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pg-large-object

node-pg-large-object

Large object support for PostgreSQL clients using the node-postgres library.

The API of this library resembles the JDBC library for PostgreSQL.

Installation

npm install --save pg-large-object

You will also need to install either the pg library, or the pg-promise library:

npm install --save pg
# or
npm install --save pg-promise

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.

Large Objects

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.

Examples

The easiest way to use this library is in combination with promises and pg-promise. This library exposes a callback style interface (for backwards compatibility) and a promise style interface (see API Documentation). All functions that end with "Async" will return a promise

Reading a large object using a stream and pg-promise:

const pgp = require('pg-promise')();
const {LargeObjectManager} = require('pg-large-object');
const {createWriteStream} = require('fs');
 
const db = pgp('postgres://postgres:1234@localhost/postgres');
 
// When working with Large Objects, always use a transaction 
db.tx(tx => {
  const man = new LargeObjectManager({pgPromise: tx});
 
  // A LargeObject oid, probably stored somewhere in one of your own tables. 
  const oid = 123;
 
  // If you are on a high latency connection and working with 
  // large LargeObjects, you should increase the buffer size. 
  // The buffer should be divisible by 2048 for best performance 
  // (2048 is the default page size in PostgreSQL, see LOBLKSIZE) 
  const bufferSize = 16384;
 
  return man.openAndReadableStreamAsync(oid, bufferSize)
  .then(([size, stream]) => {
    console.log('Streaming a large object with a total size of', size);
 
    // Store it as an image 
    const fileStream = createWriteStream('my-file.png');
    stream.pipe(fileStream);
 
    return new Promise((resolve, reject) => {
      stream.on('end', resolve);
      stream.on('error', reject);
    });
  });
})
.then(() => {
  console.log('Done!');
})
.catch(error => {
  console.log('Something went horribly wrong!', error);
});

Creating a new large object using a stream and pg-promise:

const pgp = require('pg-promise')();
const {LargeObjectManager} = require('pg-large-object');
const {createReadStream} = require('fs');
 
const db = pgp('postgres://postgres:1234@localhost/postgres');
 
// When working with Large Objects, always use a transaction 
db.tx(tx => {
  const man = new LargeObjectManager({pgPromise: tx});
 
  // If you are on a high latency connection and working with 
  // large LargeObjects, you should increase the buffer size. 
  // The buffer should be divisible by 2048 for best performance 
  // (2048 is the default page size in PostgreSQL, see LOBLKSIZE) 
  const bufferSize = 16384;
 
  return man.createAndWritableStreamAsync(bufferSize)
  .then(([oid, stream]) => {
    // The server has generated an oid 
    console.log('Creating a large object with the oid', oid);
 
    const fileStream = createReadStream('upload-my-file.png');
    fileStream.pipe(stream);
 
    return new Promise((resolve, reject) => {
      stream.on('finish', resolve);
      stream.on('error', reject);
    });
  });
})
.then(() => {
  console.log('Done!');
})
.catch(error => {
  console.log('Something went horribly wrong!', error);
});

Reading a large object using a stream and callbacks:

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({pg: client});
 
  // When working with Large Objects, always use a transaction 
  client.query('BEGIN', function(err, result)
  {
    if (err)
    {
      done(err);
      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. 
    // The buffer should be divisible by 2048 for best performance 
    // (2048 is the default page size in PostgreSQL, see LOBLKSIZE) 
    var bufferSize = 16384;
    man.openAndReadableStream(oid, bufferSize, function(err, size, stream)
    {
      if (err)
      {
        done(err);
        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({pg: client});
 
  // When working with Large Objects, always use a transaction 
  client.query('BEGIN', function(err, result)
  {
    if (err)
    {
      done(err);
      return client.emit('error', err);
    }
 
