flamegraph: add live baseline reset hotkey

author: Paul Buetow <paul@buetow.org> 2026-02-27 18:52:23 +0200
committer: Paul Buetow <paul@buetow.org> 2026-02-27 18:52:23 +0200
commit: 5f23af510bd9031c515f2a3cc495bd996c795e69 (patch)
tree: 151d94f6ffacf7446b72481d51f8f8925d5dee8d /internal
parent: 3783d23b8d608c3bf4a2dedd6b4bfb9165439bed (diff)
7 files changed, 246 insertions, 2 deletions
diff --git a/internal/flamegraph/livehtml.go b/internal/flamegraph/livehtml.go
index 9531f85..8ca74cd 100644
--- a/internal/flamegraph/livehtml.go
+++ b/internal/flamegraph/livehtml.go
@@ -109,6 +109,7 @@ const liveHTML = `<!doctype html>
     <button id="btn-reset-search" type="button">Reset Search</button>
     <button id="btn-undo-zoom" type="button">Undo Zoom</button>
     <button id="btn-reset-zoom" type="button">Reset Zoom</button>
+    <button id="btn-reset-baseline" type="button">Reset Baseline</button>
     <span id="status">LIVE</span>
   </div>
 
@@ -118,6 +119,7 @@ const liveHTML = `<!doctype html>
     (function () {
       var fg = {
         paused: false,
+        resetting: false,
         pendingData: null,
         searchQuery: '',
         zoomStack: [],
@@ -133,6 +135,7 @@ const liveHTML = `<!doctype html>
         resetSearchBtn: document.getElementById('btn-reset-search'),
         undoZoomBtn: document.getElementById('btn-undo-zoom'),
         resetZoomBtn: document.getElementById('btn-reset-zoom'),
+        resetBaselineBtn: document.getElementById('btn-reset-baseline'),
         cfg: {
           width: 1200,
           frameHeight: 16,
@@ -465,6 +468,39 @@ const liveHTML = `<!doctype html>
         }
       }
 
+      function fgClearLocalState() {
+        fg.pendingData = null;
+        fg.searchQuery = '';
+        fg.zoomStack = [];
+        fg.zoomRange = null;
+      }
+
+      function fgResetBaseline() {
+        if (fg.resetting) {
+          return;
+        }
+        fg.resetting = true;
+        fgSetStatus('resetting baseline...');
+        fetch('/reset', { method: 'POST' })
+          .then(function (resp) {
+            if (!resp.ok) {
+              throw new Error('reset failed');
+            }
+            return resp.text();
+          })
+          .then(function (payload) {
+            fgClearLocalState();
+            fgProcessUpdate(payload);
+            fgSetStatus('baseline reset');
+          })
+          .catch(function () {
+            fgSetStatus('reset failed');
+          })
+          .then(function () {
+            fg.resetting = false;
+          });
+      }
+
       function fgBindFrameEvents() {
         for (var i = 0; i < fg.frames.length; i++) {
           fg.frames[i].addEventListener('mouseenter', function () { fgHover(this); });
@@ -579,6 +615,11 @@ const liveHTML = `<!doctype html>
           fgSearch();
           return;
         }
+        if (ev.key === 'r' || ev.key === 'R') {
+          ev.preventDefault();
+          fgResetBaseline();
+          return;
+        }
         if (ev.key === 'Escape') {
           ev.preventDefault();
           fgResetZoom();
@@ -591,6 +632,7 @@ const liveHTML = `<!doctype html>
       fg.resetSearchBtn.addEventListener('click', fgResetSearch);
       fg.undoZoomBtn.addEventListener('click', fgUndoZoom);
       fg.resetZoomBtn.addEventListener('click', fgResetZoom);
+      fg.resetBaselineBtn.addEventListener('click', fgResetBaseline);
       document.addEventListener('keydown', fgHandleKeydown);
 
       fgSetStatus('');
@@ -608,6 +650,7 @@ const liveHTML = `<!doctype html>
       window.fgSearch = fgSearch;
       window.fgResetSearch = fgResetSearch;
       window.fgTogglePause = fgTogglePause;
+      window.fgResetBaseline = fgResetBaseline;
       window.liveFlamegraphState = fg;
     })();
   </script>
diff --git a/internal/flamegraph/livehtml_browser_test.go b/internal/flamegraph/livehtml_browser_test.go
index d8f1951..7644084 100644
--- a/internal/flamegraph/livehtml_browser_test.go
+++ b/internal/flamegraph/livehtml_browser_test.go
@@ -135,7 +135,7 @@ function makeElement(id) {
 }
 
