Normally when you have a .PHP file and the client request it, the PHP code is run on the server and the HTML and JavaScript are sent to the client.
Question
Is it possible to have the server request a webpage (local) and run both the PHP code and the HTML with JavaScript on the server? I have created a single .html file that after 3 seconds of processing locally creates the image data for a thumbnail of the given video.
Why
I need to generate a thumbnail for a video. I used shared hosting and my hosting provider doesn't support for ffmpeg. You can, however, generate thumbnails using a canvas and JavaScript. I have already put a lot of pressure on the client. If this is possible, upload and download times would be significantly shorter than using the client.
Attempts
I've tried using file_get_contents(), but it doesn't run the code (Makes sense). Is there a way I could have it open and run for x seconds and then grab the contents?
I've tried using curl to get the file using this function here. I believe it is similar to my previous attempt in that it gets the file contents, but never executes them.
My final attempt was to use new DOMDocument(). I couldn't even get to loading the page though. First, I can't parse it with a video tag. It gives this error:
Warning: DOMDocument::load(): Specification mandates value for attribute controls in
file:\path\to\html\document.html, line: 53 in C:\path\to\php\document.php on line 50
If I were to remove the video tag (which is required), I get errors while parsing my JavaScript. So that attempt also did not work.
Is there a way that I could have PHP process the code (for something on the server) for x seconds before getting the contents? It would allow for time to generate the thumbnail data. If there is another way to do this without using ffmpeg on the server, that would be great.
So as I mentioned in comments, what I'm gonna explain is just an option (not the best one and just answering for your need of running html code!)
Where to do this?
Personally I rather to do this when the video is being uploaded by admin's browser and the best thing is that you can do this as a part of the posting procedure.
So in the page that you want this process to be done, put an invisible iframe like this.
<iframe id="myIframe" style="display: none;"></iframe>
How to begin the process?
I don't know the way you use to upload the videos (and it really is not that important!) but let's assume you want to use formdata. After the video is uploaded you need to know something unique to address the video (let's say an id). So after the video is uploaded, we can recive a code like id:20, initiateThumbnail:true as the result json data. Then we can simply use that hidden iframe to be the browser you've been asking for like this:
$("#myIframe").attr("src","dothething.php?video=20");
Now do what ever you wanted to do in it and change it's content after it's done. Now you need to wait for the result!
$('#myIframe').load(()=>{
let result = $("#myIframe").contents();
// checking result!
});
As you have already thought about, you can handle any errors by processing the result.
Notes
The event listener we used for iframe (iframe.load) fires when you initiate making the thumbnail as well. So be careful with the process of checking result (content of that iframe!)
If you don't use ajax or formdata, simply the action of your form is what I used as iframe.
One question? What happens if network connection goes down during this process? Simple answer! You can check in so many ways that the thumbnail exists or not. If not you can create it once that user requests for it in his browser and upload it back to server and save it for ever (as you did it in admin's panel!)
I think there isn’t another way to generate thumbnail on php server than with ffmpeg.
The only thing you can do, I suppose, is to force canvas generation on page load if you aren’t already doing it.
Anyway you are trying to do something wrong. Php doesn’t evaluate the html code, it’s just a preprocessor and not an interpreter like the browser. You can wait all the time of the world, but you’ll never get the content of the image that only a browser will generate.
In my webapp the user has the option to download a file containing some data, which they do by clicking on a button. For small amounts of data the file starts downloading pretty much immediately and that shows in the browser's download area. Which is good.
For large amounts of data it can take the server a substantial amount of time to calculate the data, even before we start downloading. This is not good. I want to indicate that the calculation is in progress. However I don't want to put a "busy" indicator on my UI, because the action does not block the UI - the user should be able to do other things while the file is being prepared.
