dns: include host name in error message if available

This makes errors more readable and similar to FS errors, which also
include file name.

Reviewed-By: Fedor Indutny <fedor@indutny.com>

lib/dns.js

@@ -38,7 +38,7 @@ function errnoException(err, syscall, hostname) {
   }
   var ex = null;
   if (typeof err === 'string') {  // c-ares error code.
-    ex = new Error(syscall + ' ' + err);
+    ex = new Error(syscall + ' ' + err + (hostname ? ' ' + hostname : ''));
     ex.code = err;
     ex.errno = err;
     ex.syscall = syscall;

test/internet/test-dns.js

@@ -431,6 +431,7 @@ TEST(function test_lookup_failure(done) {
     assert.strictEqual(err.errno, dns.NOTFOUND);
     assert.strictEqual(err.errno, 'ENOTFOUND');
     assert.ok(!/ENOENT/.test(err.message));
+    assert.ok(/does\.not\.exist/.test(err.message));
 
     done();
   });
@@ -553,6 +554,7 @@ TEST(function test_lookupservice_invalid(done) {
   var req = dns.lookupService('1.2.3.4', 80, function(err, host, service) {
     assert(err instanceof Error);
     assert.strictEqual(err.code, 'ENOTFOUND');
+    assert.ok(/1\.2\.3\.4/.test(err.message));
 
     done();
   });
@@ -566,6 +568,7 @@ TEST(function test_reverse_failure(done) {
     assert(err instanceof Error);
     assert.strictEqual(err.code, 'ENOTFOUND');  // Silly error code...
     assert.strictEqual(err.hostname, '0.0.0.0');
+    assert.ok(/0\.0\.0\.0/.test(err.message));
 
     done();
   });
@@ -579,6 +582,7 @@ TEST(function test_lookup_failure(done) {
     assert(err instanceof Error);
     assert.strictEqual(err.code, 'ENOTFOUND');  // Silly error code...
     assert.strictEqual(err.hostname, 'nosuchhostimsure');
+    assert.ok(/nosuchhostimsure/.test(err.message));
 
     done();
   });
@@ -601,6 +605,7 @@ TEST(function test_resolve_failure(done) {
     }
 
     assert.strictEqual(err.hostname, 'nosuchhostimsure');
+    assert.ok(/nosuchhostimsure/.test(err.message));
 
     done();
   });