Add mj_parseXML and mj_saveXML to xml_api.

PiperOrigin-RevId: 640099466
Change-Id: I75f763523c5bc8f6f7c2f2de6806d82ba37ebd4e

src/xml/xml.cc

@@ -100,7 +100,7 @@ class LocaleOverride {
 }  // namespace
 
 // Main writer function - calls mjXWrite
-std::string mjWriteXML(mjSpec* spec, char* error, int error_sz) {
+std::string mjWriteXML(const mjSpec* spec, char* error, int error_sz) {
   LocaleOverride locale_override;
 
   // check for empty model
@@ -424,9 +424,9 @@ static void RegisterResourceProvider() {
 
 
 mjSpec* ParseSpecFromString(std::string_view xml, char* error,
-                            int error_size, mjVFS* vfs) {
+                            int error_size) {
   RegisterResourceProvider();
   std::string xml2 = {xml.begin(), xml.end()};
   std::string str = "LoadModelFromString:" +  xml2;
-  return mjParseXML(str.c_str(), vfs, error, error_size);
+  return mjParseXML(str.c_str(), nullptr, error, error_size);
 }

src/xml/xml.h

@@ -24,15 +24,14 @@
 // Top level API
 
 // Main writer function
-std::string mjWriteXML(mjSpec* spec, char* error, int error_sz);
+std::string mjWriteXML(const mjSpec* spec, char* error, int error_sz);
 
 // Main parser function
-MJAPI mjSpec* mjParseXML(const char* filename, const mjVFS* vfs, char* error, int error_sz);
+mjSpec* mjParseXML(const char* filename, const mjVFS* vfs, char* error, int error_sz);
 
 // Returns a newly-allocated mjSpec, loaded from the contents of xml.
 // On failure returns nullptr and populates the error array if present.
-MJAPI mjSpec* ParseSpecFromString(std::string_view xml, char* error = nullptr,
-                                  int error_size = 0, mjVFS* vfs = nullptr);
+mjSpec* ParseSpecFromString(std::string_view xml, char* error = nullptr, int error_size = 0);
 
 
 #endif  // MUJOCO_SRC_XML_XML_H_

src/xml/xml_api.cc

@@ -209,3 +209,53 @@ mjModel* mj_loadModel(const char* filename, const mjVFS* vfs) {
   return m;
 }
 
+
+
+// parse spec from file
+mjSpec* mj_parseXML(const char* filename, const mjVFS* vfs, char* error, int error_sz) {
+  return mjParseXML(filename, vfs, error, error_sz);
+}
+
+
+
+// parse spec from string
+mjSpec* mj_parseXMLString(const char* xml, const mjVFS* vfs, char* error, int error_sz) {
+  return ParseSpecFromString(xml, error, error_sz);
+}
+
+
+
+// save spec to XML file, return 1 on success, 0 otherwise
+int mj_saveXML(const mjSpec* s, const char* filename, char* error, int error_sz) {
+  std::string result = mjWriteXML(s, error, error_sz);
+  if (result.empty()) {
+    return 0;
+  }
+
+  std::ofstream file;
+  file.open(filename);
+  file << result;
+  file.close();
+  return 1;
+}
+
+
+
+// save spec to string, return 1 on success, 0 otherwise
+int mj_saveXMLString(const mjSpec* s, char* xml, int xml_sz, char* error, int error_sz) {
+  std::string result = mjWriteXML(s, error, error_sz);
+  if (result.size() >= xml_sz) {
+    std::string error_msg = "Output string too short, should be at least " +
+                            std::to_string(result.size()+1);
+    mjCopyError(error, error_msg.c_str(), error_sz);
+    return 0;
+  }
+  if (result.empty()) {
+    return 0;
+  }
+
+  result.copy(xml, xml_sz);
+  xml[result.size()] = 0;
+  return 1;
+}
+

src/xml/xml_api.h

@@ -17,6 +17,7 @@
 
 #include <mujoco/mjexport.h>
 #include <mujoco/mjmodel.h>
+#include "user/user_api.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -43,6 +44,14 @@ MJAPI int mj_printSchema(const char* filename, char* buffer, int buffer_sz,
 // if vfs is not NULL, look up file in vfs before reading from disk
 MJAPI mjModel* mj_loadModel(const char* filename, const mjVFS* vfs);
 
+// parse spec from file or XML string.
+MJAPI mjSpec* mj_parseXML(const char* filename, const mjVFS* vfs, char* error, int error_sz);
+MJAPI mjSpec* mj_parseXMLString(const char* xml, const mjVFS* vfs, char* error, int error_sz);
+
+// Save spec to XML file and/or string, return 1 on success, 0 otherwise.
+MJAPI int mj_saveXML(const mjSpec* s, const char* filename, char* error, int error_sz);
+MJAPI int mj_saveXMLString(const mjSpec* s, char* xml, int xml_sz, char* error, int error_sz);
+
 #ifdef __cplusplus
 }
 #endif

src/xml/xml_base.cc

@@ -45,8 +45,8 @@ mjXBase::mjXBase() {
 
 
 // set model field
-void mjXBase::SetModel(mjSpec* _model) {
-  model = _model;
+void mjXBase::SetModel(const mjSpec* _model) {
+  model = (mjSpec*)_model;
 }
 
