net: make stdout & stderr block on all platforms

Previously, if a write to stdout (or stderr) was long enough that it
would have to be broken into chunks for writing, and the process was
terminated before all of those chunks were written, they would be lost.

This prevents chunks from being lost or delayed by making writes to
std{out|err} synchronous (and thus blocking).

Fixes: #784

lib/net.js

@@ -126,10 +126,7 @@ function Socket(options) {
   } else if (options.fd !== undefined) {
     this._handle = createHandle(options.fd);
     this._handle.open(options.fd);
-    if ((options.fd == 1 || options.fd == 2) &&
-        (this._handle instanceof Pipe) &&
-        process.platform === 'win32') {
-      // Make stdout and stderr blocking on Windows
+    if ((options.fd == 1 || options.fd == 2) && this._handle instanceof Pipe) {
       var err = this._handle.setBlocking(true);
       if (err)
         throw errnoException(err, 'setBlocking');

test/fixtures/stdout-producer.js

@@ -0,0 +1,17 @@
+'use strict';
+
+// Produce a very long string, so that stdout will have to break it into chunks.
+var str = 'test\n';
+for (var i = 0; i < 17; i++, str += str);
+
+// Add something so that we can identify the end.
+str += 'hey\n';
+
+process.stdout.write(str);
+
+// Close the process, attempting to close before
+// all chunked stdout writes are done.
+//
+// This is required to achieve the regression described in
+// https://github.com/nodejs/io.js/issues/784.
+process.exit();

test/parallel/test-child-process-chunked-stdout.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const fork = require('child_process').fork;
+const stream = require('stream');
+const path = require('path');
+
+const producer = fork(path.join(common.fixturesDir, 'stdout-producer.js'),
+                      { silent: true });
+
+var output = '';
+const writable = new stream.Writable({
+  write(chunk, _, next) {
+    output += chunk.toString();
+    next();
+  }
+});
+
+producer.stdout.pipe(writable);
+producer.stdout.on('close', function() {
+  assert(output.endsWith('hey\n'),
+      'Not all chunked writes were completed before process termination.');
+});
+
+producer.stderr.pipe(process.stderr);