Handling Server Errors in Streamlit: Capturing and Displaying Error Messages to Users

[Cosmin_Andrei]

Hello everyone!

I received this error: AxiosError: Request failed with status code 413 for an application built in Streamlit. I noticed that the error is from the server, and I have increased the limit in nginx.

However, I would like to capture this error and display a message to the user saying that the file size is too large. I understand that the error is received from the server and rendered in Streamlit.

So how can I retrieve that specific error? Where does Streamlit handle server errors exactly? I hope you can help me.

Thank you very much!

[dataprofessor]

Hi @Cosmin_Andrei

Thanks for your question.

Instead of capturing the error, here’s an implementation that conditionally display messages using if/else statement:

1. If no file is uploaded a warning message is displayed via st.warning() to remind the user to upload a file
2. If the file exceeds the 1 MB limit then it displays an error message via st.error()
3. Else the success message is displayed via st.success()

import streamlit as st

MAX_FILE_SIZE = 1024 * 1024  # Maximum file size in bytes

uploaded_file = st.file_uploader("Choose a file")
if uploaded_file is not None and len(uploaded_file.read()) > MAX_FILE_SIZE:
    st.error("Error: File size is too large.")
elif uploaded_file is None:
    st.warning("Please upload a file!")
else:
    st.success('File successfully uploaded and processed.')

A screencast of the app is shown below:

Hope this helps!

Best regards,
Chanin

[Cosmin_Andrei]

Thank you for the response and the idea. It could be a good approach that we will consider, but in this case, the file will be uploaded to the server, and I wanted to avoid uploading very large files. I will create a function that will delete any file in the end, but I’m trying to avoid their upload to the server. Maybe I didn’t fully explain in the first message. I looked closer now and realized that I could handle the issue differently. I could manipulate the st.file_uploader to have a limit of, for example, 20MB. I would need to add the following lines to the config.toml file in the .streamlit folder:

[server]
maxUploadSize = 20

More details can be found here - st.file_uploader - Streamlit Docs

Nevertheless, your solution is also welcome because it allows me to manage the messages that the user sees. Thank you very much!