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package flamegraph
import (
"context"
"fmt"
"net/http"
"time"
)
// ServeLive starts the live flamegraph HTTP server and blocks until ctx is canceled.
func ServeLive(ctx context.Context, lt *LiveTrie, interval time.Duration) error {
mux := http.NewServeMux()
mux.HandleFunc("/", handleLivePage())
mux.HandleFunc("/events", handleSSE(lt, interval))
srv := &http.Server{Handler: mux}
listener, err := listenRandomPort()
if err != nil {
return err
}
defer listener.Close()
hostname, port := serverHostPort(listener)
fmt.Printf("Live flamegraph available at http://%s:%d/\n", 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 live web server: %w", err)
}
serveErr := <-errCh
if serveErr != nil && serveErr != http.ErrServerClosed {
return serveErr
}
return nil
}
func handleLivePage() http.HandlerFunc {
return func(w http.ResponseWriter, _ *http.Request) {
w.Header().Set("Content-Type", "text/html; charset=utf-8")
_, _ = w.Write([]byte(liveHTML))
}
}
func handleSSE(lt *LiveTrie, interval time.Duration) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
flusher, ok := w.(http.Flusher)
if !ok {
http.Error(w, "streaming unsupported", http.StatusInternalServerError)
return
}
if interval <= 0 {
interval = time.Second
}
w.Header().Set("Content-Type", "text/event-stream")
w.Header().Set("Cache-Control", "no-cache")
lastVersion, err := sendSnapshot(w, flusher, lt, ^uint64(0))
if err != nil {
return
}
ticker := time.NewTicker(interval)
defer ticker.Stop()
for {
select {
case <-r.Context().Done():
return
case <-ticker.C:
if lt.Version() == lastVersion {
continue
}
lastVersion, err = sendSnapshot(w, flusher, lt, lastVersion)
if err != nil {
return
}
}
}
}
}
func sendSnapshot(w http.ResponseWriter, flusher http.Flusher, lt *LiveTrie, lastVersion uint64) (uint64, error) {
payload, version := lt.SnapshotJSON()
if version == lastVersion {
return lastVersion, nil
}
if _, err := fmt.Fprintf(w, "data: %s\n\n", payload); err != nil {
return lastVersion, err
}
flusher.Flush()
return version, nil
}
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