Use cache for http.client in tsdb package. (#6833)

* datasource: move caching closer to datasource struct

* tsdb: use cached version of datasource http transport

closes #6825

pkg/models/datasource_cache.go

@@ -0,0 +1,95 @@
+package models
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+type proxyTransportCache struct {
+	cache map[int64]cachedTransport
+	sync.Mutex
+}
+
+type cachedTransport struct {
+	updated time.Time
+
+	*http.Transport
+}
+
+var ptc = proxyTransportCache{
+	cache: make(map[int64]cachedTransport),
+}
+
+func (ds *DataSource) GetHttpClient() (*http.Client, error) {
+	transport, err := ds.GetHttpTransport()
+
+	if err != nil {
+		return nil, err
+	}
+
+	return &http.Client{
+		Timeout:   time.Duration(30 * time.Second),
+		Transport: transport,
+	}, nil
+}
+
+func (ds *DataSource) GetHttpTransport() (*http.Transport, error) {
+	ptc.Lock()
+	defer ptc.Unlock()
+
+	if t, present := ptc.cache[ds.Id]; present && ds.Updated.Equal(t.updated) {
+		return t.Transport, nil
+	}
+
+	transport := &http.Transport{
+		TLSClientConfig: &tls.Config{
+			InsecureSkipVerify: true,
+		},
+		Proxy: http.ProxyFromEnvironment,
+		Dial: (&net.Dialer{
+			Timeout:   30 * time.Second,
+			KeepAlive: 30 * time.Second,
+		}).Dial,
+		TLSHandshakeTimeout:   10 * time.Second,
+		ExpectContinueTimeout: 1 * time.Second,
+		MaxIdleConns:          100,
+		IdleConnTimeout:       90 * time.Second,
+	}
+
+	var tlsAuth, tlsAuthWithCACert bool
+	if ds.JsonData != nil {
+		tlsAuth = ds.JsonData.Get("tlsAuth").MustBool(false)
+		tlsAuthWithCACert = ds.JsonData.Get("tlsAuthWithCACert").MustBool(false)
+	}
+
+	if tlsAuth {
+		transport.TLSClientConfig.InsecureSkipVerify = false
+
+		decrypted := ds.SecureJsonData.Decrypt()
+
+		if tlsAuthWithCACert && len(decrypted["tlsCACert"]) > 0 {
+			caPool := x509.NewCertPool()
+			ok := caPool.AppendCertsFromPEM([]byte(decrypted["tlsCACert"]))
+			if ok {
+				transport.TLSClientConfig.RootCAs = caPool
+			}
+		}
+
+		cert, err := tls.X509KeyPair([]byte(decrypted["tlsClientCert"]), []byte(decrypted["tlsClientKey"]))
+		if err != nil {
+			return nil, err
+		}
+		transport.TLSClientConfig.Certificates = []tls.Certificate{cert}
+	}
+
+	ptc.cache[ds.Id] = cachedTransport{
+		Transport: transport,
+		updated:   ds.Updated,
+	}
+
+	return transport, nil
+}