Add support for HTTP API compatibility header (#266) (#273)

* Transport: Add compatibility header

Author: Anaethelion

estransport/estransport.go

@@ -30,20 +30,26 @@ import (
 	"os"
 	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
 
 	"github.com/elastic/go-elasticsearch/v7/internal/version"
 )
 
-// Version returns the package version as a string.
-//
-const Version = version.Client
+const (
+	// Version returns the package version as a string.
+	Version = version.Client
+
+	// esCompatHeader defines the env var for Compatibility header.
+	esCompatHeader = "ELASTIC_CLIENT_APIVERSIONING"
+)
 
 var (
 	userAgent   string
 	metaHeader  string
+	compatibilityHeader bool
 	reGoVersion = regexp.MustCompile(`go(\d+\.\d+\..+)`)
 
 	defaultMaxRetries    = 3
@@ -53,6 +59,9 @@ var (
 func init() {
 	userAgent = initUserAgent()
 	metaHeader = initMetaHeader()
+
+	compatHeaderEnv := os.Getenv(esCompatHeader)
+	compatibilityHeader, _ = strconv.ParseBool(compatHeaderEnv)
 }
 
 // Interface defines the interface for HTTP client.
@@ -221,6 +230,14 @@ func (c *Client) Perform(req *http.Request) (*http.Response, error) {
 		err error
 	)
 
+	// Compatibility Header
+	if compatibilityHeader {
+		if req.Body != nil {
+			req.Header.Set("Content-Type", "application/vnd.elasticsearch+json;compatible-with=7")
+		}
+		req.Header.Set("Accept", "application/vnd.elasticsearch+json;compatible-with=7")
+	}
+
 	// Record metrics, when enabled
 	if c.metrics != nil {
 		c.metrics.Lock()

estransport/estransport_internal_test.go

@@ -915,3 +915,69 @@ func TestMaxRetries(t *testing.T) {
 		})
 	}
 }
+
+func TestCompatibilityHeader(t *testing.T) {
+	tests := []struct {
+		name                string
+		compatibilityHeader bool
+		bodyPresent         bool
+		expectsHeader       []string
+	}{
+		{
+			name:                "Compatibility header disabled",
+			compatibilityHeader: false,
+			bodyPresent: false,
+			expectsHeader:       []string{"application/json"},
+		},
+		{
+			name:                "Compatibility header enabled",
+			compatibilityHeader: true,
+			bodyPresent: false,
+			expectsHeader:       []string{"application/vnd.elasticsearch+json;compatible-with=7"},
+		},
+		{
+			name: "Compatibility header enabled with body",
+			compatibilityHeader: true,
+			bodyPresent: true,
+			expectsHeader:       []string{"application/vnd.elasticsearch+json;compatible-with=7"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			compatibilityHeader = test.compatibilityHeader
+
+			c, _ := New(Config{
+				URLs: []*url.URL{{}},
+				Transport: &mockTransp{
+					RoundTripFunc: func(req *http.Request) (*http.Response, error) {
+						if test.compatibilityHeader {
+							if !reflect.DeepEqual(req.Header["Accept"], test.expectsHeader) {
+								t.Errorf("Compatibility header enabled but header is, not in request headers, got: %s, want: %s", req.Header["Accept"], test.expectsHeader)
+							}
+						}
+						if test.bodyPresent {
+							if !reflect.DeepEqual(req.Header["Content-Type"], test.expectsHeader) {
+								t.Errorf("Compatibility header with Body enabled, not in request headers, got: %s, want: %s", req.Header["Content-Type"], test.expectsHeader)
+							}
+						}
+
+						return &http.Response{
+							StatusCode: http.StatusOK,
+							Status:     "MOCK",
+						}, nil
+					},
+				},
+			})
+
+			req := &http.Request{URL: &url.URL{}, Header: make(http.Header)}
+			if test.bodyPresent {
+				req.Body = ioutil.NopCloser(strings.NewReader("{}"))
+			}
+
+			_, _ = c.Perform(req)
+
+			compatibilityHeader = false
+		})
+	}
+}