Editing Openai/693d2c26-d52c-8010-af9d-5870274165bf (section)

== gpt-5-1-thinking ==
=== User: the X-Accel-Redirect is a response header. ===
the X-Accel-Redirect is a response header. this means that our backed will be returning it. this is not a header that the frontend or our users send. when nginx sees this header in the response, it will look at the uri attached to it and match it to a directory we define in our nginx virtual hosts configuration file. it will then serve the file our backend specified from that directory. -- explain

=== Assistant: Think of X-Accel-Redirect as a secret note your backend hands to nginx saying: ===
Think of X-Accel-Redirect as a secret note your backend hands to nginx saying:

: “Don’t send this response body. Instead, quietly go fetch that file from over there and send that to the user.”

Breaking your text down:

: “the X-Accel-Redirect is a response header. this means that our backend will be returning it.”
* Your backend (app server) adds a header like: X-Accel-Redirect: /protected/files/manual.pdf
* The client never sends this header. It only comes from your backend to nginx.

: “this is not a header that the frontend or our users send.”
* Correct. Browsers / frontends don’t know or care about this header.
* It’s an internal contract between your app and nginx.

: “when nginx sees this header in the response, it will look at the uri attached to it and match it to a directory we define in our nginx virtual hosts configuration file.”
* In nginx config, you define special internal locations, for example: ``<code>nginx location /protected/ {     internal;     alias /var/www/secret_files/; } </code>``
* The value of X-Accel-Redirect must match one of these locations, such as /protected/manual.pdf.

: “it will then serve the file our backend specified from that directory.”
* When nginx sees X-Accel-Redirect: /protected/manual.pdf: 1. It ignores any body your backend was going to send. 2. It internally maps /protected/manual.pdf to /var/www/secret_files/manual.pdf. 3. It streams that file to the user as the response. 4. The user just sees a normal file download; they never see /protected/... and never see X-Accel-Redirect.

===== Why this is useful =====
* Your backend: - Handles authentication/authorization. - Decides which file the user is allowed to get.
* nginx: - Handles efficient file serving (large files, caching, zero-copy sendfile, etc.).

So the flow is:
# User requests /download/123.
# Backend checks permissions, finds it maps to /protected/manual.pdf.
# Backend responds with headers (status 200, maybe some Content-Type, and X-Accel-Redirect: /protected/manual.pdf) and usually an empty body.
# nginx intercepts X-Accel-Redirect, internally fetches /protected/manual.pdf from the configured directory, and streams it to the user.

Result: your app controls access, nginx does the heavy lifting of serving the actual file 🧱📂.