A good solution from my point of view would be to start the download process before I have finished the calculation. We always know (or can quickly calculate) the first few hundred bytes of the file. Is there a mechanism where I can have the server respond to a download request with those few bytes, thus starting the download and making the file show up in the download area, and provide the rest of the file when I have finished calculating it? I'm aware that it will look like the download is stalled, and that's not a problem.
I can make a pretty good estimate of the file size very quickly. I would prefer not to have to use a third-party package to achieve this, unless it's a very simple one. We are using Angular but happy to code raw JS if needed.
To indicate that the link points to a download on the client, the easiest way is the download attribute on the link. The presence of the attribute tells the browser not to unload the current tab or create a new one; the value of the attribute is the suggested filename.
For the back-end part, after setting the correct response headers, just write the data to the output stream as it becomes available.
You asked for a general solution
1) First, at your HTML/JS you can prevent the UI from being blocked by setting you download target to any other WebPage, the preferred way for doing this is to set the target to an IFRAME:
<!-- your link must target the iframe "downloader-iframe" -->
<a src="../your-file-generator-api/some-args?a=more-args" target="downloader-iframe">Download</a>
<!-- you don't need the file to be shown -->
<iframe id="downloader-iframe" style="display: none"></iframe>
2) Second, at your back-end you'll have to use both Content-Disposition and Content-Length(optional) headers, be careful using the "length" one, if you miss calculate the fileSize it will not be downloaded. If you don't use Content-Length you'll not see the "downloading progress".
3) Third, at you'r back-end you have to make sure that you are writing your bytes directly at your response! that way your Browser and your Web-Server will know that the download is "in progress",
Example for Java:
Using ServletOutputStream to write very large files in a Java servlet without memory issues
Example for C#:
Writing MemoryStream to Response Object
HOW this 3 steps are built will be up to you, frameworks and libraries you are using, for example Dojo & JQuery have great IFRAME manipulation utilities, all thought you can do the coding by yourself, this is a JQuery sample:
Using jQuery and iFrame to Download a File
Also:
Adding a "busy" animation is ok! you just have to make sure that it's not blocking you'r UI, something like this:
I know it's possible to force reload from server using location.reload(true). However, let's say I used that to refresh index.html. If index.html loads a bunch of javascript files, those are still coming from the cache for me. Is there any way to ignore the cache for the duration of a request?
My use case is that I'm doing AB testing on my app, and want to provide a way for users to go back to the old version if something isn't working. But some of the URLs are the same, even though the files between versions are different. It would be nice to be able to handle this in JS rather than having to change every URL on the new version.
There is actually at least 535 different ways to reload a page via javascript, FYI ;).
Have you tried to put document on front? document.location.reload(true);
Try also this other option:
window.location.href = window.location.href;
or
history.go(0);
Sure, both are soft reload, but seems to work in certain situation.
If nothing works, you have to append random data to the url (like timestamp) to force the download from server, bypassing the cache.
If you want to bypass browser taking js files from cache, you need to fetch from server not just files like script.js but rather script.12345.js When you update your file on server, you change file's hash number to let's say script.54321.js And browser understands that the file is different, it must download it again. You can actually use Webpack for this purpose to automate things. In output instead of {filename: bundle.js} you write {filename: bundle.[hash].js}
So, i was doing a link to download an image from a data url(a LARGE one):
<a download='fileName' href="data:image/png;base64,/9j/4WSsRX...">something</a>
However, whenever i try to click in that link i receive an error telling me some net problems.
I have make a fiddle test, but its LARGE(15mb of text) and it will take sometime to load:
https://jsfiddle.net/jjydp1ek/
As the jsfiddle is hard to load, i added a file in mediafire:
http://www.mediafire.com/download/p85y1g442ne9v6m/new++7.html
The test is an image with the same data url value as the link, the image is visible, however i see that the option to open image in a new tab on chrome isn't working.
I do it with canvas in ie 11 and is failing too
Questions:
It is ever possible to make it work with the download link as it is now?
