Issue 4125 - [emscripten] Convert filter classes to C++

compiled/bindings.ipp

+#pragma once
+
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <exception>
+#include <map>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include <emscripten.h>
+
+#include "String.h"
+#include "intrusive_ptr.h"
+
+namespace bindings_internal
+{
+  typedef void* TYPEID;
+
+  enum class TypeCategory
+  {
+    UNKNOWN,
+    VOID,
+    INT,
+    DEPENDENT_STRING,
+    OWNED_STRING,
+    STRING_REF,
+    CLASS_PTR
+  };
+
+  template<typename T>
+  struct TypeInfo
+  {
+    /*
+     * Since TypeInfo is a templated type, in practice the compiler will define
+     * a new type for each possible template parameter value. We use that fact
+     * to generate type identifiers: each of these TypeInfo types has a
+     * different s_typeIDHelper member, so we use a pointer to that static
+     * variable as a type identifier - it will be different for each template
+     * parameter.
+     */
+    static char s_typeIDHelper;
+    constexpr operator TYPEID() const
+    {
+      return &s_typeIDHelper;
+    }
+
+    constexpr operator TypeCategory() const
+    {
+      if (std::is_void<T>())
+        return TypeCategory::VOID;
+
+      if (std::is_integral<T>() || std::is_enum<T>())
+        return TypeCategory::INT;
+
+      if (std::is_same<DependentString, T>() || std::is_same<const DependentString, T>())
+        return TypeCategory::DEPENDENT_STRING;
+
+      if (std::is_same<OwnedString, T>() || std::is_same<const OwnedString, T>())
+        return TypeCategory::OWNED_STRING;
+
+      if (std::is_same<String&, T>() || std::is_same<const String&, T>() ||
+        std::is_same<DependentString&, T>())
+      {
+        return TypeCategory::STRING_REF;
+      }
+
+      if (std::is_pointer<T>() && std::is_class<typename std::remove_pointer<T>::type>())
+        return TypeCategory::CLASS_PTR;
+
+      return TypeCategory::UNKNOWN;
+    }
+
+    constexpr TYPEID pointer_type() const
+    {
+      if (std::is_pointer<T>())
+        return TypeInfo<typename std::remove_pointer<T>::type>();
+      else
+        return nullptr;
+    }
+  };
+
+  template<typename T>
+  char TypeInfo<T>::s_typeIDHelper;
+
+  struct FunctionInfo
+  {
+    TypeCategory returnType;
+    TYPEID pointerType;
+    std::vector<TypeCategory> args;
+    bool instance_function;
+    int effectiveArgs;
+    TypeCategory effectiveReturnType;
+    char name[1024];
+
+    FunctionInfo()
+    {
+      name[0] = '\0';
+    }
+
+    FunctionInfo(TypeCategory returnType, TYPEID pointerType,
+        std::initializer_list<TypeCategory> argTypes, bool instance_function,
+        void* function)
+        : returnType(returnType), pointerType(pointerType),
+          instance_function(instance_function)
+    {
+      name[0] = '\0';
+
+      // The function parameter is a pointer to the function pointer.
+      // Emscripten's "function pointers" are actually integers indicating the
+      // position in the call table. 0 represents nullptr.
+      if (!*reinterpret_cast<int*>(function))
+        return;
+
+      for (const auto& item : argTypes)
+      {
+        if (item != TypeCategory::INT && item != TypeCategory::STRING_REF &&
+            item != TypeCategory::CLASS_PTR)
+        {
+          throw std::runtime_error("Unexpected function argument type");
+        }
+        args.push_back(item);
+      }
+
+      if (returnType != TypeCategory::VOID && returnType != TypeCategory::INT &&
+          returnType != TypeCategory::DEPENDENT_STRING &&
+          returnType != TypeCategory::OWNED_STRING &&
+          returnType != TypeCategory::STRING_REF &&
+          returnType != TypeCategory::CLASS_PTR)
+      {
+        throw std::runtime_error("Unexpected function return type");
+      }
+
+      effectiveArgs = args.size();
+      effectiveReturnType = returnType;
+      if (instance_function)
+        effectiveArgs++;
+
+      if (returnType == TypeCategory::DEPENDENT_STRING ||
+          returnType == TypeCategory::OWNED_STRING)
