Translate log level to string in production logs

This involves a regex to replace the level in the string as per pinojs/pino#279

.eslintignore

@@ -0,0 +1 @@
+coverage

README.md

@@ -12,17 +12,17 @@ The logger's API is identical to that of pino with the following exceptions:
 
 * The property `sourcetype: _json` is added to logs in production for Splunk compatibility.
 * Lambda related environment variables are added by default:
-  * AWS_EXECUTION_ENV,
-  * AWS_LAMBDA_FUNCTION_NAME,
-  * AWS_LAMBDA_FUNCTION_MEMORY_SIZE,
-  * AWS_LAMBDA_FUNCTION_VERSION
+    * `AWS_EXECUTION_ENV`,
+    * `AWS_LAMBDA_FUNCTION_NAME`,
+    * `AWS_LAMBDA_FUNCTION_MEMORY_SIZE`,
+    * `AWS_LAMBDA_FUNCTION_VERSION`
 * Defaults to ISO timestamp logging for splunk compatiblity. At the time of writing this incurs a 25% pino performance penalty.
 
 ### Pino properties
 
 Pino adds the following properties to logs by default:
 
-* `level` - the log level in integer form. Refer to the `pino` documentation to translate this.
+* `level` - the log level in string form. This is translated from the `pino` default of logging an integer representation.
 * `v` - the pino logger API version.
 * `hostname` - the hostname the process is running on.
 * `pid` - the process PID.

lib/__tests__/logger.test.js

@@ -1,3 +1,4 @@
+import pino from 'pino';
 import createLogger from '../logger';
 
 const setupEnv = ({ envKey, value, setter }) => {
@@ -65,7 +66,7 @@ describe('log formatting', () => {
 
     test('it logs JSON to stdout in the correct format', () => {
         const expectedLog = {
-            level: 30,
+            level: 'info',
             message: 'someMessage',
             someObject: { withNesting: true },
             sourceType: '_json',
@@ -79,6 +80,16 @@ describe('log formatting', () => {
         expect(callJson).toEqual(expectedLog);
     });
 
+    Object.keys(pino.levels.values).forEach(level => {
+        test(`it writes log level as the appropriate strings when the level is ${level}`, () => {
+            logger = createLogger();
+            logger[level]({ someObject: { withNesting: true } }, 'someMessage');
+
+            const callJson = getLogObject();
+            expect(callJson).toHaveProperty('level', level);
+        });
+    });
+
     test('it includes variable properties', () => {
         logger = createLogger();
         logger.info({ someObject: { withNesting: true } }, 'someMessage');

lib/logger.js

@@ -7,24 +7,43 @@ const isLambda = () =>
         false
     );
 
-const getBaseLogger = () => {
-    const level = process.env.CONSOLE_LOG_LEVEL || 'trace';
+const stringifyVersion = chunk =>
+    chunk.replace(
+        /("level":\s*)(\d+)/,
+        (match, keyString, levelString) =>
+            `${keyString}"${pino.levels.labels[parseInt(levelString, 10)]}"`,
+    );
 
-    let prettyPrint;
+const writeLog = chunk => {
+    process.stdout.write(stringifyVersion(chunk));
+};
 
-    if (!isProduction()) {
-        prettyPrint = pino.pretty({ forceColor: true });
+const getProductionStream = () => ({
+    write: writeLog,
+});
 
-        prettyPrint.pipe(process.stdout);
-    }
+const getPrettyPrintedStream = () => {
+    const stream = pino.pretty({ forceColor: true });
 
-    return pino({
-        prettyPrint,
-        level,
-        messageKey: 'message',
-        // enable ISO time stamps rather than epoch time
-        timestamp: pino.stdTimeFunctions.slowTime,
-    });
+    stream.pipe(process.stdout);
+    return stream;
+};
+
+const getBaseLogger = () => {
+    const level = process.env.CONSOLE_LOG_LEVEL || 'trace';
+    const stream = isProduction()
+        ? getProductionStream()
+        : getPrettyPrintedStream();
+
+    return pino(
+        {
+            level,
+            messageKey: 'message',
+            // enable ISO time stamps rather than epoch time
+            timestamp: pino.stdTimeFunctions.slowTime,
+        },
+        stream,
+    );
 };
 
 const getMetaData = () => ({

package.json

@@ -1,8 +1,7 @@
 {
     "name": "@financial-times/lambda-logger",
     "version": "1.0.0",
-    "description":
-        "Logger used by the lambda team. Logs in JSON format using pino",
+    "description": "Logger used by the lambda team. Logs in JSON format using pino",
     "main": "dist/@financial-times/lambda-logger.js",
     "browser": "dist/@financial-times/lambda-logger.umd.js",
     "module": "dist/@financial-times/lambda-logger.m.js",
@@ -16,7 +15,10 @@
         "precommit": "lint-staged"
     },
     "lint-staged": {
-        "*.js": ["eslint --cache --fix", "git add"]
+        "*.js": [
+            "eslint --cache --fix",
+            "git add"
+        ]
     },
     "engines": {
         "node": ">= 6.10.0"