fix https://github.com/kataras/iris/issues/1569#issuecomment-663739177

Former-commit-id: c55f1023f4d93f6712c7fa4d299bcf1098872ecf

_examples/routing/http-errors/reset-body/main.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/kataras/iris/v12"
+)
+
+func main() {
+	app := newApp()
+	app.Listen(":8080")
+}
+
+func newApp() *iris.Application {
+	app := iris.New()
+	app.Use(iris.Compression)
+
+	app.OnAnyErrorCode(onErrorCode)
+	app.Get("/", handler)
+
+	app.Configure(iris.WithResetOnFireErrorCode)
+	return app
+}
+
+// This is the default error handler Iris uses for any error codes.
+func onErrorCode(ctx iris.Context) {
+	if err := ctx.GetErr(); err != nil {
+		ctx.WriteString(err.Error())
+	} else {
+		ctx.WriteString(iris.StatusText(ctx.GetStatusCode()))
+	}
+}
+
+func handler(ctx iris.Context) {
+	ctx.Record()
+
+	ctx.WriteString("This should NOT be written")
+
+	// [....something bad happened after we "write"]
+	err := fmt.Errorf("custom error")
+	ctx.StopWithError(iris.StatusBadRequest, err)
+}

_examples/routing/http-errors/reset-body/main_test.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/kataras/iris/v12/httptest"
+)
+
+func TestResetCompressionAndFireError(t *testing.T) { // #1569
+	app := newApp()
+
+	e := httptest.New(t, app)
+	e.GET("/").Expect().Status(httptest.StatusBadRequest).Body().Equal("custom error")
+}