From 17247650963e7ab9c9b954abbe81a68745afdc42 Mon Sep 17 00:00:00 2001
From: Tim Gross <tgross@hashicorp.com>
Date: Wed, 6 Apr 2022 16:14:53 -0400
Subject: [PATCH] api: use `cleanhttp.DefaultPooledTransport` for default API
 client (#12492)

We expect every Nomad API client to use a single connection to any
given agent, so take advantage of keep-alive by switching the default
transport to `DefaultPooledClient`. Provide a facility to close idle
connections for testing purposes.

Restores the previously reverted #12409


Co-authored-by: Ben Buzbee <bbuzbee@cloudflare.com>
---
 .changelog/12492.txt       |  3 +++
 api/api.go                 | 14 +++++++++++++-
 command/agent/http_test.go |  2 ++
 3 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 .changelog/12492.txt

diff --git a/.changelog/12492.txt b/.changelog/12492.txt
new file mode 100644
index 000000000..9cf526e85
--- /dev/null
+++ b/.changelog/12492.txt
@@ -0,0 +1,3 @@
+```release-note:improvement
+api: default to using `DefaultPooledTransport` client to support keep-alive by default
+```
diff --git a/api/api.go b/api/api.go
index 2dc00a3f6..e32707ebf 100644
--- a/api/api.go
+++ b/api/api.go
@@ -264,7 +264,7 @@ func (t *TLSConfig) Copy() *TLSConfig {
 }
 
 func defaultHttpClient() *http.Client {
-	httpClient := cleanhttp.DefaultClient()
+	httpClient := cleanhttp.DefaultPooledClient()
 	transport := httpClient.Transport.(*http.Transport)
 	transport.TLSHandshakeTimeout = 10 * time.Second
 	transport.TLSClientConfig = &tls.Config{
@@ -476,6 +476,18 @@ func NewClient(config *Config) (*Client, error) {
 	return client, nil
 }
 
+// Close closes the client's idle keep-alived connections. The default
+// client configuration uses keep-alive to maintain connections and
+// you should instantiate a single Client and reuse it for all
+// requests from the same host. Connections will be closed
+// automatically once the client is garbage collected. If you are
+// creating multiple clients on the same host (for example, for
+// testing), it may be useful to call Close() to avoid hitting
+// connection limits.
+func (c *Client) Close() {
+	c.httpClient.CloseIdleConnections()
+}
+
 // Address return the address of the Nomad agent
 func (c *Client) Address() string {
 	return c.config.Address
diff --git a/command/agent/http_test.go b/command/agent/http_test.go
index e5cb11571..834624317 100644
--- a/command/agent/http_test.go
+++ b/command/agent/http_test.go
@@ -1113,6 +1113,8 @@ func TestHTTPServer_Limits_OK(t *testing.T) {
 			conf.Address = a.HTTPAddr()
 			conf.TLSConfig.Insecure = true
 			client, err := api.NewClient(conf)
+			defer client.Close()
+
 			require.NoError(t, err)
 
 			// Assert a blocking query isn't timed out by the