sdk/node: enable Keep-Alive in HTTP agent

Don't re-negotiate TLS for each request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Keep-Alive

Closes #3383

Author: Dan Croak <dan@statusok.com>
Date: Wed Apr 18 10:25:43 2018 -0700
upstream:faf2b90112a5a3a090ffa141bf4afba085e90755

Author: croaky

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Sequence Node SDK changelog
 
+## 2.0.0-rc.3 (201804??)
+
+* Enable `keepAlive` on the HTTP agent.
+
 ## 2.0.0-rc.2 (20180416)
 
 * Omit deprecated attributes returned from the API from all response objects.
@@ -10,6 +14,10 @@
 * Removed assets, balances, contracts, and all other deprecated code.
 * Added `Stats#ledgerType`.
 
+## 1.5.1 (20180417)
+
+* Enable `keepAlive` on the HTTP agent.
+
 ## 1.5.0 (20180316)
 
 For full details on the 1.5 release and how to migrate your code,

src/connection.ts

@@ -195,8 +195,12 @@ export class Connection {
     const cafile = process.env.SEQTLSCA
     if (cafile) {
       req.agent = new Agent({ ca: readFileSync(cafile) })
+    } else {
+      req.agent = new Agent()
     }
 
+    req.agent.keepAlive = true
+
     let resp: Response
 
     try {