tests: do not hardcode service name in test-dns.

Instead of hard-coding http service name in test-dns, retrieve it from
/etc/services. This is not ideal, but it's still better than hard-coding
it.

Fixes nodejs#8047.

test/common.js

@@ -22,6 +22,7 @@
 var path = require('path');
 var fs = require('fs');
 var assert = require('assert');
+var child_process = require('child_process');
 
 exports.testDir = path.dirname(__filename);
 exports.fixturesDir = path.join(exports.testDir, 'fixtures');
@@ -219,3 +220,31 @@ exports.checkSpawnSyncRet = function(ret) {
   assert.strictEqual(ret.status, 0);
   assert.strictEqual(ret.error, undefined);
 };
+
+/*
+ * Sometimes, the service for port 80/tcp is not mentioned in
+ * /etc/services, and in this case getnameinfo will return the port
+ * number as the service name.
+ */
+exports.defaultHttpServiceName = '80'
+
+exports.getServiceNameFromEtcServices = function(port, protocol, callback) {
+  var shellCmd = "grep -v '^#' /etc/services"         +
+  " | grep '\\b" + port + '/' + protocol + "\\b' "    +
+  " | tr \"\\t\" \" \" "                              +
+  " | cut -d ' ' -f 1";
+
+  var servicesGrep = child_process.exec(shellCmd, function (err, stdout, stderr) {
+    if (err) {
+      callback({ stderr: stderr});
+    } else {
+      var serviceName;
+      var services = stdout.split('\n', 1);
+      if (services.length > 0) {
+        serviceName = services[0].toString().replace(/\n|\r/g, "");
+      }
+
+      callback(null, serviceName);
+    }
+  });
+}

test/internet/test-dns.js

@@ -495,9 +495,22 @@ TEST(function test_lookupservice_ip_ipv4(done) {
   var req = dns.lookupService('127.0.0.1', 80, function(err, host, service) {
     if (err) throw err;
     assert.strictEqual(host, 'localhost');
-    assert.strictEqual(service, 'http');
 
-    done();
+    /*
+     * Retrieve the actual HTTP service name as setup on the host currently
+     * running the test by reading it from /etc/services. This is not ideal,
+     * as the service name lookup could use another mechanism (e.g nscd), but
+     * it's already better than hardcoding it.
+     */
+    var httpServiceName = common.defaultHttpServiceName;
+    common.getServiceNameFromEtcServices(80, 'tcp', function (err, serviceName) {
+      if (!err) {
+        httpServiceName = serviceName;
+      }
+
+      assert.strictEqual(service, httpServiceName);
+      done();
+    });
   });
 
   checkWrap(req);
@@ -515,9 +528,22 @@ TEST(function test_lookupservice_ip_ipv6(done) {
      * that most sane platforms use either one of these two by default.
      */
     assert(host === 'localhost' || host === 'ip6-localhost');
-    assert.strictEqual(service, 'http');
 
-    done();
+    /*
+     * Retrieve the actual HTTP service name as setup on the host currently
+     * running the test by reading it from /etc/services. This is not ideal,
+     * as the service name lookup could use another mechanism (e.g nscd), but
+     * it's already better than hardcoding it.
+     */
+    var httpServiceName = common.defaultHttpServiceName;
+    common.getServiceNameFromEtcServices(80, 'tcp', function (err, serviceName) {
+      if (!err) {
+        httpServiceName = serviceName;
+      }
+
+      assert.strictEqual(service, httpServiceName);
+      done();
+    });
   });
 
   checkWrap(req);