Is there a limit size with the data url to download a file, which is?
How do i do to make the user able to download that image?
Also, ask questions here, or correct any error in the text you see if you think its not understandable.
Thanks.
I have a 70Mb broadband and a powerhouse of a PC and that JS fiddle won't even open.
I don't think it's feasible to have a 15MB encoded string, since that has to be downloaded onto the page each time on every visit. I would try the following:
Optimise the image, you could incorporate gulp-imagemin if you have/want to have Gulp for a build system. I think there are alternatives for Grunt if you wanted to go that way.
Store the file on the server and just place a link to the path, this is the preferred solution.
In response to your questions
The limit:
Length limitations
Although Mozilla supports data URIs of essentially
unlimited length, browsers are not required to support any particular
maximum length of data. For example, the Opera 11 browser limits data
URIs to around 65000 characters.
Source: data URIs - MDN
Downloading
The above suggestion on optimising the image as small as you can get without losing quality if that's a concern. Try it then. If not, it's not a problem to give the user a link to the image / display it on the page. The user can right click and save.
Note
By the time I finished writing this response JSFiddle timed out.
I know there are many ways to prevent image caching (such as via META tags), as well as a few nice tricks to ensure that the current version of an image is shown with every page load (such as image.jpg?x=timestamp), but is there any way to actually clear or replace an image in the browsers cache so that neither of the methods above are necessary?
As an example, lets say there are 100 images on a page and that these images are named "01.jpg", "02.jpg", "03.jpg", etc. If image "42.jpg" is replaced, is there any way to replace it in the cache so that "42.jpg" will automatically display the new image on successive page loads? I can't use the META tag method, because I need everuthing that ISN"T replaced to remain cached, and I can't use the timestamp method, because I don't want ALL of the images to be reloaded every time the page loads.
I've racked my brain and scoured the Internet for a way to do this (preferrably via javascript), but no luck. Any suggestions?
If you're writing the page dynamically, you can add the last-modified timestamp to the URL:
<img src="image.jpg?lastmod=12345678" ...
<meta> is absolutely irrelevant. In fact, you shouldn't try use it for controlling cache at all (by the time anything reads content of the document, it's already cached).
In HTTP each URL is independent. Whatever you do to the HTML document, it won't apply to images.
To control caching you could change URLs each time their content changes. If you update images from time to time, allow them to be cached forever and use a new filename (with a version, hash or a date) for the new image — it's the best solution for long-lived files.
If your image changes very often (every few minutes, or even on each request), then send Cache-control: no-cache or Cache-control: max-age=xx where xx is the number of seconds that image is "fresh".
Random URL for short-lived files is bad idea. It pollutes caches with useless files and forces useful files to be purged sooner.
If you have Apache and mod_headers or mod_expires then create .htaccess file with appropriate rules.
<Files ~ "-nocache\.jpg">
Header set Cache-control "no-cache"
</Files>
Above will make *-nocache.jpg files non-cacheable.
You could also serve images via PHP script (they have awful cachability by default ;)
Contrary to what some of the other answers have said, there IS a way for client-side javascript to replace a cached image. The trick is to create a hidden <iframe>, set its src attribute to the image URL, wait for it to load, then forcibly reload it by calling location.reload(true). That will update the cached copy of the image. You may then replace the <img> elements on your page (or reload your page) to see the updated version of the image.
(Small caveat: if updating individual <img> elements, and if there are more than one having the image that was updated, you've got to clear or remove them ALL, and then replace or reset them. If you do it one-by-one, some browsers will copy the in-memory version of the image from other tags, and the result is you might not see your updated image, despite its being in the cache).
I posted some code to do this kind of update here.
Change the image url like this, add a random string to the querystring.
"image1.jpg?" + DateTime.Now.ToString("ddMMyyyyhhmmsstt");
I'm sure most browsers respect the Last-Modified HTTP header. Send those out and request a new image. It will be cached by the browser if the Last-Modified line doesn't change.
