feat: add before_screenshot hook

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+**Features**:
+
+- Add `before_screenshot` hook. ([#1641](https://github.com/getsentry/sentry-native/pull/1641))
+
 **Fixes**:
 
 - Reset client report counters during initialization ([#1632](https://github.com/getsentry/sentry-native/pull/1632))

include/sentry.h

@@ -1580,13 +1580,47 @@ SENTRY_API void sentry_options_add_view_hierarchy_n(
  * Enables or disables attaching screenshots to fatal error events. Disabled by
  * default.
  *
- * This feature is currently supported by all backends on Windows. Only the
- * `crashpad` backend can capture screenshots of fast-fail crashes that bypass
- * SEH (structured exception handling).
+ * This feature is currently supported by all backends on Windows. The
+ * `crashpad` and `native` backends capture screenshots from an out-of-process
+ * handler. Only the `crashpad` backend can capture screenshots of fast-fail
+ * crashes that bypass SEH (structured exception handling).
+ *
+ * To decide per-event whether a screenshot should be captured, set a
+ * `before_screenshot` callback via `sentry_options_set_before_screenshot`.
  */
 SENTRY_EXPERIMENTAL_API void sentry_options_set_attach_screenshot(
     sentry_options_t *opts, int val);
 
+/**
+ * Type of the `before_screenshot` callback.
+ *
+ * The callback is invoked before a screenshot is captured for an event. It
+ * receives the event (without ownership) and should return non-zero to capture
+ * the screenshot, or zero to skip it. The `attach_screenshot` option must be
+ * enabled for screenshots to be considered at all.
+ *
+ * Capturing screenshots is only supported on Windows, so the callback is
+ * only invoked there. The callback is not supported by the `crashpad`
+ * backend, which captures screenshots from its out-of-process handler.
+ *
+ * The callback may be called from inside an `UnhandledExceptionFilter`, see
+ * the documentation on SEH (structured exception handling) for more
+ * information
+ * https://docs.microsoft.com/en-us/windows/win32/debug/structured-exception-handling
+ */
+typedef int (*sentry_before_screenshot_function_t)(
+    sentry_value_t event, void *user_data);
+
+/**
+ * Sets the `before_screenshot` callback.
+ *
+ * See the `sentry_before_screenshot_function_t` typedef above for more
+ * information.
+ */
+SENTRY_EXPERIMENTAL_API void sentry_options_set_before_screenshot(
+    sentry_options_t *opts, sentry_before_screenshot_function_t func,
+    void *user_data);
+
 /**
  * Sets the path to the crashpad handler if the crashpad backend is used.
  *

src/backends/native/sentry_crash_daemon.c

@@ -2392,7 +2392,7 @@ write_envelope_with_native_stacktrace(const sentry_options_t *options,
     }
 
     // Add screenshot attachment if captured by the daemon
-    if (options && options->attach_screenshot && run_folder) {
+    if (ctx->attach_screenshot && run_folder) {
         sentry_path_t *screenshot_path
             = sentry__path_join_str(run_folder, "screenshot.png");
         if (screenshot_path) {
@@ -2417,8 +2417,9 @@ write_envelope_with_native_stacktrace(const sentry_options_t *options,
  */
 static bool
 write_envelope_with_minidump(const sentry_options_t *options,
-    const char *envelope_path, const char *event_msgpack_path,
-    const char *minidump_path, sentry_path_t *run_folder)
+    const sentry_crash_context_t *ctx, const char *envelope_path,
+    const char *event_msgpack_path, const char *minidump_path,
+    sentry_path_t *run_folder)
 {
     // Read event JSON data
     size_t event_size = 0;
@@ -2626,7 +2627,7 @@ write_envelope_with_minidump(const sentry_options_t *options,
     }
 
     // Add screenshot attachment if captured by the daemon
-    if (options && options->attach_screenshot && run_folder) {
+    if (ctx->attach_screenshot && run_folder) {
         sentry_path_t *screenshot_path
             = sentry__path_join_str(run_folder, "screenshot.png");
         if (screenshot_path) {
@@ -2802,7 +2803,7 @@ sentry__process_crash(const sentry_options_t *options, sentry_crash_ipc_t *ipc)
     // This is done in the daemon process (out-of-process) because
     // screenshot capture is NOT signal-safe (uses LoadLibrary, GDI+, etc.)
 #if defined(SENTRY_PLATFORM_WINDOWS)
-    if (options && options->attach_screenshot && run_folder) {
+    if (ctx->attach_screenshot && run_folder) {
         SENTRY_DEBUG("Capturing screenshot");
         sentry_path_t *screenshot_path
             = sentry__path_join_str(run_folder, "screenshot.png");
@@ -2867,7 +2868,7 @@ sentry__process_crash(const sentry_options_t *options, sentry_crash_ipc_t *ipc)
         // Mode 0 (MINIDUMP only)
         SENTRY_DEBUG("Writing envelope with minidump");
         envelope_written = write_envelope_with_minidump(
-            options, envelope_path, event_path, minidump_path, run_folder);
+            options, ctx, envelope_path, event_path, minidump_path, run_folder);
     }
 
