Compare two different sets of prometheus metrics based on the output of the `/metrics` endpoint

prom-compare.js

#!/usr/bin/env deno run -A
import { readStringDelim } from "https://deno.land/std@0.186.0/io/read_string_delim.ts";
import * as path from "https://deno.land/std@0.186.0/path/mod.ts";

async function extractMetricNames(f) {
  const filename = path.join(Deno.cwd(), f);
  let fileReader = await Deno.open(filename);

  let metrics = new Set();

  for await (let line of readStringDelim(fileReader, "\n")) {
    if (!line.startsWith("#") && line.length !== 0) {
      let end = line.indexOf("{");
      if (end === -1) {
        end = line.indexOf(" ");
      }
      if (end === -1) {
        end = line.indexOf("\n");
      }
      const metricName = line.slice(0, end);
      metrics.add(metricName);
    }
  }
  
  metrics = [...metrics];
  metrics.sort();
  return metrics;
}

let [left, right] = await Promise.all([
  extractMetricNames(Deno.args[0]),
  extractMetricNames(Deno.args[1]),
]);

for (const l of left) {
  if (!right.includes(l)) {
    console.log(`%c-${l}`, "color: red");
  }
}

for (const r of right) {
  if (!left.includes(r)) {
    console.log(`%c+${r}`, "color: green");
  }
}