### Implementation bugs

For pipelining to work, responses must come back in the order they were requested.  A naive server implementation might just send the response as soon as it has been calculated.  If multiple requests are sent in parallel, and the first request one takes longer to process (e.g. processing a larger image), then the responses will be out of order.

This is a problem for the client since HTTP is a stateless protocol, the client has no way to match the requests with the responses.  It is reliant on the order the responses came back in.

&gt; [A server MUST send its responses to those requests in the same order that the requests were received.][2]

 * Safari apparently used HTTP pipelining for images at least.  [This results in an issue where images would be swapped around][3]. 
 * [AFNetworking][4] used to use pipelining, but it was pulled after a [reported issue][5].
 * All major browsers (other than Opera) have HTTP pipelining is disabled or not implemented.

### Performance issues

Even if the server does properly support pipelining, performance issues can arise because all subsequent requests have to wait for the first one to be complete (Head of Line blocking).  

- [This article][6], talks about performance *loss* in some circumstances and a potential of denial of service attack.

- [This article][7] also suggest that pipelining isn&#39;t a massive win.

- [WWDC 2015 - Networking with NSURLSession][8] explains head of line blocking really well. (The solution is to switch to HTTP 2 which support priorities)

[![Head of line blocking][9]][9]

So in summary the issues with HTTP pipelining are:

 - Some servers &amp; [most proxies][10] don&#39;t support it. (Perhaps due to security / reliability / or performance concerns)
 - Some servers support it incorrectly and this can lead to client bugs.
 - It is not necessarily a performance win.
 - Susceptible to head of line blocking


  [1]: http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol
  [2]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html
  [3]: http://tech.vg.no/2011/12/14/safari-on-ios-5-randomly-switches-images/
  [4]: https://github.com/AFNetworking/AFNetworking/blob/master/AFNetworking/UIImageView+AFNetworking.m
  [5]: https://github.com/AFNetworking/AFNetworking/issues/528
  [6]: https://devcentral.f5.com/blogs/us/http-pipelining-a-security-risk-without-real-performance-benefits
  [7]: http://www.guypo.com/technical/http-pipelining-not-so-fast-nor-slow/
  [8]: https://developer.apple.com/videos/wwdc/2015/?id=711
  [9]: http://i.stack.imgur.com/sdCNX.png
  [10]: https://en.wikipedia.org/wiki/HTTP_pipelining#Implementation_in_web_proxies

I have the following:

    function checkPalindrom(palindrom)
	{

		for( var i = palindrom.length; i &gt; 0; i-- )
		{
			if( palindrom[i] = palindrom.charAt(palindrom.length)-1 )
			{
				document.write(&#39;the word is palindrome.&#39;);
			}else{
				document.write(&#39;the word is not palindrome!&#39;);
			}
		}
	}
	checkPalindrom(&#39;wordthatwillbechecked&#39;);

What is wrong with my code? I want to check if the word is a palindrome.

Palindrome check in Javascript

When inside a `with` or `range`, the scope of `.` is changed. How do you access the calling scope?

In a template how do you access an outer scope while inside of a &quot;with&quot; or &quot;range&quot; scope?

[WWDC 2012 session 706 - Networking Best Practices][1] explains [HTTP Pipelining][2].  

- By default [its disabled][3] on iOS
- In the talk its described it as a huge performance win.

Why might you not want to use it?

![pipelining][4]


  [1]: https://developer.apple.com/videos/wwdc/2012/?id=706
  [2]: http://en.wikipedia.org/wiki/HTTP_pipelining
  [3]: https://developer.apple.com/documentation/foundation/nsmutableurlrequest/1412705-httpshouldusepipelining
  [4]: http://i.stack.imgur.com/MbAOA.png

What are the disadvantage(s) of using HTTP pipelining?

<a href="https://developer.apple.com/videos/wwdc/2012/?id=706" target="_blank" rel="noopener noreferrer">WWDC 2012 session 706 - Networking Best Practices</a> explains <a href="http://en.wikipedia.org/wiki/HTTP_pipelining" target="_blank" rel="noopener noreferrer">HTTP Pipelining</a>.
<ul>
<li>By default <a href="https://developer.apple.com/documentation/foundation/nsmutableurlrequest/1412705-httpshouldusepipelining" target="_blank" rel="noopener noreferrer">its disabled</a> on iOS</li>
<li>In the talk its described it as a huge performance win.</li>
</ul>
Why might you not want to use it?
<img src="http://i.stack.imgur.com/MbAOA.png" alt="pipelining">

I&#39;m simply trying to create a node server that outputs the HTTP status of a given URL.

When I try to flush the response with res.write, I get the error: throw new TypeError(&#39;first argument must be a string or Buffer&#39;);

But if I replace them with console.log, everything is fine (but I need to write them to the browser not the console).

