feat: allow customize parse line

README.md

@@ -60,9 +60,43 @@ stream, it emits the following events:
 
 #### Options
 
+* `parse` an option to change to data format passed to build function. Default: `undefined`.
+
 * `close(err, cb)` a function that is called to shutdown the transport. It's called both on error and non-error shutdowns.
   It can also return a promise. In this case discard the the `cb` argument.
 
+* `parseLine(line)` a function that is used to parse line recieved from `pino`.
+
+## Example
+
+### custom parseLine
+
+You can allow custom `parseLine` from users while providing a simple and safe default parseLine.
+
+```js
+'use strict'
+
+const build = require('pino-abstract-transport')
+
+function defaultParseLine (line) {
+  const obj = JSON.parse(line)
+  // property foo will be added on each line
+  obj.foo = 'bar'
+  return obj
+}
+
+module.exports = function (opts) {
+  const parseLine = typeof opts.parseLine === 'function' ? opts.parseLine : defaultParseLine
+  return build(function (source) {
+    source.on('data', function (obj) {
+      console.log(obj)
+    })
+  }, {
+    parseLine: parseLine
+  })
+}
+```
+
 ## License
 
 MIT

index.js

@@ -5,12 +5,13 @@ const split = require('split2')
 
 module.exports = function build (fn, opts = {}) {
   const parseLines = opts.parse === 'lines'
+  const parseLine = typeof opts.parseLine === 'function' ? opts.parseLine : JSON.parse
   const close = opts.close || defaultClose
   const stream = split(function (line) {
     let value
 
     try {
-      value = JSON.parse(line)
+      value = parseLine(line)
     } catch (error) {
       this.emit('unknown', line, error)
       return

test/base.test.js

@@ -206,6 +206,48 @@ test('parse lines', ({ same, plan, equal }) => {
   stream.end()
 })
 
+test('custom parse line function', ({ same, plan, equal }) => {
+  plan(11)
+
+  const expected = [{
+    level: 30,
+    time: 1617955768092,
+    pid: 2942,
+    hostname: 'MacBook-Pro.local',
+    msg: 'hello world'
+  }, {
+    level: 30,
+    time: 1617955768092,
+    pid: 2942,
+    hostname: 'MacBook-Pro.local',
+    msg: 'another message',
+    prop: 42
+  }]
+  let num = 0
+
+  function parseLine (str) {
+    const obj = JSON.parse(str)
+    same(expected[num], obj)
+    return obj
+  }
+
+  const stream = build(function (source) {
+    source.on('data', function (line) {
+      const obj = expected[num]
+      same(this.lastLevel, obj.level)
+      same(this.lastTime, obj.time)
+      same(this.lastObj, obj)
+      same(obj, line)
+      num++
+    })
+  }, { metadata: true, parseLine })
+
+  equal(stream[Symbol.for('pino.metadata')], true)
+  const lines = expected.map(JSON.stringify).join('\n')
+  stream.write(lines)
+  stream.end()
+})
+
 test('set metadata (default)', ({ same, plan, equal }) => {
   plan(9)