Add modified callback for VFS resource provider.

PiperOrigin-RevId: 616152275
Change-Id: I417f9b204eaa1eb9fc68a15927f86031dcd20575

src/engine/engine_vfs.c

@@ -347,6 +347,29 @@ static void vfs_getdir_callback(mjResource* resource, const char** dir, int* ndi
 }
 
 
+// modified callback for the VFS resource provider
+// return > 0 if modified and 0 if unmodified
+static int vfs_modified_callback(const mjResource* resource, const char* timestamp) {
+  uint64_t filestamp;
+  if (mju_isValidBase64(timestamp) > sizeof(uint64_t)) {
+    return 2;  // error (assume modified)
+  }
+
+  mju_decodeBase64((uint8_t*) &filestamp, timestamp);
+  if (!filestamp) return 3;  // no hash (assume modified)
+
+  if (resource) {
+    const mjVFS* vfs = (const mjVFS*) resource->data;
+    int i = mj_findFileVFS(vfs, resource->name);
+    if (i < 0) return 4;  // missing file (assume modified)
+    if (!vfs->filestamp[i]) return 5;  // missing filestamp (assume modified)
+
+    if (vfs->filestamp[i] == filestamp) {
+      return 0;  // unmodified
+    }
+  }
+  return 1;  // modified
+}
 
 // open VFS resource
 mjResource* mju_openVfsResource(const char* name, const mjVFS* vfs) {
@@ -362,7 +385,7 @@ mjResource* mju_openVfsResource(const char* name, const mjVFS* vfs) {
     .read     = &vfs_read_callback,
     .close    = &vfs_close_callback,
     .getdir   = &vfs_getdir_callback,
-    .modified = NULL
+    .modified = &vfs_modified_callback,
   };
 
   // create resource

test/engine/engine_vfs_test.cc

@@ -20,6 +20,8 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 #include <mujoco/mujoco.h>
+#include "src/engine/engine_resource.h"
+#include "src/engine/engine_vfs.h"
 #include "test/fixture.h"
 
 namespace mujoco {
@@ -28,7 +30,7 @@ namespace {
 using ::testing::NotNull;
 using EngineVfsTest = MujocoTest;
 
-TEST_F(EngineVfsTest, AddFileTest) {
+TEST_F(EngineVfsTest, AddFile) {
   constexpr char path[] = "engine/testdata/actuation/";
   const std::string dir = GetTestDataFilePath(path);
   std::string file1 = "activation.xml";
@@ -81,7 +83,7 @@ TEST_F(EngineVfsTest, AddFileTest) {
   mj_deleteVFS(vfs.get());
 }
 
-TEST_F(EngineVfsTest, AddBufferTest) {
+TEST_F(EngineVfsTest, AddBuffer) {
   auto vfs = std::make_unique<mjVFS>();
   mj_defaultVFS(vfs.get());
   std::string buffer = "<mujoco/>";
@@ -94,5 +96,32 @@ TEST_F(EngineVfsTest, AddBufferTest) {
   mj_deleteVFS(vfs.get());
 }
 
+TEST_F(EngineVfsTest, Timestamps) {
+  static constexpr char cube[] = R"(
+  v -0.500000 -0.500000  0.500000
+  v  0.500000 -0.500000  0.500000
+  v -0.500000  0.500000  0.500000
+  v  0.500000  0.500000  0.500000
+  v -0.500000  0.500000 -0.500000
+  v  0.500000  0.500000 -0.500000
+  v -0.500000 -0.500000 -0.500000
+  v  0.500000 -0.500000 -0.500000)";
+
+  auto vfs = std::make_unique<mjVFS>();
+  mj_defaultVFS(vfs.get());
+  mj_addBufferVFS(vfs.get(), "cube.obj", cube, sizeof(cube));
+
+  mjResource* resource = mju_openVfsResource("cube.obj", vfs.get());
+
+  // same timestamps
+  EXPECT_EQ(mju_isModifiedResource(resource, resource->timestamp), 0);
+
+  // different timestamps
+  EXPECT_EQ(mju_isModifiedResource(resource, "QQ=="), 1);
+
+  mju_closeResource(resource);
+  mj_deleteVFS(vfs.get());
+}
+
 }  // namespace
 }  // namespace mujoco