fs: fs.read into zero buffer should not throw exception

Fixes: #4517.
PR-URL: #4518
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/fs.js

@@ -609,6 +609,12 @@ fs.read = function(fd, buffer, offset, length, position, callback) {
     };
   }
 
+  if (length === 0) {
+    return process.nextTick(function() {
+      callback && callback(null, 0, buffer);
+    });
+  }
+
   function wrapper(err, bytesRead) {
     // Retain a reference to buffer so that it can't be GC'ed too soon.
     callback && callback(err, bytesRead || 0, buffer);
@@ -648,6 +654,14 @@ fs.readSync = function(fd, buffer, offset, length, position) {
     offset = 0;
   }
 
+  if (length === 0) {
+    if (legacy) {
+      return ['', 0];
+    } else {
+      return 0;
+    }
+  }
+
   var r = binding.read(fd, buffer, offset, length, position);
   if (!legacy) {
     return r;

test/parallel/test-fs-read-buffer-zero-length.js

@@ -0,0 +1,19 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const path = require('path');
+const Buffer = require('buffer').Buffer;
+const fs = require('fs');
+const filepath = path.join(common.fixturesDir, 'x.txt');
+const fd = fs.openSync(filepath, 'r');
+const bufferAsync = new Buffer(0);
+const bufferSync = new Buffer(0);
+
+fs.read(fd, bufferAsync, 0, 0, 0, common.mustCall(function(err, bytesRead) {
+  assert.equal(bytesRead, 0);
+  assert.deepEqual(bufferAsync, new Buffer(0));
+}));
+
+const r = fs.readSync(fd, bufferSync, 0, 0, 0);
+assert.deepEqual(bufferSync, new Buffer(0));
+assert.equal(r, 0);

test/parallel/test-fs-read-zero-length.js

@@ -0,0 +1,18 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs');
+const filepath = path.join(common.fixturesDir, 'x.txt');
+const fd = fs.openSync(filepath, 'r');
+const expected = '';
+
+fs.read(fd, 0, 0, 'utf-8', common.mustCall(function(err, str, bytesRead) {
+  assert.ok(!err);
+  assert.equal(str, expected);
+  assert.equal(bytesRead, 0);
+}));
+
+const r = fs.readSync(fd, 0, 0, 'utf-8');
+assert.equal(r[0], expected);
+assert.equal(r[1], 0);