express-transform-bare-module-specifiers/dist/transform-middleware.js

Express middleware to transform bare module specifiers on-the-fly.

"use strict";
/**
 * Based entirely on:
 * https://github.com/Polymer/tools/blob/dd1c8bbb44f37f67974fbabf878b7a495ffeb6f6/packages/polyserve/src/transform-middleware.ts
 */
Object.defineProperty(exports, "__esModule", { value: true });
function transformResponse(transformer) {
    return (req, res, next) => {
        let ended = false;
        const chunks = [];
        let _shouldTransform = null;
        // Note: this function memoizes its result.
        function shouldTransform() {
            if (_shouldTransform === null) {
                const successful = res.statusCode >= 200 && res.statusCode < 300;
                _shouldTransform =
                    successful && Boolean(transformer.shouldTransform(req, res));
            }
            return _shouldTransform;
        }
        const _write = res.write;
        res.write = function (chunk, cbOrEncoding, cbOrFd) {
            if (ended) {
                _write.call(this, chunk, cbOrEncoding, cbOrFd);
                return false;
            }
            if (shouldTransform()) {
                const buffer = (typeof chunk === 'string') ?
                    Buffer.from(chunk, cbOrEncoding) :
                    chunk;
                chunks.push(buffer);
                return true;
            }
            return _write.call(this, chunk, cbOrEncoding, cbOrFd);
        };
        const _end = res.end;
        res.end = function (cbOrChunk, cbOrEncoding, cbOrFd) {
            if (ended) {
                return false;
            }
            ended = true;
            if (shouldTransform()) {
                if (Buffer.isBuffer(cbOrChunk)) {
                    chunks.push(cbOrChunk);
                }
                else if (typeof cbOrChunk === 'string') {
                    chunks.push(Buffer.from(cbOrChunk, cbOrEncoding));
                }
                const body = Buffer.concat(chunks).toString('utf8');
                let newBody = body;
                try {
                    newBody = transformer.transform(req, res, body);
                }
                catch (e) {
                    console.warn('Error', e);
                }
                // TODO(justinfagnani): re-enable setting of content-length when we know
                // why it was causing truncated files. Could be multi-byte characters.
                // Assumes single-byte code points!
                // res.setHeader('Content-Length', `${newBody.length}`);
                res.removeHeader('Content-Length');
                // TODO(aomarks) Shouldn't we call the callbacks?
                return _end.call(this, newBody);
            }
            return _end.call(this, cbOrChunk, cbOrEncoding, cbOrFd);
        };
        next();
    };
}
exports.transformResponse = transformResponse;
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