JavaScript file to byte[] - javascript

Is it possible to read a file in from a path in JavaScript and create a byte[] of that file?

Yes, you can — in Firefox, anyway. Other browsers may or may not choose to allow it in the future.
Make a file upload field for the user to pick the file, and read it through the input.files list. eg. document.getElementById('myuploadfield').files[0].getAsBinary(). This puts each byte in a single character of a JavaScript String, which is about as close to a byte[] as you're going to get.
This is quite a specialized interface and probably Not The Right Thing — heed the other replies, because it's very possible you are trying to do something in a inappropriate way. Difficult to tell without context.

There are two forms of JavaScript: client-side and server-side. In client-side JavaScript it is not possible, while in server-side JavaScript, it is possible. So it depends on whether you are using client-side or server-side JavaScript.
That said, client-side JavaScript is much more common and if you were using server-side JavaScript, you would probably know the answer to your question. So I'm going to go out on a limb and say that no, it is not possible to read in from a path in JavaScript and create a byte[] from that file.
(Also, it's unclear what you mean by a byte[]; that's not a common notation when using JavaScript. Are you sure you aren't talking about Java? Java is completely different from JavaScript: in Java byte[] is a more common notation.)

No. JavaScript is purposely designed to have very minimal file IO (think cookies) because allowing it to access arbitrary files (local and remote) would be a massive security risk.

You guys seem to have completely forgotten mobile platforms and javascript designed to run with no-security flags set what-so-ever. I access my files just fine in my javascript code, which runs on my iPhone. You just cant access the users filesystem, only your own filesystem which is basically a folder isolated from the rest of the system.
Sp his question was perfectly valid.
Also - you should look up Javascript blobs (binary large objects) and typed arrays. You can allocate "normal" byte, word and longword arrays in JS - but people rarely use them.

File I/O in Javascript is considered a serious security risk:
http://forums.devshed.com/javascript-development-115/file-i-o-with-javascript-10376.html

Related

How to load a file using javascript without revealing the source? [duplicate]

Is there any way to hide the CSS and JavaScript file from the client-side user and still embed it in the webpage shown to the user?
No. CSS and Javascript must be parsable and readable by the browser, therefore a human can get access to the same data.
It is possible to obscure/compress/minify the javascript, but all that generally does is remove whitespace and rename/shorten variable names. The script is still functional and anyone interesting in how it really works can still figure it out (perhaps by using some tools to reformat it) with a little more time.
The typical reasons for minification is to reduce the download size of your scripts (speeding up site performance), but it also has the side effect of making the code harder to read by a human. One should not count on minification providing any real protection as the code can be reformatted and still understood by anyone determined to do so.
If you need to keep something private, keep the logic on the server and don't put it in the client. Clients can access server-based functionality via ajax if need be.
I've never heard of anyone thinking there was a business reason to protect CSS. It's layout/presentation formatting.
You can always minify the JavaScript file to make it harder for someone to reads it or to modify it.
For example : http://www.minifyjavascript.com/
You can also do the same thing with CSS.
http://developer.yahoo.com/yui/compressor/
(it can do both JavaScript and CSS)
There are other sites that offers a way to minify the files, but there is no way to hide it completely from the client-side.
Minification and base64 encoding. Here's SO questions about base64 encoding. Be mindful that all you're doing is making the process of looking at your code miserable and no more.
Online encoder/decoder.

Freeswitch, fileaccess with javascript?

I have a FreeSwtich solution running on Linux with quite a lot of configuration scripts written in javascript.
The problem is that we need to write and read files; which javascript normally doesn't support.
I tried the SpiderMonkey File Object but it doesn't work and has been marked as obsolete..
The setup is a bit special; there is really only one dial plan with one javascript handling the call initially. Depending on a number of parameters the call is then 'handed over' to one of 20 or so Javascripts dynamically included. It is actually a data base lookup that returns the name of the script to run.
So looking for other options if there are any? Rewriting the entire thing in LUA is an option of course but to keep the current structure that would mean rewriting a lot of javascripts. Unless someone can think of a magic way to call LUA script from javascript?
There's a bunch of various programming languages supported by FreeSWITCH: Perl, Python, Lua, Ruby. Take whatever suits you better :)
You can provide those files via an HTTP interface and fetch them from your Javascript scripts.
You can also fetch them as BLOB objects from your SQL database.
But this whole setup seems like a lot of CPU work for every call, so I wonder if performance is not already an issue.

Any way to hide CSS and JavaScript file from the client-side user?

