How to use

head

function

in

RequestAPI

fs.createReadStream(process.argv[2])
 .pipe(split())
 .pipe(new LimitedParallelStream(2, (url, enc, push, done) => {
  if(!url) return done();
  request.head(url, (err, response) => {
   push(url + ' is ' + (err ? 'down' : 'up') + '\n');
   done();
  });
 }))
 .pipe(fs.createWriteStream('results.txt'))
 .on('finish', () => console.log('All urls were checked'))
;

// function to preforms the data transformation
function transformer(url, enc, done) {
 if(!url) {
  return done();
 }

 request.head(url, (err, response) => {
  done(null, url + ' is ' + (err ? 'down' : 'up') + '\n');
 });
}

var download = function(uri, filename, callback){
 request.head(uri, function(err, res, body){
  console.log(uri);
  request(uri).pipe(fs.createWriteStream(filename)).on('close', callback);
 });
}

request.head(doc.origin, function (err, res) {
    if (err) {
     return reject(err)
    }

    doc.attachments.push({
     key: hash.hashUrl(doc.origin),
     stream: request.get(doc.origin),
     contentType: res.headers['content-type'],
     contentLength: res.headers['content-length'],
     origin: doc.origin
    })

    resolve(doc)
   })

function saveImg($,news_title){
    $('.article-content img').each(function(index,item){
      var title=$(this).parent().next().text().trim();  // 获取图片标题
      var img_filname=title+'.jpg';

      var img_src="http://www.ss.pku.edu.cn"+$(this).attr('src');

      request.head(img_src,function(err,res,body){        // 用head请求只是为了验证路径是否存在
          if(err){
            console.log(err);
            return;
          }
      })
      request(img_src).pipe(fs.createWriteStream('./image/'+news_title+'-'+img_filname)); // 以流的形式保存图片到本地
      

    });
}

function _downloadFile(url, pathName) {
  return new Promise((resolve, reject) => {
    request.head(url, function(){
      request(url).pipe(fs.createWriteStream(pathName))
        .on('close', () => resolve(pathName))
        .on('error', error =>  reject(error))
    });
  })
}

//Downloads posts from reddit
async function download(url, postTitle, nsfw) {
  //Check length of post title
  if (postTitle.length > 250)
    return;
  //Format the file name so that it can be stored in filesystem
  let filename = await formatFileName(postTitle, url, nsfw);
  request.head(url, function(err, res, body) {
    //If the file already exists, it means that it was downloaded before, thus it will not download again.
    if (!fs.existsSync(filename)) {
      var filetoPipe = fs.createWriteStream(filename);
      filetoPipe.on('open', function() {
        request(url).pipe(filetoPipe).on('close', function() {
          filetoPipe.end();
          console.log("Downloaded: " + postTitle);
        });
      });
    }
  });
}

const getHead = url => bluebird.promisify(request.head)(url)

function downloadFile(uri, filename) {
  spinner.start()

  request.head(uri, function (err, res, body) {
    request(uri).pipe(fs.createWriteStream(filename)).on("close", function () {
      var fileSize = formatBytes(res.headers["content-length"]);
      console.log("\nsize: " + fileSize);

      spinner.succeed("Download completed");
    });
  });
}

// function to preforms the data transformation
function transformer(url, enc, push, done) {
 if(!url) {
  return done();
 }

 request.head(url, (err, response) => {
  push(url + ' is ' + (err ? 'down' : 'up') + '\n');
  done();
 });
}

function downloadThumbnail(url, _path, cb) {
  request.head(url, function(error, response, body) {
    if (error) {
      return cb(error);
    }
    request(url).pipe(fs.createWriteStream(_path)).on('close', () => {
      return cb(null);
    });
  });
}

fs.createReadStream(process.argv[2])
 .pipe(split())
 .pipe(throughParallel.obj({concurrency: 2}, function (url, enc, done) {
  if(!url) return done();
  request.head(url, (err, response) => {
   this.push(url + ' is ' + (err ? 'down' : 'up') + '\n');
   done();
  });
 }))
 .pipe(fs.createWriteStream('results.txt'))
 .on('finish', () => console.log('All urls were checked'))
;

fs.createReadStream(process.argv[2])         //[1]
 .pipe(split())                             //[2]
 .pipe(new ParallelStream((url, enc, done, push) => {     //[3]
  if(!url) return done();
  request.head(url, (err, response) => {
   push(url + ' is ' + (err ? 'down' : 'up') + '\n');
   done();
  });
 }))
 .pipe(fs.createWriteStream('results.txt'))   //[4]
 .on('finish', () => console.log('All urls were checked'))
;

// function to preforms the data transformation
function transformer(url, enc, push, done) {
 if(!url) {
  return done();
 }

 request.head(url, (err, response) => {
  push(url + ' is ' + (err ? 'down' : 'up') + '\n');
  done();
 });
}

fs.createReadStream(process.argv[2])
 .pipe(split())
 .pipe(
  new ParallelStream((url, enc, push, done) => {
   if (!url) return done && done();
   request.head(url, (err, response) => {
    push(`${url} is ${err ? "down" : "up"} \n`);
    done && done();
   });
  })
 )
 .pipe(fs.createWriteStream("results.txt"))
 .on("finish", () => console.log("All urls were checked"));