 const elements = {};
-["flamegraph", "status", "btn-pause", "btn-search", "btn-reset-search", "btn-undo-zoom", "btn-reset-zoom"].forEach((id) => {
+["flamegraph", "status", "btn-pause", "btn-search", "btn-reset-search", "btn-undo-zoom", "btn-reset-zoom", "btn-reset-baseline"].forEach((id) => {
   elements[id] = makeElement(id);
 });
 elements["body"] = makeElement("body");
diff --git a/internal/flamegraph/livehtml_interaction_test.go b/internal/flamegraph/livehtml_interaction_test.go
index 3dbba60..59aaef9 100644
--- a/internal/flamegraph/livehtml_interaction_test.go
+++ b/internal/flamegraph/livehtml_interaction_test.go
@@ -32,6 +32,13 @@ type pauseKeyboardResult struct {
 	TypingIgnoresShortcuts bool `json:"typingIgnoresShortcuts"`
 }
 
+type resetBaselineResult struct {
+	HotkeyPrevented    bool `json:"hotkeyPrevented"`
+	HotkeyResetApplied bool `json:"hotkeyResetApplied"`
+	ButtonResetApplied bool `json:"buttonResetApplied"`
+	ResetCallsValid    bool `json:"resetCallsValid"`
+}
+
 func TestLiveHTMLJSZoomSearchStatePreservedAcrossUpdates(t *testing.T) {
 	if _, err := exec.LookPath("node"); err != nil {
 		t.Skip("node not available")
@@ -287,6 +294,94 @@ console.log(JSON.stringify({
 	}
 }
 
+func TestLiveHTMLJSResetBaselineHotkeyAndButton(t *testing.T) {
+	if _, err := exec.LookPath("node"); err != nil {
+		t.Skip("node not available")
+	}
+
+	snippet := `
+const fg = liveFlamegraphState;
+const keydown = __docListeners["keydown"];
+
+function keyEvent(key, code, target) {
+  let prevented = false;
+  keydown({
+    key: key,
+    code: code,
+    target: target || { tagName: "BODY", isContentEditable: false },
+    preventDefault: function(){ prevented = true; }
+  });
+  return prevented;
+}
+
+const frame = makeFrame("needle", "needle", 1, 0, 1200);
+fg.frames = [frame];
+fg.rootWidth = 1200;
+fgZoom(frame);
+prompt = function(){ return "needle"; };
+fgSearch();
+
+const resetPayload = "{\"n\":\"\",\"v\":0,\"t\":0}";
+const resetCalls = [];
+fetch = function(url, opts) {
+  resetCalls.push({
+    url: url,
+    method: (opts && opts.method) || "GET"
+  });
+  return Promise.resolve({
+    ok: true,
+    text: function() { return Promise.resolve(resetPayload); }
+  });
+};
+
+const hotkeyPrevented = keyEvent("r", "KeyR");
+
+setTimeout(function() {
+  const hotkeyResetApplied = fg.zoomRange === null && fg.searchQuery === "" && fg.frames.length === 0;
+
+  const frame2 = makeFrame("again", "again", 1, 0, 1200);
+  fg.frames = [frame2];
+  fg.rootWidth = 1200;
+  fgZoom(frame2);
+  fg.searchQuery = "again";
+  document.getElementById("btn-reset-baseline").listeners.click();
+
+  setTimeout(function() {
+    const buttonResetApplied = fg.zoomRange === null && fg.searchQuery === "" && fg.frames.length === 0;
+    const resetCallsValid = resetCalls.length === 2 &&
+      resetCalls[0].url === "/reset" && resetCalls[0].method === "POST" &&
+      resetCalls[1].url === "/reset" && resetCalls[1].method === "POST";
+
+    console.log(JSON.stringify({
+      hotkeyPrevented,
+      hotkeyResetApplied,
+      buttonResetApplied,
+      resetCallsValid
+    }));
+  }, 0);
+}, 0);
+`
+
+	out := runLiveHTMLNodeSnippet(t, snippet)
+	var got resetBaselineResult
+	if err := json.Unmarshal([]byte(out), &got); err != nil {
+		t.Fatalf("decode node result: %v\nraw:\n%s", err, out)
+	}
+
+	if !got.HotkeyPrevented {
+		t.Fatalf("expected reset hotkey to prevent default browser handling")
+	}
+	if !got.HotkeyResetApplied {
+		t.Fatalf("expected 'r' hotkey to reset baseline and clear UI state")
+	}
+	if !got.ButtonResetApplied {
+		t.Fatalf("expected Reset Baseline button to clear UI state")
+	}
+	if !got.ResetCallsValid {
+		t.Fatalf("expected reset interactions to POST /reset")
+	}
+}
+
 func runLiveHTMLNodeSnippet(t *testing.T, snippet string) string {
 	t.Helper()
 