The code is

    var server = http.createServer(function (req, res) {
    	res.writeHead(200, {&quot;Content-Type&quot;: &quot;text/plain&quot;});
    
    	request({
    		uri: &#39;http://www.google.com&#39;,
    		method: &#39;GET&#39;,
    		maxRedirects:3
    	}, function(error, response, body) {
    		if (!error) {
    			res.write(response.statusCode);
    		} else {
    			//response.end(error);
    			res.write(error);
    		}
    	});		
    
    	res.end();
    });
    server.listen(9999);

I believe I should add a callback somewhere but pretty confused and any help is appreciated.



nodejs - first argument must be a string or Buffer - when using response.write with http.request

My script is called by server. From server I&#39;ll receive `ID_OF_MESSAGE` and `TEXT_OF_MESSAGE`. 

In my script I&#39;ll handle incoming text and generate response with params: `ANSWER_TO_ID` and `RESPONSE_MESSAGE`.

The problem is that I&#39;m sending response to incomming `&quot;ID_OF_MESSAGE&quot;`, but server which send me message to handle will set his message as delivered to me (It means I can send him response to that ID), after receiving http response 200. 

One of solution is to save message to database and make some cron which will be running each minute, but I need to generate response message immediately. 

Is there some solution how to send to server http response 200 and than continue executing php script?

Thank you a lot

continue processing php after sending http response

*Cross-origin resource sharing* is a mechanism that allows a web page to make XMLHttpRequests to another domain (from [Wikipedia][1]).

I&#39;ve been fiddling with CORS for the last couple of days and I think I have a pretty good understanding of how everything works. 

So my question is not about how CORS / preflight work, it&#39;s about **the reason behind coming up with preflights as a new request type**. I fail to see any reason why server A needs to send a preflight (PR) to server B just to find out if the real request (RR) will be accepted or not - it would certainly be possible for B to accept/reject RR without any prior PR. 

After searching quite a bit I found [this piece][2] of information at www.w3.org (7.1.5):

&gt; *To protect resources against cross-origin requests that could not originate from certain user agents before this specification existed a
&gt; preflight request is made to ensure that the resource is aware of this
&gt; specification.*

I find this is the hardest to understand sentence ever. My interpretation (should better call it &#39;best guess&#39;) is that it&#39;s about protecting server B against requests from server C that is not aware of the spec. 

Can someone please explain a scenario / show a problem that PR + RR solves better than RR alone?



  [1]: https://en.wikipedia.org/wiki/Cross-origin_resource_sharing
  [2]: https://www.w3.org/TR/cors/#preflight-request

What is the motivation behind the introduction of preflight CORS requests?

At the end of last week I noticed a problem on one of my medium AWS instances where Nginx always returns a HTTP 499 response if a request takes more than 60 seconds.  The page being requested is a PHP script

I&#39;ve spent several days trying to find answers and have tried everything that I can find on the internet including several entries here on Stack Overflow, nothing works.

I&#39;ve tried modifying the PHP settings, PHP-FPM settings and Nginx settings. You can see a question I raised on the NginX forums on Friday (http://forum.nginx.org/read.php?9,237692) though that has received no response so I am hoping that I might be able to find an answer here before I am forced to moved back to Apache which I know just works.

This **is not** the same problem as the HTTP 500 errors reported in other entries.

I&#39;ve been able to replicate the problem with a fresh micro AWS instance of NginX using PHP 5.4.11.

To help anyone who wishes to see the problem in action I&#39;m going to take you through the set-up I ran for the latest Micro test server.

You&#39;ll need to launch a new AWS Micro instance (so it&#39;s free) using the AMI ami-c1aaabb5

This PasteBin entry has the complete set-up to run to mirror my test environment. You&#39;ll just need to change *example.com* within the NginX config at the end

http://pastebin.com/WQX4AqEU

Once that&#39;s set-up you just need to create the sample PHP file which I am testing with which is


    &lt;?php
    sleep(70);
    die( &#39;Hello World&#39; );
    ?&gt;

Save that into the webroot and then test.  If you run the script from the command line using php or php-cgi, it will work.  If you access the script via a webpage and tail the access log */var/log/nginx/example.access.log*, you will notice that you receive the HTTP 1.1 499 response after 60 seconds.

Now that you can see the timeout, I&#39;ll go through some of the config changes I&#39;ve made to both PHP and NginX to try to get around this.  For PHP I&#39;ll create several config files so that they can be easily disabled

**Update the PHP FPM Config to include external config files**

    sudo echo &#39;
    include=/usr/local/php/php-fpm.d/*.conf
    &#39; &gt;&gt; /usr/local/php/etc/php-fpm.conf

**Create  a new PHP-FPM config to override the request timeout**

    sudo echo &#39;[www]
    request_terminate_timeout = 120s
    request_slowlog_timeout = 60s
    slowlog = /var/log/php-fpm-slow.log &#39; &gt;
    /usr/local/php/php-fpm.d/timeouts.conf

