify the username of the admin account.
$oldUsername =& $_TD[''old''][''username''];
$newUsername =& $_TD[''new''][''username''];

if ($oldUsername == ''admin'' && ($oldUsername != $newUsername)) {
      echo "You cannot change the admin username.\n";
      return ''SKIP'';
   } else {
      return ''MODIFY'';
   }
' LANGUAGE 'plphp';

CREATE TRIGGER before_update_protect_admin_trigger BEFORE UPDATE ON
users FOR EACH ROW EXECUTE PROCEDURE protect_admin();

sklassen=> select * from users;
id | username | email
----+----------+----------------------------
1 | sklassen | sklassen@commandprompt.com
2 | admin | admin@yourhost.com
(2 rows)

sklassen=> update users set username = 'frobotz' where id = 2::bigint;
You cannot change the admin username.
UPDATE 0

sklassen=> delete from users where username = 'admin';
You cannot delete the admin user.
DELETE 0

}}}

Trusted vs. Untrusted

Normally, plPHP is installed as a "trusted" procedural language named
'plphp'. In this configuration, PHP will run in "safe mode". Read
more about the restrictions here:

http://www.php.net/manual/en/features.safe-mode.functions.php

In general, the operations that are restricted are those that interact
with the environment. This includes file operations, require, and use
(for external modules).

Since there is no way to gain access to the internals of the database
backend process or the operating system itself, any unprivileged
database user may use functions written in this language.

An example of a NON-working function due to security constraints:

{{{
CREATE FUNCTION read_passwd_file() RETURNS text AS '
readfile("/etc/passwd");
return 0;
' LANGUAGE 'plphp';

}}}

It will appear to execute, but depending on your log level, you'll may
see something like the following:

{{{
Warning: readfile(): SAFE MODE Restriction in effect. The script
whose uid is 500 is not allowed to access /etc/passwd owned by uid 0
in Command line code on line 3

Warning: readfile(/etc/passwd): failed to open stream: Success in
plphp function source on line 3
}}}

Sometimes it is desirable to write PHP functions that are not
restricted. In this case, you can create the language as 'plphpu' to
enable the previously unavailable functions.

{{{
CREATE LANGUAGE plphpu HANDLER plphp_call_handler;
}}}

Composite Type Arguments

Composite-type arguments are passed to the function as associative
array. The keys of the array are the attribute names of
the composite type. Here is an example:

{{{
CREATE TABLE employee (
name text,
basesalary integer,
bonus integer
);

CREATE FUNCTION empcomp(employee) RETURNS integer AS '
return $args⁰[''basesalary''] + $args⁰[''bonus''];
' LANGUAGE 'plphp';

SELECT name, empcomp(employee) FROM employee;

}}}

Returning A Row (composite type)

To return a row or composite-type value from a PL/php-language
function, you can use an indexed array:

{{{
CREATE TYPE __testrowphp AS (f1 integer, f2 text, f3 text);

CREATE OR REPLACE FUNCTION php_row(integer) RETURNS __testrowphp AS '
$ret[f1]=$args⁰;
$ret[f2]="hello";
$ret[f3]="world";
return $ret;
' LANGUAGE 'plphp';

select * FROM php_row(1);

Will return:
f1 | f2 | f3
----+-------+-------
1 | hello | world
}}}

Returning multiple rows (SRF functions)

SRF stands for "set-returning functions". This means you can return
multiple rows, like in the following example:

{{{
CREATE TYPE __testsetphp AS (f1 integer, f2 text, f3 text);

CREATE OR REPLACE FUNCTION php_set(integer) RETURNS SETOF __testsetphp AS '
$ret⁰[f1]=$args⁰;
$ret⁰[f2]="hello";
$ret⁰[f3]="world";

$ret[1][f1]=2*$args[0];
   $ret[1][f2]="hello";
   $ret[1][f3]="postgres";

$ret[2][f1]=3*$args[0];
   $ret[2][f2]="hello";
   $ret[2][f3]="plphp";
   return $ret;
' LANGUAGE 'plphp';

SELECT * FROM php_set(1);

Will return:
f1 | f2 | f3
----+-------+----------
1 | hello | world
2 | hello | postgres
3 | hello | plphp

}}}

Limitations

plPHP functions cannot call each other directly because they are
anonymous subroutines inside PHP.

TODO

Implement elog() function for notices.