我正在 Node.js 中创建一个应用程序来下载图像文件。但是,我一直遇到一个问题,如果我的下载速度很慢或者我失去连接,我正在下载的图像将是 truncated。 .如果我的程序抛出一个错误警告我图片没有完成下载,这并没有那么糟糕,但是,它并没有像图片下载成功一样解析。下载后检查响应代码或探测图像时没有收到错误。
这是我用来下载图片的当前代码。
const fs = require('fs-extra');
const request = require('request');
var probe = require('probe-image-size');
var progress = require('request-progress');
var filename = 'C:/Users/User/Desktop/myimage.jpg';
var req = request(createRequestHeaders('www.linktomyimage.com/image.jpg'));
downloadImage(req, filename)
function createRequestHeaders(url) {
var cookie = `userid=${userid}; phash=${phash};`;
return {
'url': url,
'method': 'GET',
'gzip': true,
'headers': {
'Referer': `https://${website}/`,
'Cookie': cookie
}
};
}
function downloadImage(req, filename) {
return new Promise((resolve, reject) => {
var response = null;
var bytes;
var dirname = path.dirname(filename);
if (!fs.existsSync(dirname)) fs.ensureDirSync(dirname);
progress(req, { delay: 0 }).on('progress', function (state) {
updateDownloadSpeed(state.speed);
}).on('end', function () {
if (response.statusCode == 200) {
var input = require('fs').createReadStream(filename);
probe(input).then(result => {
input.destroy();
if (result != null) {
resolve({bytes: bytes, width: result.width,
height: result.height,});
} else {
// The image size probe does not detect if the download was truncated
reject({ 'name': 'ImageMissingOrCorrupt');
}
}).catch((error) => {
reject(error);
});
} else {
// This is never triggered when the download stops and the image is truncated
reject({ 'name': 'StatusCodeError', 'message': response.statusCode });
}
}).on('response', function (resp) {
response = resp;
bytes = response.headers['content-length'];
}).on('error', function (error) {
// This does not detect when an image is truncated either
reject(error);
}).pipe(fs.createWriteStream(filename));
});
}
我问过这个问题的早期版本here但是在实现答案中的建议后,我的下载器仍然存在相同的问题。从那时起,我的下载器的代码也发生了变化。
我如何检测图像何时被 chop 以便我可以指示下载器重新尝试下载它?
编辑 1
看完this我认为我的问题可能与我正在下载的网站有关,该网站要求我使用 gzip,而当服务器停止响应时,客户端无法判断内容是否已真正完成下载。但是,我不确定如何测试这种情况。
编辑2
这是我的下载器成功连接到图像时响应 header 的样子。
cache-control:"public, max-age=31536000"
connection:"close"
content-disposition:"inline; filename=129.jpg"
content-length:"185756"
content-transfer-encoding:"binary"
content-type:"image/jpeg"
date:"Thu, 05 Sep 2019 00:15:11 GMT"
expires:"Fri, 04 Sep 2020 00:15:11 GMT"
server:"Apache"
最佳答案
我建议您尝试检查 writeStream
的 bytesWritten
属性等于您收到的 content-length
header 。
我一直在研究你的代码,我发现请求的 end
事件在 writeStream
关闭之前被触发,所以我认为实际上此时您无法检查此属性。相反,您应该在 writeStream
的 close
事件上验证它。
试试这个示例代码并告诉我们它是怎么回事:
const fs = require('fs-extra');
const request = require('request');
var probe = require('probe-image-size');
var progress = require('request-progress');
var filename = 'C:/Users/User/Desktop/myimage.jpg';
var writeSteam = fs.createWriteStream(filename)
var req = request(createRequestHeaders('www.linktomyimage.com/image.jpg'));
downloadImage(req, filename)
function createRequestHeaders(url) {
var cookie = `userid=${userid}; phash=${phash};`;
return {
'url': url,
'method': 'GET',
'gzip': true,
'headers': {
'Referer': `https://${website}/`,
'Cookie': cookie
}
};
}
function downloadImage(req, filename) {
return new Promise((resolve, reject) => {
var response = null;
var bytes;
var dirname = path.dirname(filename);
if (!fs.existsSync(dirname)) fs.ensureDirSync(dirname);
// NEW CODE
writeSteam.on('close', () => {
if (bytes !== writeSteam.bytesWritten) { // NEW CODE
// Here the write stream is closed, so we can compare the property bytesWritten with the bytes we expected to receive
console.log('The size is not equal! Image is corrupt!')
reject({ 'name': 'ImageCorrupt'})
} else if (response.statusCode === 200) {
var input = require('fs').createReadStream(filename);
probe(input).then(result => {
input.destroy();
if (result != null) {
resolve({bytes: bytes, width: result.width,
height: result.height,});
} else {
// The image size probe does not detect if the download was truncated
reject({ 'name': 'ImageMissingOrCorrupt'});
}
}).catch((error) => {
reject(error);
});
} else {
// This is never triggered when the download stops and the image is truncated
reject({ 'name': 'StatusCodeError', 'message': response.statusCode });
}
})
progress(req, { delay: 0 }).on('progress', function (state) {
updateDownloadSpeed(state.speed);
}).on('end', function () {
console.log('Ended request!!') // NEW CODE
}).on('response', function (resp) {
response = resp;
bytes = response.headers['content-length'];
}).on('error', function (error) {
// This does not detect when an image is truncated either
reject(error);
}).pipe(writeSteam);
});
}
关于javascript - Node JS/Gzip : Image file download ends prematurely with no error,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57735784/