Mujoco_WASM/test/xml/mjz/mjz_encoder_test.cc

// Copyright 2026 DeepMind Technologies Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Tests for the MJZ encoder plugin.

#include <array>
#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <filesystem> // NOLINT
#include <string>
#include <vector>

#include <gmock/gmock.h>
#include <gtest/gtest.h>
#include <absl/strings/match.h>
#include <mujoco/mjmodel.h>
#include <mujoco/mjplugin.h>
#include <mujoco/mjspec.h>
#include <mujoco/mujoco.h>
#include "src/xml/xml_numeric_format.h"
#include "test/compare_model.h"
#include "test/fixture.h"

namespace mujoco {

namespace fs = std::filesystem;
using ::testing::NotNull;

static mjSpec* MakeSimpleSpec() {
  mjSpec* s = mj_makeSpec();
  mjsBody* world = mjs_findBody(s, "world");
  mjsBody* body = mjs_addBody(world, nullptr);
  mjsGeom* geom = mjs_addGeom(body, nullptr);
  geom->size[0] = 1.0;
  geom->size[1] = 1.0;
  geom->size[2] = 1.0;
  return s;
}

static std::string SanitizePathForTestName(const std::string& path) {
  fs::path p(path);
  std::string name = p.stem().string();
  std::string full_name = p.string();
  size_t pos = full_name.find("third_party/mujoco");
  if (pos != std::string::npos) {
    full_name = full_name.substr(pos);
  }
  std::string sanitized;
  for (char c : full_name) {
    if (std::isalnum(c)) {
      sanitized += c;
    } else {
      sanitized += '_';
    }
  }
  return sanitized;
}

std::vector<std::string> GetWriteReadTestModels() {
  std::vector<std::string> models;
  std::string ext(".xml");
  for (const auto& path : {GetTestDataFilePath("."), GetModelPath(".")}) {
    for (const auto& p : std::filesystem::recursive_directory_iterator(path)) {
      if (p.path().extension() == ext) {
        std::string xml = p.path().string();
        if (  // if file is meant to fail, skip it
            absl::StrContains(xml, "malformed_") ||
            absl::StrContains(xml, "_fail") ||
            // exclude files that are too slow to load
            absl::StrContains(xml, "cow") || absl::StrContains(xml, "gmsh_") ||
            absl::StrContains(xml, "shark_") ||
            absl::StrContains(xml, "perf") ||
            // exclude files that fail the comparison test
            absl::StrContains(xml, "rfcamera") ||
            absl::StrContains(xml, "tactile") ||
            absl::StrContains(xml, "makemesh") ||
            absl::StrContains(xml, "carousel") ||
            absl::StrContains(xml, "many_dependencies") ||
            absl::StrContains(xml, "usd") ||
            absl::StrContains(xml, "torus_maxhull") ||
            absl::StrContains(xml, "fitmesh_") ||
            absl::StrContains(xml, "lengthrange") ||
            absl::StrContains(xml, "hfield_xml") ||
            absl::StrContains(xml, "fromto_convex") ||
            absl::StrContains(xml, "cube_skin") ||
            absl::StrContains(xml, "cube_3x3x3") ||
            // exclude files that fail since we do not save pinned flex nodes
            absl::StrContains(xml, "gripper_trilinear") ||
            absl::StrContains(xml, "strain") ||
            // exclude conflict test assets (designed to fail compile)
            absl::StrContains(xml, "xml/testdata/parent_") ||
            // exclude mjz test data with VFS files
            absl::StrContains(xml, "mixed_test")) {
          continue;
        }
        models.push_back(xml);
      }
    }
  }
  return models;
}

using MjzEncoderTest = MujocoTest;

TEST_F(MjzEncoderTest, EncoderIsRegistered) {
  const mjpEncoder* enc = mjp_findEncoder("model.mjz", nullptr);
  ASSERT_THAT(enc, testing::NotNull());
  ASSERT_THAT(enc->encode, testing::NotNull());
}

