MongoDB::GridFSBucket::DownloadStream - File handle abstraction for downloading


version v2.2.2


    # OO API
    $stream = $bucket->open_download_stream($file_id)
    while ( my $line = $stream->readline ) {

    # Tied-handle API
    $fh = $stream->fh;
    while ( my $line = <$fh> ) {


This class provides a file abstraction for downloading. You can stream data from an object of this class using method calls or a tied-handle interface.



The file document for the file to be downloaded.

Valid file documents typically include the following fields:

  • _id – a unique ID for this document, typically a BSON::OID object. Legacy GridFS files may store this value as a different type.

  • length – the length of this stored file, in bytes

  • chunkSize – the size, in bytes, of each full data chunk of this file.

  • uploadDate – the date and time this file was added to GridFS, stored as a BSON datetime value and inflated per the bucket's bson_codec attribute.

  • filename – the name of this stored file; this does not need to be unique

  • metadata – any additional application-specific data

  • md5 – DEPRECATED

  • contentType – DEPRECATED

  • aliases – DEPRECATED



    my $fh = $downloadstream->fh;
    while ( <$fh> ) {

Returns a new Perl file handle tied to this instance of DownloadStream that can be operated on with the built-in functions read, readline, getc, eof, fileno and close.

Important notes:

Allowing one of these tied filehandles to fall out of scope will NOT cause close to be called. This is due to the way tied file handles are implemented in Perl. For close to be called implicitly, all tied filehandles and the original object must go out of scope.

Each file handle retrieved this way is tied back to the same object, so calling close on multiple tied file handles and/or the original object will have the same effect as calling close on the original object multiple times.



Works like the builtin close.

Important notes:

  • Calling close will also cause any tied file handles created for the stream to also close.

  • close will be automatically called when a stream object is destroyed.

  • Calling close repeatedly will warn.


    if ( $stream->eof() ) { ... }

Works like the builtin eof.


    if ( $stream->fileno() ) { ... }

Works like the builtin fileno, but it returns -1 if the stream is open and undef if closed.


    $char = $stream->getc();

Works like the builtin getc.


    $data = $stream->read($buf, $length, $offset)

Works like the builtin read.


    $line  = $stream->readline();
    @lines = $stream->readline();

Works like the builtin readline.


  • David Golden <>

  • Rassi <>

  • Mike Friedman <>

  • Kristina Chodorow <>

  • Florian Ragwitz <>


This software is Copyright (c) 2020 by MongoDB, Inc.

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004