feat: add system logger (#457)

Adds a system logger for internal usage, closely modeled after the
edge-functions one.

src/internal.ts

@@ -0,0 +1,5 @@
+// this file is exported as @netlify/functions/internal,
+// and only meant for consumption by Netlify Teams.
+// While we try to adhere to semver, this file is not considered part of the public API.
+
+export { systemLogger, LogLevel } from './lib/system_logger.js'

src/lib/system_logger.ts

@@ -0,0 +1,79 @@
+const systemLogTag = '__nfSystemLog'
+
+const serializeError = (error: Error): Record<string, unknown> => {
+  const cause = error?.cause instanceof Error ? serializeError(error.cause) : error.cause
+
+  return {
+    error: error.message,
+    error_cause: cause,
+    error_stack: error.stack,
+  }
+}
+
+// eslint pretends there's a different enum at the same place - it's wrong!
+// eslint-disable-next-line no-shadow
+export enum LogLevel {
+  Debug = 1,
+  Log,
+  Error,
+}
+
+class SystemLogger {
+  private readonly fields: Record<string, unknown>
+  private readonly logLevel: LogLevel
+
+  constructor(fields: Record<string, unknown> = {}, logLevel = LogLevel.Log) {
+    this.fields = fields
+    this.logLevel = logLevel
+  }
+
+  private doLog(logger: typeof console.log, message: string) {
+    logger(systemLogTag, JSON.stringify({ msg: message, fields: this.fields }))
+  }
+
+  log(message: string) {
+    if (this.logLevel > LogLevel.Log) {
+      return
+    }
+
+    this.doLog(console.log, message)
+  }
+
+  debug(message: string) {
+    if (this.logLevel > LogLevel.Debug) {
+      return
+    }
+
+    this.doLog(console.debug, message)
+  }
+
+  error(message: string) {
+    if (this.logLevel > LogLevel.Error) {
+      return
+    }
+
+    this.doLog(console.error, message)
+  }
+
+  withLogLevel(level: LogLevel) {
+    return new SystemLogger(this.fields, level)
+  }
+
+  withFields(fields: Record<string, unknown>) {
+    return new SystemLogger(
+      {
+        ...this.fields,
+        ...fields,
+      },
+      this.logLevel,
+    )
+  }
+
+  withError(error: unknown) {
+    const fields = error instanceof Error ? serializeError(error) : { error }
+
+    return this.withFields(fields)
+  }
+}
+
+export const systemLogger = new SystemLogger()

test/unit/system_logger.js

@@ -0,0 +1,37 @@
+const test = require('ava')
+
+const { systemLogger, LogLevel } = require('../../dist/internal')
+
+test('Log Level', (t) => {
+  const originalDebug = console.debug
+
+  const debugLogs = []
+  console.debug = (...message) => debugLogs.push(message)
+
+  systemLogger.debug('hello!')
+  t.is(debugLogs.length, 0)
+
+  systemLogger.withLogLevel(LogLevel.Debug).debug('hello!')
+  t.is(debugLogs.length, 1)
+
+  systemLogger.withLogLevel(LogLevel.Log).debug('hello!')
+  t.is(debugLogs.length, 1)
+
+  console.debug = originalDebug
+})
+
+test('Fields', (t) => {
+  const originalLog = console.log
+  const logs = []
+  console.log = (...message) => logs.push(message)
+  systemLogger.withError(new Error('boom')).withFields({ foo: 'bar' }).log('hello!')
+  t.is(logs.length, 1)
+  t.is(logs[0][0], '__nfSystemLog')
+  const log = JSON.parse(logs[0][1])
+  t.is(log.msg, 'hello!')
+  t.is(log.fields.foo, 'bar')
+  t.is(log.fields.error, 'boom')
+  t.is(log.fields.error_stack.split('\n').length > 2, true)
+
+  console.log = originalLog
+})

tsconfig.json

@@ -11,7 +11,7 @@
     // "disableReferencedProjectLoad": true,             /* Reduce the number of projects loaded automatically by TypeScript. */
 
     /* Language and Environment */
-    "target": "ES2020" /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */,
+    "target": "ES2022" /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */,
     // "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
     // "jsx": "preserve",                                /* Specify what JSX code is generated. */
     // "experimentalDecorators": true,                   /* Enable experimental support for TC39 stage 2 draft decorators. */