v8/samples/shell.cc

// Copyright 2012 the V8 project authors. All rights reserved.
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#include <v8.h>
#include <assert.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#ifdef COMPRESS_STARTUP_DATA_BZ2
#error Using compressed startup data is not supported for this sample
#endif

/**
 * This sample program shows how to implement a simple javascript shell
 * based on V8.  This includes initializing V8 with command line options,
 * creating global functions, compiling and executing strings.
 *
 * For a more sophisticated shell, consider using the debug shell D8.
 */


v8::Persistent<v8::Context> CreateShellContext();
void RunShell(v8::Handle<v8::Context> context);
int RunMain(int argc, char* argv[]);
bool ExecuteString(v8::Handle<v8::String> source,
                   v8::Handle<v8::Value> name,
                   bool print_result,
                   bool report_exceptions);
v8::Handle<v8::Value> Print(const v8::Arguments& args);
v8::Handle<v8::Value> Read(const v8::Arguments& args);
v8::Handle<v8::Value> Load(const v8::Arguments& args);
v8::Handle<v8::Value> Quit(const v8::Arguments& args);
v8::Handle<v8::Value> Version(const v8::Arguments& args);
v8::Handle<v8::String> ReadFile(const char* name);
void ReportException(v8::TryCatch* handler);


static bool run_shell;


int main(int argc, char* argv[]) {
  v8::V8::SetFlagsFromCommandLine(&argc, argv, true);
  run_shell = (argc == 1);
  int result;
  {
    v8::HandleScope handle_scope;
    v8::Persistent<v8::Context> context = CreateShellContext();
    if (context.IsEmpty()) {
      printf("Error creating context\n");
      return 1;
    }
    context->Enter();
    result = RunMain(argc, argv);
    if (run_shell) RunShell(context);
    context->Exit();
    context.Dispose();
  }
  v8::V8::Dispose();
  return result;
}


// Extracts a C string from a V8 Utf8Value.
const char* ToCString(const v8::String::Utf8Value& value) {
  return *value ? *value : "<string conversion failed>";
}


// Creates a new execution environment containing the built-in
// functions.
v8::Persistent<v8::Context> CreateShellContext() {
  // Create a template for the global object.
  v8::Handle<v8::ObjectTemplate> global = v8::ObjectTemplate::New();
  // Bind the global 'print' function to the C++ Print callback.
  global->Set(v8::String::New("print"), v8::FunctionTemplate::New(Print));
  // Bind the global 'read' function to the C++ Read callback.
  global->Set(v8::String::New("read"), v8::FunctionTemplate::New(Read));
  // Bind the global 'load' function to the C++ Load callback.
  global->Set(v8::String::New("load"), v8::FunctionTemplate::New(Load));
  // Bind the 'quit' function
  global->Set(v8::String::New("quit"), v8::FunctionTemplate::New(Quit));
  // Bind the 'version' function
  global->Set(v8::String::New("version"), v8::FunctionTemplate::New(Version));

  return v8::Context::New(NULL, global);
}


// The callback that is invoked by v8 whenever the JavaScript 'print'
// function is called.  Prints its arguments on stdout separated by
// spaces and ending with a newline.
v8::Handle<v8::Value> Print(const v8::Arguments& args) {
  bool first = true;
  for (int i = 0; i < args.Length(); i++) {
    v8::HandleScope handle_scope;
    if (first) {
      first = false;
    } else {
      printf(" ");
    }
    v8::String::Utf8Value str(args[i]);
    const char* cstr = ToCString(str);
    printf("%s", cstr);
  }
  printf("\n");
  fflush(stdout);
  return v8::Undefined();
}


// The callback that is invoked by v8 whenever the JavaScript 'read'
// function is called.  This function loads the content of the file named in
// the argument into a JavaScript string.
v8::Handle<v8::Value> Read(const v8::Arguments& args) {
  if (args.Length() != 1) {
    return v8::ThrowException(v8::String::New("Bad parameters"));
  }
  v8::String::Utf8Value file(args[0]);
  if (*file == NULL) {
    return v8::ThrowException(v8::String::New("Error loading file"));
  }
  v8::Handle<v8::String> source = ReadFile(*file);
  if (source.IsEmpty()) {
    return v8::ThrowException(v8::String::New("Error loading file"));
  }
  return source;
}


// The callback that is invoked by v8 whenever the JavaScript 'load'
// function is called.  Loads, compiles and executes its argument
// JavaScript file.
v8::Handle<v8::Value> Load(const v8::Arguments& args) {
  for (int i = 0; i < args.Length(); i++) {
    v8::HandleScope handle_scope;
    v8::String::Utf8Value file(args[i]);
    if (*file == NULL) {
      return v8::ThrowException(v8::String::New("Error loading file"));
    }
    v8::Handle<v8::String> source = ReadFile(*file);
    if (source.IsEmpty()) {
      return v8::ThrowException(v8::String::New("Error loading file"));
    }
    if (!ExecuteString(source, v8::String::New(*file), false, false)) {
      return v8::ThrowException(v8::String::New("Error executing file"));
    }
  }
  return v8::Undefined();
}


