Web Messaging SDK: Handling file upload MIME type restrictions

NICE CXone API & Integrations
1

Quick question about the Web Messaging SDK file upload logic.

  • We’ve built a custom integration using the genesys-cloud-messaging-sdk to handle customer file submissions.
  • The requirement is strict: only PDF and JPG files under 5MB.
  • I’m trying to enforce this client-side before hitting the API, but the SDK doesn’t expose a clear onFileSelect validator hook in the docs.
  • Here’s my current config:
const config = {
organizationId: 'my-org-id',
messaging: {
fileUpload: {
enabled: true,
maxFileSize: 5242880 // 5MB
}
}
};
  • When I try to intercept the file object to check file.type against ['application/pdf', 'image/jpeg'], the UI still allows the selection and sends a 415 Unsupported Media Type on the backend.
  • Is there a specific event listener I’m missing to drop invalid files before the send() method triggers?
  • Or should I just parse the error response from the /api/v2/messaging/contacts/webmessaging endpoint and retry?
  • Need a code snippet if possible. Prefer not to hack the DOM.
2

You need to bypass the SDK’s built-in upload handler if you want strict validation. The standard genesys-cloud-messaging-sdk doesn’t expose a pre-flight validator for file types because it relies on server-side schema enforcement. trying to hack the config object won’t work reliably across versions.

Cause:
The SDK assumes the API gateway will reject invalid MIME types. It doesn’t care about your 5MB limit or PDF-only rule until the blob hits Genesys Cloud. By then, you’ve wasted bandwidth and UX.

Solution:
Intercept the file input at the DOM level before the SDK processes it. Use a custom render prop or override the attachment component.

// Intercept file selection
const handleFileChange = (e) => {
 const file = e.target.files[0];
 const allowed = ['application/pdf', 'image/jpeg'];
 const maxSize = 5 * 1024 * 1024; // 5MB

 if (!allowed.includes(file.type)) {
 alert('Only PDF and JPG allowed');
 return;
 }
 if (file.size > maxSize) {
 alert('File too large');
 return;
 }
 
 // Now pass to SDK or custom upload endpoint
 sdk.sendFile(file); 
};

handle the validation in your wrapper component. don’t trust the SDK to filter.

3

It depends, but generally… the SDK doesn’t give you that hook because it’s designed to be a dumb pipe to the API gateway. trying to patch the config object is a dead end. you’ll need to intercept the file selection event before the SDK processes it. in my grafana plugins, i often have to do similar pre-processing on raw telemetry streams to avoid bloating the db. here’s how you can hook into the DOM event directly if you’re using the standard web component. you can attach a listener to the file input element that the SDK renders.

document.querySelector('genesys-cloud-messaging').shadowRoot.querySelector('input[type="file"]').addEventListener('change', (e) => {
 const file = e.target.files[0];
 if (!file) return;
 const allowedTypes = ['application/pdf', 'image/jpeg'];
 if (!allowedTypes.includes(file.type) || file.size > 5 * 1024 * 1024) {
 alert('Invalid file type or size');
 e.target.value = ''; // clear selection
 return;
 }
});

this works, but it’s fragile. shadow dom selectors can break if genesys updates the internal component structure. a more solid approach is to wrap the SDK instance and override the sendFile method if you have access to the underlying javascript object, or just handle the upload via your own backend proxy. validate the file there, then use the /api/v2/communications/interactions endpoint to attach it manually. keeps the validation logic server-side and out of the client code. much cleaner for long term maintenance. i usually prefer the proxy route anyway since i need to log the metadata for my analytics dashboards. the sdk just gives you the conversation id, not the file hash or mime type details you might want to track in influxdb.

4

The easiest fix here is this is…
Cause: the sdk doesn’t care about mime types until the blob hits the gateway. you’ll get a 400 if you don’t check it yourself.
Solution: intercept the input change event in your wrapper component.

input.addEventListener('change', (e) => {
 const file = e.target.files[0];
 if (!['application/pdf', 'image/jpeg'].includes(file.type) || file.size > 5 * 1024 * 1024) {
 e.target.value = ''; // clear invalid selection
 alert('Invalid file type or size');
 }
});