http: Corrects IPv6 address in Host header

IPv6 addresses in Host header (URI), must be enclosed within
square brackets, in order to properly separate the host address
from any port reference.

test: add test for IPv6 hostname conformance in Host header
http: Ensure IPv6 is enclosed within square brackets in Host header
http: use net.isIPv6 in ClientRequest
test: update test with const instead of var
test: use common.mustCall and cleanup
http: ClientRequest, drop isIPv6() in favor of indexOf() checks
http: ClientRequest, replace concatenation with string literal
test: use const
test: clean-up
test: move test to parallel
test: skip if no IPv6 support

lib/_http_client.js

@@ -87,6 +87,17 @@ function ClientRequest(options, cb) {
     }
     if (host && !this.getHeader('host') && setHost) {
       var hostHeader = host;
+      var posColon = -1;
+
+      // For the Host header, ensure that IPv6 addresses are enclosed
+      // in square brackets, as defined by URI formatting
+      // https://tools.ietf.org/html/rfc3986#section-3.2.2
+      if (-1 !== (posColon = hostHeader.indexOf(':')) &&
+          -1 !== (posColon = hostHeader.indexOf(':', posColon)) &&
+          '[' !== hostHeader[0]) {
+        hostHeader = `[${hostHeader}]`;
+      }
+
       if (port && +port !== defaultPort) {
         hostHeader += ':' + port;
       }

test/parallel/test-http-host-header-ipv6-fail.js

@@ -0,0 +1,41 @@
+'use strict';
+/*
+ * When using the object form of http.request and using an IPv6 address
+ * as a hostname, and using a non-standard port, the Host header
+ * is improperly formatted.
+ * Issue: https://github.com/nodejs/node/issues/5308
+ * As per https://tools.ietf.org/html/rfc7230#section-5.4 and
+ * https://tools.ietf.org/html/rfc3986#section-3.2.2
+ * the IPv6 address should be enclosed in square brackets
+ */
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+const hostname = '::1';
+const port = common.PORT;
+
+function httpreq() {
+  var req = http.request({
+    host: hostname,
+    port: port,
+    path: '/',
+    method: 'GET'
+  });
+  req.end();
+}
+
+if (!common.hasIPv6) {
+  console.error('Skipping test, no IPv6 support');
+  return;
+}
+
+const server = http.createServer(common.mustCall(function(req, res) {
+  assert.ok(req.headers.host, `[${hostname}]`);
+  res.end();
+  server.close(true);
+}));
+
+server.listen(port, hostname, () => httpreq());
+