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Text Moderation with Firebase Cloud Functions
This template shows how to perform server side moderation of text written to a Firebase DB.
For instance if a user added the message "I DON'T LIKE THIS APP!! This is POOP!!!" this will get moderated to a - more civilized - non uppercase message: "I don't like this app. This is ****".
Cloud Function Code
See file index.js and moderation-string-utils.js for the moderation code.
Moderation of the messages is performed using bad-words a bad words remover that uses an external list of bad-words and is currently mostly aimed at filtering english bad words. Also messages that contains mostly upper case characters are re-capitalized correctly using capitalize-sentence.
The dependencies are listed in package.json.
Sample Database Structure
Users anonymously add a message text to the /messages list:
/functions-project-12345
/messages
/key-123456
text: "This is my first message!"
/key-123457
text: "This is my second message!"
Trigger rules
Below is the trigger rule for the moderator function making sure it's triggered only when a new message is created and not every time it's updated.
"functions": {
".source": "functions",
"moderator": {
"triggers": {
"database": {
"path": "/messages/$message",
"condition": "!data.exists()" // Only run the function once on new messages
}
}
}
}
Security Rules
The following security rules ensures users cannot read a message before it has been sanitized. The function adds a sanitize attribute (boolean) to the messages once they have been moderated.
Also we make sure that users can only create a message and not edit them. We also make sure they cannot set the sanitized flag already.
{
"rules": {
"messages": {
"$message": {
// Users can only add new messages. Not modify or delete them. Also makes sure they cannot mark a message as
// already sanitized.
".write": "!data.exists() && !newData.child('sanitized').exists()'"
".read": "data.child('sanitized').val() === true"
}
}
}
}