140 lines
4.6 KiB
TypeScript
140 lines
4.6 KiB
TypeScript
import type { Logger } from 'homebridge'
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import type { HttpConfig, HttpResponse, HttpServer } from './adapters/http'
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import type { Metric } from './metrics'
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import { strTrimRight } from './std'
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export class MetricsRenderer {
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private readonly prefix: string
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constructor(prefix: string) {
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this.prefix = strTrimRight(prefix, '_')
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}
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render(metric: Metric): string {
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const name = this.metricName(metric.name)
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return [
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`# TYPE ${name} ${name.endsWith('_total') ? 'counter' : 'gauge'}`,
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`${name}${this.renderLabels(metric.labels)} ${metric.value}${
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metric.timestamp !== null ? ' ' + String(metric.timestamp.getTime()) : ''
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}`,
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].join('\n')
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}
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private renderLabels(labels: Metric['labels']): string {
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const rendered = Object.entries(labels)
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.map(([label, val]) => `${sanitizePrometheusMetricName(label)}="${escapeAttributeValue(val)}"`)
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.join(',')
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return rendered !== '' ? '{' + rendered + '}' : ''
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}
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private metricName(name: string): string {
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name = name.replace(/^(.*_)?(total)_(.*)$/, '$1$3_$2')
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return sanitizePrometheusMetricName(`${this.prefix}_${name}`)
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}
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}
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const retryAfterWhileDiscovery = 15
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const textContentType = 'text/plain; charset=utf-8'
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const prometheusSpecVersion = '0.0.4'
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const metricsContentType = `${textContentType}; version=${prometheusSpecVersion}`
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function withHeaders(contentType: string, headers: Record<string, string> = {}): Record<string, string> {
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return { ...headers, 'Content-Type': contentType }
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}
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export class PrometheusServer implements HttpServer {
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private metricsDiscovered = false
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private metricsResponse = ''
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constructor(
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public readonly config: HttpConfig,
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public readonly log: Logger | null = null,
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private readonly renderer: MetricsRenderer = new MetricsRenderer(config.prefix),
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) {}
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onRequest(): HttpResponse | null {
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if (this.metricsDiscovered) {
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return null
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}
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return {
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statusCode: 503,
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headers: withHeaders(textContentType, { 'Retry-After': String(retryAfterWhileDiscovery) }),
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body: 'Metrics discovery pending',
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}
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}
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onMetrics(): HttpResponse {
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return {
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statusCode: 200,
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headers: withHeaders(metricsContentType),
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body: this.metricsResponse,
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}
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}
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onNotFound(): HttpResponse {
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return {
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statusCode: 404,
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headers: withHeaders(textContentType),
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body: 'Not found. Try /metrics',
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}
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}
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onError(error: Error): HttpResponse {
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this.log?.error('HTTP request error: %o', error)
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return {
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headers: withHeaders(textContentType),
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body: error.message,
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}
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}
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onMetricsDiscovery(metrics: Metric[]): void {
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this.metricsResponse = metrics.map((metric) => this.renderer.render(metric)).join('\n')
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this.metricsDiscovered = true
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}
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}
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// From https://github.com/open-telemetry/opentelemetry-js/blob/main/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
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function escapeString(str: string) {
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return str.replace(/\\/g, '\\\\').replace(/\n/g, '\\n')
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}
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/**
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* String Attribute values are converted directly to Prometheus attribute values.
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* Non-string values are represented as JSON-encoded strings.
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*
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* `undefined` is converted to an empty string.
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*/
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function escapeAttributeValue(str: Metric['labels'][keyof Metric['labels']]) {
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if (typeof str !== 'string') {
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str = JSON.stringify(str)
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}
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return escapeString(str).replace(/"/g, '\\"')
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}
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const invalidCharacterRegex = /[^a-z0-9_]/gi
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/**
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* Ensures metric names are valid Prometheus metric names by removing
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* characters allowed by OpenTelemetry but disallowed by Prometheus.
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*
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* https://prometheus.io/docs/concepts/data_model/#metric-names-and-attributes
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*
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* 1. Names must match `[a-zA-Z_:][a-zA-Z0-9_:]*`
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*
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* 2. Colons are reserved for user defined recording rules.
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* They should not be used by exporters or direct instrumentation.
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*
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* OpenTelemetry metric names are already validated in the Meter when they are created,
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* and they match the format `[a-zA-Z][a-zA-Z0-9_.\-]*` which is very close to a valid
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* prometheus metric name, so we only need to strip characters valid in OpenTelemetry
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* but not valid in prometheus and replace them with '_'.
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*
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* @param name name to be sanitized
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*/
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function sanitizePrometheusMetricName(name: string): string {
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return name.replace(invalidCharacterRegex, '_') // replace all invalid characters with '_'
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}
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