flamegraph: improve interactive zoom and serve svg over embedded http

1 files changed, 108 insertions, 0 deletions

diff --git a/internal/flamegraph/webserver.go b/internal/flamegraph/webserver.go
new file mode 100644
index 0000000..7925011
--- /dev/null
+++ b/internal/flamegraph/webserver.go
@@ -0,0 +1,108 @@
+package flamegraph
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"time"
+)
+
+func ServeSVG(svgFile string) error {
+	absPath, err := filepath.Abs(svgFile)
+	if err != nil {
+		return fmt.Errorf("resolve svg path: %w", err)
+	}
+	urlPath := buildURLPath(absPath)
+	srv := &http.Server{Handler: buildSVGHandler(absPath, urlPath)}
+
+	listener, err := listenRandomPort()
+	if err != nil {
+		return err
+	}
+	defer listener.Close()
+
+	hostname, port := serverHostPort(listener)
+	printServerURL(hostname, port, urlPath)
+
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- srv.Serve(listener)
+	}()
+
+	return waitForStop(srv, errCh)
+}
+
+func buildURLPath(absPath string) string {
+	urlPath := filepath.ToSlash(absPath)
+	if !strings.HasPrefix(urlPath, "/") {
+		return "/" + urlPath
+	}
+	return urlPath
+}
+
+func buildSVGHandler(absPath, urlPath string) http.Handler {
+	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 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 waitForStop(srv *http.Server, errCh <-chan error) error {
+	stopCh := make(chan os.Signal, 1)
+	signal.Notify(stopCh, os.Interrupt, syscall.SIGTERM)
+	defer signal.Stop(stopCh)
+
+	select {
+	case sig := <-stopCh:
+		_ = sig
+	case serveErr := <-errCh:
+		if serveErr != nil && serveErr != http.ErrServerClosed {
+			return serveErr
+		}
+		return nil
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	if err := srv.Shutdown(ctx); err != nil {
+		return fmt.Errorf("shutdown web server: %w", err)
+	}
+
+	serveErr := <-errCh
+	if serveErr != nil && serveErr != http.ErrServerClosed {
+		return serveErr
+	}
+	return nil
+}