update response content-length when response body is updated by copro…

…cess response hook

coprocess/grpc/coprocess_grpc_test.go

@@ -5,12 +5,14 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"github.com/TykTechnologies/tyk/header"
 	"io/ioutil"
 	"math/rand"
 	"mime/multipart"
 	"net"
 	"net/http"
 	"os"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -567,6 +569,9 @@ func TestGRPCDispatch(t *testing.T) {
 			Code:      http.StatusOK,
 			Headers:   headers,
 			BodyMatch: "newbody",
+			HeadersMatch: map[string]string{
+				header.ContentLength: strconv.Itoa(len("newbody")),
+			},
 		})
 	})
 

gateway/coprocess.go

@@ -598,6 +598,12 @@ func (h *CustomMiddlewareResponseHook) HandleResponse(rw http.ResponseWriter, re
 	bodyBuf := bytes.NewBuffer(retObject.Response.RawBody)
 	res.Body = ioutil.NopCloser(bodyBuf)
 
+	//set response body length with the size of response body returned from the hook
+	//so that it is updated accordingly in the response object
+	responseBodyLen := len(retObject.Response.RawBody)
+	res.ContentLength = int64(responseBodyLen)
+	res.Header.Set("Content-Length", fmt.Sprintf("%d", responseBodyLen))
+
 	res.StatusCode = int(retObject.Response.StatusCode)
 	return nil
 }