You can append a random number to the image which is like giving it a new version. I have implemented the similar logic and it's working perfectly.
<script>
var num = Math.random();
var imgSrc= "image.png?v="+num;
$(function() {
$('#imgID').attr("src", imgSrc);
})
</script>
I found this article on how to cache bust any file
There are many ways to force a cache bust in this article but this is the way I did it for my image:
fetch('/thing/stuck/in/cache', {method:'POST', credentials:'include'});
The reason the ?x=timestamp trick is used is because that's the only way to do it on a per image basis. That or dynamically generate image names and point to an application that outputs the image.
I suggest you figure out, server side, if the image has been changed/updated, and if so then output your tag with the ?x=timestamp trick to force the new image.
No, there is no way to force a file in a browser cache to be deleted, either by the web server or by anything that you can put into the files it sends. The browser cache is owned by the browser, and controlled by the user.
Hence, you should treat each file and each URL as a precious resource that should be managed carefully.
Therefore, porneL's suggestion of versioning the image files seems to be the best long-term answer. The ETAG is used under normal circumstances, but maybe your efforts have nullified it? Try changing the ETAG, as suggested.
Change the ETAG for the image.
See http://en.wikipedia.org/wiki/URI_scheme
Notice that you can provide a unique username:password# combo as a prefix to the domain portion of the uri. In my experimentation, I've found that inclusion of this with a fake ID (or password I assume) results in the treatment of the resource as unique - thus breaking the caching as you desire.
Simply use a timestamp as the username and as far as I can tell the server ignores this portion of the uri as long as authentication is not turned on.
Btw - I also couldn't use the tricks above with a google map marker icon caching problem I was having where the ?param=timestamp trick worked, but caused issues with disappearing overlays. Never could figure out why this was happening, but so far so good using this method. What I'm unsure of, is if passing fake credentials will have any adverse server performance affects. If anyone knows I'd be interested to know as I'm not yet in high volume production.
Please report back your results.
Since most, if not all, answers and comments here are copies of parts the question, or close enough, I shall throw my 2 cents in.
I just want to point out that even if there is a way it is going to be difficult to implement. The logic of it traps us. From a logical stance telling the browser to replace it's cached images for each changed image on a list since a certain date is ideal BUT... When would you take the list down and how would you know if everyone has the latest version who would visit again?
So my 1st "suggestion", as the OP asked for, is this list theory.
How I see doing this is:
A.) Have a list that our dynamic and manual changed image urls can be stored.
B.) Set a dead date where the catch will be reset and the list will be truncated regardless.
C.0) Check list on site entrance vs browser via i frame which could be ran in the background with a shorter cache header set to re-cache them all against the farthest date on the list or something of that nature.
C.1) Using the Iframe or ajax/xhr request I'm thinking you could loop through each image of the list refreshing the page to show a different image and check the cache against it's own modified date. So on this image's onload use serverside to decipher if it is not the last image when it is loaded go to the next image.
C.1a) This would mean that our list may need more information per image and I think the obvious one is the possible need of some server side script to adjust the headers as required by each image to minimize the footstep of re-caching changed site images.
My 2nd "suggestion" would be to notify the user of changes and direct them to clear their cache. (Carefully, remove only images and files when possible or warn them of data removal due to the process)
P.S. This is just an educated ideation. A quick theory. If/when I make it I will post the final. Probably not here because it will require server side scripting. This is at least a suggestion not mentioned in the OP's question that he say's he already tried.
It sounds like the base of your question is how to get the old version of the image out of the cache. I've had success just making a new call and specifying in the header not to pull from cache. You're just throwing this away once you fetch it, but the browser's cache should have the updated image at that point.
var headers = new Headers()
headers.append('pragma', 'no-cache')
headers.append('cache-control', 'no-cache')
var init = {
method: 'GET',
headers: headers,
mode: 'no-cors',
cache: 'no-cache',
}
fetch(new Request('path/to.file'), init)
However, it's important to recognize that this only affects the browser this is called from. If you want a new version of the file for any browser once the image is replaced, that will need to be accomplished via server configuration.
