@stordata/grammars/src/visitors/PrometheusMetricsParserVisitor.js

A collection of ANTLR grammars used at Stordata. This project exists so that we can package the grammars (and various utilities) as a CommonJS module. The `antlr4` Javascript runtime is only available as an ES module at the time of writing.

import PrometheusMetricsVisitor from '../../generated/src/grammars/PrometheusMetricsVisitor.js';

export default class PrometheusMetricsParserVisitor extends PrometheusMetricsVisitor {

  visitLine(ctx) {
    const metric = ctx.metric();

    return new Metric(metric.name, ctx.value, ctx.timestamp, metric.label());
  }

}

class Metric {

  name = '';
  labels = {};
  value = null;
  timestamp = null;

  constructor(name, value, timestamp, labels) {
    this.name = getText(name);
    this.value = parseNumber(getText(value));
    this.timestamp = parseNumber(getText(timestamp));
    this.labels = labels.reduce(toKeyedLabelsReducer, {});
  }

}

function getText(ctx) {
  const text = ctx?.text;

  if (!text) {
    return null;
  }

  if (!text.startsWith('"')) {
    return text;
  }

  return text
    .slice(1, text.length - 1)
    .replaceAll('\\\\', '\\')
    .replaceAll('\\"', '"')
    .replaceAll('\\r', '\r')
    .replaceAll('\\n', '\n');
}

function parseNumber(text) {
  if (!text) {
    return null;
  }

  switch (text) {
    case 'NaN':
      return NaN;
    case '+Inf':
      return Infinity;
    case '-Inf':
      return -Infinity;
    default:
      return parseFloat(text);
  }
}

function toKeyedLabelsReducer(acc, ctx) {
  acc[getText(ctx.name)] = getText(ctx.value);

  return acc;
}