how to download file as a stream

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Hi,

I want to test download speed for which I need to download a file of 100kb. This file is located on my server and I have written following code to download file using Ajax.

C#

xhr = new XMLHttpRequest();
   xhr.onreadystatechange=function()
   {
       if (xhr.readyState==4 && xhr.status==200)
       {
       alert("success");
       }
   }
 xhr.open("GET", "www.myserver.com/100kb.txt", false);
 xhr.responseType = "arraybuffer";
 xhr.send();

But I an unable to get the file. Do I need to write any .php script on server so that I can download this file in a background or I can get this file as payload.
On chrome and Mozilla it is not giving any error though I put my code in try and catch but on IE8.0 it gives permission denied.

Is there any XDomain issue.

Please suggest.

Regds
SNI

Posted 13-Nov-13 20:20pm

SNI

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Sergey Alexandrovich Kryukov 14-Nov-13 2:33am

If you are already using jQuery, why not using jQuery Ajax?
—SA

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Manujith Pallewatte · Answer 1 · 2013-11-14T20:13:00

Solution 1

yes you cannot do cross domain AJAX requests due to security reasons
you enable it from client side from the browser but that isnt really a solution
the preferred way is to make a php script that download the file and then use AJAX to present it to the client

Posted 14-Nov-13 20:13pm

Manujith Pallewatte

Comments

SNI 19-Nov-13 6:44am

Hi, the above code working fine when I write a php code at server side. I have setInterval to 2000ms. So after every 2000ms the request is sent to the server and data get downloaded in terms of http response but now my problem is since I am downloading a huge payload it is taking time (say 6-8 seconds) to load XMLHttp responses for concurrent requests. Can you pls advice what needs to be done to get faster faster response so that user can feel the data is downloading.

Manujith Pallewatte 20-Nov-13 1:05am

heyy,
its your good time, only last week i made a php -> js library for just this purpose :)
https://github.com/ManZzup/pjstreamer
now this is actually not made for transfering byte data, but with some modifications you can make it transfer bytes over ajax
----------------
OR you can modify the solution to buffer data than downloading periodically, that is you tell the browser that the file is buffering and the browser will download byte stream till the server stops sending

SNI 20-Nov-13 5:09am

Thanks. I opted the second option. Now I am able to get the heavy payload using php, which pushes the data to client but I need to wait till the data is completely downloaded to client. I tried to stop this outputting of buffer by clearing it at server side. But no success. Please let me know how to stop this kind of buffer caching at client side either in HTML or javascript after some time interval?

Manujith Pallewatte 20-Nov-13 5:47am

you need to flush the buffer to break it, you need to tweak the browser to support this feature
i assume that the data you are transferring is okay with this breaking, following tip shows how to output php in realtime, in which the buffer is interrupted to show the output. Same concept can be used to tell the browser to stop receiving at a given time.
http://www.codeproject.com/Tips/680085/Real-time-Updating-of-PHP-Output

read more about http://php.net/manual/en/function.ob-flush.php (ob_flush()) as well

SNI 21-Nov-13 2:43am

I tried with this but it doesn't work. I will explain what I am trying. In php I am reading a huge file (say 100MB) and I am echoing that. Pls see code below
$val=readfile("100mb.file");
ob_start ();
ob_flush();
echo $val;
sleep(10);
echo " <br />";
ob_flush();
ob_end_clean();
ob_end_flush();
I am clearing everything after 10 secs. After 10 secs I want to stop browser to stop this buffer downlaod/caching. But this does not work. Pls let me know where I am going wrong.

Manujith Pallewatte 21-Nov-13 5:51am

it wont work like that since echo $val; would output the hwole file only then it enter the sleep mode
for buffering you also have to do some browser tricks you missed in the above code [please refer that article again, you have to send the 1024 bytes + <br> before everything ]

to acheieve what you want, you have to read the file by a buffer as well
ex:
loop:
read 100 kb from the file
output 100 kb
timer++
if(timer==10) sleep(10);
like wise