 

src/xml/xml_base.h

@@ -87,7 +87,7 @@ class mjXBase : public mjXUtil {
   };
 
   // set the model allocated externally
-  virtual void SetModel(mjSpec*);
+  virtual void SetModel(const mjSpec*);
 
   // read alternative orientation specification
   static int ReadAlternative(tinyxml2::XMLElement* elem, mjsOrientation& alt);

src/xml/xml_native_writer.cc

@@ -769,7 +769,7 @@ mjXWriter::mjXWriter(void) {
 
 
 // cast model
-void mjXWriter::SetModel(mjSpec* spec) {
+void mjXWriter::SetModel(const mjSpec* spec) {
   if (spec) {
     model = (mjCModel*)spec->element;
   }

src/xml/xml_native_writer.h

@@ -27,7 +27,7 @@ class mjXWriter : public mjXBase {
  public:
   mjXWriter();                                        // constructor
   virtual ~mjXWriter() = default;                     // destructor
-  void SetModel(mjSpec* spec);
+  void SetModel(const mjSpec* spec);
 
   // write XML document to string
   std::string Write(char *error, std::size_t error_sz);

test/user/user_api_test.cc

@@ -25,7 +25,7 @@
 #include <absl/strings/match.h>
 #include <mujoco/mujoco.h>
 #include "src/user/user_api.h"
-#include "src/xml/xml.h"
+#include "src/xml/xml_api.h"
 #include "src/xml/xml_numeric_format.h"
 #include "test/fixture.h"
 
@@ -125,7 +125,7 @@ TEST_F(PluginTest, RecompileCompare) {
 
         // load spec
         std::array<char, 1000> err;
-        mjSpec* s = mjParseXML(xml.c_str(), nullptr, err.data(), err.size());
+        mjSpec* s = mj_parseXML(xml.c_str(), 0, err.data(), err.size());
 
         ASSERT_THAT(s, NotNull())
             << "Failed to load " << xml << ": " << err.data();
@@ -417,7 +417,7 @@ TEST_F(MujocoTest, AttachSame) {
   </mujoco>)";
 
   // create parent
-  mjSpec* parent = ParseSpecFromString(xml_child, er.data(), er.size());
+  mjSpec* parent = mj_parseXMLString(xml_child, 0, er.data(), er.size());
   EXPECT_THAT(parent, NotNull()) << er.data();
 
   // get frame
@@ -530,7 +530,7 @@ TEST_F(MujocoTest, AttachDifferent) {
   </mujoco>)";
 
   // model with one free sphere and a frame
-  mjSpec* parent = ParseSpecFromString(xml_parent, er.data(), er.size());
+  mjSpec* parent = mj_parseXMLString(xml_parent, 0, er.data(), er.size());
   EXPECT_THAT(parent, NotNull()) << er.data();
 
   // get frame
@@ -538,7 +538,7 @@ TEST_F(MujocoTest, AttachDifferent) {
   EXPECT_THAT(frame, NotNull());
 
   // model with one cylinder and a hinge
-  mjSpec* child = ParseSpecFromString(xml_child, er.data(), er.size());
+  mjSpec* child = mj_parseXMLString(xml_child, 0, er.data(), er.size());
   EXPECT_THAT(child, NotNull()) << er.data();
 
   // get subtree
@@ -642,7 +642,7 @@ TEST_F(MujocoTest, AttachFrame) {
   </mujoco>)";
 
   // model with one free sphere and a frame
-  mjSpec* parent = ParseSpecFromString(xml_parent, er.data(), er.size());
+  mjSpec* parent = mj_parseXMLString(xml_parent, 0, er.data(), er.size());
   EXPECT_THAT(parent, NotNull()) << er.data();
 
   // get frame
@@ -650,7 +650,7 @@ TEST_F(MujocoTest, AttachFrame) {
   EXPECT_THAT(body, NotNull());
 
   // model with one cylinder and a hinge
-  mjSpec* child = ParseSpecFromString(xml_child, er.data(), er.size());
+  mjSpec* child = mj_parseXMLString(xml_child, 0, er.data(), er.size());
   EXPECT_THAT(child, NotNull()) << er.data();
 
   // get subtree
@@ -711,7 +711,7 @@ void TestDetachBody(bool compile) {
   </mujoco>)";
 
   // model with one cylinder and a hinge
-  mjSpec* child = ParseSpecFromString(xml_child, er.data(), er.size());
+  mjSpec* child = mj_parseXMLString(xml_child, 0, er.data(), er.size());
   EXPECT_THAT(child, NotNull()) << er.data();
 
