fs: set encoding if option argument is string

lib/fs.js

@@ -1815,6 +1815,10 @@ function WriteStream(path, options) {
     this.pos = this.start;
   }
 
+  if (options.encoding) {
+    this.setDefaultEncoding(options.encoding);
+  }
+
   if (typeof this.fd !== 'number')
     this.open();
 

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

@@ -0,0 +1,17 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+const stream = require('stream');
+const encoding = 'base64';
+
+const example = path.join(common.fixturesDir, 'x.txt');
+const assertStream = new stream.Writable({
+  write: function(chunk, enc, next) {
+    const expected = new Buffer('xyz');
+    assert(chunk.equals(expected));
+  }
+});
+assertStream.setDefaultEncoding(encoding);
+fs.createReadStream(example, encoding).pipe(assertStream);

test/parallel/test-fs-read-stream-throw-type-error.js

@@ -1,3 +1,4 @@
+'use strict';
 const common = require('../common');
 const assert = require('assert');
 const fs = require('fs');

test/parallel/test-fs-write-stream-encoding.js

@@ -0,0 +1,23 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+const stream = require('stream');
+const firstEncoding = 'base64';
+const secondEncoding = 'binary';
+
+const example = path.join(common.fixturesDir, 'x.txt');
+const dummy = path.join(common.tmpDir, '/x.txt');
+const exampleReadStream = fs.createReadStream(example, firstEncoding);
+const dummyWriteStream = fs.createWriteStream(dummy, firstEncoding);
+exampleReadStream.pipe(dummyWriteStream).on('finish', function(){
+  const assertWriteStream = new stream.Writable({
+    write: function(chunk, enc, next) {
+      const expected = new Buffer('xyz\n');
+      assert(chunk.equals(expected));
+    }
+  });
+  assertWriteStream.setDefaultEncoding(secondEncoding);
+  fs.createReadStream(dummy, secondEncoding).pipe(assertWriteStream);
+});

test/parallel/test-fs-write-stream-throw-type-error.js

@@ -1,3 +1,4 @@
+'use strict';
 const common = require('../common');
 const assert = require('assert');
 const fs = require('fs');