+      {
+        effectiveArgs++;
+        effectiveReturnType = TypeCategory::VOID;
+      }
+
+      get_function_name(function, effectiveArgs,
+          effectiveReturnType == TypeCategory::VOID);
+    }
+
+    template<typename ReturnType, typename... Args>
+    FunctionInfo(ReturnType (*function)(Args...))
+        : FunctionInfo(TypeInfo<ReturnType>(),
+          TypeInfo<ReturnType>().pointer_type(), { TypeInfo<Args>()... }, false,
+          &function)
+    {
+    }
+
+    template<typename ClassType, typename ReturnType, typename... Args>
+    FunctionInfo(ReturnType (ClassType::*function)(Args...))
+        : FunctionInfo(TypeInfo<ReturnType>(),
+          TypeInfo<ReturnType>().pointer_type(), { TypeInfo<Args>()... }, true,
+          &function)
+    {
+    }
+
+    template<typename ClassType, typename ReturnType, typename... Args>
+    FunctionInfo(ReturnType (ClassType::*function)(Args...) const)
+        : FunctionInfo(TypeInfo<ReturnType>(),
+          TypeInfo<ReturnType>().pointer_type(), { TypeInfo<Args>()... }, true,
+          &function)
+    {
+    }
+
+    bool empty() const
+    {
+      return name[0] == '\0';
+    }
+
+    void get_function_name(void* ptr, int numArgs, bool voidResult)
+    {
+      // This is a hack, C++ won't let us get the mangled function name.
+      // JavaScript is more dynamic so we pass the pointer to our function
+      // there. With that and the function signature we can call the function -
+      // with a full stack so that we will cause it to abort. Sometimes the
+      // function we are calling will also be missing from the build. The result
+      // is the same: abort() is called which in turn calls stackTrace(). By
+      // replacing stackTrace() we get access to the call stack and search it
+      // for the name of our function.
+
+      EM_ASM_ARGS({
+        var signature = $3 ? "v" : "i";
+        var args = [];
+        for (var i = 0; i < $2; i++)
+        {
+          signature += "i";
+          args.push(0);
+        }
+
+        var oldPrint = Module.print;
+        var oldPrintErr = Module.printErr;
+        var oldStackTrace = stackTrace;
+        var sp = Runtime.stackSave();
+        Module.print = function(){};
+        Module.printErr = function(){};
+        stackTrace = function()
+        {
+          var stack = [];
+          for (var f = arguments.callee.caller; f; f = f.caller)
+          {
+            if (f.name)
+            {
+              if (f.name.indexOf("dynCall") == 0)
+                break;
+              else
+                stack.push(f.name);
+            }
+          }
+
+          result = stack[stack.length - 1];
+          if (result && result.indexOf("__wrapper") >= 0)
+            result = stack[stack.length - 2];
+          throw result;
+        };
+
+        Runtime.stackRestore(STACK_MAX);
+
+        try
+        {
+          Runtime.dynCall(signature, HEAP32[$1 >> 2], args);
+        }
+        catch(e)
+        {
+          Module.stringToAscii(e, $0);
+        }
+        finally
+        {
+          Runtime.stackRestore(sp);
+          Module.print = oldPrint;
+          Module.printErr = oldPrintErr;
+          stackTrace = oldStackTrace;
+        }
+      }, name, ptr, numArgs, voidResult);
+    }
+  };
+
+  class NoBaseClass
+  {
+  };
+
+  struct PropertyInfo
+  {
+    std::string name;
+    FunctionInfo getter;
+    FunctionInfo setter;
+    std::string jsValue;
+  };
+
+  struct MethodInfo
+  {
+    std::string name;
+    FunctionInfo call;
+  };
+
+  struct DifferentiatorInfo
+  {
+    size_t offset;
+    std::vector<std::pair<int, std::string>> mapping;
+  };
+
+  struct ClassInfo
+  {
+    ClassInfo* baseClass;
+    std::string name;
+    std::vector<PropertyInfo> properties;
+    std::vector<MethodInfo> methods;
+    std::vector<FunctionInfo> initializers;
+    DifferentiatorInfo subclass_differentiator;
+    int ref_counted_offset;

[sergei, 2017/03/20 17:07:18]

Can we use ptrdiff_t for ref_counted_offset?

