SSE
SSE is short for Server-Sent Events, which is a server push technology that allows the server to send events to clients through simple HTTP responses.
Hertz’s implementation can be found here.
Installation
go get github.com/hertz-contrib/sse
Example Code
In the following example code, when accessing /sse, the server will push a timestamp to the client every second.
package main
import (
"context"
"net/http"
"time"
"github.com/hertz-contrib/sse"
"github.com/cloudwego/hertz/pkg/app"
"github.com/cloudwego/hertz/pkg/app/server"
"github.com/cloudwego/hertz/pkg/common/hlog"
)
func main() {
h := server.Default()
h.GET("/sse", func(ctx context.Context, c *app.RequestContext) {
lastEventID := sse.GetLastEventID(c)
// The client can inform the server of the last event received through Last-Event-ID.
hlog.CtxInfof(ctx, "last event ID: %s", lastEventID)
// You must set status code and response headers before calling Render for first time.
c.SetStatusCode(http.StatusOK)
s := sse.NewStream(c)
for t := range time.NewTicker(1 * time.Second).C {
event := &sse.Event{
Event: "timestamp",
Data: []byte(t.Format(time.RFC3339)),
}
err := s.Publish(event)
if err != nil {
return
}
}
})
h.Spin()
}
Configuration
NewStream
NewStream is used to create a stream for sending events. By default, Content-Type is set as text/event-stream (it’s better not to modify the Content-Type). Cache-Control is set as no-cache.
If there are any proxies between server and client, it’s recommended to set the response header of X-Accel-Buffering as no.
Function signature:
func NewStream(c *app.RequestContext) *Stream
Example code:
package main
func main() {
h := server.Default()
h.GET("/sse", func(ctx context.Context, c *app.RequestContext) {
c.SetStatusCode(http.StatusOK)
c.Response.Header.Set("X-Accel-Buffering", "no")
s := sse.NewStream(c)
// ...
})
}
Publish
Publish is used to send an event message to the client. The format of the event message should be as follows:
type Event struct {
// Name of this event.
Event string
// Data associated with this event.
Data []byte
// ID number assigned by Server Sent Events protocol.
ID string
// Retry duration time specified in milliseconds; if present then browser will attempt reconnect after that many milliseconds have elapsed since last message received from server.
Retry time.Duration
}
Function signature:
func (c *Stream) Publish(event *Event) error
GetLastEventID
GetLastEventID retrieves the ID number of last received SSE message from client. If no SSE messages were sent yet returns empty string.
Function signature:
func GetLastEventID(c *app.RequestContext) string