avoid body reordering on really fast lines (#1615)

lib/api/readable.js

@@ -93,7 +93,7 @@ module.exports = class BodyReadable extends Readable {
   }
 
   push (chunk) {
-    if (this[kConsume] && chunk !== null) {
+    if (this[kConsume] && chunk !== null && this.readableLength === 0) {
       consumePush(this[kConsume], chunk)
       return this[kReading] ? super.push(chunk) : true
     }

test/readable.test.js

@@ -0,0 +1,23 @@
+'use strict'
+
+const { test } = require('tap')
+const Readable = require('../lib/api/readable')
+
+test('avoid body reordering', async function (t) {
+  function resume () {
+  }
+  function abort () {
+  }
+  const r = new Readable(resume, abort)
+
+  r.push(Buffer.from('hello'))
+
+  process.nextTick(() => {
+    r.push(Buffer.from('world'))
+    r.push(null)
+  })
+
+  const text = await r.text()
+
+  t.equal(text, 'helloworld')
+})