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<?php

/**
 * Handles download requests for files stored by File Upload fields.
 *
 * Class GF_Download
 */
class GF_Download {

    /**
     * If the request is for a Gravity Forms file download then validate and deliver.
     *
     * @since 2.0
     */
    public static function maybe_process() {
        if ( isset( $_GET['gf-download'] ) ) {

            $file     = $_GET['gf-download'];
            $form_id  = rgget( 'form-id' );
            $field_id = rgget( 'field-id' );

            if ( empty( $file ) || empty( $form_id ) ) {
                return;
            }

            $hash = rgget( 'hash' );
            GFCommon::log_debug( __METHOD__ . "(): Starting file download process. file: {$file}, hash: {$hash}." );
            if ( self::validate_download( $form_id, $field_id, $file, $hash ) ) {
                GFCommon::log_debug( __METHOD__ . '(): Download validated. Proceeding.' );
                self::deliver( $form_id, $file );
            } else {
                GFCommon::log_debug( __METHOD__ . '(): Download validation failed. Aborting with 401.' );
                self::die_401();
            }
        }
    }

    /**
     * Verifies the hash for the download.
     *
     * @param int $form_id
     * @param int $field_id
     * @param string $file
     * @param string $hash
     *
     * @return bool
     */
    private static function validate_download( $form_id, $field_id, $file, $hash ) {
        if ( empty( $hash ) ) {
            return false;
        }

        /**
         * Allows login to be required to access the file.
         *
         * @since 2.2.3.16
         *
         * @param bool $require_login Does the user need to be logged in to access the file? Default false.
         * @param int  $form_id       The ID of the form used to upload the requested file.
         * @param int  $field_id      The ID of the field used to upload the requested file.
         */
        $require_login = apply_filters( 'gform_require_login_pre_download', false, $form_id, $field_id );

        if ( $require_login && ! is_user_logged_in() ) {
            return false;
        }

        $hash_check = GFCommon::generate_download_hash( $form_id, $field_id, $file );
        $valid      = hash_equals( $hash, $hash_check );

        return $valid;
    }

    /**
     * Send the file.
     *
     * @param $form_id
     * @param $file
     */
    private static function deliver( $form_id, $file ) {
        $path      = GFFormsModel::get_upload_path( $form_id );
        $file_path = trailingslashit( $path ) . $file;

        GFCommon::log_debug( __METHOD__ . "(): Checking if file exists: {$file_path}." );

        if ( file_exists( $file_path ) ) {
            GFCommon::log_debug( __METHOD__ . '(): File exists. Starting delivery.' );

            $content_type        = self::get_content_type( $file_path );
            $content_disposition = rgget( 'dl' ) ? 'attachment' : 'inline';

            nocache_headers();
            header( 'X-Robots-Tag: noindex', true );
            header( 'Content-Type: ' . $content_type );
            header( 'Content-Description: File Transfer' );
            header( 'Content-Disposition: ' . $content_disposition . '; filename="' . basename( $file ) . '"' );
            header( 'Content-Transfer-Encoding: binary' );
            // Clear buffer AND turn off output buffering before starting delivery of files requested for download to prevent third-parties to corrupt the file content.
            if ( ob_get_contents() ) {
                ob_end_clean();
            }
            self::readfile_chunked( $file_path );
            die();
        } else {
            GFCommon::log_debug( __METHOD__ . '(): File does not exist. Aborting with 404.' );
            self::die_404();
        }
    }

    /**
     * Returns the appropriate mime type for the file extension.
     *
     * @param $file_path
     *
     * @return mixed|null|string
     */
    private static function get_content_type( $file_path ) {
        $info = wp_check_filetype( $file_path );
        $type = rgar( $info, 'type' );

        return $type;
    }

    /**
     * Reads file in chunks so big downloads are possible without changing PHP.INI
     * See https://github.com/bcit-ci/CodeIgniter/wiki/Download-helper-for-large-files
     *
     * @access   public
     * @param    string  $file      The file
     * @param    boolean $retbytes  Return the bytes of file
     * @return   bool|string        If string, $status || $cnt
     */
    private static function readfile_chunked( $file, $retbytes = true ) {

        $chunksize = 1024 * 1024;
        $buffer    = '';
        $cnt       = 0;
        $handle    = @fopen( $file, 'r' );

        if ( $size = @filesize( $file ) ) {
            header( 'Content-Length: ' . $size );
        }

        if ( false === $handle ) {
            return false;
        }

        while ( ! @feof( $handle ) ) {
            $buffer = @fread( $handle, $chunksize );
            echo $buffer;

            if ( $retbytes ) {
                $cnt += strlen( $buffer );
            }
        }

        $status = @fclose( $handle );

        if ( $retbytes && $status ) {
            return $cnt;
        }

        return $status;
    }

    /**
     * Ends the request with a 404 (Not Found) HTTP status code. Loads the 404 template if it exists.
     */
    private static function die_404() {
        global $wp_query;
        status_header( 404 );
        $wp_query->set_404();
        $template_path = get_404_template();
        if ( file_exists( $template_path ) ) {
            require_once( $template_path );
        }
        die();
    }

    /**
     * Ends the request with a 401 (Unauthorized) HTTP status code.
     */
    private static function die_401() {
        status_header( 401 );
        die();
    }
}