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package flamegraph
import (
"context"
"fmt"
"net"
"net/http"
"os"
"os/signal"
"path/filepath"
"strings"
"syscall"
"time"
)
type serverTimeouts struct {
readTimeout time.Duration
writeTimeout time.Duration
idleTimeout time.Duration
}
var defaultServerTimeouts = serverTimeouts{
readTimeout: 10 * time.Second,
writeTimeout: 30 * time.Second,
idleTimeout: 60 * time.Second,
}
// ServeSVG starts a small HTTP server that serves a single flamegraph SVG.
//
// It prints a URL of the form http://HOSTNAME:PORT/abs/path/to.svg and blocks until
// the user presses Ctrl+C or the process receives SIGTERM, at which point the server
// is shut down gracefully.
func ServeSVG(svgFile string) error {
absPath, err := filepath.Abs(svgFile)
if err != nil {
return fmt.Errorf("resolve svg path: %w", err)
}
urlPath := buildURLPath(absPath)
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()
return runServer(ctx, buildSVGHandler(absPath, urlPath), defaultServerTimeouts, func(hostname string, port int) {
printServerURL(hostname, port, urlPath)
})
}
// ServeSVGAutoReload serves an SVG viewer page that periodically reloads the SVG.
//
// The SVG file itself is still served directly at its absolute URL path, while "/"
// serves a small HTML wrapper that appends a cache-busting query parameter on each
// refresh interval to pick up newly written SVG content.
func ServeSVGAutoReload(svgFile string, refreshInterval time.Duration) error {
if refreshInterval <= 0 {
return fmt.Errorf("refresh interval must be > 0")
}
absPath, err := filepath.Abs(svgFile)
if err != nil {
return fmt.Errorf("resolve svg path: %w", err)
}
urlPath := buildURLPath(absPath)
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()
mux := buildSVGAutoReloadHandler(absPath, urlPath, refreshInterval)
return runServer(ctx, mux, defaultServerTimeouts, func(hostname string, port int) {
printServerURL(hostname, port, "/")
})
}
func buildURLPath(absPath string) string {
urlPath := filepath.ToSlash(absPath)
if !strings.HasPrefix(urlPath, "/") {
return "/" + urlPath
}
return urlPath
}
func buildSVGHandler(absPath, urlPath string) *http.ServeMux {
mux := http.NewServeMux()
mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
http.Redirect(w, r, urlPath, http.StatusFound)
})
mux.HandleFunc(urlPath, func(w http.ResponseWriter, r *http.Request) {
http.ServeFile(w, r, absPath)
})
return mux
}
func buildSVGAutoReloadHandler(absPath, urlPath string, refreshInterval time.Duration) *http.ServeMux {
intervalMs := refreshInterval.Milliseconds()
mux := http.NewServeMux()
mux.HandleFunc("/", func(w http.ResponseWriter, _ *http.Request) {
w.Header().Set("Content-Type", "text/html; charset=utf-8")
_, _ = fmt.Fprintf(w, `<!doctype html>
<html>
<head>
<meta charset="utf-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<title>I/O Flamegraph (Auto-Reload)</title>
<style>
body { margin: 0; font-family: monospace; }
.bar { padding: 8px 12px; border-bottom: 1px solid #ddd; }
.viewer { width: 100%%; height: calc(100vh - 42px); border: 0; display: block; }
</style>
</head>
<body>
<div class="bar">
Auto-refresh every %d ms.
<button type="button" onclick="refreshNow()">Refresh now</button>
</div>
<iframe id="fg" class="viewer" src="%s"></iframe>
<script>
const base = %q;
function refreshNow() {
document.getElementById("fg").src = base + "?t=" + Date.now();
}
setInterval(refreshNow, %d);
</script>
</body>
</html>
`, intervalMs, urlPath, urlPath, intervalMs)
})
mux.HandleFunc(urlPath, func(w http.ResponseWriter, r *http.Request) {
http.ServeFile(w, r, absPath)
})
return mux
}
func listenRandomPort() (net.Listener, error) {
listener, err := net.Listen("tcp", ":0")
if err != nil {
return nil, fmt.Errorf("start web server: %w", err)
}
return listener, nil
}
func serverHostPort(listener net.Listener) (string, int) {
hostname, err := os.Hostname()
if err != nil {
hostname = "localhost"
}
port := listener.Addr().(*net.TCPAddr).Port
return hostname, port
}
func printServerURL(hostname string, port int, urlPath string) {
fmt.Printf("Flamegraph available at http://%s:%d%s\n", hostname, port, urlPath)
fmt.Println("Press Ctrl+C to stop the web server.")
}
func newHTTPServer(mux *http.ServeMux, timeouts serverTimeouts) *http.Server {
return &http.Server{
Handler: mux,
ReadTimeout: timeouts.readTimeout,
WriteTimeout: timeouts.writeTimeout,
IdleTimeout: timeouts.idleTimeout,
}
}
func runServer(ctx context.Context, mux *http.ServeMux, timeouts serverTimeouts, printURL func(hostname string, port int)) error {
srv := newHTTPServer(mux, timeouts)
listener, err := listenRandomPort()
if err != nil {
return err
}
defer listener.Close()
hostname, port := serverHostPort(listener)
if printURL != nil {
printURL(hostname, port)
}
errCh := make(chan error, 1)
go func() {
errCh <- srv.Serve(listener)
}()
select {
case <-ctx.Done():
case serveErr := <-errCh:
if serveErr != nil && serveErr != http.ErrServerClosed {
return serveErr
}
return nil
}
shutdownCtx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
defer cancel()
if err := srv.Shutdown(shutdownCtx); err != nil {
return fmt.Errorf("shutdown web server: %w", err)
}
serveErr := <-errCh
if serveErr != nil && serveErr != http.ErrServerClosed {
return serveErr
}
return nil
}
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