Streamlit upload limit logs omit configured maxUploadSize value

Answer the Exact Question First

1. No configuration flag exists to embed server.maxUploadSize into the standard INFO‑level error message.

2. Enabling DEBUG logging reliably produces a traceback that includes the configured limit value.

3. Operators can rely on DEBUG logs for log‑only diagnosis, but for high‑traffic or production environments they should also monitor metrics or configuration change events to avoid excessive log volume.

Likely Explanation

Streamlit’s upload‑size check is performed in streamlit.web.server.uploads. When the file exceeds server.maxUploadSize, the code raises a StreamlitError that contains the actual size but deliberately omits the limit from the INFO‑level message to keep logs concise. The exception’s __repr__ does, however, reference max_upload_size when the logger is set to DEBUG, producing a full traceback that shows the value read from config.toml or overridden by environment variables.

Why the INFO Log Omits the Limit

• Reduces noise for common upload failures that are not limit‑related.
• Keeps the default log output lightweight for production deployments.
• The limit is considered part of the configuration context, not the runtime error itself.

Confirmed Facts & Practical Steps

1. Locate or create .streamlit/config.toml in your app directory.

2. Add or adjust the limit:

   [server]
   maxUploadSize = 1   # megabytes
   

3. To enable DEBUG logging, add the following block:

4. [logger]
   level = "debug"
   

5. Restart the Streamlit process.
6. Upload a file larger than the configured limit.

7. On stderr you should now see a traceback similar to:

   Traceback (most recent call last):
     File "/usr/local/lib/python3.11/site-packages/streamlit/web/server/uploads.py", line 89, in _handle_file_upload
       raise StreamlitError(f"File too large: {size} bytes, limit {max_upload_size} MB")
   StreamlitError: File too large: 2.5 MB, limit 1 MB
   

8. When DEBUG is disabled, the log will only contain:

9. Uploaded file size 2.5 MB exceeds the maximum allowed size.
   

Operational Considerations

• DEBUG logs can generate a high volume of entries in busy apps; enable it only temporarily for troubleshooting.
• The configured limit may be overridden by STREAMLIT_SERVER_MAX_UPLOAD_SIZE environment variable or command‑line flags; verify the active value before diagnosing.
• Future Streamlit releases might change the traceback format or remove the limit reference; keep your monitoring logic version‑agnostic where possible.
• For continuous monitoring, consider exposing the limit as a Prometheus gauge or alerting on upload‑size metrics that exceed the threshold.

Missing Diagnostic Detail

To tailor the recommendation further, could you confirm which Streamlit version you are running? Different releases may have subtle differences in logging behavior.