     if (!envelope_written) {

src/backends/sentry_backend_breakpad.cpp

@@ -162,6 +162,16 @@ breakpad_backend_callback(const google_breakpad::MinidumpDescriptor &descriptor,
         }
 
         if (should_handle) {
+            bool capture_screenshot = options->attach_screenshot;
+#ifdef SENTRY_PLATFORM_WINDOWS
+            if (capture_screenshot && options->before_screenshot_func) {
+                SENTRY_DEBUG("invoking `before_screenshot` hook");
+                capture_screenshot = options->before_screenshot_func(
+                                         event, options->before_screenshot_data)
+                    != 0;
+            }
+#endif
+
             sentry_envelope_t *envelope = sentry__prepare_event(
                 options, event, nullptr, !options->on_crash_func, nullptr);
             sentry_session_t *session = sentry__end_current_session_with_status(
@@ -180,7 +190,7 @@ breakpad_backend_callback(const google_breakpad::MinidumpDescriptor &descriptor,
                     sentry_value_new_string(sentry__path_filename(dump_path)));
             }
 
-            if (options->attach_screenshot) {
+            if (capture_screenshot) {
                 sentry_attachment_t *screenshot = sentry__attachment_from_path(
                     sentry__screenshot_get_path(options));
                 if (screenshot

src/backends/sentry_backend_inproc.c

@@ -1198,6 +1198,16 @@ process_ucontext_deferred(const sentry_ucontext_t *uctx,
         }
         TEST_CRASH_POINT("before_capture");
         if (should_handle) {
+            bool capture_screenshot = options->attach_screenshot;
+#ifdef SENTRY_PLATFORM_WINDOWS
+            if (capture_screenshot && options->before_screenshot_func) {
+                SENTRY_DEBUG("invoking `before_screenshot` hook");
+                capture_screenshot = options->before_screenshot_func(
+                                         event, options->before_screenshot_data)
+                    != 0;
+            }
+#endif
+
             sentry_envelope_t *envelope = sentry__prepare_event(options, event,
                 NULL, !options->on_crash_func && !skip_hooks, NULL);
             // TODO(tracing): Revisit when investigating transaction flushing
@@ -1207,7 +1217,7 @@ process_ucontext_deferred(const sentry_ucontext_t *uctx,
                 SENTRY_SESSION_STATUS_CRASHED);
             sentry__envelope_add_session(envelope, session);
 
-            if (options->attach_screenshot) {
+            if (capture_screenshot) {
                 sentry_attachment_t *screenshot = sentry__attachment_from_path(
                     sentry__screenshot_get_path(options));
                 if (screenshot

src/backends/sentry_backend_native.c

@@ -857,6 +857,24 @@ native_backend_except(sentry_backend_t *backend, const sentry_ucontext_t *uctx)
                     device_context, "arch", sentry_value_new_string("arm64"));
 #    endif
                 sentry_value_set_by_key(contexts, "device", device_context);
+
+                // The screenshot is captured by the daemon out-of-process, so
+                // we invoke the hook here (in the crashing process, where
+                // user callbacks can run) and communicate the decision to the
+                // daemon by flipping attach_screenshot in the shared crash
+                // context. Screenshots are only captured on Windows.
+                if (options->attach_screenshot
+                    && options->before_screenshot_func && state && state->ipc
+                    && state->ipc->shmem) {
+                    SENTRY_DEBUG("invoking `before_screenshot` hook");
+                    if (options->before_screenshot_func(
+                            event, options->before_screenshot_data)
+                        == 0) {
+                        SENTRY_DEBUG("screenshot skipped by "
+                                     "`before_screenshot` hook");
+                        state->ipc->shmem->attach_screenshot = false;
+                    }
+                }
 #endif
 
                 // Write event as JSON file

src/sentry_options.c

@@ -631,6 +631,14 @@ sentry_options_set_attach_screenshot(sentry_options_t *opts, int val)
     opts->attach_screenshot = !!val;
 }
 
+void
+sentry_options_set_before_screenshot(sentry_options_t *opts,
+    sentry_before_screenshot_function_t func, void *user_data)
+{
+    opts->before_screenshot_func = func;
+    opts->before_screenshot_data = user_data;
+}
+
 void
 sentry_options_set_handler_path(sentry_options_t *opts, const char *path)
 {

src/sentry_options.h

@@ -41,6 +41,8 @@ struct sentry_options_s {
     bool symbolize_stacktraces;
     bool system_crash_reporter_enabled;
     bool attach_screenshot;
+    sentry_before_screenshot_function_t before_screenshot_func;
+    void *before_screenshot_data;
     bool crashpad_wait_for_upload;
     bool enable_logging_when_crashed;
     bool propagate_traceparent;