   // compile model (for testing double compilation)

test/xml/xml_api_test.cc

@@ -24,6 +24,8 @@
 #include <mujoco/mjdata.h>
 #include <mujoco/mjmodel.h>
 #include <mujoco/mujoco.h>
+#include "src/user/user_api.h"
+#include "src/xml/xml_api.h"
 #include "test/fixture.h"
 
 namespace mujoco {
@@ -33,6 +35,21 @@ using ::testing::IsNull;
 using ::testing::NotNull;
 using ::testing::StartsWith;
 
+static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <joint/>
+        <geom size="1"/>
+      </body>
+      <body>
+        <joint/>
+        <geom size="0.5"/>
+      </body>
+    </worldbody>
+  </mujoco>
+  )";
+
 // ---------------------------- test mj_loadXML --------------------------------
 
 using LoadXmlTest = MujocoTest;
@@ -66,20 +83,6 @@ TEST_F(LoadXmlTest, InvalidXmlFailsToLoad) {
 }
 
 TEST_F(LoadXmlTest, MultipleBodies) {
-  static constexpr char xml[] = R"(
-  <mujoco>
-    <worldbody>
-      <body>
-        <joint/>
-        <geom size="1"/>
-      </body>
-      <body>
-        <joint/>
-        <geom size="0.5"/>
-      </body>
-    </worldbody>
-  </mujoco>
-  )";
   std::array<char, 1000> error;
   mjModel* model = LoadModelFromString(xml, error.data(), error.size());
 
@@ -92,7 +95,6 @@ TEST_F(LoadXmlTest, MultipleBodies) {
   mj_deleteData(data);
   mj_deleteModel(model);
 }
-
 using SaveLastXmlTest = MujocoTest;
 
 TEST_F(SaveLastXmlTest, EmptyModel) {
@@ -112,5 +114,51 @@ TEST_F(SaveLastXmlTest, EmptyModel) {
   mj_deleteModel(model);
 }
 
+TEST_F(MujocoTest, SaveXmlShortString) {
+  std::array<char, 1000> error;
+
+  mjSpec* spec = mj_parseXMLString(xml, 0, error.data(), error.size());
+  EXPECT_THAT(spec, NotNull()) << "Failed to parse spec: " << error.data();
+  mjModel* model = mjs_compile(spec, 0);
+  EXPECT_THAT(model, NotNull()) << "Failed to compile model: " << error.data();
+
+  std::array<char, 10> out;
+  EXPECT_THAT(mj_saveXMLString(spec, out.data(), out.size(),
+                               error.data(), error.size()), 0);
+  EXPECT_STREQ(error.data(), "Output string too short, should be at least 273");
+
+  mjs_deleteSpec(spec);
+  mj_deleteModel(model);
+}
+
+TEST_F(MujocoTest, SaveXml) {
+  std::array<char, 1000> error;
+
+  mjSpec* spec = mj_parseXMLString(xml, 0, error.data(), error.size());
+  EXPECT_THAT(spec, NotNull()) << "Failed to parse spec: " << error.data();
+  mjModel* model = mjs_compile(spec, 0);
+  EXPECT_THAT(model, NotNull()) << "Failed to compile model: " << error.data();
+
+  std::array<char, 273> out;
+  EXPECT_THAT(mj_saveXMLString(spec, out.data(), out.size(), error.data(),
+                               error.size()), 1) << error.data();
+
+  mjSpec* saved_spec = mj_parseXMLString(xml, 0, error.data(), error.size());
+  EXPECT_THAT(saved_spec, NotNull()) << "Invalid saved spec: " << error.data();
+  mjModel* saved_model = mjs_compile(saved_spec, 0);
+  EXPECT_THAT(saved_model, NotNull()) << "Invalid model: " << error.data();
+
+  mjtNum tol = 0;
+  std::string field = "";
+  EXPECT_LE(CompareModel(model, saved_model, field), tol)
+            << "Expected and attached models are different!\n"
+            << "Different field: " << field << '\n';
+
+  mjs_deleteSpec(spec);
+  mjs_deleteSpec(saved_spec);
+  mj_deleteModel(model);
+  mj_deleteModel(saved_model);
+}
+
 }  // namespace
 }  // namespace mujoco

test/xml/xml_native_reader_test.cc

@@ -28,7 +28,7 @@
 #include "src/cc/array_safety.h"
 #include "src/engine/engine_util_errmem.h"
 #include "src/user/user_api.h"
-#include "src/xml/xml.h"
+#include "src/xml/xml_api.h"
 #include "test/fixture.h"
 
 namespace mujoco {
@@ -1084,7 +1084,7 @@ TEST_F(XMLReaderTest, ParseReplicateDefaultPropagate) {
   </mujoco>
   )";
   std::array<char, 1024> error;
-  mjSpec* spec = ParseSpecFromString(xml, error.data(), error.size());
+  mjSpec* spec = mj_parseXMLString(xml, 0, error.data(), error.size());
   EXPECT_THAT(spec, NotNull()) << error.data();
 
   mjsBody* torso = mjs_findBody(spec, "torso-0");