Documentation

PHP partitioned upload handler

Evidently, partitioned uploading requires sophisticated processing on the server in order to reconstruct original file. However, overall idea is quiet simple — store partitions on the server until we acquire all of them, then join into single file.

PHP code snippet below implements this functionality:

//----------------------------------------------
//    partitioned upload file handler script
//----------------------------------------------

//
//    specify upload directory - storage 
//    for reconstructed uploaded files
$upload_dir = $_SERVER[ 'DOCUMENT_ROOT' ] . "/uploaded/";

//
//    specify stage directory - temporary storage 
//    for uploaded partitions
$stage_dir = $_SERVER[ 'DOCUMENT_ROOT' ] . "/uploaded/stage/";

//
//    retrieve request parameters
$file_param_name = 'file';
$file_name = $_FILES[ $file_param_name ][ 'name' ];
$file_id = $_POST[ 'fileId' ];
$partition_index = $_POST[ 'partitionIndex' ];
$partition_count = $_POST[ 'partitionCount' ];
$file_length = $_POST[ 'fileLength' ];

//
//    the $client_id is an essential variable, 
//    this is used to generate uploaded partitions file prefix, 
//    because we can not rely on 'fileId' uniqueness in a 
//    concurrent environment - 2 different clients (applets) 
//    may submit duplicate fileId. thus, this is responsibility 
//    of a server to distribute unique clientId values
//    (or other variable, for example this could be session id) 
//    for instantiated applets.
$client_id = $_GET[ 'clientId' ];

//
//    move uploaded partition to the staging folder 
//    using following name pattern:
//    ${clientId}.${fileId}.${partitionIndex}
$source_file_path = $_FILES[ $file_param_name ][ 'tmp_name' ];
$target_file_path = $stage_dir . $client_id . "." . $file_id . 
    "." . $partition_index;
if( !move_uploaded_file( $source_file_path, $target_file_path ) ) {
    echo "Error:Can't move uploaded file";
    return;
}

//
//    check if we have collected all partitions properly
$all_in_place = true;
$partitions_length = 0;
for( $i = 0; $all_in_place && $i < $partition_count; $i++ ) {
    $partition_file = $stage_dir . $client_id . "." . $file_id . "." . $i;
    if( file_exists( $partition_file ) ) {
        $partitions_length += filesize( $partition_file );
    } else {
        $all_in_place = false;
    }
}

//
//    issue error if last partition uploaded, but partitions validation failed
if( $partition_index == $partition_count - 1 &&
        ( !$all_in_place || $partitions_length != intval( $file_length ) ) ) {
    echo "Error:Upload validation error";
    return;
}

//
//    reconstruct original file if all ok
if( $all_in_place ) {
    $file = $upload_dir . $client_id . "." . $file_id;
    $file_handle = fopen( $file, 'a' );
    for( $i = 0; $all_in_place && $i < $partition_count; $i++ ) {
        //
        //    read partition file
        $partition_file = $stage_dir . $client_id . "." . $file_id . "." . $i;
        $partition_file_handle = fopen( $partition_file, "rb" );
        $contents = fread( $partition_file_handle, filesize( $partition_file ) );
        fclose( $partition_file_handle );
        //
        //    write to reconstruct file
        fwrite( $file_handle, $contents );
        //
        //    remove partition file
        unlink( $partition_file );
    }
    fclose( $file_handle );
}

Please note, this script is for demonstration purpose. This lacks security and additional features that production system should have.

For example, it is necessary to perform staging folder periodical cleanup, just because some clients may abort transfers, thus partitions transferred so far remain unclaimed.