[Wladimir Palant, 2017/03/21 10:10:15]

Done.

+  };
+
+  std::map<TYPEID, ClassInfo> classes;
+
+  void register_class(const char* name, TYPEID classID, TYPEID baseClassID,
+                      int ref_counted_offset)
+  {
+    auto it = classes.find(classID);
+    if (it != classes.end())
+      throw std::runtime_error(std::string("Duplicate definition for class ") + name);
+
+    ClassInfo* baseClass = nullptr;
+    if (baseClassID != TypeInfo<NoBaseClass>())
+    {
+      it = classes.find(baseClassID);
+      if (it == classes.end())
+        throw std::runtime_error(std::string("Unknown base class defined for class ") + name);
+      baseClass = &(it->second);
+    }
+
+    ClassInfo classInfo;
+    classInfo.baseClass = baseClass;
+    classInfo.name = name;
+    classInfo.subclass_differentiator.offset = SIZE_MAX;
+    classInfo.ref_counted_offset = ref_counted_offset;
+    classes[classID] = classInfo;
+  }
+
+  void register_property(TYPEID classID, const char* name,
+      const FunctionInfo& getter, const FunctionInfo& setter,
+      const char* jsValue = "")
+  {
+    auto it = classes.find(classID);
+    if (it == classes.end())
+      throw std::runtime_error(std::string("Property defined on unknown class: ") + name);
+
+    PropertyInfo propertyInfo;
+    propertyInfo.name = name;
+    propertyInfo.getter = getter;
+    propertyInfo.setter = setter;
+    propertyInfo.jsValue = jsValue;
+    it->second.properties.push_back(propertyInfo);
+  }
+
+  void register_method(TYPEID classID, const char* name,
+      const FunctionInfo& call)
+  {
+    auto it = classes.find(classID);
+    if (it == classes.end())
+      throw std::runtime_error(std::string("Method defined on unknown class: ") + name);
+
+    MethodInfo methodInfo;
+    methodInfo.name = name;
+    methodInfo.call = call;
+    it->second.methods.push_back(methodInfo);
+  }
+
+  void register_initializer(TYPEID classID, const FunctionInfo& call)
+  {
+    auto it = classes.find(classID);
+    if (it == classes.end())
+      throw std::runtime_error("Initializer defined on unknown class");
+
+    it->second.initializers.push_back(call);
+  }
+
+  void register_differentiator(TYPEID classID, size_t offset,
+      std::vector<std::pair<int, std::string>>& mapping)
+  {
+    auto it = classes.find(classID);
+    if (it == classes.end())
+      throw std::runtime_error("Subclass differentiator defined on unknown class");
+
+    if (it->second.subclass_differentiator.offset != SIZE_MAX)
+      throw std::runtime_error("More than one subclass differentiator defined for class " + it->second.name);
+
+    DifferentiatorInfo differentiatorInfo;
+    differentiatorInfo.offset = offset;
+    differentiatorInfo.mapping = mapping;
+    it->second.subclass_differentiator = differentiatorInfo;
+  }
+
+  const std::string generateCall(const FunctionInfo& call,
+      std::vector<std::string>& params)
+  {
+    if (call.returnType == TypeCategory::DEPENDENT_STRING ||
+        call.returnType == TypeCategory::OWNED_STRING)
+    {
+      params.insert(params.begin(), "string");
+    }
+
+    std::string call_str(call.name);
+    call_str += "(";
+    for (int i = 0; i < params.size(); i++)
+    {
+      if (i > 0)
+        call_str += ", ";
+      call_str += params[i];
+    }
+    call_str += ")";
+
+    if (call.returnType == TypeCategory::VOID)
+      return "  " + call_str + ";\n";
+    else if (call.returnType == TypeCategory::INT)
+      return "  var result = " + call_str + ";\n";
+    else if (call.returnType == TypeCategory::DEPENDENT_STRING ||
+        call.returnType == TypeCategory::OWNED_STRING)
+    {
+      std::string result;
+      result += "  var string = createString();\n";
+      result += "  " + call_str + ";\n";
+      result += "  var result = readString(string);\n";
+      if (call.returnType == TypeCategory::OWNED_STRING)
+        result += "  Module._DestroyString(string);\n";
+      return result;
