dimensions are not escaped

[AZm87]

I developed a API (based on vapor 4) that throws errors with additional information

enum APIError: Error {
    ...
    case invalidParameter(String),
    ...
}

I want to monitor the reasons for a failed response with prometheus so I added the following line:

prometheus.makeCounter(label: "response_error", dimensions: [("error", "\(error)")]).increment(by: 1)

But this results in the following line in the output:

response_error{error="invalidParameter("Invalid value for parameter <code>")"} 28

According to the documentation the "Label values may contain any Unicode characters." but Prometheus can't read this.

Steps to reproduce

import Prometheus

let prometheus = PrometheusClient()
prometheus.makeCounter(label: "response_error", dimensions: [("error", "a\"b\"c")]).increment(by: 1)
let f : (String) -> () = { print($0) }
prometheus.collect(f)

Actual behavior

the result is response_error{error="a"b"c"} 1

Expected behavior

the result should be escaped to response_error{error="a'b'c"} 1. In my first tests response_error{error="a\"b\"c"} 1 also worked but not sure.

Environment

• OS version: MacOS Big Sur Version 11.0.1
• Swift version: Apple Swift version 5.3.1 (swiftlang-1200.0.41 clang-1200.0.32.8)
• SwiftPrometheus 1.0.0-alpha

[MrLotU]

Thanks for opening this issue, and my apologies for the time it took me to respond!

From my initial research I couldn't find anywhere where Prometheus mentions " should be an illegal character in metrics, but it does make sense. I will dig a bit deeper into how this can be solved, and also take a look at what other languages' prometheus clients do in this case.