API: Add convenience method for accessing the deprecation warnings in the response headers

(cherry picked from commit 6c66577)

Author: karmi

esapi/esapi.response.go

@@ -78,3 +78,15 @@ func (r *Response) Status() string {
 func (r *Response) IsError() bool {
 	return r.StatusCode > 299
 }
+
+// Warnings returns the deprecation warnings from response headers.
+//
+func (r *Response) Warnings() []string {
+	return r.Header["Warning"]
+}
+
+// HasWarnings returns true when the response headers contain deprecation warnings.
+//
+func (r *Response) HasWarnings() bool {
+	return len(r.Warnings()) > 0
+}

esapi/esapi_response_internal_test.go

@@ -9,6 +9,7 @@ package esapi
 import (
 	"errors"
 	"io/ioutil"
+	"net/http"
 	"strings"
 	"testing"
 )
@@ -79,4 +80,19 @@ func TestAPIResponse(t *testing.T) {
 			t.Errorf("Expected error for response: %s", res.Status())
 		}
 	})
+
+	t.Run("Warnings", func(t *testing.T) {
+		hdr := http.Header{}
+		hdr.Add("Warning", "Foo 1")
+		hdr.Add("Warning", "Foo 2")
+		res = &Response{StatusCode: 201, Header: hdr}
+
+		if !res.HasWarnings() {
+			t.Errorf("Expected response to have warnings")
+		}
+
+		if len(res.Warnings()) != 2 {
+			t.Errorf("Expected [2] warnings, got: %d", len(res.Warnings()))
+		}
+	})
 }