+    }
+    else if (call.returnType == TypeCategory::STRING_REF)
+    {
+      return "  var result = readString(" + call_str + ");\n";
+    }
+    else if (call.returnType == TypeCategory::CLASS_PTR)
+    {
+      std::string result;
+      result += "  var result = " + call_str + ";\n";
+      result += "  if (result)\n";
+      result += "  {\n";
+
+      auto it = classes.find(call.pointerType);
+      if (it == classes.end())
+        throw std::runtime_error("Function " + std::string(call.name) + " returns pointer to unknown class");
+
+      const ClassInfo& cls = it->second;
+      auto offset = cls.subclass_differentiator.offset;
+      if (offset == SIZE_MAX)
+        result += "    result = " + cls.name + "(result);\n";
+      else
+      {
+        result += "    var type = HEAP32[result + " + std::to_string(offset)+ " >> 2];\n";
+        result += "    if (type in " + cls.name + "_mapping)\n";
+        result += "      result = new (exports[" + cls.name + "_mapping[type]])(result);\n";
+        result += "    else\n";
+        result += "      throw new Error('Unexpected " + cls.name + " type: ' + type);\n";
+      }
+
+      result += "  }\n";
+      return result;
+    }
+    else
+      throw std::runtime_error("Unexpected return type for " + std::string(call.name));
+  }
+
+  const std::string wrapCall(const FunctionInfo& call)
+  {
+    char buffer[20];
+    bool hasStringArgs = false;
+    std::vector<std::string> params;
+    std::string prefix = "function(";
+    for (int i = 0; i < call.args.size(); i++)
+    {
+      sprintf(buffer, "arg%i", i);
+      if (i > 0)
+        prefix += ", ";
+      prefix += buffer;
+
+      if (call.args[i] == TypeCategory::STRING_REF)
+      {
+        hasStringArgs = true;
+        params.push_back(std::string("createString(") + buffer + ")");
+      }
+      else
+        params.push_back(buffer);
+    }
+    prefix += ")\n{\n";
+
+    std::string suffix = "}";
+    if (call.returnType != TypeCategory::VOID)
+      suffix = "  return result;\n" + suffix;
+
+    if (call.returnType == TypeCategory::DEPENDENT_STRING ||
+        call.returnType == TypeCategory::OWNED_STRING || hasStringArgs)
+    {
+      prefix += "  var sp = Runtime.stackSave();\n";
+      suffix = "  Runtime.stackRestore(sp);\n" + suffix;
+    }
+
+    if (call.instance_function)
+      params.insert(params.begin(), "this._pointer");
+
+    return prefix + generateCall(call, params) + suffix;
+  }
+
+  std::string generatePropertyDescriptor(const PropertyInfo& property)
+  {
+    if (!property.jsValue.empty())
+      return "value: " + property.jsValue;
+
+    std::string result("get: " + wrapCall(property.getter));
+    if (!property.setter.empty())
+      result += ", set: " + wrapCall(property.setter);
+    return result;
+  }
+
+  void printHelpers()
+  {
+    printf("var sizeofString = %i;\n", sizeof(String));
+
+    puts(R"(
+  function copyString(str, buffer)
+  {
+    var length = str.length;
+    for (var i = 0, pointer = (buffer >> 1); i < length; i++, pointer++)
+      HEAP16[pointer] = str.charCodeAt(i);
+    return length;
+  }
+
+  function createString(str)
+  {
+    var length = 0;
+    var buffer = 0;
+    if (str)
+    {
+      buffer = Runtime.stackAlloc(str.length * 2);
+      length = copyString(str, buffer);
+    }
+
+    var result = Module.Runtime.stackAlloc(sizeofString);
+    Module._InitString(result, buffer, length);
+    return result;
+  }
+
+  function readString(str)
+  {
+    var length = Module._GetStringLength(str);
+    var pointer = Module._GetStringData(str) >> 1;
+    return String.fromCharCode.apply(String, HEAP16.slice(pointer, pointer + length));
+  }
+
+  function createClass(superclass, ref_counted_offset)
+  {
+    var result = function(pointer)
+    {
+      this._pointer = pointer;
+    };
+    if (superclass)
+      result.prototype = Object.create(superclass.prototype);
+    result.prototype.delete = function()
