Makes "logger/compat" more focused on compatibility. Fixes #697 (#701)

Author: mbleigh

CHANGELOG.md

@@ -9,10 +9,10 @@
   });
   ```
 
-  The logger can also override default behavior of `console.*` methods through a special require:
+- Adds a special require that mimics Node.js 8 runtime logging in Node.js 10 and later runtimes:
 
   ```js
   require('firebase-functions/logger/compat');
   ```
 
-  In older runtimes, logger prints to the console, and no structured data is saved.
+  In newer runtimes, requiring this will emit text logs with multi-line support and appropriate severity. In the Node.js 8 runtime, the `compat` module has no effect.

src/logger.ts

@@ -1,32 +1,10 @@
 import { format } from 'util';
 
-// safely preserve unpatched console.* methods in case of compat require
-const unpatchedConsole = {
-  debug: console.debug,
-  info: console.info,
-  log: console.log,
-  warn: console.warn,
-  error: console.error,
-};
-
-// Determine if structured logs are supported (node >= 10). If something goes wrong,
-// assume no since unstructured is safer.
-const SUPPORTS_STRUCTURED_LOGS =
-  parseInt(process.versions?.node?.split('.')?.[0] || '8', 10) >= 10;
-
-// Map LogSeverity types to their equivalent `console.*` method.
-const CONSOLE_SEVERITY: {
-  [severity: string]: 'debug' | 'info' | 'warn' | 'error';
-} = {
-  DEBUG: 'debug',
-  INFO: 'info',
-  NOTICE: 'info',
-  WARNING: 'warn',
-  ERROR: 'error',
-  CRITICAL: 'error',
-  ALERT: 'error',
-  EMERGENCY: 'error',
-};
+import {
+  SUPPORTS_STRUCTURED_LOGS,
+  CONSOLE_SEVERITY,
+  UNPATCHED_CONSOLE,
+} from './logger/common';
 
 /**
  * `LogSeverity` indicates the detailed severity of the log entry. See [LogSeverity](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#logseverity) for more.
@@ -57,7 +35,7 @@ export interface LogEntry {
  */
 export function write(entry: LogEntry) {
   if (SUPPORTS_STRUCTURED_LOGS) {
-    unpatchedConsole[CONSOLE_SEVERITY[entry.severity]](JSON.stringify(entry));
+    UNPATCHED_CONSOLE[CONSOLE_SEVERITY[entry.severity]](JSON.stringify(entry));
     return;
   }
 
@@ -73,7 +51,7 @@ export function write(entry: LogEntry) {
   if (jsonKeyCount > 0) {
     message = `${message} ${JSON.stringify(jsonPayload, null, 2)}`;
   }
-  unpatchedConsole[CONSOLE_SEVERITY[entry.severity]](message);
+  UNPATCHED_CONSOLE[CONSOLE_SEVERITY[entry.severity]](message);
 }
 
 /**

src/logger/common.ts

@@ -0,0 +1,27 @@
+// Determine if structured logs are supported (node >= 10). If something goes wrong,
+// assume no since unstructured is safer.
+export const SUPPORTS_STRUCTURED_LOGS =
+  parseInt(process.versions?.node?.split('.')?.[0] || '8', 10) >= 10;
+
+// Map LogSeverity types to their equivalent `console.*` method.
+export const CONSOLE_SEVERITY: {
+  [severity: string]: 'debug' | 'info' | 'warn' | 'error';
+} = {
+  DEBUG: 'debug',
+  INFO: 'info',
+  NOTICE: 'info',
+  WARNING: 'warn',
+  ERROR: 'error',
+  CRITICAL: 'error',
+  ALERT: 'error',
+  EMERGENCY: 'error',
+};
+
+// safely preserve unpatched console.* methods in case of compat require
+export const UNPATCHED_CONSOLE = {
+  debug: console.debug,
+  info: console.info,
+  log: console.log,
+  warn: console.warn,
+  error: console.error,
+};

src/logger/compat.ts

@@ -1,8 +1,26 @@
-import { debug, info, warn, error } from '../logger';
+import {
+  SUPPORTS_STRUCTURED_LOGS,
+  UNPATCHED_CONSOLE,
+  CONSOLE_SEVERITY,
+} from './common';
+import { format } from 'util';
+
+function patchedConsole(severity: string): (data: any, ...args: any[]) => void {
+  return function(data: any, ...args: any[]): void {
+    if (SUPPORTS_STRUCTURED_LOGS) {
+      UNPATCHED_CONSOLE[CONSOLE_SEVERITY[severity]](
+        JSON.stringify({ severity, message: format(data, ...args) })
+      );
+      return;
+    }
+
+    UNPATCHED_CONSOLE[CONSOLE_SEVERITY[severity]](data, ...args);
+  };
+}
 
 // IMPORTANT -- "../logger" must be imported before monkeypatching!
-console.debug = debug;
-console.info = info;
-console.log = info;
-console.warn = warn;
-console.error = error;
+console.debug = patchedConsole('DEBUG');
+console.info = patchedConsole('INFO');
+console.log = patchedConsole('INFO');
+console.warn = patchedConsole('WARNING');
+console.error = patchedConsole('ERROR');