Is there any way to hide the CSS and JavaScript file from the client-side user and still embed it in the webpage shown to the user?
No. CSS and Javascript must be parsable and readable by the browser, therefore a human can get access to the same data.
It is possible to obscure/compress/minify the javascript, but all that generally does is remove whitespace and rename/shorten variable names. The script is still functional and anyone interesting in how it really works can still figure it out (perhaps by using some tools to reformat it) with a little more time.
The typical reasons for minification is to reduce the download size of your scripts (speeding up site performance), but it also has the side effect of making the code harder to read by a human. One should not count on minification providing any real protection as the code can be reformatted and still understood by anyone determined to do so.
If you need to keep something private, keep the logic on the server and don't put it in the client. Clients can access server-based functionality via ajax if need be.
I've never heard of anyone thinking there was a business reason to protect CSS. It's layout/presentation formatting.
You can always minify the JavaScript file to make it harder for someone to reads it or to modify it.
For example : http://www.minifyjavascript.com/
You can also do the same thing with CSS.
http://developer.yahoo.com/yui/compressor/
(it can do both JavaScript and CSS)
There are other sites that offers a way to minify the files, but there is no way to hide it completely from the client-side.
Minification and base64 encoding. Here's SO questions about base64 encoding. Be mindful that all you're doing is making the process of looking at your code miserable and no more.
Online encoder/decoder.

Is it possible to compute a file's SHA1 ID using Javascript?

If this were possible to do prior to posting a form, it may save me having to upload the file to my server...
To do that you would have to load the file's binary information into JavaScript. Which is not possible.
But here's an implementation of SHA1 in JavaScript.
Actually you can read the contents of a client-side file now, as long as it's chosen in a file upload field and you are using Firefox. See the input.files array. You can then indeed hash it, although it might be rather slow.
See How would I get a Hash value of a users file with Javascript or Flash? for an example and a compact SHA-1 implementation.
It is possible to use SHA1, though performance isn't going to be the best...
For anything over a few hundred KB's you will have to run some benchmarks and determine if indeed its a viable solution.
See this link for a good implementation (passpack and quite a few OS projects use it)
Edit:
As other have already replied, actually getting the file contents may be a whole different matter - so unless you use something like Google Gears or Adobe AIR it should be virtually impossible.
One can read their local file using the HTML5 File interface: https://developer.mozilla.org/en-US/docs/Web/API/File
And then you can use a library for like Crypto.js https://code.google.com/p/crypto-js/ to finish the hash over the read text.
No, you can't access a file from a local computer using JavaScript .
You're going to have to upload it first to the server, then checking the checksum of the file.
Not natively, no, and this is a bad idea anyway. Every byte in the file will have to be loaded into memory by Javascript, and you'd need a way to get it there.
If you must do this and you've got a way to put the file's binary information into your script, then there's plenty of third-party scripts you can use. Here's one, for example.
You could do this with a Java applet. I've never used any of them, but there are quite a few Java upload applets out there. The hash algorithm itself is available with Java and can be accessed through java.security.MessageDigest. If the client doesn't have the Java plug-in available you could just fail back to a regular upload and hash on the server.
A side note: depending upon why you're hashing the file you'll probably want to re-hash it on the server after the upload rather than trust the client.

Is it possible to write to a file (on a disk) using JavaScript?

I am a novice-intermediate programmer taking a stab at AJAX. While reading up on JavaScript I found it curious that most of the examples I've been drawing on use PHP for such an operation. I know many of you may argue that 'I'm doing it wrong' or 'JavaScript is a client-side language' etc. but the question stands. . .can you write a file in only JavaScript?
Yes, of course you can. It just depends on what API objects your javascript engine makes available to you.
However, odds are the javascript engine you're thinking about does not provide this capability. Definitely none of the major web browsers will allow it.
You can write cookies with Javascript, on newer browsers you also have an SQLite database to store client side data. You cannot store data in an arbitrary location on the disk though.
You can use something like Google Gears to produce JS applications which are capable of storing data in a local cache or database. You can't read or write arbitrary areas of the disk though. (This was written in 2009 - Google Gears is now deprecated)
These days, you should be looking at the local storage capabilities provided by HTML5
No. You could use JavaScript to create an AJAX request to a server-side processing script, but allowing JS to directly write to disk - either client-side or server-side - would be a massive, nasty, glaring, unforgivable browser security hole.
The short answer is no; you cannot by default write a file to the local disk, by using plain JavaScript in a browser. You'll need a helper to do that. For example, TiddlyWiki is a wiki engine that is just a single, static HTML file, but it can write itself to disk with the help of a Java applet (Tiddly Saver).
You can in Windows Scripting Host.
Next version of chrome (v52) made this possible with fetch api + service worker + streams, you can enable streams now with a flag...
you can go to the StreamSaver.js to see some examples of how to use it.
You can do something like this:
const writeStream = fs.createWriteStream('filename.txt')
const encoder = new TextEncoder
let data = 'a'.repeat(1024)
let uint8array = encoder.encode(data + "\n\n")
writeStream.write(uint8array)
writeStream.close()
Or just go ahead and look at the demos: https://jimmywarting.github.io/StreamSaver.js/example.html
Nope, Javascript is not allowed to access the filesystem at all, its a security restriction in the browser. The only way you can really do it is with ActiveX, but then your limiting yourself to using IE.
Edit:
AS the above post states, it could be possible if your engine allowed it, however I don't know of one browser engine (which is what I asusme you are writing it for) that will allow you to.
If you just need to let user download a file (.txt, .csv, images and others) via browser download dialog, you can use data URIs with <a href=... download=.../> tag.
For example (for text file):
Click to download
You can also set the attribute href and download using javascript, and use element.click() to trigger the download.
However, this method cannot write a file without user confirming the file download dialog.

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