Here is a solution using the PHP function filemtime():
<?php
$addthis = filemtime('myimf.jpg');
?>
<img src="myimg.jpg?"<?= $addthis;?> >
Use the file modified time as a parameter will cause it to read from a cached version until the file has changed. This approach is better than using e.g. a random number as caching will still work if the file has not changed.
In the event that an image is re-uploaded, is there a way to CLEAR or REPLACE the previously cached image client-side? In my example above, the goal is to make the browser forget what "42.jpg" is
You're running firefox right?
Find the Tools Menu
Select Clear Private Data
Untick all the checkboxes except make sure Cache is Checked
Press OK
:-)
In all seriousness, I've never heard of such a thing existing, and I doubt there is an API for it. I can't imagine it'd be a good idea on part of browser developers to let you go poking around in their cache, and there's no motivation that I can see for them to ever implement such a feature.
I CANNOT use the META tag method OR the timestamp method, because I want all of the images cached under normal circumstances.
Why can't you use a timestamp (or etag, which amounts to the same thing)? Remember you should be using the timestamp of the image file itself, not just Time.Now.
I hate to be the bearer of bad news, but you don't have any other options.
If the images don't change, neither will the timestamp, so everything will be cached "under normal circumstances". If the images do change, they'll get a new timestamp (which they'll need to for caching reasons), but then that timestamp will remain valid forever until someone replaces the image again.
When changing the image filename is not an option then use a server side session variable and a javascript window.location.reload() function. As follows:
After Upload Complete:
Session("reload") = "yes"
On page_load:
If Session("reload") = "yes" Then
Session("reload") = Nothing
ClientScript.RegisterStartupScript(Me.GetType), "ReloadImages", "window.location.reload();", True)
End If
This allows the client browser to refresh only once because the session variable is reset after one occurance.
Hope this helps.
To replace cache for pictore you can store on server-side some version value and when you load picture just send this value instead timestamp. When your image will be changed change it`s version.
Try this code snippet:
var url = imgUrl? + Math.random();
This will make sure that each request is unique, so you will get the latest image always.
After much testing, the solution I have found in the following way.
1- I create a temporary folder to copy the images with the name adding time () .. (if the folder exists I delete content)
2- load the images from that temporary local folder
in this way I always make sure that the browser never caches images and works 100% correctly.
if (!is_dir(getcwd(). 'articulostemp')){
$oldmask = umask(0);mkdir(getcwd(). 'articulostemp', 0775);umask($oldmask);
}else{
rrmfiles(getcwd(). 'articulostemp');
}
foreach ($images as $image) {
$tmpname = time().'-'.$image;
$srcimage = getcwd().'articulos/'.$image;
$tmpimage = getcwd().'articulostemp/'.$tmpname;
copy($srcimage,$tmpimage);
$urlimage='articulostemp/'.$tmpname;
echo ' <img loading="lazy" src="'.$urlimage.'"/> ';
}
try below solutions,
myImg.src = "http://localhost/image.jpg?" + new Date().getTime();
Above solutions work for me :)
I usually do the same as #Greg told us, and I have a function for that:
function addMagicRefresh(url)
{
var symbol = url.indexOf('?') == -1 ? '?' : '&';
var magic = Math.random()*999999;
return url + symbol + 'magic=' + magic;
}
This will work since your server accepts it and you don't use the "magic" parameter any other way.
I hope it helps.
I have tried something ridiculously simple:
Go to FTP folder of the website and rename the IMG folder to IMG2. Refresh your website and you will see the images will be missing. Then rename the folder IMG2 back to IMG and it's done, at least it worked for me in Safari.