TEST_F(MjzEncoderTest, EncodeReturnsPositiveByteCount) {
  mjSpec* spec = MakeSimpleSpec();
  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  const mjpEncoder* enc = mjp_findEncoder("model.mjz", nullptr);
  ASSERT_THAT(enc, testing::NotNull());

  mjResource resource = {};
  resource.name = const_cast<char*>("model.mjz");

  int nbytes = enc->encode(spec, model, nullptr, &resource);
  EXPECT_GT(nbytes, 0);
  EXPECT_THAT(resource.data, testing::NotNull());

  std::free(resource.data);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

TEST_F(MjzEncoderTest, RoundTrip) {
  mjSpec* spec = MakeSimpleSpec();
  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  const std::string tmp_path =
      testing::TempDir() + "/mjz_encoder_roundtrip.mjz";

  char error[1024] = {0};
  int nbytes = mj_encode(spec, model, tmp_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mjSpec* decoded =
      mj_parse(tmp_path.c_str(), nullptr, &vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &vfs);
  ASSERT_THAT(decoded_model, testing::NotNull());

  EXPECT_EQ(decoded_model->nbody, model->nbody);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);
  EXPECT_EQ(decoded_model->njnt, model->njnt);

  std::remove(tmp_path.c_str());
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, RoundTripFromXmlString) {
  const char* xml = R"(
    <mujoco model="test">
      <worldbody>
        <body name="body1" pos="0 0 1">
          <joint type="hinge"/>
          <geom type="sphere" size="0.1"/>
        </body>
      </worldbody>
    </mujoco>
  )";

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  const std::string tmp_path = testing::TempDir() + "/xml_string.mjz";
  int nbytes = mj_encode(spec, model, tmp_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mjSpec* decoded =
      mj_parse(tmp_path.c_str(), nullptr, &vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &vfs);
  ASSERT_THAT(decoded_model, testing::NotNull());

  EXPECT_EQ(decoded_model->nbody, model->nbody);
  EXPECT_EQ(decoded_model->njnt, model->njnt);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  std::remove(tmp_path.c_str());
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, RoundTripPreservesModelCounts) {
  const char* xml = R"(
    <mujoco model="counts_test">
      <worldbody>
        <body name="b1" pos="0 0 1">
          <joint type="hinge"/>
          <geom type="sphere" size="0.1"/>
          <body name="b2" pos="0 0 2">
            <joint type="slide"/>
            <geom type="box" size="0.1 0.1 0.1"/>
          </body>
        </body>
      </worldbody>
    </mujoco>
  )";

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  const std::string tmp_path = testing::TempDir() + "/counts.mjz";
  int nbytes = mj_encode(spec, model, tmp_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mjSpec* decoded =
      mj_parse(tmp_path.c_str(), nullptr, &vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &vfs);
  ASSERT_THAT(decoded_model, testing::NotNull());

  EXPECT_EQ(decoded_model->nbody, model->nbody);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);
  EXPECT_EQ(decoded_model->njnt, model->njnt);
  EXPECT_EQ(decoded_model->nq, model->nq);
  EXPECT_EQ(decoded_model->nv, model->nv);

  std::remove(tmp_path.c_str());
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, RoundTripWithMeshFromVfs) {
  const char* xml = R"(
    <mujoco model="vfs_mesh">
      <asset>
        <mesh name="box" file="box.obj"/>
      </asset>
      <worldbody>
        <body name="b1">
          <geom type="mesh" mesh="box"/>
        </body>
      </worldbody>
    </mujoco>
  )";

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mj_addFileVFS(
      &vfs, nullptr,
      GetTestDataFilePath("xml/mjz/testdata/disk_mesh/box.obj").c_str());

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, &vfs, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;
  auto* mesh = mjs_asMesh(mjs_firstElement(spec, mjOBJ_MESH));
  ASSERT_THAT(mesh, testing::NotNull());
  ASSERT_THAT(mesh->file, testing::NotNull());

  mjModel* model = mj_compile(spec, &vfs);
  ASSERT_THAT(model, testing::NotNull()) << mjs_getError(spec);

  const std::string tmp_path = testing::TempDir() + "/vfs_mesh.mjz";
  int nbytes = mj_encode(spec, model, tmp_path.c_str(), nullptr, &vfs, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  // Reset VFS
  mj_deleteVFS(&vfs);
  mj_defaultVFS(&vfs);

  mjSpec* decoded =
      mj_parse(tmp_path.c_str(), nullptr, &vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  EXPECT_EQ(decoded_model->nmesh, model->nmesh);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  std::remove(tmp_path.c_str());
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, RoundTripWithMeshFromDisk) {
  std::string xml_path =
      GetTestDataFilePath("xml/mjz/testdata/disk_mesh/model.xml");

  char error[1024] = {0};
  mjSpec* spec = mj_parseXML(xml_path.c_str(), nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  fs::path tmpdir = fs::path(testing::TempDir()) / "disk_mesh_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();

