Fix connection leak (#31)

Connections were being left around after requests and in some cases this could
result in file descriptor errors when open files built up.

Closing the http response body and the tcp connection, as well as disabling http
keep alives seems to resolve this.

ssl_exporter.go

@@ -5,6 +5,7 @@ import (
 	"crypto/x509"
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net"
 	"net/http"
@@ -96,8 +97,9 @@ func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
 				return http.ErrUseLastResponse
 			},
 			Transport: &http.Transport{
-				TLSClientConfig: e.tlsConfig,
-				Proxy:           http.ProxyFromEnvironment,
+				TLSClientConfig:   e.tlsConfig,
+				Proxy:             http.ProxyFromEnvironment,
+				DisableKeepAlives: true,
 			},
 			Timeout: e.timeout,
 		}
@@ -111,6 +113,13 @@ func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
 			)
 			return
 		}
+		defer func() {
+			_, err := io.Copy(ioutil.Discard, resp.Body)
+			if err != nil {
+				log.Errorln(err)
+			}
+			resp.Body.Close()
+		}()
 
 		// Check if the response from the target is encrypted
 		if resp.TLS == nil {
@@ -136,6 +145,7 @@ func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
 			)
 			return
 		}
+		defer conn.Close()
 
 		state = conn.ConnectionState()
 	} else {