Add FlexMeasures-Version and API-Version response headers

[Copilot]

Clients have no programmatic way to identify the server version or API version from HTTP responses alone.

Changes

• flexmeasures/api/__init__.py: Registers an app.after_request hook in register_at() that injects version headers based on request path prefix:

  • FlexMeasures-Version: <version> on all responses under /api/
  • API-Version: v3_0 additionally on all responses under /api/v3_0

• flexmeasures/api/tests/test_headers.py: New test file covering header presence on v3_0 and non-v3_0 API endpoints, and absence of API-Version on non-v3_0 endpoints.

• documentation/api/introduction.rst: Added description of the new response headers at the end of the "Main endpoint and API versions" section; removed an outdated note from that section.

• documentation/api/change_log.rst: Added entries under v3.0-30 documenting the new FlexMeasures-Version and API-Version response headers.

Example

GET /api/v3_0/health/ready HTTP/1.1

HTTP/1.1 200 OK
FlexMeasures-Version: 0.32.0
API-Version: v3_0
...

GET /api/ops/ping HTTP/1.1

HTTP/1.1 200 OK
FlexMeasures-Version: 0.32.0
...

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Use custom headers to communicate server/API versions</issue_title>
<issue_description>- All API responses should include the FlexMeasures-Version: 0.32.0 header, updated with the current server version.

• All API responses under the v3_0 blueprint should also include the API-Version: v3_0 header.
• See flexmeasures.api.get_versions (in __init__.py) for some implementation details.
• Add tests
• Create a corresponding PR in https://github.com/FlexMeasures/flexmeasures-client, noting related work in:
  • Feat/check server version flexmeasures-client#119
  • Add minimum_server_version parameter to client.request flexmeasures-client#151
    </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Use custom headers to communicate server/API versions #2020

---

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[read-the-docs-community]

Documentation build overview

📚 flexmeasures | 🛠️ Build #31793606 | 📁 Comparing 391e59f against latest (c6bb60f)

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Show files changed (4 files in total): 📝 4 modified | ➕ 0 added | ➖ 0 deleted

File	Status
changelog.html	📝 modified
api/change_log.html	📝 modified
api/introduction.html	📝 modified
api/v3_0.html	📝 modified

[nhoening]

I suggest using the dedicated Header field: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Server

So maybe: Server: FlexMeasures/0.31.2

[Flix6x]

I suggest using the dedicated Header field: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Server

So maybe: Server: FlexMeasures/0.31.2

• From what I've read the Server header is typically used for things like:
  • Server: Apache/2.4.1 (Unix)
  • Server: nginx/1.24.0
  • Server: gunicorn
• It is considered a security risk and actually recommended to mask the version
• I believe having Flask set this header is pointless, as the reverse proxy server would override it.

[nhoening]

I believe having Flask set this header is pointless, as the reverse proxy server would override it.

That might be true. FlexMeasures can be considered to not be the server.

Another thing I'd like in this PR is to mention this setting in the documentation which talks about the API, maybe below the Authentication section.

[Flix6x]

@copilot a few follow-ups:

• Mention the new headers at the end of the Main endpoint and API versions section
• Remove the existing note in that section, as it's outdated.
• Add an entry to documentation/api/change_log.rst under v3.0-30, mentioning the exact headers introduced.
• The /api/v3_0 endpoint currently fails on a 500 status error with 'NoneType' object is not iterable". Write a test for this endpoint, and fix the underlying issue, in a separate PR.

[Copilot]

I believe having Flask set this header is pointless, as the reverse proxy server would override it.

That might be true. FlexMeasures can be considered to not be the server.
...

Done in commit 391e59f — added documentation about the new version headers at the end of the "Main endpoint and API versions" section.

@copilot a few follow-ups:

• Mention the new headers at the end of [the Main endpoint and API versions section](https://flexmeasures.readthedocs.io/stable/api/introduction.html#ma...

Done in commit 391e59f:

• Mentioned the new headers at the end of the "Main endpoint and API versions" section in documentation/api/introduction.rst
• Removed the outdated note from that section
• Added entries to documentation/api/change_log.rst under v3.0-30 for both headers

The /api/v3_0 500 error fix will be addressed in a separate PR as requested.