  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  EXPECT_EQ(decoded_model->nmesh, model->nmesh);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

TEST_F(MjzEncoderTest, RoundTripWithMeshInSubdirectory) {
  std::string xml_path =
      GetTestDataFilePath("xml/mjz/testdata/subdir_mesh/model.xml");

  char error[1024] = {0};
  mjSpec* spec = mj_parseXML(xml_path.c_str(), nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  fs::path tmpdir = fs::path(testing::TempDir()) / "subdir_mesh_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();

  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  EXPECT_EQ(decoded_model->nmesh, model->nmesh);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

TEST_F(MjzEncoderTest, RoundTripWithMeshdir) {
  std::string xml_path =
      GetTestDataFilePath("xml/mjz/testdata/meshdir_test/model.xml");

  char error[1024] = {0};
  mjSpec* spec = mj_parseXML(xml_path.c_str(), nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  fs::path tmpdir = fs::path(testing::TempDir()) / "meshdir_test_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();

  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  EXPECT_EQ(decoded_model->nmesh, model->nmesh);

  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

TEST_F(MjzEncoderTest, RoundTripWithInclude) {
  std::string xml_path =
      GetTestDataFilePath("xml/mjz/testdata/include_test/parent.xml");

  char error[1024] = {0};
  mjSpec* spec = mj_parseXML(xml_path.c_str(), nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  fs::path tmpdir = fs::path(testing::TempDir()) / "include_test_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();

  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &vfs);
  ASSERT_THAT(decoded_model, testing::NotNull());

  EXPECT_EQ(decoded_model->nbody, model->nbody);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  fs::remove_all(tmpdir);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, RoundTripTransitiveInclude) {
  std::string xml_path =
      GetTestDataFilePath("xml/mjz/testdata/transitive_test/parent.xml");

  char error[1024] = {0};
  mjSpec* spec = mj_parseXML(xml_path.c_str(), nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  fs::path tmpdir = fs::path(testing::TempDir()) / "transitive_test_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();

  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &vfs);
  ASSERT_THAT(decoded_model, testing::NotNull());

  EXPECT_EQ(decoded_model->nbody, model->nbody);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  fs::remove_all(tmpdir);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, RoundTripMixedDiskAndVfs) {
  static const char* xml = R"(
    <mujoco model="mixed_test">
      <asset>
        <mesh name="disk_box" />
        <mesh name="vfs_box" file="xml/mjz/testdata/disk_mesh/box.obj"/>
      </asset>
      <worldbody>
        <body name="b1">
          <geom type="mesh" mesh="disk_box"/>
        </body>
        <body name="b2">
          <geom type="mesh" mesh="vfs_box"/>
        </body>
      </worldbody>
    </mujoco>

  )";

  mjVFS vfs;
  mj_defaultVFS(&vfs);
  mj_addFileVFS(
      &vfs, nullptr,
      GetTestDataFilePath("xml/mjz/testdata/disk_mesh/box.obj").c_str());

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, &vfs, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  // Fix the on disk mesh path
  mjsMesh* mesh = mjs_asMesh(mjs_findElement(spec, mjOBJ_MESH, "disk_box"));
  ASSERT_THAT(mesh, testing::NotNull());
  mjs_setString(
      mesh->file,
      GetTestDataFilePath("xml/mjz/testdata/mixed_test/disk_box.obj").c_str());

  mjModel* model = mj_compile(spec, &vfs);
  ASSERT_THAT(model, testing::NotNull()) << mjs_getError(spec);

  fs::path tmpdir = fs::path(testing::TempDir()) / "mixed_test_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();

  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, &vfs, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  EXPECT_EQ(decoded_model->nmesh, model->nmesh);
  EXPECT_EQ(decoded_model->ngeom, model->ngeom);

  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
  mj_deleteVFS(&vfs);
}

TEST_F(MjzEncoderTest, AttachedSpecsWithCollidingAssetNames) {
  std::string child_a_xml = GetTestDataFilePath(
      "xml/mjz/testdata/asset_collision_test/child_a/child.xml");
  std::string child_b_xml = GetTestDataFilePath(
      "xml/mjz/testdata/asset_collision_test/child_b/child.xml");

  char error[1024] = {0};

