Force Twilio to respond to request slowly in order to test app's handling - testing

Question

I'm debugging an application that sends SMS messages via the Twilio REST API. The other day we had a strange bug that we can't reproduce, and I think it may have been happening because the Twilio API took very long to respond (2-3 seconds) and the app didn't handle the delay well.
We're working on improving the app to better handle a scenario like this, but I'm not sure how to test if we've really fixed the issue. Is there a way to force Twilio to respond slowly, in order to test this?
I realize that I could make my own mock web service with a long delay and substitute it in for Twilio -- but I'd like to avoid that if possible. In particular, I'm using one of the Twilio helper libraries for all of my call-outs, and would like to avoid monkey-patching them if at all possible.

Answer 1

You might want to try configuring a proxy server in your tests, that responds very slowly. Here's one that we use, in Nginx. Note it requires the nginx-lua module.
location ~ /slow {
# Proxy pass is necessary so the incoming request is accepted and
# processed by nginx.
proxy_pass http://127.0.0.1:11418;
}
server {
listen 127.0.0.1:11418;
location ~ / {
# return a funny HTTP code here, so it's clear that the slow block got
# hit.
add_header 'X-Served-By: slow-as-heck';
content_by_lua 'ngx.sleep(25); ngx.exit(418)';
}
}
You can also try connecting a dead IP that won't send back a TCP reset, like 10.255.255.1.
Hope it helps,
Kevin

Answer 2

Twilio evangelist here.
There is not currently a way to tell Twilio to simulate a slow HTTP response or an HTTP response timeout.
Depending on your platform there may be a way to catch a network timeout, which is what it sounds like you suspect caused the problem.
Hope that helps.