Add "User-Agent" header to request in Perform()

In order to better identify/debug requests with the client, set the `User-Agent`
header in the Perform() method of the transport.

Author: karmi

elasticsearch_internal_test.go

@@ -108,7 +108,7 @@ func TestClientInterface(t *testing.T) {
 			t.Errorf("Unexpected call to transport by client")
 		}
 
-		c.Perform(&http.Request{URL: &url.URL{}}) // errcheck ignore
+		c.Perform(&http.Request{URL: &url.URL{}, Header: make(http.Header)}) // errcheck ignore
 
 		if called != true { // megacheck ignore
 			t.Errorf("Expected client to call transport")

estransport/estransport.go

@@ -9,6 +9,12 @@ import (
 	"github.com/elastic/go-elasticsearch/esapi"
 )
 
+var userAgent string
+
+func init() {
+	userAgent = strings.Join([]string{"go-elasticsearch", Version}, "/")
+}
+
 // Version returns the package version as a string.
 //
 const Version = esapi.Version
@@ -70,6 +76,7 @@ func (c *Client) Perform(req *http.Request) (*http.Response, error) {
 
 	c.setURL(u, req)
 	c.setBasicAuth(u, req)
+	c.setUserAgent(req)
 
 	// TODO(karmi): Wrap error
 	return c.transport.RoundTrip(req)
@@ -114,3 +121,8 @@ func (c *Client) setBasicAuth(u *url.URL, req *http.Request) *http.Request {
 
 	return req
 }
+
+func (c *Client) setUserAgent(req *http.Request) *http.Request {
+	req.Header.Set("User-Agent", userAgent)
+	return req
+}

estransport/estransport_internal_test.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"strings"
 	"testing"
 )
 
@@ -125,6 +126,18 @@ func TestTransportPerform(t *testing.T) {
 		}
 	})
 
+	t.Run("Sets UserAgent", func(t *testing.T) {
+		u, _ := url.Parse("http://example.com")
+		tp := New(Config{URLs: []*url.URL{u}})
+
+		req, _ := http.NewRequest("GET", "/abc", nil)
+		tp.setUserAgent(req)
+
+		if !strings.HasPrefix(req.UserAgent(), "go-elasticsearch") {
+			t.Errorf("Unexpected user agent: %s", req.UserAgent())
+		}
+	})
+
 	t.Run("Error No URL", func(t *testing.T) {
 		tp := New(Config{
 			URLs: []*url.URL{},