  // Parse both children from their respective directories.
  mjSpec* child_a =
      mj_parse(child_a_xml.c_str(), nullptr, nullptr, error, sizeof(error));
  ASSERT_THAT(child_a, testing::NotNull()) << error;
  mjSpec* child_b =
      mj_parse(child_b_xml.c_str(), nullptr, nullptr, error, sizeof(error));
  ASSERT_THAT(child_b, testing::NotNull()) << error;

  // Create parent spec and attach both children.
  mjSpec* parent = mj_makeSpec();
  ASSERT_THAT(parent, testing::NotNull());
  mjsBody* world = mjs_findBody(parent, "world");

  // Attach child_a with prefix "a_".
  mjsFrame* frame_a = mjs_addFrame(world, nullptr);
  mjs_attach(frame_a->element, mjs_findBody(child_a, "body")->element, "a_",
             "");

  // Attach child_b with prefix "b_".
  mjsFrame* frame_b = mjs_addFrame(world, nullptr);
  mjs_attach(frame_b->element, mjs_findBody(child_b, "body")->element, "b_",
             "");

  // Compile the combined model.
  mjModel* model = mj_compile(parent, nullptr);
  ASSERT_THAT(model, testing::NotNull()) << mjs_getError(parent);
  EXPECT_EQ(model->nmesh, 2) << "Expected two distinct meshes";

  // Record the original vertex counts for both meshes.
  int mesh0_nvert = model->mesh_vertnum[0];
  int mesh1_nvert = model->mesh_vertnum[1];
  EXPECT_NE(mesh0_nvert, mesh1_nvert)
      << "The two meshes should have different vertex counts";

  // Encode to MJZ.
  fs::path tmpdir = fs::path(testing::TempDir()) / "asset_collision_test_out";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();
  int nbytes = mj_encode(parent, model, out_path.c_str(), nullptr, nullptr,
                         error, sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  // Decode from MJZ.
  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  // Verify both meshes survived with correct, distinct vertex counts.
  EXPECT_EQ(decoded_model->nmesh, 2) << "Decoded model should have two meshes";
  EXPECT_EQ(decoded_model->mesh_vertnum[0], mesh0_nvert)
      << "First mesh vertex count mismatch after roundtrip";
  EXPECT_EQ(decoded_model->mesh_vertnum[1], mesh1_nvert)
      << "Second mesh vertex count mismatch after roundtrip";

  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(parent);
  mj_deleteSpec(child_a);
  mj_deleteSpec(child_b);
}

// --- Fake resource provider for URI stripping tests ---

const char* kBoxObj = R"(
v 0 0 0
v 1 0 0
v 1 1 0
v 0 1 0
v 0 0 1
v 1 0 1
v 1 1 1
v 0 1 1
f 1 2 3
f 1 3 4
f 5 6 7
f 5 7 8
f 1 2 6
f 1 6 5
f 2 3 7
f 2 7 6
f 3 4 8
f 3 8 7
f 4 1 5
f 4 5 8
)";

// Static STL data served by the fake provider.
static std::vector<char> g_fake_data;

int FakeUriOpen(mjResource* resource) {
  if (g_fake_data.empty()) return 0;
  resource->data = g_fake_data.data();
  return 1;
}

int FakeUriRead(mjResource* resource, const void** buffer) {
  if (!resource->data) return -1;
  *buffer = resource->data;
  return static_cast<int>(g_fake_data.size());
}

void FakeUriClose(mjResource* resource) { resource->data = nullptr; }

// Register the fake provider once (idempotent due to AppendIfUnique).
static void EnsureFakeProviderRegistered() {
  static bool registered = false;
  if (registered) return;
  mjpResourceProvider provider = {};
  mjp_defaultResourceProvider(&provider);
  provider.prefix = "testmjzenc";
  provider.open = FakeUriOpen;
  provider.read = FakeUriRead;
  provider.close = FakeUriClose;
  mjp_registerResourceProvider(&provider);
  registered = true;
}

TEST_F(MjzEncoderTest, RoundTripStripsUriPrefix) {
  EnsureFakeProviderRegistered();