**Change some of the global settings to ensure the emergency restart interval is 2 minutes**

    # Create a global tweaks
    sudo echo &#39;[global]
    error_log = /var/log/php-fpm.log
    emergency_restart_threshold = 10
    emergency_restart_interval = 2m
    process_control_timeout = 10s
    &#39; &gt; /usr/local/php/php-fpm.d/global-tweaks.conf

Next, we will change some of the PHP.INI settings, again using separate files

    # Log PHP Errors
    sudo echo &#39;[PHP]
    log_errors = on
    error_log = /var/log/php.log
    &#39; &gt; /usr/local/php/conf.d/errors.ini

    sudo echo &#39;[PHP]
    post_max_size=32M
    upload_max_filesize=32M
    max_execution_time = 360
    default_socket_timeout = 360
    mysql.connect_timeout = 360
    max_input_time = 360
    &#39; &gt; /usr/local/php/conf.d/filesize.ini

As you can see, this is increasing the socket timeout to 3 minutes and will help log errors.

Finally, I&#39;ll edit some of the NginX settings to increase the timeout&#39;s that side

First I edit the file */etc/nginx/nginx.conf* and add this to the http directive
    fastcgi_read_timeout 300;

Next, I edit the file */etc/nginx/sites-enabled/example* which we created earlier (See the pastebin entry) and add the following settings into the **server** directive

    client_max_body_size    200;
    client_header_timeout   360;
    client_body_timeout     360;
    fastcgi_read_timeout    360;
    keepalive_timeout       360;
    proxy_ignore_client_abort on;
    send_timeout            360;
    lingering_timeout       360;

Finally I add the following into the *location ~ \.php$* section of the server dir

	fastcgi_read_timeout 360;
	fastcgi_send_timeout 360;
	fastcgi_connect_timeout 1200;

Before retrying the script, start both nginx and php-fpm to ensure that the new settings have been picked up. I then try accessing the page and still receive the HTTP/1.1 499 entry within the NginX example.error.log.

So, where am I going wrong?  This just works on apache when I set PHP&#39;s max execution time to 2 minutes.

I can see that the PHP settings have been picked up by running **phpinfo()** from a web-accessible page.  I just don&#39;t get, I actually think that too much has been increased as it should just need PHP&#39;s *max_execution_time*, *default_socket_timeout* changed as well as NginX&#39;s *fastcgi_read_timeout* within just the server-&gt;location directive.

##Update 1##

Having performed some further test to show that the problem is not that the client is dying I have modified the test file to be

    &lt;?php
    file_put_contents(&#39;/www/log.log&#39;, &#39;My first data&#39;);
    sleep(70);
    file_put_contents(&#39;/www/log.log&#39;,&#39;The sleep has passed&#39;);
    die(&#39;Hello World after sleep&#39;);
    ?&gt;

If I run the script from a web page then I can see the content of the file be set to the first string. 60 seconds later the error appears in the NginX log. 10 seconds later the  contents of the file changes to the 2nd string, proving that PHP is completing the process.

##Update 2##
Setting **fastcgi_ignore_client_abort on;** does change the response from a HTTP 499 to a HTTP 200 though nothing is still returned to the end client.

##Update 3##
Having installed Apache and PHP (5.3.10) onto the box straight (using apt) and then increasing the execution time the problem does appear to also happen on Apache as well.  The symptoms are the same as NginX now, a HTTP200 response but the actual client connection times out before hand.

I&#39;ve also started to notice, in the NginX logs, that if I test using Firefox, it makes a double request (like this https://stackoverflow.com/questions/13261327/php-script-executes-twice-when-longer-than-60-seconds). Though that does appear to be the client requesting upon the script failing


NginX issues HTTP 499 error after 60 seconds despite config. (PHP and AWS)

I&#39;m trying to use `file_get_contents` together with `stream_context_create` to make POST requests. My code so far:

		$options = array(&#39;http&#39; =&gt; array(
			&#39;method&#39;  =&gt; &#39;POST&#39;,
			&#39;content&#39; =&gt; $data,
			&#39;header&#39;  =&gt; 
				&quot;Content-Type: text/plain\r\n&quot; .
		    	&quot;Content-Length: &quot; . strlen($data) . &quot;\r\n&quot;
		));
		$context  = stream_context_create($options);
		$response = file_get_contents($url, false, $context);

It works fine, however, when an HTTP error occurs, it spits out a warning:

    file_get_contents(...): failed to open stream: HTTP request failed! HTTP/1.0 400 Bad Request

and returns false. Is there a way to:

- suppress a warning (I&#39;m planning to throw my own exception in case of failure)
- obtain the error information (at least, the response code) from the stream



Content Type	Original Author	Original Content on Stackoverflow
Question	Robert	View Question on Stackoverflow
Solution 1 - Http	Robert	View Answer on Stackoverflow

What are the disadvantage(s) of using HTTP pipelining?

Http Problem Overview

Http Solutions

Solution 1 - Http

Implementation bugs

Performance issues

In a template how do you access an outer scope while inside of a "with" or "range" scope?

Palindrome check in Javascript

Attributions