Streaming Response

This recipe streams a JSON response to the client as each record is produced, using chunked transfer encoding:

• Send data as it is produced.
• Stream a JSON response with chunked transfer encoding.

The handler encodes one record at a time and calls http.NewResponseController(...).Flush() after each to push it to the client immediately, pausing one second between records.

Server

package main

import (
  "context"
  "encoding/json"
  "net/http"
  "time"

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

type (
  Geolocation struct {
    Altitude  float64
    Latitude  float64
    Longitude float64
  }
)

var (
  locations = []Geolocation{
    {-97, 37.819929, -122.478255},
    {1899, 39.096849, -120.032351},
    {2619, 37.865101, -119.538329},
    {42, 33.812092, -117.918974},
    {15, 37.77493, -122.419416},
  }
)

func main() {
  e := echo.New()
  e.GET("/", func(c *echo.Context) error {
    c.Response().Header().Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
    c.Response().WriteHeader(http.StatusOK)

    enc := json.NewEncoder(c.Response())
    for _, l := range locations {
      if err := enc.Encode(l); err != nil {
        return err
      }
      if err := http.NewResponseController(c.Response()).Flush(); err != nil {
        return err
      }
      select {
      case <-c.Request().Context().Done():
        return nil
      case <-time.After(1 * time.Second):
        continue
      }
    }
    return nil
  })

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

Client

curl localhost:1323

Output

{"Altitude":-97,"Latitude":37.819929,"Longitude":-122.478255}
{"Altitude":1899,"Latitude":39.096849,"Longitude":-120.032351}
{"Altitude":2619,"Latitude":37.865101,"Longitude":-119.538329}
{"Altitude":42,"Latitude":33.812092,"Longitude":-117.918974}
{"Altitude":15,"Latitude":37.77493,"Longitude":-122.419416}