Checking if file being uploaded is unique

Hey Folks,

I am building a feature which allos the users to upload files through Trix editor. So people could paste snapshots as well as drag and drop files into the editor. I then process this and upload it on S3 bucket.

Can someone let me know how I can check that the file (not just the name but content) is unique before I upload it to S3

My client side code is this

document.addEventListener("trix-attachment-add", function(event){
		        	var attachment = event.attachment;
		        	console.log(attachment.file)
		        	if (attachment.file)
		        	{
		        		var file=attachment.file;
					       
					       let formData = new FormData();
					       formData.append("attachments", file);
					       		axios.post('/fileuploads', formData, {
			                    headers: {
			      					'Content-Type': 'multipart/form-data'
			    				}
			                })
			                .then(response=>{
			                    this.response_message=response;
			                    
			                    attachment.setAttributes({
			                    	url: this.response_message['data']['data'],
			                    	href: this.response_message['data']['data']
			                    });
			                    
			                }, (error) => {
			                    
			                   
			                })
		        	}
		        }); // Listen to the changes on the 

And server side is this

Route::post('/fileuploads', function() {
		$fileUploadResponse=request()->file('attachments')->store('problems/'.\Auth::id(),'s3');
		$url = Storage::url($fileUploadResponse);
		return response()->json(['isvalid'=>true,'data'=>$url ,'message'=>'File uploaded successfully.']);
	});

I am ok to do that validation either on client or server. I don't have a preference. Any help is very appreciated.