@@ -374,7 +469,7 @@ function makeFrame(name, path, depth, x, w) {
 }
 
 const elements = {};
-["flamegraph", "status", "btn-pause", "btn-search", "btn-reset-search", "btn-undo-zoom", "btn-reset-zoom"].forEach((id) => {
+["flamegraph", "status", "btn-pause", "btn-search", "btn-reset-search", "btn-undo-zoom", "btn-reset-zoom", "btn-reset-baseline"].forEach((id) => {
   elements[id] = makeElement(id);
 });
 elements["body"] = makeElement("body");
diff --git a/internal/flamegraph/liveserver.go b/internal/flamegraph/liveserver.go
index 6b9a72b..5790cb0 100644
--- a/internal/flamegraph/liveserver.go
+++ b/internal/flamegraph/liveserver.go
@@ -12,6 +12,7 @@ func ServeLive(ctx context.Context, lt *LiveTrie, interval time.Duration) error
 	mux := http.NewServeMux()
 	mux.HandleFunc("/", handleLivePage())
 	mux.HandleFunc("/events", handleSSE(lt, interval))
+	mux.HandleFunc("/reset", handleReset(lt))
 	srv := &http.Server{Handler: mux}
 
 	listener, err := listenRandomPort()
@@ -96,6 +97,21 @@ func handleSSE(lt *LiveTrie, interval time.Duration) http.HandlerFunc {
 	}
 }
 
+func handleReset(lt *LiveTrie) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			w.Header().Set("Allow", http.MethodPost)
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+
+		lt.Reset()
+		payload, _ := lt.SnapshotJSON()
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write(payload)
+	}
+}
+
 func sendSnapshot(w http.ResponseWriter, flusher http.Flusher, lt *LiveTrie, lastVersion uint64) (uint64, error) {
 	payload, version := lt.SnapshotJSON()
 	if version == lastVersion {
diff --git a/internal/flamegraph/liveserver_test.go b/internal/flamegraph/liveserver_test.go
index 0d55794..15e8f37 100644
--- a/internal/flamegraph/liveserver_test.go
+++ b/internal/flamegraph/liveserver_test.go
@@ -132,6 +132,53 @@ func TestHandleSSEDelayedClientLargeTrieGetsValidSnapshot(t *testing.T) {
 	}
 }
 
