add new streamWrite hook

docs/api.md

@@ -375,6 +375,23 @@ const hooks = {
 }
 ```
 
+
+<a id="streamWrite"></a>
+##### `streamWrite`
+
+Allows for manipulating the _stringified_ JSON log data just before writing to various transports.
+
+The method receives the stringified JSON and must return valid stringified JSON.
+
+For example:
+```js
+const hooks = {
+  streamWrite (s) {
+    return s.replaceAll('sensitive-api-key', 'XXX')
+  }
+}
+```
+
 <a id=opt-formatters></a>
 #### `formatters` (Object)
 

lib/proto.js

@@ -27,7 +27,8 @@ const {
   stringifySym,
   formatOptsSym,
   stringifiersSym,
-  msgPrefixSym
+  msgPrefixSym,
+  hooksSym
 } = require('./symbols')
 const {
   getLevel,
@@ -185,6 +186,7 @@ function write (_obj, msg, num) {
   const messageKey = this[messageKeySym]
   const mixinMergeStrategy = this[mixinMergeStrategySym] || defaultMixinMergeStrategy
   let obj
+  const streamWriteHook = this[hooksSym].streamWrite
 
   if (_obj === undefined || _obj === null) {
     obj = {}
@@ -214,7 +216,7 @@ function write (_obj, msg, num) {
     stream.lastTime = t.slice(this[timeSliceIndexSym])
     stream.lastLogger = this // for child loggers
   }
-  stream.write(s)
+  stream.write(streamWriteHook ? streamWriteHook(s) : s)
 }
 
 function noop () {}

pino.d.ts

@@ -641,6 +641,12 @@ declare namespace pino {
              * using apply, like so: method.apply(this, newArgumentsArray).
              */
             logMethod?: (this: Logger, args: Parameters<LogFn>, method: LogFn, level: number) => void;
+
+            /**
+             * Allows for manipulating the stringified JSON log output just before writing to various transports.
+             * This function must return a string and must be valid JSON.
+             */
+            streamWrite?: (s: string) => string;
         };
 
         /**

pino.js

@@ -70,7 +70,8 @@ const defaultOptions = {
     }
   }),
   hooks: {
-    logMethod: undefined
+    logMethod: undefined,
+    streamWrite: undefined
   },
   timestamp: epochTime,
   name: undefined,

test/hooks.test.js

@@ -95,3 +95,24 @@ tap.test('log method hook', t => {
 
   t.end()
 })
+
+tap.test('streamWrite hook', t => {
+  t.test('gets invoked', async t => {
+    t.plan(1)
+
+    const stream = sink()
+    const logger = pino({
+      hooks: {
+        streamWrite (s) {
+          return s.replaceAll('redact-me', 'XXX')
+        }
+      }
+    }, stream)
+
+    const o = once(stream, 'data')
+    logger.info('hide redact-me in this string')
+    t.match(await o, { msg: 'hide XXX in this string' })
+  })
+
+  t.end()
+})