# Go Responsiveness

In late 2021 and early 2022, researchers at Apple took to heart the internet-wide call for giving users more actionable information about the state of their network connections and proposed a new metric, RPM:

> This document specifies the "RPM Test" for measuring responsiveness. It uses common protocols and mechanisms to measure user experience especially when the network is under working conditions. The measurement is expressed as "Round-trips Per Minute" (RPM) and should be included with throughput (up and down) and idle latency as critical indicators of network quality.

Apple wrote and released an implementation of the test in its iOS and macOS operating systems in [versions 15 and Monterey](https://support.apple.com/en-gb/HT212313), respectively.

The researchers at Apple, in collaboration with others throughout the internet-measurement community, proposed RPM as an [IETF RFC](https://github.com/network-quality/draft-ietf-ippm-responsiveness/blob/master/draft-ietf-ippm-responsiveness.txt).

## Independent Implementation

To become a Draft Standard, "at least two independent and interoperable implementation[s]" must exist [RFC2026]. The goal of this implementation of the standard is to satisfy that requirement.

## Operation

### Requirements

1. Go (1.21 -- see below)
2. The source code

**Note**: When go 1.22 is released, this client will upgrade to that version of go. There is an important fix to the runtime ([see here](https://github.com/golang/go/commit/7830180dcd13c028a1619f41bed0ac5e10a720e7)) that we need to incorporate for correctness.

### Satisfy Requirements

To install Go, follow the excellent documentation [online](https://go.dev/doc/install).

To get the source code, 

```console
$ git clone https://github.com/network-quality/goresponsiveness.git
```

For the remainder of the instructions, we will assume that `${RSPVNSS_SOURCE_DIR}` is the location of the source code.

### Build

From `${RSPVNSS_SOURCE_DIR}` grab all the required modules:
```console
$ go mod download
```

And then build:
```console
$ go build networkQuality.go
```

That will create an executable in `${RSPVNSS_SOURCE_DIR}` named `networkQuality`.

> As a bonus, there are now `make`able targets (`all`, `build`, `test`, `clean`) in case that's easier to remember!

### Run

From `${RSPVNSS_SOURCE_DIR}`, running the client is straightforward. Simply 

```console
$ ./networkQuality
```

Without any options, the tool will attempt to contact `networkquality.example.com` on port 4043 to conduct a measurement. That's likely *not* what you intended. To find out all the options for configuring the execution of the tool, specify the `--help` option:

```console
$ ./networkQuality --help
```

`networkQuality` with the `-help` option will generate the following output:

```
  -config string
    	name/IP of responsiveness configuration server. (default "networkquality.example.com")
  -debug
    	Enable debugging.
  -path string
    	path on the server to the configuration endpoint. (default "config")
  -port int
    	port number on which to access responsiveness configuration server. (default 4043)
  -profile string
    	Enable client runtime profiling and specify storage location. Disabled by default.
  -ssl-key-file string
    	Store the per-session SSL key files in this file.
  -sattimeout int
    	Maximum time to spend measuring saturation. (default 20)
  -rpmtimeout int
      Maximum time to spend calculating RPM. (default 10)
```

To facilitate testing, you may want to use the open-source RPM server available from [Apple on GitHub](https://github.com/network-quality/server/tree/main/go).

You can also test against the Apple infrastructure using:

```console
$ ./networkQuality --config mensura.cdn-apple.com --port 443 --path /api/v1/gm/config
```

## Dockerfile

This repo contains a Dockerfile for running the binary so you
don't have to install any languages or build tools.
To use it:

```bash
# build the container
docker build -t goresp .   

# run the RPM test
docker run --rm goresp     

# run the RPM test with full options, testing against Apple infrastructure
docker run --rm goresp --config mensura.cdn-apple.com --port 443 --path /api/v1/gm/config --debug
```

## Contributing

We *love* contributions. Before submitting a patch, first format your code with `go fmt`. Then, run `golines`:

```console
$ golines -w .
```

You can easily install `golines` in to your `${GOPATH}` with

```console
$ go install github.com/segmentio/golines@latest
```

As a bonus, there are unit tests to check for regressions:

```console
$ go test ./timeoutat ./ms ./utilities  ./traceable
```

### IDE Configuration

If you are developing with VSCode, you can use `ide/settings.json` as the
[workspace's](https://code.visualstudio.com/docs/editor/workspaces) `settings.json` file
in order to meet the project's existing style. In particular, this file will configure
VSCode to use an alternate go formatter known as [`gofumpt`](https://github.com/mvdan/gofumpt)
and, in turn, give `gofumpt` specific configuration directives.

To use the included `settings.json` file, simply drop it in the `.vscode` directory of the folder
containing this `README.md` file.

>Note: If you have existing workspace settings, you may be required to take additional
steps to incorporate the information in the given `settings.json` file.

> You may have to create the `.vscode` directory if it does not already exist.

## References

[RFC2026] https://datatracker.ietf.org/doc/html/rfc2026