execl 使 C++ node.js-addon 崩溃

Question

正常的 C++ execl 工作正常（用 g++ ok.cc -o ok.elf 编译）

#include <unistd.h>
int main(){
  execl("/usr/bin/python", "/usr/bin/python", nullptr);
}

但是当作为 node.js C++ 插件工作时崩溃

#include <node.h>
#include <unistd.h>

namespace bug{
  void wtf(const v8::FunctionCallbackInfo<v8::Value>& args){
    execl("/usr/bin/python", "/usr/bin/python", nullptr);
  }

  void init(v8::Local<v8::Object> exports){
    NODE_SET_METHOD(exports, "wtf", bug::wtf);
  }
  NODE_MODULE(NODE_GYP_MODULE_NAME, init)
}

node.js v8.9.1
节点 gyp v3.6.2
gcc 版本 6.3.0 20170406 (Ubuntu 6.3.0-12ubuntu2)

Answer 1

节点不支持所有 posix 系统调用。

查看此线程

崩溃是预料之中的，因为您正在使用您无法使用的东西。正如上面讨论的那样，您需要创建自己的 exec

index.cc

#include <nan.h>
#include <fcntl.h>
#include <unistd.h>

int doNotCloseStreamsOnExit(int desc) {
  int flags = fcntl(desc, F_GETFD, 0);
  if (flags < 0) return flags;
  flags &= ~FD_CLOEXEC; //clear FD_CLOEXEC bit
  return fcntl(desc, F_SETFD, flags);
}

void copyArray(char* dest[], unsigned int offset, v8::Local<v8::Array> src) {
  unsigned int length = src->Length();
  for (unsigned int i = 0; i < length; i++) {
    v8::String::Utf8Value arrayElem(Nan::Get(src, i).ToLocalChecked()->ToString());
    std::string arrayElemStr (*arrayElem);
    char* tmp = new char[arrayElemStr.length() +1];
    strcpy(tmp, arrayElemStr.c_str());
    dest[i + offset] = tmp;
  }
}

void setEnv(v8::Local<v8::Array> src) {
  unsigned int length = src->Length();
  v8::Local<v8::String> keyProp = Nan::New<v8::String>("key").ToLocalChecked();
  v8::Local<v8::String> valueProp = Nan::New<v8::String>("value").ToLocalChecked();
  for (unsigned int i = 0; i < length; i++) {
    v8::Local<v8::Object> obj = Nan::Get(src, i).ToLocalChecked()->ToObject();

    v8::String::Utf8Value objKey(Nan::Get(obj, keyProp).ToLocalChecked()->ToString());
    v8::String::Utf8Value objValue(Nan::Get(obj, valueProp).ToLocalChecked()->ToString());

    std::string objKeyStr (*objKey);
    char *key = const_cast<char*> ( objKeyStr.c_str() );
    std::string objValueStr (*objValue);
    char *value = const_cast<char*> ( objValueStr.c_str() );

    setenv(key, value, 1);
  }
}

void Method(const Nan::FunctionCallbackInfo<v8::Value>& info) {
  if (info.Length() < 3) {
    return;
  }
  if (!info[0]->IsString()) {
    return;
  }

  // get command
  v8::String::Utf8Value val(info[0]->ToString());
  std::string str (*val);
  char *command = const_cast<char*> ( str.c_str() );

  // set env on the current process
  v8::Local<v8::Array> envArr = v8::Local<v8::Array>::Cast(info[1]);
  setEnv(envArr);

  // build args: command, ...args, NULL
  v8::Local<v8::Array> argsArr = v8::Local<v8::Array>::Cast(info[2]);
  char* args[argsArr->Length() + 2];
  args[0] = command;
  copyArray(args, 1, argsArr);
  args[argsArr->Length() + 1] = NULL;

  // fix stream flags
  doNotCloseStreamsOnExit(0); //stdin
  doNotCloseStreamsOnExit(1); //stdout
  doNotCloseStreamsOnExit(2); //stderr

  execvp(command, args);
}

void Init(v8::Local<v8::Object> exports) {
  exports->Set(Nan::New("exec").ToLocalChecked(),
               Nan::New<v8::FunctionTemplate>(Method)->GetFunction());
}

NODE_MODULE(exec, Init)

index.js

'use strict';

var addon = require('bindings')('addon');
var path = require('path');
var fs = require('fs');

module.exports = function(cmd, env, args) {
  if (!cmd) {
    throw new Error('Command is required');
  }

  var envArr = Object.keys(env || {}).map(key => {
    return {
      key,
      value: env[key],
    };
  });

  addon.exec(cmd, envArr, args || []);
};

PS：从 https://github.com/OrKoN/native-exec 发布的代码，以防 link 将来失效

还有一件事你不应该尝试做的是执行一些需要获取 TTY 的东西，在那种情况下你会增加很多复杂性。所以运行 python 需要控制你的 TTY。

execl 使 C++ node.js-addon 崩溃

execl crashes C++ node.js-addon

linux

crash

node.js-addon

unistd.h