salix/back/methods/dms/downloadFile.js

const UserError = require('vn-loopback/util/user-error');

module.exports = Self => {
    Self.remoteMethodCtx('downloadFile', {
        description: 'Download a document',
        accessType: 'READ',
        accepts: [
            {
                arg: 'id',
                type: 'Number',
                description: 'Document id',
                http: {source: 'path'}
            }
        ],
        returns: [
            {
                arg: 'body',
                type: 'file',
                root: true
            }, {
                arg: 'Content-Type',
                type: 'String',
                http: {target: 'header'}
            }, {
                arg: 'Content-Disposition',
                type: 'String',
                http: {target: 'header'}
            }
        ],
        http: {
            path: `/:id/downloadFile`,
            verb: 'GET'
        }
    });

    Self.downloadFile = async function(ctx, id) {
        const storageConnector = Self.app.dataSources.storage.connector;
        const models = Self.app.models;
        const dms = await Self.findById(id);

        const hasReadRole = await models.DmsType.hasReadRole(ctx, dms.dmsTypeFk);
        if (!hasReadRole)
            throw new UserError(`You don't have enough privileges`);

        const pathHash = storageConnector.getPathHash(dms.id);
        try {
            await models.Container.getFile(pathHash, dms.file);
        } catch (e) {
            if (e.code != 'ENOENT')
                throw e;

            const error = new UserError(`File doesn't exists`);
            error.statusCode = 404;

            throw error;
        }

        const stream = models.Container.downloadStream(pathHash, dms.file);

        return [stream, dms.contentType, `filename="${dms.file}"`];
    };
};