Large object support for PostgreSQL clients using the node-postgres library.
The API of this library resembles the JDBC library for PostgreSQL.
npm install pg-large-object
You will also need to install the pg library:
npm install pg
Some of the methods in this library require PostgreSQL 9.3 (server) and up:
- LargeObject.seek()
- LargeObject.tell()
- LargeObject.size()
- LargeObject.truncate()
All other methods should work on PostgreSQL 8.4 and up.
You can generate documentation using jsdoc:
npm install -g jsdoc
jsdoc pg-large-object/lib
Also see: http://www.postgresql.org/docs/9.3/static/largeobjects.html
Large Objects in PostgreSQL lets you store files/objects up to 4 TiB in size. The main benefit of using Large Objects instead of a simple column is that the data can be read and written in chunks (e.g. as a stream), instead of having to load the entire column into memory.
Reading a large object using a stream:
var pg = require('pg');
var LargeObjectManager = require('pg-large-object').LargeObjectManager;
var conString = "postgres://postgres:1234@localhost/postgres";
pg.connect(conString, function(err, client, done)
{
if (err)
{
return console.error('could not connect to postgres', err);
}
var man = new LargeObjectManager(client);
// When working with Large Objects, always use a transaction
client.query('BEGIN', function(err, result)
{
if (err)
{
done();
return client.emit('error', err);
}
// A LargeObject oid, probably stored somewhere in one of your own tables.
var oid = 123;
// If you are on a high latency connection and working with
// large LargeObjects, you should increase the buffer size
var bufferSize = 16384;
man.openAndReadableStream(oid, bufferSize, function(err, size, stream)
{
if (err)
{
done();
return console.error('Unable to read the given large object', err);
}
console.log('Streaming a large object with a total size of ', size);
stream.on('end', function()
{
client.query('COMMIT');
done();
});
// Store it as an image
var fileStream = require('fs').createWriteStream('my-file.png');
stream.pipe(fileStream);
});
});
});Creating a new large object using a stream:
var pg = require('pg');
var LargeObjectManager = require('pg-large-object').LargeObjectManager;
var conString = "postgres://postgres:1234@localhost/postgres";
pg.connect(conString, function(err, client, done)
{
if (err)
{
return console.error('could not connect to postgres', err);
}
var man = new LargeObjectManager(client);
// When working with Large Objects, always use a transaction
client.query('BEGIN', function(err, result)
{
if (err)
{
done();
return client.emit('error', err);
}
// If you are on a high latency connection and working with
// large LargeObjects, you should increase the buffer size
var bufferSize = 16384;
man.createAndWritableStream(bufferSize, function(err, oid, stream)
{
if (err)
{
done();
return console.error('Unable to create a new large object', err);
}
// The server has generated an oid
console.log('Creating a large object with the oid ', oid);
stream.on('finish', function()
{
client.query('COMMIT');
done();
});
// Upload an image
var fileStream = require('fs').createReadStream('upload-my-file.png');
fileStream.pipe(stream);
});
});
});Using LargeObject methods.
var pg = require('pg');
var LargeObjectManager = require('pg-large-object').LargeObjectManager;
var LargeObject = require('pg-large-object').LargeObject;
var conString = "postgres://postgres:1234@localhost/postgres";
pg.connect(conString, function(err, client, done)
{
if (err)
{
return console.error('could not connect to postgres', err);
}
var man = new LargeObjectManager(client);
// When working with Large Objects, always use a transaction
client.query('BEGIN', function(err, result)
{
if (err)
{
done();
return client.emit('error');
}
// A LargeObject oid, probably stored somewhere in one of your own tables.
var oid = 123;
// Open with READWRITE if you would like to use
// write() and truncate()
man.open(oid, LargeObjectManager.READ, function(err, obj)
{
if (err)
{
done();
return console.error(
'Unable to open the given large object',
oid,
err);
}
// Read the first 50 bytes
obj.read(50, function(err, buf)
{
// buf is a standard node.js Buffer
console.log(buf.toString('hex'));
});
// pg uses a query queue, this guarantees the LargeObject
// will be executed in the order you call them, even if you do not
// wait on the callbacks.
// In this library the callback for methods that only return an error
// is optional (such as for seek below). If you do not give a callback
// and an error occurs, this error will me emit()ted on the client object.
// Set the position to byte 5000
obj.seek(5000, LargeObject.SEEK_SET);
obj.tell(function(err, position)
{
console.log(err, position); // 5000
});
obj.size(function(err, size)
{
console.log(err, size); // The size of the entire LargeObject
});
// Done with the object, close it
obj.close();
client.query('COMMIT');
done();
});
});
});You can test this library by running:
npm install pg-large-object
npm test
The test assumes that postgres://nodetest:nodetest@localhost/nodetest is a valid database. You also need to place a large file named "test.jpg" in the test folder.
The MIT License (MIT)
Copyright (c) 2014 Joris van der Wel
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