    // If you are on a high latency connection and working with 
    // large LargeObjects, you should increase the buffer size. 
    // The buffer should be divisible by 2048 for best performance 
    // (2048 is the default page size in PostgreSQL, see LOBLKSIZE) 
    var bufferSize = 16384;
    man.createAndWritableStream(bufferSize, function(err, oid, stream)
    {
      if (err)
      {
        done(err);
        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()
      {
        // Actual writing of the large object in DB may 
        // take some time, so one should provide a 
        // callback to client.query. 
        client.query('COMMIT', done);
      });
 
      // Upload an image 
      var fileStream = require('fs').createReadStream('upload-my-file.png');
      fileStream.pipe(stream);
    });
  });
});

Using low level LargeObject functions:

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({pg: client});
 
  // When working with Large Objects, always use a transaction 
  client.query('BEGIN', function(err, result)
  {
    if (err)
    {
      done(err);
      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(err);
        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);
    });
  });
});

Testing

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.

API Documentation

Modules

pg-large-object
pg-large-object/lib/LargeObject

Represents an opened large object.

pg-large-object/lib/LargeObjectManager

This class lets you use the Large Object functionality of PostgreSQL. All usage of Large Object should take place within a transaction block! (BEGIN ... COMMIT)

pg-large-object/lib/promiseFromCallbackPromise
pg-large-object/lib/ReadStreamstream.Readable
pg-large-object/lib/WriteStreamstream.Writable

pg-large-object

pg-large-object.LargeObjectManager : function

pg-large-object/lib/LargeObjectManager

Kind: static constant of pg-large-object

pg-large-object.LargeObject : function

pg-large-object/lib/LargeObject

Kind: static constant of pg-large-object

pg-large-object.ReadStream : function

pg-large-object/lib/ReadStream

Kind: static constant of pg-large-object

pg-large-object.WriteStream : function

pg-large-object/lib/WriteStream

Kind: static constant of pg-large-object

pg-large-object/lib/LargeObject

Represents an opened large object.

pg-large-object/lib/LargeObject.close([callback])

Closes this large object. You should no longer call any methods on this object.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type
[callback] closeCallback

pg-large-object/lib/LargeObject.closeAsync() ⇒ Promise

Closes this large object. You should no longer call any methods on this object.

Kind: instance method of pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObject.read(length, callback)

Reads some data from the large object.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type Description
length Number How many bytes to read
callback readCallback

pg-large-object/lib/LargeObject.readAsync(length) ⇒ Promise.<Buffer>

Reads some data from the large object.

Kind: instance method of pg-large-object/lib/LargeObject
Returns: Promise.<Buffer> - The binary data that was read. If the length of this buffer is less than the supplied length param, there is no more data to be read.

Param Type Description
length Number How many bytes to read

pg-large-object/lib/LargeObject.write(buffer, [callback])

Writes some data to the large object.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type Description
buffer Buffer data to write
[callback] writeCallback

pg-large-object/lib/LargeObject.writeAsync(buffer) ⇒ Promise

Writes some data to the large object.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type Description
buffer Buffer data to write

pg-large-object/lib/LargeObject.seek(position, ref, [callback])

Sets the position within the large object. Beware floating point rounding with values greater than 2^53 (8192 TiB)

Kind: instance method of pg-large-object/lib/LargeObject

Param Type Description
position Number
ref Number One of SEEK_SET, SEEK_CUR, SEEK_END
[callback] seekCallback

pg-large-object/lib/LargeObject.seekAsync(position, ref) ⇒ Promise.<number>

Sets the position within the large object. Beware floating point rounding with values greater than 2^53 (8192 TiB)

Kind: instance method of pg-large-object/lib/LargeObject
Returns: Promise.<number> - The new position

Param Type Description
position Number
ref Number One of SEEK_SET, SEEK_CUR, SEEK_END

pg-large-object/lib/LargeObject.tell(callback)

Retrieves the current position within the large object. Beware floating point rounding with values greater than 2^53 (8192 TiB)

Kind: instance method of pg-large-object/lib/LargeObject

Param Type
callback tellCallback

pg-large-object/lib/LargeObject.tellAsync() ⇒ Promise.<number>

Retrieves the current position within the large object. Beware floating point rounding with values greater than 2^53 (8192 TiB)

Kind: instance method of pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObject.size(callback)

Find the total size of the large object.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type
callback sizeCallback

pg-large-object/lib/LargeObject.sizeAsync() ⇒ Promise.<number>

Find the total size of the large object.