  // Set up the fake STL data that the provider will serve.
  g_fake_data.assign(kBoxObj, kBoxObj + std::strlen(kBoxObj));

  const char* xml = R"(
    <mujoco model="uri_test">
      <asset>
        <mesh name="uri_box" file="testmjzenc:meshes/box.obj"/>
      </asset>
      <worldbody>
        <body name="body">
          <geom type="mesh" mesh="uri_box"/>
        </body>
      </worldbody>
    </mujoco>
  )";

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  // Compile.
  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull()) << mjs_getError(spec);
  EXPECT_EQ(model->nmesh, 1);

  // Encode to MJZ.
  fs::path tmpdir = fs::path(testing::TempDir()) / "uri_strip_test";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();
  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  // Decode from MJZ.
  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  // Verify the decoded mesh file attribute does NOT contain the URI prefix.
  auto* decoded_mesh = mjs_asMesh(mjs_firstElement(decoded, mjOBJ_MESH));
  ASSERT_THAT(decoded_mesh, testing::NotNull());
  const char* decoded_file = mjs_getString(decoded_mesh->file);
  ASSERT_THAT(decoded_file, testing::NotNull());
  EXPECT_FALSE(absl::StrContains(decoded_file, ":"))
      << "Decoded mesh file should not contain ':': " << decoded_file;
  EXPECT_THAT(decoded_file, testing::HasSubstr("box.obj"));

  // Verify the model compiles correctly from the decoded spec.
  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);
  EXPECT_EQ(decoded_model->nmesh, model->nmesh);

  // Cleanup.
  g_fake_data.clear();
  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

TEST_F(MjzEncoderTest, RoundTripStripsUriWithSpecialChars) {
  EnsureFakeProviderRegistered();

  // Set up the fake STL data.
  g_fake_data.assign(kBoxObj, kBoxObj + std::strlen(kBoxObj));

  const char* xml = R"(
    <mujoco model="uri_special_test">
      <asset>
        <mesh name="uri_box" file="testmjzenc://store/abc+123%20v2/box.obj"/>
      </asset>
      <worldbody>
        <body name="body">
          <geom type="mesh" mesh="uri_box"/>
        </body>
      </worldbody>
    </mujoco>
  )";

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull());

  // Encode to MJZ.
  fs::path tmpdir = fs::path(testing::TempDir()) / "uri_special_test";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();
  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  // Decode and verify no URI prefix and no special chars in the file attr.
  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  // Check the decoded mesh file attribute.
  auto* decoded_mesh = mjs_asMesh(mjs_firstElement(decoded, mjOBJ_MESH));
  ASSERT_THAT(decoded_mesh, testing::NotNull());
  const char* decoded_file = mjs_getString(decoded_mesh->file);
  ASSERT_THAT(decoded_file, testing::NotNull());
  EXPECT_FALSE(absl::StrContains(decoded_file, "testmjzenc://"))
      << "Decoded mesh file should not contain the URI prefix: "
      << decoded_file;
  EXPECT_FALSE(absl::StrContains(decoded_file, "+"))
      << "Decoded mesh file should not contain '+': " << decoded_file;
  EXPECT_FALSE(absl::StrContains(decoded_file, "%"))
      << "Decoded mesh file should not contain '%': " << decoded_file;
  EXPECT_THAT(decoded_file, testing::HasSubstr(".obj"));

  // Verify roundtrip compiles.
  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);
  EXPECT_EQ(decoded_model->nmesh, model->nmesh);

  g_fake_data.clear();
  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

class MjzEncoderParameterizedTest
    : public MujocoTest,
      public ::testing::WithParamInterface<std::string> {};

TEST_P(MjzEncoderParameterizedTest, WriteReadCompare) {
  mujoco::FullFloatPrecision increase_precision;

  std::string xml = GetParam();
  std::array<char, 1000> error;

  mjSpec* s = mj_parseXML(xml.c_str(), nullptr, error.data(), error.size());
  ASSERT_THAT(s, NotNull()) << error.data();

  mjModel* m = mj_compile(s, nullptr);
  ASSERT_THAT(m, NotNull()) << mjs_getError(s);

  const std::string tmp_path = testing::TempDir() + "/mjz_roundtrip.mjz";
  int nbytes = mj_encode(s, m, tmp_path.c_str(), nullptr, nullptr, error.data(),
                         error.size());
  ASSERT_GT(nbytes, 0) << error.data();
  mj_deleteSpec(s);

