Add virus scan stage when uploading a letter

app/main/views/uploads.py

@@ -1,8 +1,10 @@
 import uuid
+from io import BytesIO
 
-from flask import redirect, render_template, request, url_for
+from flask import flash, redirect, render_template, request, url_for
 
 from app import current_service
+from app.extensions import antivirus_client
 from app.main import main
 from app.main.forms import PDFUploadForm
 from app.utils import user_has_permissions
@@ -20,6 +22,13 @@ def upload_letter(service_id):
     form = PDFUploadForm()
 
     if form.validate_on_submit():
+        pdf_file_bytes = form.file.data.read()
+
+        virus_free = antivirus_client.scan(BytesIO(pdf_file_bytes))
+        if not virus_free:
+            flash('Your file has failed the virus check', 'dangerous')
+            return render_template('views/uploads/choose-file.html', form=form), 400
+
         upload_id = uuid.uuid4()
 
         return redirect(