Kind: instance method of pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObject.truncate(length, [callback])

Truncates the large object to the given length in bytes. If the number of bytes is larger than the current large object length, the large object will be filled with zero bytes. This method does not modify the current file offset.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type
length Number
[callback] truncateCallback

pg-large-object/lib/LargeObject.truncateAsync(length) ⇒ Promise

Truncates the large object to the given length in bytes. If the number of bytes is larger than the current large object length, the large object will be filled with zero bytes. This method does not modify the current file offset.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type
length Number

pg-large-object/lib/LargeObject.getReadableStream([bufferSize]) ⇒ pg-large-object/lib/ReadStream

Return a stream to read this large object. Call this within a transaction block.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type Default Description
[bufferSize] Number 16384 A larger buffer size will require more memory on both the server and client, however it will make transfers faster because there is less overhead (less read calls to the server). his overhead is most noticeable on high latency connections because each ransfered chunk will incur at least RTT of additional transfer time.

pg-large-object/lib/LargeObject.getWritableStream([bufferSize]) ⇒ pg-large-object/lib/WriteStream

Return a stream to write to this large object. Call this within a transaction block.

Kind: instance method of pg-large-object/lib/LargeObject

Param Type Default Description
[bufferSize] Number 16384 A larger buffer size will require more memory on both the server and client, however it will make transfers faster because there is less overhead (less read calls to the server). his overhead is most noticeable on high latency connections because each ransfered chunk will incur at least RTT of additional transfer time.

pg-large-object/lib/LargeObject.SEEK_SET : Number

A seek from the beginning of a object

Kind: static constant of pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObject.SEEK_CUR : Number

A seek from the current position

Kind: static constant of pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObject.SEEK_END : Number

A seek from the end of a object

Kind: static constant of pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObject~closeCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.

pg-large-object/lib/LargeObject~readCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.
data Buffer The binary data that was read. If the length of this buffer is less than the supplied length param, there is no more data to be read.

pg-large-object/lib/LargeObject~writeCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.

pg-large-object/lib/LargeObject~seekCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.
position Number The new position

pg-large-object/lib/LargeObject~tellCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.
position Number The position

pg-large-object/lib/LargeObject~sizeCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.
size Number Object size in bytes

pg-large-object/lib/LargeObject~truncateCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObject

Param Type Description
error Error If set, an error occurred.

pg-large-object/lib/LargeObjectManager

This class lets you use the Large Object functionality of PostgreSQL. All usage of Large Object should take place within a transaction block! (BEGIN ... COMMIT)

Param Type Description
options object Either pg or pgPromise must be given
options.pg module:pg/Client A pg (https://www.npmjs.com/package/pg) Client object
options.pgPromise module:pg-promise/Task A pg-promise (https://www.npmjs.com/package/pg-promise) transaction object as given by db.tx()

Example

new LargeObjectManager(client)

pg-large-object/lib/LargeObjectManager.open(oid, mode, callback)

Open an existing large object, based on its OID. In mode READ, the data read from it will reflect the contents of the large object at the time of the transaction snapshot that was active when open was executed, regardless of later writes by this or other transactions. If opened using WRITE (or READWRITE), data read will reflect all writes of other committed transactions as well as writes of the current transaction.

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type Description
oid Number
mode Number One of WRITE, READ, or READWRITE
callback openCallback

pg-large-object/lib/LargeObjectManager.openAsync(oid, mode) ⇒ Promise.<pg-large-object/lib/LargeObject>

Open an existing large object, based on its OID. In mode READ, the data read from it will reflect the contents of the large object at the time of the transaction snapshot that was active when open was executed, regardless of later writes by this or other transactions. If opened using WRITE (or READWRITE), data read will reflect all writes of other committed transactions as well as writes of the current transaction.