  mjVFS vfs;
  mj_defaultVFS(&vfs);

  mjSpec* stemp =
      mj_parse(tmp_path.c_str(), nullptr, &vfs, error.data(), error.size());
  ASSERT_THAT(stemp, NotNull()) << error.data();

  mjModel* mtemp = mj_compile(stemp, &vfs);
  ASSERT_THAT(mtemp, NotNull()) << mjs_getError(stemp);
  mj_deleteSpec(stemp);

  mjtNum tol = 0;
  if (absl::StrContains(xml, "belt.xml") ||
      absl::StrContains(xml, "cable.xml")) {
    tol = 1e-13;
  }

  // Make paths identical to avoid failure in CompareModel due to localization.
  // For example, we might localize "../../y" to "y", which changes the paths.
  char* old_m_paths = m->paths;
  char* old_mtemp_paths = mtemp->paths;
  int old_m_npaths = m->npaths;
  int old_mtemp_npaths = mtemp->npaths;

  std::string dummy = "ignored_path";
  int dummy_len = dummy.length() + 1;

  m->paths = (char*)mju_malloc(dummy_len);
  mtemp->paths = (char*)mju_malloc(dummy_len);

  std::memcpy(m->paths, dummy.c_str(), dummy_len);
  std::memcpy(mtemp->paths, dummy.c_str(), dummy_len);

  m->npaths = dummy_len;
  mtemp->npaths = dummy_len;

  std::string field = "";
  mjtNum result = CompareModel(m, mtemp, field);

  // Restore old pointers and sizes so mj_deleteModel can free them correctly!
  mju_free(m->paths);
  mju_free(mtemp->paths);
  m->paths = old_m_paths;
  mtemp->paths = old_mtemp_paths;
  m->npaths = old_m_npaths;
  mtemp->npaths = old_mtemp_npaths;

  EXPECT_LE(result, tol) << "Loaded and saved models are different!\n"
                         << "Affected file: " << xml << '\n'
                         << "Different field: " << field << '\n';

  mj_deleteVFS(&vfs);
  mj_deleteModel(mtemp);
  mj_deleteModel(m);
  std::remove(tmp_path.c_str());
}

INSTANTIATE_TEST_SUITE_P(MjzEncoderParameterizedTests,
                         MjzEncoderParameterizedTest,
                         ::testing::ValuesIn(GetWriteReadTestModels()),
                         [](const ::testing::TestParamInfo<std::string>& info) {
                           return SanitizePathForTestName(info.param);
                         });

TEST_F(MjzEncoderTest, DuplicateFileReferencesRewrite) {
  EnsureFakeProviderRegistered();

  // Set up the fake data that the provider will serve.
  g_fake_data.assign(kBoxObj, kBoxObj + std::strlen(kBoxObj));

  // Two meshes referencing the same URI-prefixed file.
  const char* xml = R"(
    <mujoco model="dup_file_test">
      <asset>
        <mesh name="box_a" file="testmjzenc:meshes/box.obj"/>
        <mesh name="box_b" file="testmjzenc:meshes/box.obj"/>
      </asset>
      <worldbody>
        <body name="a">
          <geom type="mesh" mesh="box_a"/>
        </body>
        <body name="b">
          <geom type="mesh" mesh="box_b"/>
        </body>
      </worldbody>
    </mujoco>
  )";

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull()) << mjs_getError(spec);

  // Encode to MJZ.
  fs::path tmpdir = fs::path(testing::TempDir()) / "dup_file_test";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();
  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  // Decode from MJZ.
  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  // Both decoded meshes should have sanitized file paths (no URI prefix).
  auto* mesh_a = mjs_asMesh(mjs_firstElement(decoded, mjOBJ_MESH));
  ASSERT_THAT(mesh_a, testing::NotNull());
  const char* file_a = mjs_getString(mesh_a->file);
  ASSERT_THAT(file_a, testing::NotNull());
  EXPECT_FALSE(absl::StrContains(file_a, ":"))
      << "First mesh file should not contain ':': " << file_a;

  auto* mesh_b = mjs_asMesh(mjs_nextElement(decoded, mesh_a->element));
  ASSERT_THAT(mesh_b, testing::NotNull());
  const char* file_b = mjs_getString(mesh_b->file);
  ASSERT_THAT(file_b, testing::NotNull());
  EXPECT_FALSE(absl::StrContains(file_b, ":"))
      << "Second mesh file should not contain ':': " << file_b;