// The callback that is invoked by v8 whenever the JavaScript 'quit'
// function is called.  Quits.
v8::Handle<v8::Value> Quit(const v8::Arguments& args) {
  // If not arguments are given args[0] will yield undefined which
  // converts to the integer value 0.
  int exit_code = args[0]->Int32Value();
  fflush(stdout);
  fflush(stderr);
  exit(exit_code);
  return v8::Undefined();
}


v8::Handle<v8::Value> Version(const v8::Arguments& args) {
  return v8::String::New(v8::V8::GetVersion());
}


// Reads a file into a v8 string.
v8::Handle<v8::String> ReadFile(const char* name) {
  FILE* file = fopen(name, "rb");
  if (file == NULL) return v8::Handle<v8::String>();

  fseek(file, 0, SEEK_END);
  int size = ftell(file);
  rewind(file);

  char* chars = new char[size + 1];
  chars[size] = '\0';
  for (int i = 0; i < size;) {
    int read = static_cast<int>(fread(&chars[i], 1, size - i, file));
    i += read;
  }
  fclose(file);
  v8::Handle<v8::String> result = v8::String::New(chars, size);
  delete[] chars;
  return result;
}


// Process remaining command line arguments and execute files
int RunMain(int argc, char* argv[]) {
  for (int i = 1; i < argc; i++) {
    const char* str = argv[i];
    if (strcmp(str, "--shell") == 0) {
      run_shell = true;
    } else if (strcmp(str, "-f") == 0) {
      // Ignore any -f flags for compatibility with the other stand-
      // alone JavaScript engines.
      continue;
    } else if (strncmp(str, "--", 2) == 0) {
      printf("Warning: unknown flag %s.\nTry --help for options\n", str);
    } else if (strcmp(str, "-e") == 0 && i + 1 < argc) {
      // Execute argument given to -e option directly.
      v8::Handle<v8::String> file_name = v8::String::New("unnamed");
      v8::Handle<v8::String> source = v8::String::New(argv[++i]);
      if (!ExecuteString(source, file_name, false, true)) return 1;
    } else {
      // Use all other arguments as names of files to load and run.
      v8::Handle<v8::String> file_name = v8::String::New(str);
      v8::Handle<v8::String> source = ReadFile(str);
      if (source.IsEmpty()) {
        printf("Error reading '%s'\n", str);
        continue;
      }
      if (!ExecuteString(source, file_name, false, true)) return 1;
    }
  }
  return 0;
}


// The read-eval-execute loop of the shell.
void RunShell(v8::Handle<v8::Context> context) {
  printf("V8 version %s [sample shell]\n", v8::V8::GetVersion());
  static const int kBufferSize = 256;
  // Enter the execution environment before evaluating any code.
  v8::Context::Scope context_scope(context);
  v8::Local<v8::String> name(v8::String::New("(shell)"));
  while (true) {
    char buffer[kBufferSize];
    printf("> ");
    char* str = fgets(buffer, kBufferSize, stdin);
    if (str == NULL) break;
    v8::HandleScope handle_scope;
    ExecuteString(v8::String::New(str), name, true, true);
  }
  printf("\n");
}


// Executes a string within the current v8 context.
bool ExecuteString(v8::Handle<v8::String> source,
                   v8::Handle<v8::Value> name,
                   bool print_result,
                   bool report_exceptions) {
  v8::HandleScope handle_scope;
  v8::TryCatch try_catch;
  v8::Handle<v8::Script> script = v8::Script::Compile(source, name);
  if (script.IsEmpty()) {
    // Print errors that happened during compilation.
    if (report_exceptions)
      ReportException(&try_catch);
    return false;
  } else {
    v8::Handle<v8::Value> result = script->Run();
    if (result.IsEmpty()) {
      assert(try_catch.HasCaught());
      // Print errors that happened during execution.
      if (report_exceptions)
        ReportException(&try_catch);
      return false;
    } else {
      assert(!try_catch.HasCaught());
      if (print_result && !result->IsUndefined()) {
        // If all went well and the result wasn't undefined then print
        // the returned value.
        v8::String::Utf8Value str(result);
        const char* cstr = ToCString(str);
        printf("%s\n", cstr);
      }
      return true;
    }
  }
}


void ReportException(v8::TryCatch* try_catch) {
  v8::HandleScope handle_scope;
  v8::String::Utf8Value exception(try_catch->Exception());
  const char* exception_string = ToCString(exception);
  v8::Handle<v8::Message> message = try_catch->Message();
  if (message.IsEmpty()) {
    // V8 didn't provide any extra information about this error; just
    // print the exception.
    printf("%s\n", exception_string);
  } else {
    // Print (filename):(line number): (message).
    v8::String::Utf8Value filename(message->GetScriptResourceName());
    const char* filename_string = ToCString(filename);
    int linenum = message->GetLineNumber();
    printf("%s:%i: %s\n", filename_string, linenum, exception_string);
    // Print line of source code.
    v8::String::Utf8Value sourceline(message->GetSourceLine());
    const char* sourceline_string = ToCString(sourceline);
    printf("%s\n", sourceline_string);
    // Print wavy underline (GetUnderline is deprecated).
    int start = message->GetStartColumn();
    for (int i = 0; i < start; i++) {
      printf(" ");
    }
    int end = message->GetEndColumn();
    for (int i = start; i < end; i++) {
      printf("^");
    }
    printf("\n");
    v8::String::Utf8Value stack_trace(try_catch->StackTrace());
    if (stack_trace.length() > 0) {
      const char* stack_trace_string = ToCString(stack_trace);
      printf("%s\n", stack_trace_string);
    }
  }
}