Add a test for the bug of unwanted openSSL errors

* bad_sign() would inject an error into OpenSSL's error stack
* Second time of calling requestThunk would make the error be thrown

Author: pmq20

test/fixtures/bad_rsa_privkey.pem

@@ -0,0 +1,9 @@
+-----BEGIN RSA PRIVATE KEY-----
+MIIBSwIBADCCASwGByqGSM44BAEwggEfAoGBAP1/U4EddRIpUt9KnC7s5Of2EbdS
+PO9EAMMeP4C2USZpRV1AIlH7WT2NWPq/xfW6MPbLm1Vs14E7gB00b/JmYLdrmVCl
+pJ+f6AR7ECLCT7up1/63xhv4O1fnxqimFQ8E+4P208UewwI1VBNaFpEy9nXzrith
+1yrv8iIDGZ3RSAHHAhUAl2BQjxUjC8yykrmCouuEC/BYHPUCgYEA9+GghdabPd7L
+vKtcNrhXuXmUr7v6OuqC+VdMCz0HgmdRWVeOutRZT+ZxBxCBgLRJFnEj6EwoFhO3
+zwkyjMim4TwWeotUfI0o4KOuHiuzpnWRbqN/C/ohNWLx+2J6ASQ7zKTxvqhRkImo
+g9/hWuWfBpKLZl6Ae1UlZAFMO/7PSSoEFgIUV6pvYD6fM1L4KxjlIUIeN+yvq/U=
+-----END RSA PRIVATE KEY-----

test/openssl.test.js

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+/**!
+ * urllib - openssl.test.js
+ *
+ * Copyright(c) node-modules and other contributors.
+ * MIT Licensed
+ *
+ * Authors:
+ *   P.S.V.R <pmq2001@gmail.com> (http://www.ofpsvr.com)
+ */
+
+'use strict';
+
+/**
+ * This is a test for the bug of unwanted openSSL errors.
+ */
+
+var should = require('should');
+var urllib = require('../');
+var crypto = require('crypto');
+var fs = require('fs');
+var path = require('path');
+var Agent = require('agentkeepalive');
+var HttpsAgent = require('agentkeepalive').HttpsAgent;
+
+var bad_sign = function () {
+  // This triggers an implicit error
+  // that is recorded onto OpenSSL's error stack
+  var privateKey = fs.readFileSync(path.join(__dirname, './fixtures/bad_rsa_privkey.pem'), 'utf8');
+  var s = crypto.createSign('sha1');
+  var sign = s.sign(privateKey);
+};
+
+describe('httpclient.test.js', function () {
+  it('should requestThunk()', function (done) {
+    var conf = {
+      "keepAlive": true,
+      "keepAliveTimeout": 300000,
+      "timeout": 300000,
+      "maxSockets": null,
+      "maxFreeSockets": 10,
+      "enableStatusLog": false
+    };
+
+    var httpAgent = new Agent(conf);
+    var httpsAgent = new HttpsAgent(conf);
+
+    var client = urllib.create({
+      agent: httpAgent,
+      httpsAgent: httpsAgent
+    });
+
+    bad_sign();
+    // 1st time when we establish a https connection,
+    // ~ClearErrorOnReturn is called so the errors of bad_sign() won't be thrown
+    client.requestThunk('https://www.alipay.com')(function (err, result) {
+      should.not.exist(err);
+      result.data.should.be.a.Buffer;
+      result.status.should.equal(200);
+
+      setImmediate(function () {
+        // 2nd time when we reuse an existing connection,
+        // ~ClearErrorOnReturn will not be called,
+        // making the errors of bad_sign() be thrown
+        // A fix of this bug should prevent this from happening
+        bad_sign();
+        client.requestThunk('https://www.alipay.com')(function (err, result) {
+          should.not.exist(err);
+          result.data.should.be.a.Buffer;
+          result.status.should.equal(200);
+          done();
+        });
+      });
+    });
+  });
+});