CODEWITHSUNDEEP
phppostgresql
edwardmp
edwardmp

Reputation: 6601

Store BLOB-like data in PostgreSQL

I recently switched from MySQL to PostgreSQL. I have one problem left however.

Previously, I would store small images in the BLOB format in MySQL.

PostgreSQL doesn't know such thing as a BLOB.

I tried using BYTEA field type instead. This actually inserts an large (hexadecimal?) string I guess, but now I'm stuck trying to get this string back to displaying an actual image in PHP..

Any ideas? Thanks in advance.

Here is a piece of code I use to save the image in the database:

$data = bin2hex(file_get_contents('php://input'));

if (!empty($data)) {
  $sql = "UPDATE asset SET data = X'%s' WHERE uuid = '%s'";
  $args = array($data, $asset_uuid);
}

psql (9.1.3) and php 5.3.6 are used

Upvotes: 1

Views: 11566

Answers (3)

edwardmp
edwardmp

Reputation: 6601

Both answers posted here gave me some thoughts, but none were 100% of the answer.

So, I will explain in this answer what I did to get it to work.

When displaying the image, I used this:

header('Content-Type: image/jpeg');

$data = pack("H*", pg_unescape_bytea($data));

echo $data;

I'm running PHP 5.3.8, in PHP 5.4.0 it turns out you can use hex2bin instead of pack.

When adding the image to the database, I used this:

$data = pg_escape_bytea($data); // Escape input for PostgreSQL
$sql  = "UPDATE asset SET data = '%s'WHERE uuid = '%s'";

I'm glad it is working now. Thank you both Daniel and Johann!

Upvotes: 3

Daniel Vérité
Daniel Vérité

Reputation: 61606

To insert bytea contents with the pg_* API, the binary value should always be run through the pg_escape_bytea() function, even if it's passed to the pg_execute or pg_query_params functions. This is because the pg_* layer doesn't "know" that a particular parameter has binary contents, and it does not implement any real support for parameter types anyway. So the text representation must be used. It can either be in the escape form or the hex form, it doesn't matter to the PG server, and it's independant of the value of bytea_output, which is meaningful only for values read from the server.

Example:

$esc=pg_escape_bytea("\000\001\002");
pg_query_params('INSERT INTO some_table(some_col) VALUES($1)', array($esc));

To read bytea contents with the pg_* API, the value must be run through pg_unescape_bytea() after the fetch. Assuming the client library is not older than 9.0 (libq.so.5.3 or higher), it can decode the contents whether it's in hex form or escape form and it will autodetect it. Only with an older library would it be necessary to force bytea_output to escape for it to decode properly, either dynamically with SET or statically for the whole database (ALTER DATABASE SET bytea_output=escape) or in postgresql.conf for the whole instance.

Example:

  $p=pg_query("SELECT some_col FROM some_table WHERE...");
  $r=pg_fetch_array($p);
  $contents = pg_unescape_bytea($r[0]);

Upvotes: 3

Johann Oskarsson
Johann Oskarsson

Reputation: 816

Bytea is a byte array. It's not a bit pattern. See section 4.2.1.5 of PostgreSQL Lexical Structure.

The correct way to enter bytea is '\x...' with hex values. So what you want is SET data = '\x%s'.

You might also want to look into prepared statements with pg_prepare.

Edit: I was able to insert a (text) file into a bytea with this:

$source = file_get_contents( 'hello.php' );
$insert = pg_prepare( $conn, '', 'insert into t (name, data) values($1,$2)' );
pg_execute( $conn, '', array( 'hello.php', $source ) );

3rd Edit: This works fine to insert the file into the database. However, the pgsql driver in PHP is quite impolite. The only way to retrieve the actual data back is using the old bytea escape mechanism, as detailed here: pg_unescape_bytea.

pg_query('SET bytea_output = "escape";');

$result = pg_query( 'select data from t' );

while ( $row = pg_fetch_row( $result ) ) {
    echo pg_unescape_bytea( $row[0] );
}

I'm sorry about how annoying this is. The PostgreSQL interface in PHP can do with some major overhaul for binary values.

Upvotes: 3

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