goslow

Why?

Imagine Facebook/Twitter/Whatever API going down and responding really slow.
Imagine your application using this API and slowing down because of that.
Need an always-slow API to reproduce this situation reliably?
Goslow is that API.

Quick start

Let's say you're developing an application against the Facebook graph API and you want to know how your app behaves when the endpoint graph.facebook.com/me responds in 10 seconds.

Just configure your app to make requests to 10.goslow.link instead of the graph.facebook.com and you're set. 10.goslow.link responds with 10 seconds delay:

time curl 10.goslow.link/me
{"goslow": "response"}
10.423 total

Well, you're almost set, because you received a canned response {"goslow": "response"}. You probably wanted to get the usual graph API response: {"name": "zuck", "gender": "male"}.
No worries, we'll get to that later.

By the way, different endpoints and POST requests also work:

time curl -X POST -d 'your payload' '10.goslow.link/me/feed?message="test"'
{"goslow": "response"}
10.223 total

Need to fake a 6 seconds delay? Just use 6.goslow.link instead of 10.goslow.link

time curl 6.goslow.link/any-endpoint-works
{"goslow": "response"}
6.178 total

Need to simulate some serious delay? Use 199.goslow.link:

time curl 199.goslow.link/me
{"goslow": "response"}
199.204 total

Need to fake a 500 seconds delay? Use 500.goslow.link, right?

Nope! Domains 200.goslow.link, 201.goslow.link, ..., 599.goslow.link respond with HTTP status code 200, 201, ..., 599 without any delay:

time curl -w "%{http_code}" 500.goslow.link/me
{"goslow": "response"}500
0.152 total

301.goslow.link and 302.goslow.link redirect to 0.goslow.link:

time curl -w "%{redirect_url}" 302.goslow.link/me
{"goslow": "response"}HTTP://0.goslow.link
0.107 total

Not-so-quick start

No worries, we'll get to that later.

Remember that bit? It's later time!

Back to the Facebook graph API example. You're using the endpoint graph.facebook.com/me and you want to:

1. Slow it down by 5 seconds.
2. Get {"name": "zuck", "gender": "male"} in response.

Just make a POST request to create.goslow.link/me?delay=5 with the payload {"name": "zuck", "gender": "male"} and you're set. cURL is a great way to do it:

curl -d '{"name": "zuck", "gender": "male"}' 'create.goslow.link/me?delay=5'
Hooray!
Endpoint http://5wx55yijr.goslow.link/me responds to any HTTP method with 5s delay.
Response is: {"name": "zuck", "gender": "male"}

Your personal goslow domain is 5wx55yijr.goslow.link
...

Awesome, you're really set this time:

time curl 5wx55yijr.goslow.link/me
{"name": "zuck", "gender": "male"}
5.382 total

Now, what's the deal with the "your personal goslow domain is 5wx55yijr.goslow.link"? Well, the domain 5wx55yijr.goslow.link is all yours and you can add your custom endpoints to it.

Quick aside: when you POST to create.goslow.link your personal goslow domain will be a little different from the 5wx55yijr.goslow.link. Domain names are randomly generated. For the sake of example let's pretend that the randomly generated domain name was 5wx55yijr.goslow.link. End of quick aside.

You can add new endpoints to your personal domain by POSTing to admin-5wx55yijr.goslow.link

Simple rule. Want an endpoint 5wx55yijr.goslow.link/your-path to respond with your-response? Post your-response to admin-5wx55yijr.goslow.link/your-path.

Let's make the endpoint 5wx55yijr.goslow.link/another/ to respond to POST requests with {"another": "response"} and 3.4 seconds delay:

curl -d '{"another": "response"}' 'admin-5wx55yijr.goslow.link/another/?delay=3.4&method=POST'
Hooray!
Endpoint http://5wx55yijr.goslow.link/another/ responds to POST with 3.4s delay.
Response is: {"another": "response"}

Now you have two endpoints sending different responses with different delays.

time curl 5wx55yijr.goslow.link/me
{"name": "zuck", "gender": "male"}
5.028 total

time curl -d 'any payload' 5wx55yijr.goslow.link/another/
'{"another": "response"}'
3.482 total

The sky's the limit.

Worried whether slow javascript CDN will bring down your app? Goslow've got you covered:

curl ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js | curl -d @- "admin-5wx55yijr.goslow.link/ajax/libs/jquery/2.1.1/jquery.min.js?delay=20"

Hooray!
Endpoint http://5wx55yijr.goslow.link/ajax/libs/jquery/2.1.1/jquery.min.js responds to any HTTP method with 20s delay.
Response is: /*! jQuery v2.1.1 | (c) 2005, 2014 jQuery Foundation, Inc. | jquery.org/licen...

Slow start

If you think that storing your data on unprotected-by-passwords-third-party-domains is not a great idea, then you're absolutely right.

The solution is to install goslow locally.

Installation

Download a precompiled binary for your operating system.

If you're feeling adventurous, you can build goslow from source.

Usage

Start server:

./goslow_darwin_amd64
# or "goslow_windows_amd64.exe" if you're on Windows
# or "goslow_linux_amd64" if you're on Linux
# or "goslow" if you compiled it by yourself

# listening on localhost:5103

By default goslow runs in a single domain mode because nobody wants to deal with the dynamically generated subdomain names on a localhost.

You can configure goslow with POST requests to the endpoint /goslow.

Simple rule for a local instance of goslow. Want an endpoint localhost:5103/your-path to respond with your-response? Post your-response to localhost:5103/goslow/your-path.

Let's add the endpoint /feed:

curl -d '{"local": "response"}' 'localhost:5103/goslow/feed?delay=4.3'
Hooray!
Endpoint http://localhost:5103/feed responds to any HTTP method with 4.3s delay.
Response is: {"local": "response"}

By default goslow stores endpoint data in memory. This means that any endpoint you add will be lost after restart. If you want to use a persistent storage, then you need to specify --driver and --data-source options.

Goslow supports sqlite3:

./goslow --driver sqlite3 --data-source /path/to/sqlite3/db/file
# actually, sqlite3 is the default driver, so this'll do:
# ./goslow --data-source /path/to/sqlite3/db/file

and postgres:

./goslow --driver postgres --data-source postgres://user@host/dbname
# prefix 'postgres://' is required

Get in touch

Got a question or a suggestion? I'd love to hear from you: codumentary.com@gmail.com

Contributing

Contributing to goslow is easy.
First, you need to sign a contributor agreement.
Second, your boss needs to sign a waiver that she's okay with you contributing to goslow.

Just kidding.

Create pull requests, open issues, send emails with patches/tarballs/links-to-pastebin to codumentary.com@gmail.com. Whatever makes you happy. Any form of contribution is welcome.

License

MIT