proxy middleware should use httputil.ReverseProxy for SSE requests #2624

aldas · 2024-04-15T17:38:16Z

Relates to #1172

Use httputil.ReverseProxy to proxy SSE requests as it has support for streaming responses. See:
https://github.com/golang/go/blob/b107d95b9a66bfe7150fd4f2915e9bb876a6999a/src/net/http/httputil/reverseproxy.go#L601

can be tested with

create separate package and execute this code to start serving proxy application at port 8080 that proxies requests to localhost:8081

package main import ( "errors" "github.com/labstack/echo/v4" "github.com/labstack/echo/v4/middleware" "log" "net/http" "net/url" ) func main() { e := echo.New() e.Use(middleware.Logger()) e.Use(middleware.Recover()) tmpURL, err := url.Parse("http://localhost:8081") if err != nil { log.Fatal(err)	} e.Use(middleware.Proxy(middleware.NewRoundRobinBalancer([]*middleware.ProxyTarget{{URL: tmpURL}}))) if err := e.Start(":8080"); err != nil && !errors.Is(err, http.ErrServerClosed) { log.Fatal(err)	} }

Create application for serving SSE

Go file for application

package main import ( "bytes" "errors" "fmt" "github.com/labstack/echo/v4" "github.com/labstack/echo/v4/middleware" "log" "net/http" "time" ) func main() { e := echo.New() e.Use(middleware.Logger()) e.Use(middleware.Recover()) e.File("/", "./index.html") e.GET("/sse", func(c echo.Context) error { log.Printf("SSE client connected, ip: %v", c.RealIP()) w := c.Response() w.Header().Set("Content-Type", "text/event-stream") w.Header().Set("Cache-Control", "no-cache") w.Header().Set("Connection", "keep-alive") ticker := time.NewTicker(1 * time.Second) defer ticker.Stop() for { select { case <-c.Request().Context().Done(): log.Printf("SSE client disconnected, ip: %v", c.RealIP()) return nil case <-ticker.C: event := Event{ Data: []byte("ping: " + time.Now().Format(time.RFC3339Nano)),	} if err := event.WriteTo(w); err != nil { return err	} w.Flush()	}	}	}) if err := e.Start(":8081"); err != nil && !errors.Is(err, http.ErrServerClosed) { log.Fatal(err)	} } // Event structure is defined here: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format type Event struct { ID []byte Data []byte Event []byte Retry []byte Comment []byte } // WriteTo writes Event to given ResponseWriter func (ev *Event) WriteTo(w http.ResponseWriter) error { // Marshalling part is taken from: https://github.com/r3labs/sse/blob/c6d5381ee3ca63828b321c16baa008fd6c0b4564/http.go#L16 if len(ev.Data) == 0 && len(ev.Comment) == 0 { return nil	} if len(ev.Data) > 0 { if _, err := fmt.Fprintf(w, "id: %s\n", ev.ID); err != nil { return err	} sd := bytes.Split(ev.Data, []byte("\n")) for i := range sd { if _, err := fmt.Fprintf(w, "data: %s\n", sd[i]); err != nil { return err	}	} if len(ev.Event) > 0 { if _, err := fmt.Fprintf(w, "event: %s\n", ev.Event); err != nil { return err	}	} if len(ev.Retry) > 0 { if _, err := fmt.Fprintf(w, "retry: %s\n", ev.Retry); err != nil { return err	}	}	} if len(ev.Comment) > 0 { if _, err := fmt.Fprintf(w, ": %s\n", ev.Comment); err != nil { return err	}	} if _, err := fmt.Fprint(w, "\n"); err != nil { return err	} return nil }

in the same folder as app create index.html

<!DOCTYPE html> <html> <body> <h1>Getting server updates</h1> <div id="result"></div> <script> // Example taken from: https://www.w3schools.com/html/html5_serversentevents.asp if (typeof (EventSource) !== "undefined") { const source = new EventSource("/sse"); source.onmessage = function (event) { document.getElementById("result").innerHTML += event.data + "<br>"; }; } else { document.getElementById("result").innerHTML = "Sorry, your browser does not support server-sent events..."; } </script> </body> </html>

Open http://localhost:8080 in your browser. You should see Ping messages streamed, assuming proxy middleware handles SSE requests as raw proxy

aldas changed the title ~~proxy middleware should use raw http proxy for SSE requests~~ proxy middleware should use raw proxy for SSE requests Apr 15, 2024

aldas force-pushed the proxy_sse branch from f62a7ee to c134df4 Compare April 15, 2024 17:47

proxy middleware should use http proxy for SSE requests

ebf0003

aldas force-pushed the proxy_sse branch from c134df4 to ebf0003 Compare April 15, 2024 18:05

aldas changed the title ~~proxy middleware should use raw proxy for SSE requests~~ proxy middleware should use httputil.ReverseProxy for SSE requests Apr 15, 2024

aldas merged commit e0f2a02 into labstack:master Apr 15, 2024

aldas deleted the proxy_sse branch April 15, 2024 18:12

aldas mentioned this pull request Apr 15, 2024

Reverse proxy for Server-Sent Events #1172

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renovate bot mentioned this pull request Nov 1, 2024

fix(deps): update all minor, patch, or digest dependencies on go cloudnativedaysjp/emtec-ecu#82

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proxy middleware should use httputil.ReverseProxy for SSE requests #2624

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aldas commented Apr 15, 2024 •

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