+    {
+      Module._ReleaseRef(this._pointer + ref_counted_offset);
+    };
+    return result;
+  })");
+  }
+
+  void printClass(const ClassInfo& cls)
+  {
+    DifferentiatorInfo differentiator = cls.subclass_differentiator;
+    if (differentiator.offset != SIZE_MAX)
+    {
+      printf("var %s_mapping = \n", cls.name.c_str());
+      puts("{");
+      for (const auto& item : differentiator.mapping)
+        printf("  %i: '%s',\n", item.first, item.second.c_str());
+      puts("};");
+    }
+
+    printf("exports.%s = createClass(%s, %i);\n", cls.name.c_str(),
+        (cls.baseClass ? ("exports." + cls.baseClass->name).c_str() : "null"),
+        cls.ref_counted_offset);
+
+    for (const auto& item : cls.properties)
+    {
+      printf("Object.defineProperty(exports.%s.prototype, '%s', {%s});\n",
+          cls.name.c_str(), item.name.c_str(),
+          generatePropertyDescriptor(item).c_str());
+    }
+
+    for (const auto& item : cls.methods)
+    {
+      std::string obj("exports." + cls.name);
+      if (item.call.instance_function)
+        obj += ".prototype";
+      printf("%s.%s = %s;\n", obj.c_str(), item.name.c_str(),
+          wrapCall(item.call).c_str());
+    }
+
+    for (const auto& item : cls.initializers)
+      printf("%s()\n", item.name);
+  }
+
+  void printBindings()
+  {
+    printHelpers();
+
+    for (const auto& item : classes)
+      printClass(item.second);
+  }
+}
+
+#if defined(PRINT_BINDINGS)
+  // Bindings generation step: collect bindings information and print
+  // corresponding JS code.
+  #define EMSCRIPTEN_BINDINGS \
+      struct BindingsInitializer {\
+          BindingsInitializer();\
+          BindingsInitializer(bool dummy)\
+          {\
+            try\
+            {\
+              BindingsInitializer();\
+              bindings_internal::printBindings();\
+            }\
+            catch (const std::exception& e)\
+            {\
+              EM_ASM_ARGS(\
+                console.error("Error occurred generating JavaScript bindings: " +\
+                    Module.AsciiToString($0)), e.what()\
+              );\
+              abort();\
+            }\
+          }\
+      } BindingsInitializer_instance(true);\
+      BindingsInitializer::BindingsInitializer()
+#else
+  // Actual compilation step: ignore bindings information but define some
+  // exported helper functions necessary for the bindings.
+  #define EMSCRIPTEN_BINDINGS \
+      extern "C"\
+      {\
+        void EMSCRIPTEN_KEEPALIVE InitString(DependentString* str,\
+            String::value_type* data, String::size_type len)\
+        {\
+          /* String is already allocated on stack, we merely need to call*/\
+          /* constructor.*/\
+          new (str) DependentString(data, len);\
+        }\
+        void EMSCRIPTEN_KEEPALIVE DestroyString(OwnedString* str)\
+        {\
+          /* Stack memory will be freed automatically, we need to call*/\
+          /* destructor explicitly however.*/\
+          str->~OwnedString();\
+        }\
+        String::size_type EMSCRIPTEN_KEEPALIVE GetStringLength(\
+            const String& str)\
+        {\
+          return str.length();\
+        }\
+        const String::value_type* EMSCRIPTEN_KEEPALIVE GetStringData(\
+            const String& str)\
+        {\
+          return str.data();\
+        }\
+        void EMSCRIPTEN_KEEPALIVE ReleaseRef(ref_counted* ptr)\
+        {\
+          ptr->ReleaseRef();\
+        }\
+      }\
+      void BindingsInitializer_dummy()
+#endif
+
+template<typename ClassType,
+    typename BaseClass = bindings_internal::NoBaseClass,
+    typename std::enable_if<std::is_base_of<ref_counted, ClassType>::value>::type* = nullptr>
+class class_
+{
+public:
+  class_(const char* name)
+  {
+    ClassType* ptr = reinterpret_cast<ClassType*>(0x10000000);
+    int ref_counted_offset =
+        reinterpret_cast<int>(dynamic_cast<ref_counted*>(ptr)) -

