Getting started with V8 Script Engine

// Copyright 2012 the V8 project authors. All rights reserved.// Redistribution and use in source and binary forms, with or without// modification, are permitted provided that the following conditions are// met:////     * Redistributions of source code must retain the above copyright//       notice, this list of conditions and the following disclaimer.//     * Redistributions in binary form must reproduce the above//       copyright notice, this list of conditions and the following//       disclaimer in the documentation and/or other materials provided//       with the distribution.//     * Neither the name of Google Inc. nor the names of its//       contributors may be used to endorse or promote products derived//       from this software without specific prior written permission.//// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.#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' functionglobal->Set(v8::String::New("quit"), v8::FunctionTemplate::New(Quit));// Bind the 'version' functionglobal->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 filesint 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);}}}