javascript 在 Node.js 中，给定一个 URL，如何检查它是否是 jpg/png/gif？
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In Node.js, given a URL, how do I check whether its a jpg/png/gif?
提问by TIMEX
My current method is this:
我目前的方法是这样的：
var request = require('request');
var mime = require('mime');
var fs = require('fs');
var uri = 'http://www.sweetslyrics.com/images/img_gal/25646_christina-perri-213968.jpg';
request({
'method':'GET',
'uri': uri
},function(err, response,body){
var tmp_path = '/tmp/123456';
fs.writeFile(tmp_path, body, function(err) {
console.log(mime.lookup(tmp_path)); //application/octet-stream ?????
});
});
The image is obviously a picture, but node-mimesays it's application/octet-stream. Why?
图片明明是图片，node-mime却说是application/octet-stream。为什么？
Note: - I do not want to rely on the Response Headers content-type, because based on my experience, sometimes those response headers are set incorrectly...and they do not determine the true file type. (that's why I save it to a file, and then have node-mime determine it for me!)
注意： - 我不想依赖 Response Headers 内容类型，因为根据我的经验，有时这些响应头设置不正确......并且它们不能确定真实的文件类型。（这就是为什么我将它保存到一个文件中，然后让 node-mime 为我确定它的原因！）
I want to know the best way to determine if a file is an image, with 0 margin of error.
我想知道确定文件是否为图像的最佳方法，误差为 0。
Edit: I just realized that node-mime isn't "magic". It just checks for the extension :( ...
编辑：我刚刚意识到 node-mime 不是“魔法”。它只是检查扩展名:( ...
Edit2: I found this: https://github.com/SaltwaterC/mime-magic
Edit2：我发现了这个：https: //github.com/SaltwaterC/mime-magic
回答by rcode
Just read the first bytes of the stream, and check it for the so called "magic number".
只需读取流的第一个字节，并检查所谓的“幻数”。
Magic numbers are the first bits of a file which uniquely identify the type of file.
幻数是文件的第一位，用于唯一标识文件类型。
For example:
-Every JPEG file begins with ff d8(hex).
-Every png file begins with a 89 50 4e 47.
-There is a comprehensive table of magic numbers here
例如：-
每个 JPEG 文件都以ff d8(hex)开头。
- 每个 png 文件都以89 50 4e 47.
-there是幻数的综合表在这里
This way even if you have a file without extension you can still detect its type.
Hope this helps.
这样即使您有一个没有扩展名的文件，您仍然可以检测到它的类型。
希望这可以帮助。
回答by simonch
This code shows a working solution for the magic numbers approach (summary of the existing answers and information on https://github.com/request/request).
此代码显示了幻数方法的有效解决方案（https://github.com/request/request上现有答案和信息的摘要）。
var request = require('request');
var url = "http://www.somedomain.com/somepicture.jpg";
var magic = {
jpg: 'ffd8ffe0',
png: '89504e47',
gif: '47494638'
};
var options = {
method: 'GET',
url: url,
encoding: null // keeps the body as buffer
};
request(options, function (err, response, body) {
if(!err && response.statusCode == 200){
var magigNumberInBody = body.toString('hex',0,4);
if (magigNumberInBody == magic.jpg ||
magigNumberInBody == magic.png ||
magigNumberInBody == magic.gif) {
// do something
}
}
});
回答by alessioalex
There are two modules that can help you achieve this:
有两个模块可以帮助您实现这一目标：
https://github.com/SaltwaterC/mime-magic
https://github.com/SaltwaterC/mime-magic
回答by Sue Spence
In the intervening time since this question was first asked, mime-magic has become unsupported and its author recommends the use of mmmagic. I don't know what happened to node-mime, the link above is a 404. I found the following article which discusses the topic as well: https://nodejsmodules.org/tags/mime
自首次提出此问题以来的中间时间， mime-magic 已不受支持，其作者建议使用mmmagic。我不知道 node-mime 发生了什么，上面的链接是 404。我发现以下文章也讨论了该主题：https: //nodejsmodules.org/tags/mime
回答by bahri noredine
i developped this code and i test it and it work for me you can use it
我开发了这段代码并测试了它，它对我有用，你可以使用它
var express = require('express')
var app = express()
var http = require('http').Server(app).listen(80)
var upload = require('express-fileupload')
app.use(upload())
app.get("/",(req,res)=>{
res.sendFile(__dirname+"/file.html")
})
app.post('/',(req,res)=>{
var options = {
method: 'GET',
url: req.files.filename,
encoding: null
}
if (req.files) {
if (req.files.filename.data.toString('hex',0,4) == '89504e47' || req.files.filename.data.toString('hex',0,4) == 'ffd8ffe0' || req.files.filename.data.toString('hex',0,4) == '47494638' ) {
var file = req.files.filename
filename = file.name
file.mv('./upload/'+filename,(err)=>{
if (err) {
console.log('small err')
} else {
res.send('DONE')
}
})
} else {
console.log('it not an image')
}
}
})
