Log tailer moved to flipper-common

Summary: Log tailer is/could/will be used in different places, move to a centralised place.

Reviewed By: antonk52

Differential Revision: D48524579

fbshipit-source-id: 81d6c4670572284ba2821a93011f5daa133b21fa

desktop/flipper-common/src/utils/LoggerTailer.tsx

@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {LoggerTypes} from './Logger';
+
+export const logLevels: LoggerTypes[] = ['debug', 'info', 'warn', 'error'];
+export type LogTailer = (level: LoggerTypes, ...data: Array<any>) => void;
+
+const logTailers: LogTailer[] = [];
+let initialized = false;
+
+export function addLogTailer(handler: LogTailer) {
+  logTailers.push(handler);
+}
+
+export function initLogTailer() {
+  if (initialized) {
+    return;
+  }
+
+  initialized = true;
+
+  const originalConsole: {[key: string]: any} = console;
+  // Store the raw console log functions here
+  const originalConsoleLogFunctions: {[key: string]: (...args: any) => void} =
+    {} as {
+      [key: string]: (...args: any) => void;
+    };
+
+  // React Devtools also patches the console methods:
+  // https://github.com/facebook/react/blob/206d61f72214e8ae5b935f0bf8628491cb7f0797/packages/react-devtools-shared/src/backend/console.js#L141
+  // Not using a proxy object here because it isn't compatible with their patching process.
+  // Instead replace the methods on the console itself.
+  // Doesn't matter who patches first, single thread means it will be consistent.
+  for (const level of logLevels) {
+    const originalConsoleLogFunction = originalConsole[level];
+    originalConsoleLogFunctions[level] = originalConsoleLogFunction;
+    const overrideMethod = (...args: Array<unknown>) => {
+      const newConsoleLogFunction = originalConsoleLogFunctions[level];
+      const result = newConsoleLogFunction(...args);
+      logTailers.forEach((handler) => {
+        handler(level, ...args);
+      });
+      return result;
+    };
+
+    overrideMethod.__FLIPPER_ORIGINAL_METHOD__ = originalConsoleLogFunction;
+    originalConsole[level] = overrideMethod;
+  }
+}