http-proxy-middleware/dist/handlers/fix-request-body.js

The one-liner node.js proxy middleware for connect, express, next.js and more

import * as querystring from 'node:querystring';
import * as zlib from 'node:zlib';
import { stringifyFormData } from './fix-request-body-utils/stringify-form-data.js';
/**
 * Fix proxied body if bodyParser is involved.
 *
 * @example
 * ```ts
 * createProxyMiddleware({
 *   target: 'http://example.com',
 *   on: {
 *     proxyReq: fixRequestBody,
 *   }
 * });
 * ```
 *
 * Alternative solution without using `fixRequestBody()`: put `http-proxy-middleware` before `bodyParser` in the middleware stack.
 *
 * @see {@link https://github.com/chimurai/http-proxy-middleware/issues/40 Github issue #40 - POST request body is not proxied}
 */
export function fixRequestBody(proxyReq, req) {
    // skip fixRequestBody() when req.readableLength not 0 (bodyParser failure)
    if (req.readableLength !== 0) {
        return;
    }
    const requestBody = req.body;
    if (!requestBody) {
        return;
    }
    const contentType = proxyReq.getHeader('Content-Type');
    if (!contentType) {
        return;
    }
    const writeBody = (bodyData) => {
        let proxyData = bodyData;
        const contentEncoding = String(proxyReq.getHeader('Content-Encoding')).toLowerCase();
        switch (contentEncoding) {
            case 'br':
                proxyData = zlib.brotliCompressSync(proxyData);
                break;
            case 'deflate':
                proxyData = zlib.deflateSync(proxyData);
                break;
            case 'gzip':
                proxyData = zlib.gzipSync(proxyData);
                break;
            case 'zstd':
                proxyData = zlib.zstdCompressSync(proxyData);
                break;
        }
        proxyReq.setHeader('Content-Length', Buffer.byteLength(proxyData));
        proxyReq.write(proxyData);
    };
    try {
        // Use if-elseif to prevent multiple writeBody/setHeader calls:
        // Error: "Cannot set headers after they are sent to the client"
        if (contentType.includes('application/json') || contentType.includes('+json')) {
            writeBody(JSON.stringify(requestBody));
        }
        else if (contentType.includes('application/x-www-form-urlencoded')) {
            writeBody(querystring.stringify(requestBody));
        }
        else if (contentType.includes('multipart/form-data')) {
            writeBody(stringifyFormData(contentType, requestBody));
        }
        else if (contentType.includes('text/plain')) {
            writeBody(requestBody);
        }
    }
    catch (error) {
        // proxyReq listeners run outside the middleware try/catch path; re-throwing here can bubble as
        // an unhandled exception in consumers, so destroy() is used to fail closed through proxy error handling.
        proxyReq.destroy(toError(error));
    }
}
function toError(error) {
    return error instanceof Error ? error : new Error(String(error));
}