+func TestHandleResetRequiresPost(t *testing.T) {
+	lt := NewLiveTrie([]string{"comm"}, "count")
+	req := httptest.NewRequest(http.MethodGet, "/reset", nil)
+	rec := httptest.NewRecorder()
+
+	handleReset(lt).ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusMethodNotAllowed {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusMethodNotAllowed)
+	}
+	if allow := rec.Header().Get("Allow"); allow != http.MethodPost {
+		t.Fatalf("allow = %q, want %q", allow, http.MethodPost)
+	}
+}
+
+func TestHandleResetClearsTrieAndReturnsEmptySnapshot(t *testing.T) {
+	lt := NewLiveTrie([]string{"path"}, "count")
+	lt.Ingest(newTestPair("reset", 1, 1001, "/tmp/a", 1, 1, 1))
+	lt.Ingest(newTestPair("reset", 1, 1002, "/tmp/b", 1, 1, 1))
+	if before := decodeLiveSnapshot(t, lt); before.Total == 0 {
+		t.Fatalf("expected non-empty trie before reset")
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/reset", nil)
+	rec := httptest.NewRecorder()
+	handleReset(lt).ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+	if ctype := rec.Header().Get("Content-Type"); !strings.Contains(ctype, "application/json") {
+		t.Fatalf("content-type = %q, want application/json", ctype)
+	}
+	var snap trieSnapshot
+	if err := json.Unmarshal(rec.Body.Bytes(), &snap); err != nil {
+		t.Fatalf("decode reset snapshot: %v", err)
+	}
+	if snap.Total != 0 {
+		t.Fatalf("reset snapshot total = %d, want 0", snap.Total)
+	}
+
+	after := decodeLiveSnapshot(t, lt)
+	if after.Total != 0 {
+		t.Fatalf("trie total after reset = %d, want 0", after.Total)
+	}
+}
+
 func TestServeLivePrintsURLAndStopsOnCancel(t *testing.T) {
 	lt := NewLiveTrie([]string{"comm"}, "count")
 	ctx, cancel := context.WithCancel(context.Background())
diff --git a/internal/flamegraph/livetrie.go b/internal/flamegraph/livetrie.go
index e061add..6ca9bc3 100644
--- a/internal/flamegraph/livetrie.go
+++ b/internal/flamegraph/livetrie.go
@@ -82,6 +82,22 @@ func (lt *LiveTrie) Ingest(ep *event.Pair) {
 	ep.Recycle()
 }
 
+// Reset clears the trie so live snapshots start from a new baseline.
+func (lt *LiveTrie) Reset() {
+	lt.mu.Lock()
+	lt.root = &trieNode{
+		childMap: make(map[string]*trieNode),
+	}
+	lt.maxDepth = 0
+	lt.version.Add(1)
+	lt.mu.Unlock()
+
+	lt.cacheMu.Lock()
+	lt.cacheVersion = 0
+	lt.cacheJSON = nil
+	lt.cacheMu.Unlock()
+}
+
 // Version returns the current ingest version of the trie.
 func (lt *LiveTrie) Version() uint64 {
 	return lt.version.Load()
diff --git a/internal/flamegraph/livetrie_test.go b/internal/flamegraph/livetrie_test.go
index 5d32209..9bd16c2 100644
--- a/internal/flamegraph/livetrie_test.go
+++ b/internal/flamegraph/livetrie_test.go
@@ -60,6 +60,33 @@ func TestLiveTrieVersionIncrementsPerIngest(t *testing.T) {
 	}
 }
 
+func TestLiveTrieResetClearsDataAndAdvancesVersion(t *testing.T) {
+	lt := NewLiveTrie([]string{"comm"}, "count")
+	lt.Ingest(newTestPair("svc", 42, 1001, "/tmp/a", 1, 1, 1))
+	lt.Ingest(newTestPair("svc", 42, 1002, "/tmp/b", 1, 1, 1))
+
+	before := lt.Version()
+	if before == 0 {
+		t.Fatalf("expected non-zero version before reset")
+	}
+
+	lt.Reset()
+	if got := lt.Version(); got != before+1 {
+		t.Fatalf("version after reset = %d, want %d", got, before+1)
+	}
+
+	snap := decodeLiveSnapshot(t, lt)
+	if snap.Total != 0 {
+		t.Fatalf("snapshot total after reset = %d, want 0", snap.Total)
+	}
+
+	lt.Ingest(newTestPair("svc", 42, 1003, "/tmp/c", 1, 1, 1))
+	next := decodeLiveSnapshot(t, lt)
+	if next.Total != 1 {
+		t.Fatalf("snapshot total after new baseline ingest = %d, want 1", next.Total)
+	}
+}
+
 func TestLiveTrieSnapshotJSONCaching(t *testing.T) {
 	lt := NewLiveTrie([]string{"comm"}, "count")
 	lt.Ingest(newTestPair("svc", 42, 1001, "/tmp/a", 1, 1, 1))
author	Paul Buetow <paul@buetow.org>	2026-02-27 18:52:23 +0200
committer	Paul Buetow <paul@buetow.org>	2026-02-27 18:52:23 +0200
commit	5f23af510bd9031c515f2a3cc495bd996c795e69 (patch)
tree	151d94f6ffacf7446b72481d51f8f8925d5dee8d /internal
parent	3783d23b8d608c3bf4a2dedd6b4bfb9165439bed (diff)