[Bug Report] Web: NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH from .env.* does not take effect in Chunk Settings

[hsiong]

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Dify version

v.11.2

Cloud or Self Hosted

Self Hosted (Source)

Steps to reproduce

1. Configure the web env exactly following web/.env.example. Set only:

   NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH=40000
   

2. Rebuild and restart the web service:

   docker compose up -d --build web
   

3. Open the web UI:
   Chunk Settings → General → Maximum chunk length

   Observe the maximum value.

4. Check the page-injected value in browser console:

   document.body.getAttribute('data-public-indexing-max-segmentation-tokens-length')
   

✔️ Expected Behavior

1. Open the web UI: Chunk Settings → General → Maximum chunk length
   The maximum value is still 8000.
2. In the browser console, the injected value is empty:

document.body.getAttribute('data-public-indexing-max-segmentation-tokens-length')

Result:

'8000'

❌ Actual Behavior

1. Open the web UI: Chunk Settings → General → Maximum chunk length
   The maximum value is still 4000 (not 8000).
2. In the browser console, the injected value is empty:

document.body.getAttribute('data-public-indexing-max-segmentation-tokens-length')

Result:

''

[dosubot]

The environment variable NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH is read at build time in the frontend (specifically in web/app/layout.tsx) and injected as a data attribute on the HTML body. If the attribute is empty in the browser, it means the variable was not present when the frontend was built or started, so the UI falls back to the default value (often 4000) see code reference.

Common causes for this include editing the wrong .env file, not rebuilding the frontend after changing the variable, or Docker volume/config issues. To troubleshoot:

1. Make sure you set the variable in the correct .env file (usually web/.env for the frontend).
2. Use the environment variable sync tool (dify-env-sync.sh) to ensure your .env matches .env.example see PR.
3. Fully rebuild the frontend: run docker compose down, then docker compose up -d --build web.
4. Check that the variable is present in the running container: docker exec -it <web_container_name> env | grep NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH.
5. If the value is still missing, check for Docker volume mount issues or misconfigured containers.

Note: The backend chunk/token length is controlled by INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH, not the NEXT_PUBLIC_ variant. The frontend UI reflects the backend value after a restart if the environment variable is set and propagated correctly see discussion.

If you need chunk sizes above 4000, make sure you're running a version after the October 2025 fix (PR #26782), which made chunking respect the environment variable dynamically see issue.

To reply, just mention @dosu.

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[hsiong]

Additional Context

After setting:

NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH=8000

and rebuilding/restarting the web service, the UI still shows the maximum value as 4000 under:

Chunk Settings → General → Maximum chunk length

In the browser console, the injected value is empty:

document.body.getAttribute('data-public-indexing-max-segmentation-tokens-length')

Result:

''

I then checked the deployment script web/docker/entrypoint.sh and found it unconditionally overwrites the public env var:

export NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH=${INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH}

This suggests the value from NEXT_PUBLIC_INDEXING_MAX_SEGMENTATION_TOKENS_LENGTH can be ignored/overwritten during container startup, leading to an empty injected value and the UI falling back to the default maximum (4000).