Declare metrics locally and use MetricsRegister

src/index.ts

@@ -11,12 +11,10 @@ import { CreateListenerOptions, DialOptions, Listener, symbol, Transport } from
 import type { AbortOptions, Multiaddr } from '@multiformats/multiaddr'
 import type { Socket, IpcSocketConnectOpts, TcpSocketConnectOpts } from 'net'
 import type { Connection } from '@libp2p/interface-connection'
-import type { TcpMetrics } from './metrics.js'
+import { getMetrics, Metrics, MetricsRegister } from './metrics.js'
 
 const log = logger('libp2p:tcp')
 
-export { TcpMetrics }
-
 export interface TCPOptions {
   /**
    * An optional number in ms that is used as an inactivity timeout after which the socket will be closed
@@ -60,11 +58,11 @@ export interface TCPCreateListenerOptions extends CreateListenerOptions, TCPSock
 
 class TCP implements Transport {
   private readonly opts: TCPOptions
-  private readonly metrics: TcpMetrics | null
+  private readonly metrics: Metrics | null
 
-  constructor (options: TCPOptions = {}, metrics?: TcpMetrics | null) {
+  constructor (options: TCPOptions = {}, metricsRegistry?: MetricsRegister | null) {
     this.opts = options
-    this.metrics = metrics ?? null
+    this.metrics = metricsRegistry != null ? getMetrics(metricsRegistry) : null
   }
 
   get [symbol] (): true {

src/listener.ts

@@ -11,7 +11,7 @@ import type { MultiaddrConnection, Connection } from '@libp2p/interface-connecti
 import type { Upgrader, Listener, ListenerEvents } from '@libp2p/interface-transport'
 import type { Multiaddr } from '@multiformats/multiaddr'
 import type { TCPCreateListenerOptions } from './index.js'
-import { ServerStatusMetric, TcpMetrics } from './metrics.js'
+import { ServerStatusMetric, Metrics } from './metrics.js'
 
 const log = logger('libp2p:tcp:listener')
 
@@ -32,7 +32,7 @@ interface Context extends TCPCreateListenerOptions {
   socketInactivityTimeout?: number
   socketCloseTimeout?: number
   maxConnections?: number
-  metrics: TcpMetrics | null
+  metrics: Metrics | null
 }
 
 type Status = {started: false} | {started: true, listeningAddr: Multiaddr, peerId: string | null }
@@ -41,7 +41,7 @@ export class TCPListener extends EventEmitter<ListenerEvents> implements Listene
   private readonly server: net.Server
   /** Keep track of open connections to destroy in case of timeout */
   private readonly connections = new Set<MultiaddrConnection>()
-  private readonly metrics: TcpMetrics | null
+  private readonly metrics: Metrics | null
 
   private status: Status = { started: false }
 

src/metrics.ts

@@ -1,11 +1,53 @@
+export enum ServerStatusMetric {
+  stopped = 0,
+  started = 1
+}
+
+export function getMetrics (register: MetricsRegister) {
+  return {
+    serverStatus: register.gauge({
+      name: 'libp2p_tcp_server_status',
+      help: 'Current status of the TCP server'
+    }),
+
+    connections: register.gauge({
+      name: 'libp2p_tcp_connections_count',
+      help: 'Current active connections in TCP listener'
+    }),
+
+    listenerErrors: register.gauge<{ error: string }>({
+      name: 'libp2p_tcp_listener_errors_total',
+      help: 'Total count of TCP listener errors by error type',
+      labelNames: ['error']
+    }),
+
+    socketEvents: register.gauge<{ event: string }>({
+      name: 'libp2p_tcp_socket_events',
+      help: 'Total count of TCP socket events by event',
+      labelNames: ['event']
+    })
+  }
+}
+
+export type Metrics = ReturnType<typeof getMetrics>
+
 /* eslint-disable etc/prefer-interface, @typescript-eslint/method-signature-style */
 
+export interface MetricsRegister {
+  gauge<T extends LabelsGeneric>(config: GaugeConfig<T>): Gauge<T>
+}
+
+interface GaugeConfig<Labels extends LabelsGeneric> {
+  name: string
+  help: string
+  labelNames?: keyof Labels extends string ? Array<keyof Labels> : undefined
+}
+
 type LabelsGeneric = Record<string, string | undefined>
 type CollectFn<Labels extends LabelsGeneric> = (metric: Gauge<Labels>) => void
 
 interface Gauge<Labels extends LabelsGeneric = never> {
-  // Sorry for this mess, `prom-client` API choices are not great
-  // If the function signature was `inc(value: number, labels?: Labels)`, this would be simpler
+  // Follows `prom-client` API choices, to require less middleware on consumer
   inc(value?: number): void
   inc(labels: Labels, value?: number): void
   inc(arg1?: Labels | number, arg2?: number): void
@@ -20,15 +62,3 @@ interface Gauge<Labels extends LabelsGeneric = never> {
 
   addCollect(collectFn: CollectFn<Labels>): void
 }
-
-export enum ServerStatusMetric {
-  stopped = 0,
-  started = 1
-}
-
-export interface TcpMetrics {
-  serverStatus: Gauge
-  connections: Gauge
-  listenerErrors: Gauge<{error: string}>
-  socketEvents: Gauge<{event: string}>
-}