rpc: use method constants instead of literal strings (ethereum#15652)

Author: vvelikodny

rpc/http.go

@@ -67,7 +67,7 @@ func (hc *httpConn) Close() error {
 
 // DialHTTP creates a new RPC clients that connection to an RPC server over HTTP.
 func DialHTTP(endpoint string) (*Client, error) {
-	req, err := http.NewRequest("POST", endpoint, nil)
+	req, err := http.NewRequest(http.MethodPost, endpoint, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -149,7 +149,7 @@ func NewHTTPServer(cors []string, srv *Server) *http.Server {
 // ServeHTTP serves JSON-RPC requests over HTTP.
 func (srv *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Permit dumb empty requests for remote health-checks (AWS)
-	if r.Method == "GET" && r.ContentLength == 0 && r.URL.RawQuery == "" {
+	if r.Method == http.MethodGet && r.ContentLength == 0 && r.URL.RawQuery == "" {
 		return
 	}
 	if code, err := validateRequest(r); err != nil {
@@ -169,7 +169,7 @@ func (srv *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 // validateRequest returns a non-zero response code and error message if the
 // request is invalid.
 func validateRequest(r *http.Request) (int, error) {
-	if r.Method == "PUT" || r.Method == "DELETE" {
+	if r.Method == http.MethodPut || r.Method == http.MethodDelete {
 		return http.StatusMethodNotAllowed, errors.New("method not allowed")
 	}
 	if r.ContentLength > maxHTTPRequestContentLength {
@@ -192,7 +192,7 @@ func newCorsHandler(srv *Server, allowedOrigins []string) http.Handler {
 
 	c := cors.New(cors.Options{
 		AllowedOrigins: allowedOrigins,
-		AllowedMethods: []string{"POST", "GET"},
+		AllowedMethods: []string{http.MethodPost, http.MethodGet},
 		MaxAge:         600,
 		AllowedHeaders: []string{"*"},
 	})

rpc/http_test.go

@@ -24,25 +24,25 @@ import (
 )
 
 func TestHTTPErrorResponseWithDelete(t *testing.T) {
-	testHTTPErrorResponse(t, "DELETE", contentType, "", http.StatusMethodNotAllowed)
+	testHTTPErrorResponse(t, http.MethodDelete, contentType, "", http.StatusMethodNotAllowed)
 }
 
 func TestHTTPErrorResponseWithPut(t *testing.T) {
-	testHTTPErrorResponse(t, "PUT", contentType, "", http.StatusMethodNotAllowed)
+	testHTTPErrorResponse(t, http.MethodPut, contentType, "", http.StatusMethodNotAllowed)
 }
 
 func TestHTTPErrorResponseWithMaxContentLength(t *testing.T) {
 	body := make([]rune, maxHTTPRequestContentLength+1)
 	testHTTPErrorResponse(t,
-		"POST", contentType, string(body), http.StatusRequestEntityTooLarge)
+		http.MethodPost, contentType, string(body), http.StatusRequestEntityTooLarge)
 }
 
 func TestHTTPErrorResponseWithEmptyContentType(t *testing.T) {
-	testHTTPErrorResponse(t, "POST", "", "", http.StatusUnsupportedMediaType)
+	testHTTPErrorResponse(t, http.MethodPost, "", "", http.StatusUnsupportedMediaType)
 }
 
 func TestHTTPErrorResponseWithValidRequest(t *testing.T) {
-	testHTTPErrorResponse(t, "POST", contentType, "", 0)
+	testHTTPErrorResponse(t, http.MethodPost, contentType, "", 0)
 }
 
 func testHTTPErrorResponse(t *testing.T, method, contentType, body string, expected int) {