Fix trace request builder func (TykTechnologies#3262)

When `tr.Path` was empty, it was giving error. So I change `httptest.NewRequest()` to `http.NewRequest()`.

Fixes TykTechnologies/tyk-analytics#2031

gateway/tracing.go

@@ -21,10 +21,11 @@ type traceHttpRequest struct {
 	Headers http.Header `json:"headers"`
 }
 
-func (tr *traceHttpRequest) toRequest() *http.Request {
-	r := httptest.NewRequest(tr.Method, tr.Path, strings.NewReader(tr.Body))
-	// It sets example.com by default. Setting it to empty will not show a value because it is not necessary.
-	r.Host = ""
+func (tr *traceHttpRequest) toRequest() (*http.Request, error) {
+	r, err := http.NewRequest(tr.Method, tr.Path, strings.NewReader(tr.Body))
+	if err != nil {
+		return nil, err
+	}
 
 	for key, values := range tr.Headers {
 		for _, v := range values {
@@ -34,7 +35,7 @@ func (tr *traceHttpRequest) toRequest() *http.Request {
 
 	ctxSetTrace(r)
 
-	return r
+	return r, nil
 }
 
 // TraceRequest is for tracing an HTTP request
@@ -125,7 +126,11 @@ func traceHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	wr := httptest.NewRecorder()
-	tr := traceReq.Request.toRequest()
+	tr, err := traceReq.Request.toRequest()
+	if err != nil {
+		doJSONWrite(w, http.StatusInternalServerError, apiError("Unexpected failure: "+err.Error()))
+		return
+	}
 	nopCloseRequestBody(tr)
 	chainObj.ThisHandler.ServeHTTP(wr, tr)
 

gateway/tracing_test.go

@@ -0,0 +1,26 @@
+package gateway
+
+import (
+	"io/ioutil"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTraceHttpRequest_toRequest(t *testing.T) {
+	const body = `{"foo":"bar"}`
+	header := http.Header{}
+	header.Add("key", "value")
+	tr := &traceHttpRequest{Path: "", Method: http.MethodPost, Body: body, Headers: header}
+
+	request, err := tr.toRequest()
+	bodyInBytes, _ := ioutil.ReadAll(request.Body)
+
+	assert.NoError(t, err)
+	assert.Equal(t, http.MethodPost, request.Method)
+	assert.Equal(t, "", request.URL.Host)
+	assert.Equal(t, "", request.URL.Path)
+	assert.Equal(t, header, request.Header)
+	assert.Equal(t, string(bodyInBytes), body)
+}