fs: fix `createReadStream(…, {end: n})` for non-seekable fds

82bdf8fba2d3f fixed an issue by silently modifying the `start`
option for the case when only `end` is passed, in order to perform
reads from a specified range in the file.

However, that approach does not work for non-seekable files, since
a numeric `start` option means that positioned reads will be used
to read data from the file.

This patch fixes that, and instead ends reading after a specified
size by adjusting the read buffer size.

This way we avoid re-introducing the bug that 82bdf8fba2d3f fixed,
and align behaviour with the native file stream mechanism
introduced in https://github.com/nodejs/node/pull/18936 as well.

PR-URL: https://github.com/nodejs/node/pull/19329
Fixes: https://github.com/nodejs/node/issues/19240
Refs: https://github.com/nodejs/node/pull/18121
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Chen Gang <gangc.cxy@foxmail.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/test/parallel/test-fs-read-stream.js b/test/parallel/test-fs-read-stream.js
index 7fc7a0d56b..8b92eb1c7a 100644
--- a/test/parallel/test-fs-read-stream.js
+++ b/test/parallel/test-fs-read-stream.js
@@ -21,7 +21,9 @@
 
 'use strict';
 const common = require('../common');
+const tmpdir = require('../common/tmpdir');
 
+const child_process = require('child_process');
 const assert = require('assert');
 const fs = require('fs');
 const fixtures = require('../common/fixtures');
@@ -178,6 +180,31 @@ common.expectsError(
   }));
 }
 
+if (!common.isWindows) {
+  // Verify that end works when start is not specified, and we do not try to
+  // use positioned reads. This makes sure that this keeps working for
+  // non-seekable file descriptors.
+  tmpdir.refresh();
+  const filename = `${tmpdir.path}/foo.pipe`;
+  const mkfifoResult = child_process.spawnSync('mkfifo', [filename]);
+  if (!mkfifoResult.error) {
+    child_process.exec(`echo "xyz foobar" > '${filename}'`);
+    const stream = new fs.createReadStream(filename, { end: 1 });
+    stream.data = '';
+
+    stream.on('data', function(chunk) {
+      stream.data += chunk;
+    });
+
+    stream.on('end', common.mustCall(function() {
+      assert.strictEqual('xy', stream.data);
+      fs.unlinkSync(filename);
+    }));
+  } else {
+    common.printSkipMessage('mkfifo not available');
+  }
+}
+
 {
   // pause and then resume immediately.
   const pauseRes = fs.createReadStream(rangeFile);