Response Writer Extension

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 {
io.Writer
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.

Example:

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

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.

ChunkedBodyWriter

Example:

h.GET("/flush/chunk", func (ctx context.Context, c *app.RequestContext) {
    // Hijack the writer of response
    c.Response.HijackWriter(resp.NewChunkedBodyWriter(&c.Response, c.GetWriter()))
    
    for i := 0; i < 10; i++ {
    c.Write([]byte(fmt.Sprintf("chunk %d: %s", i, strings.Repeat("hi~", i)))) // nolint: errcheck
    c.Flush() // nolint: errcheck
    time.Sleep(200 * time.Millisecond)
    }
})

Effect display:

Open the interface in the example at localhost:8888, and then use the following command to observe the effect:

curl -N --location localhost:8888/flush/chunk