stream: the position of _read() is wrong

Fixes: #33940 PR-URL: #38292 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

Author: helloyou2012

lib/internal/fs/streams.js

@@ -172,6 +172,10 @@ ReadStream.prototype._read = function(n) {
  }
  this.emit('error', er);
  } else if (bytesRead > 0) {
+ if (this.pos !== undefined) {
+ this.pos += bytesRead;
+ }
+
  this.bytesRead += bytesRead;
 
  if (bytesRead !== buf.length) {
@@ -188,10 +192,6 @@ ReadStream.prototype._read = function(n) {
  this.push(null);
  }
  });
-
- if (this.pos !== undefined) {
- this.pos += n;
- }
 };
 
 ReadStream.prototype._destroy = function(err, cb) {

test/parallel/test-fs-read-stream-pos.js

@@ -0,0 +1,69 @@
+'use strict';
+
+// Refs: https://github.com/nodejs/node/issues/33940
+
+const common = require('../common');
+const tmpdir = require('../common/tmpdir');
+const fs = require('fs');
+const assert = require('assert');
+const path = require('path');
+
+tmpdir.refresh();
+
+const file = path.join(tmpdir.path, '/read_stream_pos_test.txt');
+
+fs.writeFileSync(file, '');
+
+let counter = 0;
+
+setInterval(() => {
+ counter = counter + 1;
+ const line = `hello at ${counter}\n`;
+ fs.writeFileSync(file, line, { flag: 'a' });
+}, 1);
+
+const hwm = 10;
+let bufs = [];
+let isLow = false;
+let cur = 0;
+let stream;
+
+setInterval(() => {
+ if (stream) return;
+
+ stream = fs.createReadStream(file, {
+ highWaterMark: hwm,
+ start: cur
+ });
+ stream.on('data', common.mustCallAtLeast((chunk) => {
+ cur += chunk.length;
+ bufs.push(chunk);
+ if (isLow) {
+ const brokenLines = Buffer.concat(bufs).toString()
+ .split('\n')
+ .filter((line) => {
+ const s = 'hello at'.slice(0, line.length);
+ if (line && !line.startsWith(s)) {
+ return true;
+ }
+ return false;
+ });
+ assert.strictEqual(brokenLines.length, 0);
+ process.exit();
+ return;
+ }
+ if (chunk.length !== hwm) {
+ isLow = true;
+ }
+ }));
+ stream.on('end', () => {
+ stream = null;
+ isLow = false;
+ bufs = [];
+ });
+}, 10);
+
+// Time longer than 90 seconds to exit safely
+setTimeout(() => {
+ process.exit();
+}, 90000);