Add test for issue 3992

Test a getAllHeaders function. It should return an object representing
the headers in a request.

test/simple/test-http-header-get-all.js

@@ -0,0 +1,71 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var assert = require('assert');
+var http = require('http');
+
+// Verify that ServerResponse.getHeader() works correctly even after
+// the response header has been sent. Issue 752 on github.
+
+var s = http.createServer(function(req, res) {
+  var contentType = 'Content-Type';
+  var plain = 'text/plain';
+  var userAgent = 'User-Agent';
+  var browser = 'Mozilla';
+  var expected = {
+    'content-type': plain,
+    'user-agent': browser
+  }
+  res.setHeader(contentType, plain);
+  res.setHeader(userAgent, browser);
+  assert.ok(!res.headersSent);
+  res.writeHead(200);
+  assert.ok(res.headersSent);
+  res.end('hello world\n');
+  var headers;
+  // This checks that after the headers have been sent, getAllHeaders works
+  // and does not throw an exception
+  assert.doesNotThrow(
+      function() {
+        headers = res.getAllHeaders();
+      }
+  );
+  // Check that all fields in headers have the same value as expected, and
+  // vice-versa. This ensures that there no fields which *don't* exist in one
+  // or the other.
+  for (var field in headers) {
+    assert.equal(headers[field], expected[field]);
+  }
+  for (var field in expected) {
+    assert.equal(headers[field], expected[field]);
+  }
+});
+
+s.listen(process.env.PORT, runTest);
+
+function runTest() {
+  http.get({ port: process.env.PORT }, function(response) {
+    response.on('end', function() {
+      s.close();
+    });
+    response.resume();
+  });
+}