feat: support sse transfer mode

_example/default/go.mod

@@ -4,6 +4,4 @@ go 1.19
 
 require github.com/arl/statsviz v0.6.0
 
-require github.com/gorilla/websocket v1.5.0 // indirect
-
 replace github.com/arl/statsviz => ../../

_example/default/go.sum

@@ -1,5 +1,5 @@
-github.com/gorilla/websocket v1.5.0 h1:PPwGk2jz7EePpoHN/+ClbZu8SPxiqlu12wZP/3sWmnc=
-github.com/gorilla/websocket v1.5.0/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/gorilla/websocket v1.5.1 h1:gmztn0JnHVt9JZquRuzLw3g4wouNVzKL15iLr/zn/QY=
 github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
+golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
 golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=

go.mod

@@ -3,11 +3,11 @@ module github.com/arl/statsviz
 go 1.20
 
 require (
-	github.com/gorilla/websocket v1.5.0
 	github.com/rogpeppe/go-internal v1.11.0
 )
 
 require (
-	golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f // indirect
+	golang.org/x/net v0.17.0 // indirect
+	golang.org/x/sys v0.13.0 // indirect
 	golang.org/x/tools v0.1.12 // indirect
 )

go.sum

@@ -1,8 +1,10 @@
-github.com/gorilla/websocket v1.5.0 h1:PPwGk2jz7EePpoHN/+ClbZu8SPxiqlu12wZP/3sWmnc=
-github.com/gorilla/websocket v1.5.0/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/gorilla/websocket v1.5.1 h1:gmztn0JnHVt9JZquRuzLw3g4wouNVzKL15iLr/zn/QY=
+github.com/gorilla/websocket v1.5.1/go.mod h1:x3kM2JMyaluk02fnUJpQuwD2dCS5NDG2ZHL0uE0tcaY=
 github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
 github.com/rogpeppe/go-internal v1.11.0/go.mod h1:ddIwULY96R17DhadqLgMfk9H9tvdUzkipdSkR5nkCZA=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
+golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=

internal/static/js/app.js

@@ -3,15 +3,6 @@ import * as plot from "./plot.js";
 import * as theme from "./theme.js";
 import PlotsDef from './plotsdef.js';
 
-const buildWebsocketURI = () => {
-    var loc = window.location,
-        ws_prot = "ws:";
-    if (loc.protocol === "https:") {
-        ws_prot = "wss:";
-    }
-    return ws_prot + "//" + loc.host + loc.pathname + "ws"
-}
-
 const dataRetentionSeconds = 600;
 var timeout = 250;
 
@@ -26,38 +17,45 @@ let paused = false;
 let show_gc = true;
 let timerange = 60;
 
-/* WebSocket connection handling */
-const connect = () => {
-    const uri = buildWebsocketURI();
-    let ws = new WebSocket(uri);
-    console.info(`Attempting websocket connection to server at ${uri}`);
-
-    ws.onopen = () => {
+const dataProcessor = {
+    initDone: false,
+    close: () => {
+    },
+    connected: false,
+    retrying: false,
+    onopen: () => {
+        dataProcessor.initDone = false;
+        dataProcessor.connected = true;
         console.info("Successfully connected");
         timeout = 250; // reset connection timeout for next time
-    };
-
-    ws.onclose = event => {
-        console.error(`Closed websocket connection: code ${event.code}`);
-        setTimeout(connect, clamp(timeout += timeout, 250, 5000));
-    };
-
-    ws.onerror = err => {
-        console.error(`Websocket error, closing connection.`);
-        ws.close();
-    };
-
-    let initDone = false;
-    ws.onmessage = event => {
+    },
+    onclose: event => {
+        dataProcessor.connected = false;
+        console.error(`Closed connection: code ${event.code || event}`);
+        if (dataProcessor.retrying) {
+            return
+        }
+        dataProcessor.retrying = true
+        setTimeout(() => {
+            connect()
+            dataProcessor.retrying = false
+        }, clamp(timeout += timeout, 250, 5000));
+    },
+    onerror: err => {
+        console.error(`error, closing connection.`, err);
+        dataProcessor.close();
+    },
+    onmessage: event => {
         let data = JSON.parse(event.data)
-
-        if (!initDone) {
+        if (!dataProcessor.initDone) {
             configurePlots(PlotsDef);
             stats.init(PlotsDef, dataRetentionSeconds);
 
             attachPlots();
 
