HTTP/2 Server Push

HTTP/2 server push lets the server send resources to the client before they are requested, eliminating a round trip for assets the page is known to need. This recipe pushes a page’s CSS, JavaScript, and image alongside the HTML response.

1. Register a route to serve web assets

e.Static("/", "static")

2. Serve index.html and push its dependencies

Unwrap the response to access the underlying http.ResponseWriter, then push each asset if the writer implements http.Pusher:

e.GET("/", func(c *echo.Context) (err error) {
  rw, err := echo.UnwrapResponse(c.Response())
  if err != nil {
    return
  }
  if pusher, ok := rw.ResponseWriter.(http.Pusher); ok {
    if err = pusher.Push("/app.css", nil); err != nil {
      return
    }
    if err = pusher.Push("/app.js", nil); err != nil {
      return
    }
    if err = pusher.Push("/echo.png", nil); err != nil {
      return
    }
  }
  return c.File("index.html")
})

3. Start the TLS server

sc := echo.StartConfig{Address: ":1323"}
if err := sc.StartTLS(context.Background(), e, "cert.pem", "key.pem"); err != nil {
  e.Logger.Error("failed to start server", "error", err)
}

Source code

index.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>HTTP/2 Server Push</title>
  <link rel="stylesheet" href="/app.css">
  <script src="/app.js"></script>
</head>
<body>
  <img class="echo" src="/echo.png">
  <h2>The following static files are served via HTTP/2 server push</h2>
  <ul>
    <li><code>/app.css</code></li>
    <li><code>/app.js</code></li>
    <li><code>/echo.png</code></li>
  </ul>
</body>
</html>

server.go

package main

import (
  "context"
  "net/http"

  "github.com/labstack/echo/v5"
)

func main() {
  e := echo.New()
  e.Static("/", "static")
  e.GET("/", func(c *echo.Context) (err error) {
    rw, err := echo.UnwrapResponse(c.Response())
    if err != nil {
      return
    }
    if pusher, ok := rw.ResponseWriter.(http.Pusher); ok {
      if err = pusher.Push("/app.css", nil); err != nil {
        return
      }
      if err = pusher.Push("/app.js", nil); err != nil {
        return
      }
      if err = pusher.Push("/echo.png", nil); err != nil {
        return
      }
    }
    return c.File("index.html")
  })

  sc := echo.StartConfig{Address: ":1323"}
  if err := sc.StartTLS(context.Background(), e, "cert.pem", "key.pem"); err != nil {
    e.Logger.Error("failed to start server", "error", err)
  }
}