Slow Joe

Simple TCP proxy to test your services for poor network conditions.

Simplicity is the most important aspect. No one wants to spend hours looking for dependencies, then learning yet another DSL or the quirks of a config file, right? Downloading a single, static binary (see releases) and reading the description of a few flags is all you need to start. Being a Docker aficionado makes things even simpler: all you need is to run docker run, as the service image is available on Docker Hub.

WARNING: unstable product. API, configuration and behaviour may and will change without a warning.

Quick start

If docker is available it is by far the easiest way to download and run service:

docker run --rm -it adamwasila/slowjoe:latest

INFO[0000] Upstream set                                  address="127.0.0.1:8000"
INFO[0000] Listen on TCP socket                          bind="127.0.0.1:9998"

Otherwise, go to releases subpage and download latest version, unpack and put in your PATH.

Last option is to build on your own. See Install section below for details.

With the binary in your PATH, you may try the following examples. First, run a less trivial example where slowjoe works as a proxy to the httpbin service. Let's assume that 10% of requests should have throughput limited to 1kb/s.

slowjoe -a -u "httpbin.org:80" -t 0.1 -r 1024

Use curl to check proxy response:

curl http://localhost:9998/headers

{
  "headers": {
    "Accept": "*/*", 
    "Host": "localhost", 
    "User-Agent": "curl/7.64.0"
  }
}

Now hit the following link in your browser http://localhost:9998/image/jpeg and experience modem-like connection speed. Welcome back to the Internet of the 90s.

Next test closing immediately behaviour:

slowjoe -u "httpbin.org:80" -c 1.0

Now, all requests should be closed without sending any data.

Both behaviours may be mixed together. Here, half of the connections are closed immediately and half are throttled to 1000 bytes per second:

slowjoe -u "httpbin.org:80" -c 0.5 -t 0.5 -r 1000

Finally, point your browser to http://localhost:6000 to see current settings and a list of currently open connections:

Note: -a option must be set to enable web dashboard. Then -p may be used to set port other than default 6000.

Install

Go 1.26 should be installed on the system. While it should compile succesfully using older versions it is recommended to use version 1.26 or newer.

Clone project repository to your machine:

git clone https://github.com/adamwasila/slowjoe.git

To build, enter repository and run:

go build -o slowjoe ./cmd/slowjoe

Configuration

Help flag -h allows to see full configuration options:

slowjoe -h

Usage of slowjoe:
  -a, --admin                   Enable admin console service
  -p, --admin-port int          Port for admin console service (default 6000)
  -b, --bind string             Address to bind listening socket to (default "0.0.0.0:9998")
  -c, --close-chance float      Probability of closing socket abruptly
  -d, --delay duration          Initial delay when connection starts to deteriorate
  -r, --rate int                Maximum data rate of bytes per second if throttling applied (see --throttle-chance)
  -t, --throttle-chance float   Probability of throttling
  -u, --upstream string         <host>[:port] of upstream service (default "127.0.0.1:8000")
  -v, --verbose                 Enable verbose output (debug logs)
  -w, --very-verbose            Enable very verbose output (trace logs)