-            $('#play_pause').change(() => { paused = !paused; });
+            $('#play_pause').change(() => {
+                paused = !paused;
+            });
             $('#show_gc').change(() => {
                 show_gc = !show_gc;
                 updatePlots();
@@ -67,16 +65,27 @@ const connect = () => {
                 timerange = val;
                 updatePlots();
             });
-            initDone = true;
-            return;
+            dataProcessor.initDone = true;
         }
-
+        dataProcessor.onData(data);
+    },
+    onData: data => {
         stats.pushData(data);
-        if (paused) {
+        if (paused || !dataProcessor.connected) {
             return
         }
-        updatePlots(PlotsDef.events);
+        updatePlots()
+    }
+}
+/* WebSocket connection handling */
+const connect = () => {
+    const url = window.location.pathname + "ws";
+    const eventSource = new EventSource(url);
+    console.info(`Attempting sse connection to server at ${url}`);
+    for (let event in dataProcessor) {
+        eventSource[event] = dataProcessor[event];
     }
+    dataProcessor.close = eventSource.close
 }
 
 connect();
@@ -102,7 +111,31 @@ const attachPlots = () => {
     }
 }
 
-const updatePlots = () => {
+function throttle(func, delay) {
+    let initial = true;
+    let last = null;
+    let timer = null;
+    return function () {
+        const context = this;
+        const args = arguments;
+        if (initial) {
+            func.apply(context, args);
+            initial = false;
+            last = Date.now();
+        } else {
+            clearTimeout(timer);
+            timer = setTimeout(function () {
+                const now = Date.now();
+                if (now - last >= delay) {
+                    func.apply(context, args);
+                    last = now;
+                }
+            }, delay - (Date.now() - last));
+        }
+    }
+}
+
+const updatePlots = throttle(() => {
     // Create shapes.
     let shapes = new Map();
 
@@ -123,7 +156,7 @@ const updatePlots = () => {
             plot.update(xrange, data, shapes);
         }
     });
-}
+}, PlotsDef.sendFrequency||1000)
 
 const updatePlotsLayout = () => {
     plots.forEach(plot => {
@@ -139,7 +172,7 @@ theme.updateThemeMode();
 $('#color_theme_sw').change(() => {
     const themeMode = theme.getThemeMode();
     const newTheme = themeMode === "dark" && "light" || "dark";
-    localStorage.setItem("theme-mode", newTheme);    
+    localStorage.setItem("theme-mode", newTheme);
     theme.updateThemeMode();
     updatePlotsLayout();
 });

internal/static/js/stats.js

@@ -92,4 +92,4 @@ const slice = (n) => {
     return sliced;
 }
 
-export { init, pushData, slice };
+export { init, pushData, slice };

statsviz.go

@@ -43,15 +43,14 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net/http"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
 
-	"github.com/gorilla/websocket"
-
 	"github.com/arl/statsviz/internal/plot"
 	"github.com/arl/statsviz/internal/static"
 )
@@ -82,7 +81,7 @@ func Register(mux *http.ServeMux, opts ...Option) error {
 // updates metrics data and provides two essential HTTP handlers:
 //   - the Index handler serves Statsviz user interface, allowing you to
 //     visualize runtime metrics on your browser.
-//   - The Ws handler establishes a WebSocket connection allowing the connected
+//   - The Ws handler establishes a data connection allowing the connected
 //     browser to receive metrics updates from the server.
 //
 // The zero value is not a valid Server, use NewServer to create a valid one.
@@ -161,20 +160,34 @@ func (s *Server) Register(mux *http.ServeMux) {
 // intercept is a middleware that intercepts requests for plotsdef.js, which is
 // generated dynamically based on the plots configuration. Other requests are
 // forwarded as-is.
-func intercept(h http.Handler, cfg *plot.Config) http.HandlerFunc {
-	buf := bytes.Buffer{}
-	buf.WriteString("export default ")
-	enc := json.NewEncoder(&buf)
-	enc.SetIndent("", "  ")
-	if err := enc.Encode(cfg); err != nil {
-		panic("unexpected failure to encode plot definitions: " + err.Error())
+func intercept(h http.Handler, cfg *plot.Config, extraConfig map[string]any) http.HandlerFunc {
+	var plotsdefjs []byte
+	//Using parentheses helps gc
+	{
+		buf := bytes.Buffer{}
+		buf.WriteString("export default ")
+		enc := json.NewEncoder(&buf)
+		enc.SetIndent("", "  ")
+		var encodeValue any = cfg
+		if len(extraConfig) > 0 {
+			encodeValue1 := map[string]any{
+				"series": cfg.Series,
+				"events": cfg.Events,
+			}
+			for k, v := range extraConfig {
+				encodeValue1[k] = v
+			}
+			encodeValue = encodeValue1
+		}
+		if err := enc.Encode(encodeValue); err != nil {
+			panic("unexpected failure to encode plot definitions: " + err.Error())
+		}
+		buf.WriteString(";")
+		plotsdefjs = buf.Bytes()
 	}
-	buf.WriteString(";")
-	plotsdefjs := buf.Bytes()
-
 	return func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path == "js/plotsdef.js" {
-			w.Header().Add("Content-Length", strconv.Itoa(buf.Len()))
+			w.Header().Add("Content-Length", strconv.Itoa(len(plotsdefjs)))
 			w.Header().Add("Content-Type", "text/javascript; charset=utf-8")
 			w.Write(plotsdefjs)
 			return
@@ -228,7 +241,9 @@ func assetsFS() http.FileSystem {
 func (s *Server) Index() http.HandlerFunc {
 	prefix := strings.TrimSuffix(s.root, "/") + "/"
 	assets := http.FileServer(assetsFS())
-	handler := intercept(assets, s.plots.Config())
+	handler := intercept(assets, s.plots.Config(), map[string]any{
+		"sendFrequency": s.intv.Milliseconds(),
+	})
 