tests/fixtures/screenshot/screenshot_win32.c

@@ -46,6 +46,14 @@ trigger_fastfail_crash()
     __fastfail(77);
 }
 
+static int
+before_screenshot_skip(sentry_value_t event, void *user_data)
+{
+    (void)event;
+    (void)user_data;
+    return 0;
+}
+
 static LRESULT CALLBACK
 wnd_proc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
 {
@@ -74,16 +82,20 @@ int WINAPI
 wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine,
     int nCmdShow)
 {
+    int argc = 0;
+    LPWSTR *argv = CommandLineToArgvW(lpCmdLine, &argc);
+
     sentry_options_t *options = sentry_options_new();
     sentry_options_set_release(options, "sentry-screenshot");
     sentry_options_set_auto_session_tracking(options, false);
     sentry_options_set_attach_screenshot(options, true);
     sentry_options_set_debug(options, true);
+    if (has_arg(argc, argv, L"before-screenshot")) {
+        sentry_options_set_before_screenshot(
+            options, before_screenshot_skip, NULL);
+    }
     sentry_init(options);
 
-    int argc = 0;
-    LPWSTR *argv = CommandLineToArgvW(lpCmdLine, &argc);
-
 #if (WINVER >= 0x0605)
     if (has_arg(argc, argv, L"dpi-unaware")) {
         SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_UNAWARE);

tests/test_integration_screenshot.py

@@ -19,6 +19,15 @@ def assert_screenshot_file(database_path):
     assert screenshot_path.stat().st_size > 0, "Screenshot file is empty"
 
 
+def assert_no_screenshot_file(database_path):
+    run_dirs = [d for d in database_path.glob("*.run") if d.is_dir()]
+    assert (
+        len(run_dirs) == 1
+    ), f"Expected exactly one .run directory, found {len(run_dirs)}"
+    screenshot_path = run_dirs[0] / "screenshot.png"
+    assert not screenshot_path.exists(), "Unexpected screenshot file was captured"
+
+
 def assert_screenshot_envelope(envelope):
     found_screenshot = False
     for item in envelope.items:
@@ -30,7 +39,7 @@ def assert_screenshot_envelope(envelope):
             assert item.headers.get("attachment_type") == "event.attachment"
             assert len(item.payload.bytes) > 0
             found_screenshot = True
-    assert found_screenshot, "No screenshot item found in envelope"
+    return found_screenshot
 
 
 def assert_screenshot_upload(req):
@@ -79,7 +88,9 @@ def test_capture_screenshot_native(cmake, httpserver):
 
     assert len(httpserver.log) == 1
     envelope = Envelope.deserialize(httpserver.log[0][0].get_data())
-    assert_screenshot_envelope(envelope)
+    assert (
+        assert_screenshot_envelope(envelope) == True
+    ), "No screenshot item found in envelope"
 
 
 @pytest.mark.skipif(
@@ -124,3 +135,55 @@ def test_capture_screenshot_crashpad(cmake, httpserver, run_args):
 )
 def test_capture_screenshot_crashpad_wer(cmake, httpserver, run_args):
     test_capture_screenshot_crashpad(cmake, httpserver, run_args)
+
+
+@pytest.mark.skipif(
+    sys.platform != "win32",
+    reason="Screenshots are only supported on Windows",
+)
+@pytest.mark.parametrize("backend", ["inproc", "breakpad"])
+def test_before_screenshot(cmake, httpserver, backend):
+    tmp_path = cmake(
+        ["sentry_screenshot"], {"SENTRY_BACKEND": backend, "SENTRY_TRANSPORT": "none"}
+    )
+
+    env = dict(os.environ, SENTRY_DSN=make_dsn(httpserver))
+
+    run(
+        tmp_path,
+        "sentry_screenshot",
+        ["crash", "before-screenshot"],
+        expect_failure=True,
+        env=env,
+    )
+
+    assert_no_screenshot_file(tmp_path / ".sentry-native")
+
+
+@pytest.mark.skipif(
+    sys.platform != "win32",
+    reason="Screenshots are only supported on Windows",
+)
+def test_before_screenshot_native(cmake, httpserver):
+    tmp_path = cmake(["sentry_screenshot"], {"SENTRY_BACKEND": "native"})
+
+    env = dict(os.environ, SENTRY_DSN=make_dsn(httpserver))
+
+    httpserver.expect_oneshot_request("/api/123456/envelope/").respond_with_data("OK")
+
+    with httpserver.wait(timeout=10) as waiting:
+        run(
+            tmp_path,
+            "sentry_screenshot",
+            ["crash", "before-screenshot"],
+            expect_failure=True,
+            env=env,
+        )
+
+    assert waiting.result
+
+    assert len(httpserver.log) == 1
+    envelope = Envelope.deserialize(httpserver.log[0][0].get_data())
+    assert (
+        assert_screenshot_envelope(envelope) == False
+    ), "Screenshot item was unexpectedly found in envelope"