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type Description
oid Number
mode Number One of WRITE, READ, or READWRITE

pg-large-object/lib/LargeObjectManager.create(callback)

Creates a large object, returning its OID. After which you can open() it.

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type
callback createCallback

pg-large-object/lib/LargeObjectManager.createAsync() ⇒ Promise.<number>

Creates a large object, returning its OID. After which you can open() it.

Kind: instance method of pg-large-object/lib/LargeObjectManager
Returns: Promise.<number> - oid

pg-large-object/lib/LargeObjectManager.unlink(oid, [callback])

Unlinks (deletes) a large object

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type
oid number
[callback] unlinkCallback

pg-large-object/lib/LargeObjectManager.unlinkAsync(oid) ⇒ Promise

Unlinks (deletes) a large object

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type
oid number

pg-large-object/lib/LargeObjectManager.openAndReadableStream(oid, [bufferSize], callback)

Open a large object, return a stream and close the object when done streaming. Only call this within a transaction block.

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type Default
oid Number
[bufferSize] Number 16384
callback openAndReadableStreamCallback

pg-large-object/lib/LargeObjectManager.openAndReadableStreamAsync(oid, [bufferSize]) ⇒ Promise.<Array>

Open a large object, return a stream and close the object when done streaming. Only call this within a transaction block.

Kind: instance method of pg-large-object/lib/LargeObjectManager
Returns: Promise.<Array> - The total size and a ReadStream

Param Type Default
oid Number
[bufferSize] Number 16384

pg-large-object/lib/LargeObjectManager.createAndWritableStream([bufferSize], [callback])

Create and open a large object, return a stream and close the object when done streaming. Only call this within a transaction block.

Kind: instance method of pg-large-object/lib/LargeObjectManager

Param Type Default
[bufferSize] Number 16384
[callback] createAndWritableStreamCallback

pg-large-object/lib/LargeObjectManager.createAndWritableStreamAsync([bufferSize]) ⇒ promise.<Array>

Create and open a large object, return a stream and close the object when done streaming. Only call this within a transaction block.

Kind: instance method of pg-large-object/lib/LargeObjectManager
Returns: promise.<Array> - The oid and a WriteStream

Param Type Default
[bufferSize] Number 16384

pg-large-object/lib/LargeObjectManager.WRITE : Number

Kind: static constant of pg-large-object/lib/LargeObjectManager

pg-large-object/lib/LargeObjectManager.READ : Number

Kind: static constant of pg-large-object/lib/LargeObjectManager

pg-large-object/lib/LargeObjectManager.READWRITE : Number

Kind: static constant of pg-large-object/lib/LargeObjectManager

pg-large-object/lib/LargeObjectManager~openCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObjectManager

Param Type Description
error Error If set, an error occurred.
result pg-large-object/lib/LargeObject

pg-large-object/lib/LargeObjectManager~createCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObjectManager

Param Type Description
error Error If set, an error occurred.
oid Number

pg-large-object/lib/LargeObjectManager~unlinkCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObjectManager

Param Type Description
error Error If set, an error occurred.

pg-large-object/lib/LargeObjectManager~openAndReadableStreamCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObjectManager

Param Type Description
error Error If set, an error occurred.
size Number The total size of the large object
stream pg-large-object/lib/ReadStream

pg-large-object/lib/LargeObjectManager~createAndWritableStreamCallback : function

Kind: inner typedef of pg-large-object/lib/LargeObjectManager

Param Type Description
error Error If set, an error occurred.
oid Number
stream pg-large-object/lib/WriteStream

pg-large-object/lib/promiseFromCallback ⇒ Promise

Param Type
fn function
self object
[options] object

pg-large-object/lib/ReadStream ⇐ stream.Readable

Extends: stream.Readable

pg-large-object/lib/WriteStream ⇐ stream.Writable

Extends: stream.Writable