In Node.js, given a URL, how do I check whether it

问题:

My current method is this:

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-mime says it's application/octet-stream. Why?

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!)

I want to know the best way to determine if a file is an image, with 0 margin of error.

Edit: I just realized that node-mime isn't "magic". It just checks for the extension :( ...

Edit2: I found this: https://github.com/SaltwaterC/mime-magic

回答1:

Just read the first bytes of the stream, and check it for the so called "magic number".

Magic numbers are the first bits of a file which uniquely identify the type of file.

For example:
-Every JPEG file begins with ff d8 (hex).
-Every png file begins with a 89 50 4e 47.
-There is a full table of magic numbers here

This way even if you have a file without extension you can still detect its type.
Hope this helps.

回答2:

This code shows a working solution for the magic numbers approach (summary of the existing answers and information on https://github.com/request/request).

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3:

There are two modules that can help you achieve this:

https://github.com/SaltwaterC/mime-magic

https://github.com/bentomas/node-mime

回答4:

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

回答5:

i developped this code and i test it and it work for me you can use it

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')
         }
}
})