  // Both should compile correctly.
  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);
  EXPECT_EQ(decoded_model->nmesh, model->nmesh);

  // Cleanup.
  g_fake_data.clear();
  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

TEST_F(MjzEncoderTest, CubefileUriRewrite) {
  EnsureFakeProviderRegistered();

  // The fake provider serves arbitrary data; cubefiles need valid PNG data to
  // compile textures, but the encoder just packs bytes. We verify archive
  // contents and XML rewriting without requiring valid image data.
  // Use a minimal valid 1x1 white PNG for each face.
  static const unsigned char kTinyPng[] = {
      0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d,
      0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01,
      0x08, 0x02, 0x00, 0x00, 0x00, 0x90, 0x77, 0x53, 0xde, 0x00, 0x00, 0x00,
      0x0c, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9c, 0x63, 0xf8, 0xff, 0xff, 0x3f,
      0x00, 0x05, 0xfe, 0x02, 0xfe, 0x0d, 0xef, 0x46, 0xb8, 0x00, 0x00, 0x00,
      0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
  };
  g_fake_data.assign(
      reinterpret_cast<const char*>(kTinyPng),
      reinterpret_cast<const char*>(kTinyPng) + sizeof(kTinyPng));

  const char* xml = R"(
    <mujoco model="cubefile_test">
      <asset>
        <texture name="sky" type="cube"
                 fileright="testmjzenc:faces/right.png"
                 fileleft="testmjzenc:faces/left.png"
                 fileup="testmjzenc:faces/up.png"
                 filedown="testmjzenc:faces/down.png"
                 filefront="testmjzenc:faces/front.png"
                 fileback="testmjzenc:faces/back.png"/>
        <material name="sky_mat" texture="sky"/>
      </asset>
      <worldbody>
        <body name="body">
          <geom type="sphere" size="0.1" material="sky_mat"/>
        </body>
      </worldbody>
    </mujoco>
  )";

  char error[1024] = {0};
  mjSpec* spec = mj_parseXMLString(xml, nullptr, error, sizeof(error));
  ASSERT_THAT(spec, testing::NotNull()) << error;

  mjModel* model = mj_compile(spec, nullptr);
  ASSERT_THAT(model, testing::NotNull()) << mjs_getError(spec);

  // Encode to MJZ.
  fs::path tmpdir = fs::path(testing::TempDir()) / "cubefile_test";
  fs::create_directories(tmpdir);
  const std::string out_path = (tmpdir / "model.mjz").string();
  int nbytes = mj_encode(spec, model, out_path.c_str(), nullptr, nullptr, error,
                         sizeof(error));
  ASSERT_GT(nbytes, 0) << error;

  // Decode from MJZ.
  mjVFS decode_vfs;
  mj_defaultVFS(&decode_vfs);
  mjSpec* decoded =
      mj_parse(out_path.c_str(), nullptr, &decode_vfs, error, sizeof(error));
  ASSERT_THAT(decoded, testing::NotNull()) << error;

  // Verify the decoded texture's cubefile paths don't contain URI prefix.
  auto* decoded_tex = mjs_asTexture(mjs_firstElement(decoded, mjOBJ_TEXTURE));
  ASSERT_THAT(decoded_tex, testing::NotNull());
  ASSERT_THAT(decoded_tex->cubefiles, testing::NotNull());
  for (const mjString& cubefile : *decoded_tex->cubefiles) {
    EXPECT_FALSE(absl::StrContains(cubefile, ":"))
        << "Cubefile should not contain ':': " << cubefile;
    EXPECT_THAT(std::string(cubefile), testing::HasSubstr(".png"));
  }

  // Verify the model compiles correctly from the decoded spec.
  mjModel* decoded_model = mj_compile(decoded, &decode_vfs);
  ASSERT_THAT(decoded_model, testing::NotNull()) << mjs_getError(decoded);

  // Cleanup.
  g_fake_data.clear();
  fs::remove_all(tmpdir);
  mj_deleteVFS(&decode_vfs);
  mj_deleteModel(decoded_model);
  mj_deleteSpec(decoded);
  mj_deleteModel(model);
  mj_deleteSpec(spec);
}

}  // namespace mujoco