Response Writer Extension

Response Writer Extension provided by Hertz.

According to Hertz’s layered architecture, the actual write operation of the HTTP response is performed after the application layer user processing logic returns. Under this constraint, users cannot flexibly control the behavior of write operations on demand. This limitation is especially obvious in scenarios such as controlling chunked encoding write logic and SSE.

To solve this problem, Hertz provides an extension called “Response Writer Hijacking” that can vertically penetrate the limitations brought by the layered architecture in an orthogonal way. It allows users to freely customize the logic of writing responses in the application layer according to their own needs, improving the framework’s ease of use.

Core Design

Interface Definition

interface is defined in pkg/network/writer.

type ExtWriter interface {
Flush() error

// Finalize will be called by framework before the writer is released.
// Implementations must guarantee that Finalize is safe for multiple calls.
Finalize() error

Hijack Your Own Response Writer

Hertz provides Response.HijackWriter in app.RequestContext to allow users to hijack their own response writer, which provides another way for response writing process.


    h.GET("/hijack", func (c context.Context, ctx *app.RequestContext) {
// Hijack the writer of response

Supported Response Writer Extension

  • ChunkedBodyWriter: Hertz provides NewChunkedBodyWriter to create a response writer which allow users to flush chunk immediately during the handler process, it is defined under pkg/protocol/http1/resp/writer, and you can implement your own response writer.



    h.GET("/flush/chunk", func (c context.Context, ctx *app.RequestContext) {
// Hijack the writer of response
ctx.Response.HijackWriter(resp.NewChunkedBodyWriter(&ctx.Response, ctx.GetWriter()))

for i := 0; i < 10; i++ {
ctx.Write([]byte(fmt.Sprintf("chunk %d: %s", i, strings.Repeat("hi~", i)))) // nolint: errcheck
ctx.Flush() // nolint: errcheck
time.Sleep(200 * time.Millisecond)

Last modified September 22, 2023 : docs: update extWriter (#786) (71c7226)