Develop Reference

Workaround for Error 414 when opening file from PHP script

I have a PHP script that's outputting a CSV file and up until now I've been just using a link and passing parameters that are used to determine the output in the GET data. However recently the size of the data increased and now that code gets Error 414 - Request URI too Large. I tried using a hidden form to do it with POST but it just reloaded the page and didn't supply a prompt to download the file and all of the suggestions I've been able to find online about doing it with AJAX suggest using a link with GET data instead. Does anyone know a workaround that will have the browser still let the user easily download the data?
Presently I'm just setting the href attribute of a <a> tag.
$("#exportCSV").attr('href', "myscript.php/?data=" + exportData);
exportData has become too long for GET data but I want to maintain the behavior where if you click on a link that has say a CSV file being outputted the browser provides a download dialog for the user.

Upload/download/save image to a local server from a remote server using an Image URL and PHP?

I am building a Discussion Forum as part of a bigger application I am building, the forum is just 1 section of the Application.
For my TextArea fields when posting a new Topic or a Post Reply, I have decided that nothing is as good as the PageDown Markdown Library. It is the same one that StackOverflow uses on all their sites and it works better than many of it's competitors.
The way the library ships though, I am not happy with the default Insert Image functionality. You hit the button to insert an image and it allows you to enter a URL for an Image and then it inserts the proper MarkDown syntax to show the linked image.
This just won't cut it. I need the functionality that you see on StackOverflow! Very similar anyways.
I need it to show a Dialog when you click the Insert Image button, like it does now, but instead of just an input field for a Image URL, it will have 2 filed options...
Upload image from your computer
Insert an Image URL and it will then DOWNLOAD the image from that URL and insert it into the post just as if you had uploaded it from your computer. This is important to not confuse this step. IT should not simply insert the Image linking it to the original Image URL. Instead it will take that URL and download/upload the Image to the same server that the upload from computer option does and then it will insert the NEW Image URL pointing to the newly uploaded image!
Based on some simple HTML like below for a Dialog window with a filed for my Upload from Computer functionality, which I already have working. I need to come up with some JavaScript and PHP that will download/save a remote image to my upload folder on my server when a button is clicked using only the URL that will be inside the URL text input field.
So it will need to do a few things...
Fetch and save an image file to my uploads folder using PHP when the only thing that the PHP function will receive is a URL of the image which could be on the same server or most likely a remote server.
After successfully saving/uploading an image from the URL, the PHP function will return a JSON string with the status/error and if successful then it will also return the actual URL and filename of where the new image is saved on the local server. The JavaScript/AJAX script will receive this JSON response and insert the Markdown syntax for the image into the PageDown editor.
The PHP function will need to ensure that the URL that it is trying to save/download is a valid image file and not some malicious file! Also not simply just some file of the wrong filetype like a non-image file unless we are allowing the file type.
It will be part of a module installed on many dinosaur servers so it needs to work on as many servers as possible too!
From the web
From your computer
I would be greatful of any help, tips, code snippets or anything to help with this. At this stage I really just need to build a nie PHP function that will upload images from a remote URL and also ensure that the URL passed in is a real image file or even better that it is in the allowed file types array!
A couple years ago I had started this but have now lost it and I am starting over and don't remeber much about how I went about doing it then.

The easiest way to download a file from a remote server would be to use copy (http://php.net/manual/en/function.copy.php):
copy('http://someurl.com/image.png', '/var/www/uploads/image.png');
As this function returns a bool, it is easy to determine whether the operation was successful and create a JSON response.
To verify that the file is an actual image, there is unfortunately no way that is 100% sure. It is probably enough to check the mimetype though. You can use finfo for that (http://php.net/manual/en/function.finfo-file.php):
$finfo = finfo_open(FILEINFO_MIME_TYPE);
echo finfo_file($finfo, $filename);
finfo_close($finfo);
For a gif, this would return image/gif for example. You will have to hardcode a list of all mimetypes you want to allow.

How to pass an uploaded image back to html

The setup I work on is the following: A HTML-page with a canvas element displaying a Processing JS sketch and a form that allows to pass parameters to the sketch using JS-function Processing.getInstanceById(getProcessingSketchId()).setSomeParam();, which works just fine.
The user should also be able to upload an image to the server, the name/path of which is then also handed to the sketch to do loadImage(String path). The file upload (using PHP from here) works perfectly fine as well but now here is the question:
How can I get the name of the uploaded image on the server and pass it to the Processing sketch?
If the form's action tag points to a distinct PHP-file, the site with the canvas sketch is quit (variable $destination not available) or if the form's action tag points to the site itself (being a PHP-site, checking for if(isset($_POST['formSubmitted'])) {), the sketch is restarted losing all the previously changed parameters.
I also managed to have the form submission target to an internal iframe and display the uploaded image there, but that still doesn't solve my problem.
Thanks a lot in advance for any helpful hints!

It sounds like you have the data flow worked out but are struggling because a standard form upload causes a page refresh.
I would suggest using AJAX to post the image to a specific PHP image receiver service. When the AJAX upload is complete, the javascript can then call to the server to fetch the uploaded object and manipulate it as needed without refreshing the page.

Ajax/Javascript - File Download

Client (Request through XMLHttpRequest) -> Server.
Server [Builds CSV and prints it on the output stream of response] -> Client.
Now step 3 should be-> Client's browser should show a download dialogue (save, open and cancel). Since the content type is plain text from the server, and the content disposition is not set, can we create a file using javascript and prompt the user to download?
I know this question is slight stupid. But there is no other option. I have to do it this way.
Changing in the server side script will make it a one minute task. But I have to do it in the client side. The responseText property of the XMLHttpRequest object will be plain text and I have to show download prompt for the text file.
Is this possible?

Not that I'm aware of. But you could just use location.href (or a form, if POST data is needed) to request the server-side file. With the correct headers (Content-Disposition: attachment and I think there's another one) you can have the response be downloaded rather than displayed.
EDIT: Even better, use an iframe that's hidden. That way, you can still do a fancy "Loading, please wait" thing in the main page.

Theoretically it could be possible, by using Data URI's
<a download = "yourfile.csv" href="data:application/octet-stream;charset=YOURCHARSET;base64,BASE64allthedata">Generate</a>

how to download client side content

I want to let the user download the current content of a textarea into a text file on their computer. In the past I would create an iframe pointing to a URL with the data, which would trigger a file download dialog. However this time the data is client side.
So, is it possible to let the user download data without sending it server side?

If it does not need to work in "old browsers" like IE, you could open a new window with the location 'data:text/plain,' + yourTextarea.value. The user can then save that file using the File/Page menu or Ctrl+S.

is it possible to let the user download data without sending it server side?
In the general case no.
It is possible with a data: URL, as in janmoesen's answer (although you should be URL-encoding the value to include in the URL, or you may face corruption when a %nn sequence appears in the data).
However, this becomes impractical for very long data, and it's not available in old browsers or IE. (IE8 allows short data URLs to be used for images, but not direct navigation.) So whilst you can include a data-URL method to enhance the process on browsers that support it, you will still need a fallback solution of sending a formful of the data to the server side and having it spit back a file in response.
(For security reasons, this should only be allowed in a POST request, and the server should include Content-Disposition: attachment in the response. A content-echo script can give you cross-site-scripting problems otherwise.)

Check out how File and Blob types work.
You can create one and trigger a download programmaticaly:
https://www.bennadel.com/blog/3472-downloading-text-using-blobs-url-createobjecturl-and-the-anchor-download-attribute-in-javascript.htm
https://blog.logrocket.com/programmatic-file-downloads-in-the-browser-9a5186298d5c/