An API must return a multi-gigabyte export. How would you stream the response without buffering it all in memory?

Stream large HTTP responses without buffering

Designs cancellation-aware response streaming with bounded memory, correct resource ownership, and practical download behavior.

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TL;DR

I produce or open the content as a stream and let the server copy it to the response asynchronously instead of building one byte array or string. In ASP.NET Core a file or stream result can own that transfer. I set the media type and download name, propagate request cancellation, and make ownership clear so the stream and any temporary file are disposed after the response finishes or the client disconnects.

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Response streaming, FileStreamResult, async writes, cancellation, backpressure, ranges, compression, timeouts, object storage, and cleanup.

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Why this question matters
Large responses change the resource boundary of a request. A design that materializes the whole payload can exhaust memory long before network throughput becomes the visible bottleneck.
I produce or open the content as a stream and let the server copy it to the response asynchronously instead of building one byte array or string. In ASP.NET Core a file or stream result can own that transfer. I set the media type and download name, propagate request cancellation, and make ownership clear so the stream and any temporary file are disposed after the response finishes or the client disconnects.
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If the size is known I can send Content-Length; otherwise the HTTP version handles response framing while the application writes incrementally. Backpressure means writes should await the transport rather than generating data without bound. Range support helps clients resume static or seekable downloads, but it needs correct length and seek behavior. On-the-fly compression may consume substantial CPU and can be wasteful for already compressed formats. Long downloads need timeouts and rate limits that distinguish healthy slow transfer from a stuck producer.

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Details

Calling ToArray or building one giant string before writing the response.
Ignoring cancellation after the client disconnects.
Disposing the source stream before the framework finishes the response.
Enabling compression for every large binary format without measurement.

An API must return a multi-gigabyte export. How would you stream the response without buffering it all in memory?

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