Retry on EOF errors

The retry mechanism should be active when the server closes the connection unexpectedly,
eg. when an Elasticsearch node is restarting, or the underlying connection gets stale.

Fixes #111

(cherry picked from commit cb4ea94)

Author: karmi

estransport/estransport.go

@@ -254,7 +254,12 @@ func (c *Client) Perform(req *http.Request) (*http.Response, error) {
 			c.pool.OnFailure(conn)
 			c.Unlock()
 
-			// Retry only on network errors, but don't retry on timeout errors, unless configured
+			// Retry on EOF errors
+			if err == io.EOF {
+				shouldRetry = true
+			}
+
+			// Retry on network errors, but not on timeout errors, unless configured
 			if err, ok := err.(net.Error); ok {
 				if (!err.Timeout() || c.enableRetryOnTimeout) && !c.disableRetry {
 					shouldRetry = true

estransport/estransport_internal_test.go

@@ -8,6 +8,7 @@ package estransport
 
 import (
 	"fmt"
+	"io"
 	"io/ioutil"
 	"math/rand"
 	"net/http"
@@ -393,6 +394,45 @@ func TestTransportPerformRetries(t *testing.T) {
 		}
 	})
 
+	t.Run("Retry request on EOF error and return the response", func(t *testing.T) {
+		var (
+			i       int
+			numReqs = 2
+		)
+
+		u, _ := url.Parse("http://foo.bar")
+		tp := New(Config{
+			URLs: []*url.URL{u, u, u},
+			Transport: &mockTransp{
+				RoundTripFunc: func(req *http.Request) (*http.Response, error) {
+					i++
+					fmt.Printf("Request #%d", i)
+					if i == numReqs {
+						fmt.Print(": OK\n")
+						return &http.Response{Status: "OK"}, nil
+					}
+					fmt.Print(": ERR\n")
+					return nil, io.EOF
+				},
+			}})
+
+		req, _ := http.NewRequest("GET", "/abc", nil)
+
+		res, err := tp.Perform(req)
+
+		if err != nil {
+			t.Fatalf("Unexpected error: %s", err)
+		}
+
+		if res.Status != "OK" {
+			t.Errorf("Unexpected response: %+v", res)
+		}
+
+		if i != numReqs {
+			t.Errorf("Unexpected number of requests, want=%d, got=%d", numReqs, i)
+		}
+	})
+
 	t.Run("Retry request on 5xx response and return new response", func(t *testing.T) {
 		var (
 			i       int