[sergei, 2017/03/20 17:07:15]

Could we please use static_cast instead of dynamic_cast here because I find it
very unreliable because I expect that dynamic_cast uses run time info, in
particular it likely reads vtable (maybe a value at some negative offset) which
is absent here.

I would say it's still a hack and so far the offset is always zero, so what do
you think about having of some warning when the offset is not zero to come back
and check that it still works correctly.

BTW, in general I think this code does not always work, e.g. with some virtual
inheritance  but I think it will never our case and I think static_cast will do
its work in this case.

[Wladimir Palant, 2017/03/21 10:10:12]

Done.
I did test this code of course by changing the inheritance structure in such a
way that the offset is no longer zero.

+        reinterpret_cast<int>(ptr);
+    bindings_internal::register_class(name,
+        bindings_internal::TypeInfo<ClassType>(),
+        bindings_internal::TypeInfo<BaseClass>(),
+        ref_counted_offset
+      );
+  }
+
+  template<typename FieldType>
+  const class_& property(const char* name,
+      FieldType (ClassType::*getter)() const,
+      void (ClassType::*setter)(FieldType) = nullptr) const
+  {
+    bindings_internal::register_property(
+        bindings_internal::TypeInfo<ClassType>(), name, getter, setter);
+    return *this;
+  }
+
+  const class_& class_property(const char* name,
+      const char* jsValue) const
+  {
+    bindings_internal::register_property(
+        bindings_internal::TypeInfo<ClassType>(), name,
+        bindings_internal::FunctionInfo(), bindings_internal::FunctionInfo(),
+        jsValue);
+    return *this;
+  }
+
+  template<typename ReturnType, typename... Args>
+  const class_& function(const char* name, ReturnType (ClassType::*method)(Args...)) const
+  {
+    bindings_internal::register_method(
+        bindings_internal::TypeInfo<ClassType>(), name, method);
+    return *this;
+  }
+
+  template<typename ReturnType, typename... Args>
+  const class_& function(const char* name, ReturnType (ClassType::*method)(Args...) const) const
+  {
+    bindings_internal::register_method(
+        bindings_internal::TypeInfo<ClassType>(), name, method);
+    return *this;
+  }
+
+  template<typename ReturnType, typename... Args>
+  const class_& class_function(const char* name, ReturnType (*method)(Args...)) const
+  {
+    bindings_internal::register_method(
+        bindings_internal::TypeInfo<ClassType>(), name, method);
+    return *this;
+  }
+
+  const class_& class_initializer(void (*function)()) const
+  {
+    bindings_internal::register_initializer(
+        bindings_internal::TypeInfo<ClassType>(), function);
+    return *this;
+  }
+
+  template<typename ReturnType,
+      typename std::enable_if<std::is_convertible<ReturnType, int32_t>::value>::type* = nullptr>
+  const class_& subclass_differentiator(ReturnType ClassType::* member,
+      std::initializer_list<std::pair<ReturnType, const char*>> list) const
+  {
+    ClassType* instance = nullptr;
+    size_t offset = (char*)&(instance->*member) - (char*)instance;
+
+    std::vector<std::pair<int, std::string>> mapping;
+    for (const auto& item : list)
+      mapping.emplace_back(item.first, item.second);
+
+    bindings_internal::register_differentiator(
+        bindings_internal::TypeInfo<ClassType>(), offset, mapping);
+    return *this;
+  }
+};