index.js

'use strict';

const normalize = require('path').posix.normalize;

module.exports = normalizePath;

function normalizePath(opts) {
    opts = opts || {};

    if (opts.defer !== false) {
        opts.defer = opts.defer || true;
    }

    if (opts.chained !== false) {
        opts.chained = opts.chained || true;
    }

    return async function(ctx, next) {
        if (opts.defer) {
            await next();
        }

        let path;

        // We have already done a redirect and we will continue if we are in chained mode
        if (opts.chained && ctx.status === 301) {
            path = getPath(ctx.response.get('Location'), ctx.querystring);
        } else if (ctx.status !== 301) {
            path = getPath(ctx.originalUrl, ctx.querystring);
        }

        if (path) {
            const normalizedPath = normalize(path);
            if (path !== normalizedPath) {
                const query = ctx.querystring.length ? '?' + ctx.querystring : '';

                ctx.status = 301;
                ctx.redirect(normalizedPath + query);
            }
        }

        if (!opts.defer) {
            await next();
        }
    };
}

function getPath(original, querystring) {
    if (querystring.length) {
        return original.slice(0, -querystring.length - 1);
    }

    return original;
}