rpc: add HTTPError type for HTTP error responses (#22677)

The new error type is returned by client operations contains details of
the response error code and response body.

Co-authored-by: Felix Lange <fjl@twurst.com>

rpc/errors.go

@@ -18,6 +18,35 @@ package rpc
 
 import "fmt"
 
+// HTTPError is returned by client operations when the HTTP status code of the
+// response is not a 2xx status.
+type HTTPError struct {
+	StatusCode int
+	Status     string
+	Body       []byte
+}
+
+func (err HTTPError) Error() string {
+	if len(err.Body) == 0 {
+		return err.Status
+	}
+	return fmt.Sprintf("%v: %s", err.Status, err.Body)
+}
+
+// Error wraps RPC errors, which contain an error code in addition to the message.
+type Error interface {
+	Error() string  // returns the message
+	ErrorCode() int // returns the code
+}
+
+// A DataError contains some data in addition to the error message.
+type DataError interface {
+	Error() string          // returns the message
+	ErrorData() interface{} // returns the error data
+}
+
+// Error types defined below are the built-in JSON-RPC errors.
+
 var (
 	_ Error = new(methodNotFoundError)
 	_ Error = new(subscriptionNotFoundError)