Registry / http-networking / modify-response-middleware

modify-response-middleware

library1.1.0jsnpmunverified

The `modify-response-middleware` package provides an Express middleware designed to intercept and transform HTTP response bodies before they are sent to the client. It transparently handles various compression encodings like Gzip, Brotli, Deflate, and Br, allowing developers to modify response data regardless of its original compression status. As of version 1.1.0, it supports both uncompressed and compressed payloads, offering options to disable caching (`noCache`). This middleware is particularly useful for injecting data, sanitizing output, or performing last-minute transformations on API responses. Its release cadence appears stable but infrequent, typical for a focused utility. A key differentiator is its built-in handling of common compression algorithms, abstracting away the complexities of decompression and re-compression during modification.

http-networking web-framework

npm install modify-response-middleware

github ↗package ↗

INSTALL

IMPORT

SIG · MODIFY-RESPONSE-MI

modify-response-middleware

http-networkingjavascriptv1.1.0

Install

—

Import

—

Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

modifyRes

✓ import modifyRes from 'modify-response-middleware'

✗ const modifyRes = require('modify-response-middleware')

The package primarily uses an ESM default export. While CommonJS `require()` might work due to transpilation, `import` is the idiomatic way. For older CJS environments, `const modifyRes = require('modify-response-middleware').default` might be necessary if it's strictly ESM.

Buffer

✓ import { Buffer } from 'node:buffer'

✗ import { Buffer } from 'buffer'

While `Buffer` is globally available in Node.js, explicit import from `node:buffer` or `buffer` is good practice, especially in TypeScript or bundled environments. The middleware's callback expects a Buffer as a return type.

This quickstart demonstrates how to integrate `modify-response-middleware` into an Express application to intercept and modify JSON response bodies before they are sent to the client.

import express from 'express'; import modifyRes from 'modify-response-middleware'; const app = express(); app.use(express.json()); // Ensure JSON body parsing for incoming requests if needed // Apply the modification middleware early in the stack app.use(modifyRes((content, req, res) => { if (content && res.get('Content-Type')?.includes('application/json')) { try { const data = JSON.parse(content.toString()); // Example: Modify the age property of the JSON response data.age = (data.age || 0) + 2; data.message = 'Response modified by middleware!'; return Buffer.from(JSON.stringify(data)); } catch (e) { console.error('Failed to parse or modify JSON content:', e); // Return original content if modification fails return content; } } // Always return content, even if no modification occurred or type didn't match return content; }, { noCache: true, // Prevents 304 Not Modified responses, useful for dynamic content })); app.get('/user', (req, res) => { res.json({ name: 'Tom', age: 18, status: 'active' }); }); app.get('/html', (req, res) => { res.send('<h1>Hello, World!</h1><p>This is an HTML response.</p>'); }); const PORT = 3000; app.listen(PORT, () => { console.log(`Server listening on port ${PORT}`); console.log(`Test with: curl http://localhost:${PORT}/user`); console.log(`Test with: curl http://localhost:${PORT}/html`); });

Debug

Known issues

breakingMiddleware order is critical. `modify-response-middleware` must be applied *before* any route handlers or other middleware that send responses (e.g., `res.send()`, `res.json()`). Placing it after these handlers will result in it never being invoked for those responses, as headers might have already been sent.

fix

Ensure `app.use(modifyRes(...))` is declared early in your Express application's middleware stack, ideally before route definitions. If using router-level middleware, place it before route-specific handlers within that router.

affects: >=1.0.0

gotchaModifying response bodies, especially after decompression and before re-compression, can introduce performance overhead. For very large responses or high-traffic applications, this can significantly impact server throughput and latency due to CPU usage for (de)compression and memory for buffering.

fix

Profile your application with and without the middleware in production scenarios. Consider applying the middleware only to specific routes (using `app.use('/path', modifyRes(...))`) or conditionally based on response size if performance becomes an issue.

affects: >=1.0.0

gotchaWhen modifying response content, `Content-Length` and `ETag` headers can become invalid. The `noCache: true` option helps mitigate `ETag` issues by setting `Cache-Control: no-cache`, but if `Content-Length` is present and incorrect, it can lead to client-side issues or truncated responses. The middleware attempts to handle this, but explicit verification is sometimes needed.

fix

If `noCache` is not suitable, ensure your modified response handler explicitly removes or recalculates `Content-Length` and `ETag` headers if the body size changes significantly. Monitor network responses to ensure headers align with modified content.

affects: >=1.0.0

gotchaThe callback function provided to `modifyRes` expects `content` to be a `Buffer`. If your modification logic assumes a specific content type (e.g., JSON) and attempts parsing without proper checks, it can throw errors for other content types (e.g., HTML, plain text, images).

fix

Always validate the content type (e.g., `res.get('Content-Type')`) within your `modifyRes` callback before attempting type-specific parsing (e.g., `JSON.parse()`). Wrap parsing logic in `try...catch` blocks to handle malformed or unexpected data gracefully. Return the original `content` buffer if parsing/modification fails.

affects: >=1.0.0

Errors

Common errors & fixes

SyntaxError: Unexpected token < in JSON at position 0

Attempting to `JSON.parse()` a non-JSON response, often an HTML error page or another content type, because the `Content-Type` header was not checked.

fix

Before parsing, check `res.get('Content-Type')` within your `modifyRes` callback to ensure it's `application/json`. Add a `try...catch` block around `JSON.parse()` to handle non-JSON or malformed responses gracefully.

TypeError: content.toString is not a function

The `content` parameter passed to your callback is `null`, `undefined`, or not a `Buffer` instance, often for empty responses or if upstream middleware unexpectedly altered the body format.

fix

Always add a check `if (content && Buffer.isBuffer(content))` before calling `content.toString()` or attempting to process `content`. For empty responses, `content` might legitimately be `null` or an empty buffer, in which case it should be returned as is.

(Client-side) ERR_CONTENT_LENGTH_MISMATCH or truncated responses

The `Content-Length` header sent by the server does not match the actual byte length of the modified response body, causing client-side errors or incomplete downloads.

fix

When the response body is modified, the middleware should ideally reset or remove the `Content-Length` header. If issues persist, ensure the middleware or your callback removes `res.removeHeader('Content-Length')` or explicitly sets `res.setHeader('Content-Length', Buffer.byteLength(newContent))` for non-compressed content.

Upgrade

Version history

1.1.0latest on npm

Audit

Dependencies

expressrequiredThis is an Express.js middleware and requires Express to function.

Agent activity

12 hits · last 30 days

node

Resources

githubhttps://github.com/zuojiang/modify-response-middleware ↗

packagehttps://www.npmjs.com/package/modify-response-middleware ↗