 	return http.StripPrefix(prefix, handler).ServeHTTP
 }
@@ -238,46 +253,51 @@ func (s *Server) Index() http.HandlerFunc {
 // connection to the WebSocket protocol.
 func (s *Server) Ws() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		var upgrader = websocket.Upgrader{
-			ReadBufferSize:  1024,
-			WriteBufferSize: 1024,
-		}
-
-		ws, err := upgrader.Upgrade(w, r, nil)
-		if err != nil {
+		if strings.Contains(r.Header.Get("Accept"), "/event-stream") {
+			// If the connection is initiated by an already open web UI
+			// (started by a previous process, for example), then plotsdef.js won't be
+			// requested. Call plots.Config() manually to ensure that s.plots internals
+			// are correctly initialized.
+			s.plots.Config()
+
+			w.Header().Set("Content-Type", "text/event-stream")
+			w.Header().Set("Cache-Control", "no-cache")
+			w.Header().Set("Connection", "keep-alive")
+			s.startTransfer(w)
 			return
 		}
-		defer ws.Close()
-
-		// Ignore this error. This happens when the other end connection closes,
-		// for example. We can't handle it in any meaningful way anyways.
-		_ = s.sendStats(ws, s.intv)
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte("This endpoint only supports text/event-stream requests"))
 	}
 }
 
-// sendStats sends runtime statistics over the WebSocket connection.
-func (s *Server) sendStats(conn *websocket.Conn, frequency time.Duration) error {
-	tick := time.NewTicker(frequency)
-	defer tick.Stop()
-
-	// If the WebSocket connection is initiated by an already open web UI
-	// (started by a previous process, for example), then plotsdef.js won't be
-	// requested. Call plots.Config() manually to ensure that s.plots internals
-	// are correctly initialized.
-	s.plots.Config()
-
-	for range tick.C {
-		w, err := conn.NextWriter(websocket.TextMessage)
-		if err != nil {
+func (s *Server) startTransfer(w io.Writer) {
+	buffer := bytes.Buffer{}
+	buffer.WriteString("data: ")
+	callData := func() error {
+		if err := s.plots.WriteValues(&buffer); err == nil {
+			_, err = w.Write(buffer.Bytes())
+			if err != nil {
+				return err
+			}
+			if f, ok := w.(http.Flusher); ok {
+				f.Flush()
+			}
+		} else {
 			return err
 		}
-		if err := s.plots.WriteValues(w); err != nil {
-			return err
-		}
-		if err := w.Close(); err != nil {
-			return err
+		return nil
+	}
+	//the first time it was sent immediately
+	err := callData()
+	if err != nil {
+		return
+	}
+	tick := time.NewTicker(s.intv)
+	defer tick.Stop()
+	for range tick.C {
+		if callData() != nil {
+			return
 		}
 	}
-
-	panic("unreachable")
 }