fix: No infinite recursion on write error

If there is some error writing to the response writer, we
would previous have infinite recursion.

Re-closes influxdata#20249

services/httpd/response_writer.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"net/http"
 	"strconv"
+	"errors"
 	"time"
 
 	"github.com/influxdata/influxdb/models"
@@ -131,15 +132,27 @@ func (f *jsonFormatter) WriteResponse(w io.Writer, resp Response) (err error) {
 	}
 
 	if err != nil {
-		_, err = io.WriteString(w, err.Error())
+		unnestedErr := unnestError(err)
+		// ignore error when already trying to report another error
+		b2, _ := json.Marshal(unnestedErr.Error())
+		io.WriteString(w, `{"error":`)
+		w.Write(b2)
+		io.WriteString(w, "}")
 	} else {
 		_, err = w.Write(b)
 	}
-
 	w.Write([]byte("\n"))
 	return err
 }
 
+func unnestError(err error) error {
+	for errNested := err; errNested != nil; errNested = errors.Unwrap(err) {
+		err = errNested
+	}
+	return err
+}
+
+
 type csvFormatter struct {
 	statementID int
 	columns     []string