How can we implement a fully streaming-compatible middleware pipeline in Express without buffering the request/response?

[zeeshanmazhar]

I’m working on an app that needs to handle large file uploads and real-time transformations (e.g., video stream filters, compression) without buffering the entire payload in memory.

Given that most Express middleware (e.g., body parsers, logging, error handling) tend to operate on fully-buffered request bodies, how can we build a fully streaming-compatible middleware pipeline in Express?

Specific challenges:
• Avoid memory spikes on large payloads
• Keep compatibility with some Express features (e.g., next() handling, res.send)
• Ensure backpressure is handled correctly

Has anyone implemented or seen a pattern where middleware can work purely in streaming mode?

[Yasir-Rafique]

Hey Zeeshan,

I have run into this challenge before. Express by default (and most of its middleware) really aren't optimized for pure streaming scenarios. Following was what helped me solve it:

• Avoid body parsers like express.json() or urlencoded(), since they buffer the whole payload. Instead, work directly with req as a readable stream.

• Use libraries like busboy or multer (in stream mode) for uploads, or handle the stream yourself for full control.

• For real-time transformations (like compression or video processing), pipe req through a series of stream.Transform instances. Hopefully Node.js streams naturally handle backpressure for you.

• Middleware can be “streaming-friendly” if you design them to operate on the stream (not on a parsed body). You can even chain transforms with stream.pipeline() for better error and backpressure handling.

• For error handling, make sure to catch stream errors so Express can handle them cleanly.

• Logging middleware like morgan still works fine, since it just inspects headers, not the body.

• As for next() and Express middleware pipeline: as long as you don’t consume or buffer the whole stream in an earlier middleware, downstream handlers can still operate on the stream.

Hopefully this will help. It takes a bit of extra setup, but it’s totally doable!

[zeeshanmazhar]

Thanks! Quick one — if I pipe req into a transform stream in one middleware, can another middleware after that still access req as a stream? Or once consumed, is it gone?

[Yasir-Rafique]

Great question! In Node.js, request streams (req) are “consumable” once you pipe or read from them in a middleware, the data is gone and later middleware can’t re-read that stream. Basically, the stream doesn’t “reset” after it is been read.

So if you need multiple transformations, you will want to chain them together in the same middleware (using something like stream.pipeline() or by piping through multiple Transform streams in one go), rather than trying to process req in separate, later middleware.

If you must split logic across middleware, you would have to buffer the body yourself (which kinda defeats the purpose for large uploads).

That is why for streaming use cases, it is best to set up all your transformations in a single pipeline early on.

Hope that helps! Streams are powerful but definitely have their quirks.

[zeeshanmazhar]

That makes perfect sense now — really appreciate the explanation. This clears up the stream consumption behavior and helps a lot with how I’ll structure my pipeline. Definitely helped with my use case. Thanks again!