util: add guessHandleType method

With moving in the direction of deprecating process.binding,
it makes sense to expose the ability to guess the handle type
of an fd.

doc/api/util.markdown

@@ -477,6 +477,19 @@ when the deprecated API is used.  Configurable at run-time through the
 
 `process.throwDeprecation` takes precedence over `process.traceDeprecation`.
 
+## util.guessHandleType(fd)
+
+Returns the assumed handle type for the given `fd`.
+
+Possible values include:
+
+* `'FILE'`
+* `'TTY'`
+* `'PIPE'`
+* `'TCP'`
+* `'UNKNOWN'`
+
+
 ## util.debug(string)
 
     Stability: 0 - Deprecated: use console.error() instead.

lib/util.js

@@ -4,6 +4,7 @@ const uv = process.binding('uv');
 const Buffer = require('buffer').Buffer;
 const internalUtil = require('internal/util');
 var Debug;
+var TTYWrap;
 
 const formatRegExp = /%[sdj%]/g;
 exports.format = function(f) {
@@ -864,3 +865,16 @@ exports._exceptionWithHostPort = function(err,
   }
   return ex;
 };
+
+exports.guessHandleType = function(fd) {
+  if (!TTYWrap)
+    TTYWrap = process.binding('tty_wrap');
+
+  if (typeof fd !== 'number')
+    throw new TypeError('fd must be a number');
+
+  if (fd < 0)
+    throw new Error('fd cannot be less than 0');
+
+  return TTYWrap.guessHandleType(fd);
+};

test/sequential/test-util-guess-handle-type.js

@@ -0,0 +1,47 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const util = require('util');
+const fs = require('fs');
+const path = require('path');
+const net = require('net');
+
+// Throw on non-numeric fd
+assert.throws(function() {
+  util.guessHandleType('test');
+}, /fd must be a number/);
+
+// Throw on fd < 0
+assert.throws(function() {
+  util.guessHandleType(-1);
+}, /fd cannot be less than 0/);
+
+// Check for FILE handle type
+const filename = path.join(common.tmpDir, 'guess-handle');
+common.refreshTmpDir();
+fs.writeFileSync(filename, '', 'utf8');
+const fd = fs.openSync(filename, 'r+');
+assert.strictEqual(util.guessHandleType(fd), 'FILE');
+fs.closeSync(fd);
+fs.unlinkSync(filename);
+
+// Check for TTY handle type
+assert.strictEqual(util.guessHandleType(process.stdin.fd), 'TTY');
+
+// Check for PIPE handle type
+var server = net.createServer(assert.fail);
+server.listen(common.PIPE, function() {
+  assert.strictEqual(util.guessHandleType(server._handle.fd), 'PIPE');
+  server.close();
+});
+
+// Check for TCP handle type
+var server2 = net.createServer(assert.fail);
+server2.listen(common.util, function() {
+  assert.strictEqual(util.guessHandleType(server2._handle.fd), 'TCP');
+  server2.close();
+});
+
+// Check for UNKNOWN handle type
+assert.strictEqual(util.guessHandleType(123456), 'UNKNOWN');