http: expose headers on an http.ClientRequest "information" event

1xx intermediate status responses are allowed to have headers; so
expose the "httpVersion", "httpVersionMajor", "httpVersionMinor",
"headers", "rawHeaders", and "statusMessage" properties on this
event.

PR-URL: https://github.com/nodejs/node/pull/28459
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/api/http.md

@@ -421,10 +421,18 @@ added: v10.0.0
 -->
 
 * `info` {Object}
+  * `httpVersion` {string}
+  * `httpVersionMajor` {integer}
+  * `httpVersionMinor` {integer}
   * `statusCode` {integer}
+  * `statusMessage` {string}
+  * `headers` {Object}
+  * `rawHeaders` {string[]}
 
-Emitted when the server sends a 1xx response (excluding 101 Upgrade). The
-listeners of this event will receive an object containing the status code.
+Emitted when the server sends a 1xx intermediate response (excluding 101
+Upgrade). The listeners of this event will receive an object containing the
+HTTP version, status code, status message, key-value headers object,
+and array with the raw header names followed by their respective values.
 
 ```js
 const http = require('http');

lib/_http_client.js

@@ -549,7 +549,15 @@ function parserOnIncomingClient(res, shouldKeepAlive) {
       req.emit('continue');
     }
     // Send information events to all 1xx responses except 101 Upgrade.
-    req.emit('information', { statusCode: res.statusCode });
+    req.emit('information', {
+      statusCode: res.statusCode,
+      statusMessage: res.statusMessage,
+      httpVersion: res.httpVersion,
+      httpVersionMajor: res.httpVersionMajor,
+      httpVersionMinor: res.httpVersionMinor,
+      headers: res.headers,
+      rawHeaders: res.rawHeaders
+    });
 
     return 1;  // Skip body but don't treat as Upgrade.
   }

test/parallel/test-http-information-headers.js

@@ -0,0 +1,64 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const http = require('http');
+const Countdown = require('../common/countdown');
+
+const test_res_body = 'other stuff!\n';
+const countdown = new Countdown(2, () => server.close());
+
+const server = http.createServer((req, res) => {
+  console.error('Server sending informational message #1...');
+  // These function calls may rewritten as necessary
+  // to call res.writeHead instead
+  res._writeRaw('HTTP/1.1 102 Processing\r\n');
+  res._writeRaw('Foo: Bar\r\n');
+  res._writeRaw('\r\n');
+  console.error('Server sending full response...');
+  res.writeHead(200, {
+    'Content-Type': 'text/plain',
+    'ABCD': '1'
+  });
+  res.end(test_res_body);
+});
+
+server.listen(0, function() {
+  const req = http.request({
+    port: this.address().port,
+    path: '/world'
+  });
+  req.end();
+  console.error('Client sending request...');
+
+  let body = '';
+
+  req.on('information', function(res) {
+    assert.strictEqual(res.httpVersion, '1.1');
+    assert.strictEqual(res.httpVersionMajor, 1);
+    assert.strictEqual(res.httpVersionMinor, 1);
+    assert.strictEqual(res.statusCode, 102,
+                       `Received ${res.statusCode}, not 102.`);
+    assert.strictEqual(res.statusMessage, 'Processing',
+                       `Received ${res.statusMessage}, not "Processing".`);
+    assert.strictEqual(res.headers.foo, 'Bar');
+    assert.strictEqual(res.rawHeaders[0], 'Foo');
+    assert.strictEqual(res.rawHeaders[1], 'Bar');
+    console.error('Client got 102 Processing...');
+    countdown.dec();
+  });
+
+  req.on('response', function(res) {
+    // Check that all 102 Processing received before full response received.
+    assert.strictEqual(countdown.remaining, 1);
+    assert.strictEqual(res.statusCode, 200,
+                       `Final status code was ${res.statusCode}, not 200.`);
+    res.setEncoding('utf8');
+    res.on('data', function(chunk) { body += chunk; });
+    res.on('end', function() {
+      console.error('Got full response.');
+      assert.strictEqual(body, test_res_body);
+      assert.ok('abcd' in res.headers);
+      countdown.dec();
+    });
+  });
+});