Asked  7 Months ago    Answers:  5   Viewed   39 times

I wrote a simple relay script that connects to a web camera and reads from the socket, and outputs this data using the print function. The data is MJPG data with boundaries already setup. I just output the data that is read.

The problem is PHP seems to be buffering this data. When I set the camera to 1 FPS, the feed will freeze for 7-8 seconds, then quickly display 8 frames. If I set the resolution to a huge size, the camera move at more or less 1 frame per second. I assume then some buffering is happening (since huge sizes fill the buffer quickly, and low sizes don't), and I can't figure out how to disable this buffering. Does anyone know how to?

Code:

ignore_user_abort(false);

$boundary = "myboundary";

//Set this so PHP doesn't timeout during a long stream
set_time_limit(0);

$socketConn = @fsockopen ("192.168.1.6", 1989, $errno, $errstr, 2);
if (!$socketConn)
exit();
stream_set_timeout($socketConn, 10);
fputs ($socketConn, "GET /mjpeg HTTP/1.0rnrn");

//Setup Header Information
header("Cache-Control: no-cache");
header("Cache-Control: private");
header("Pragma: no-cache");
header("Content-type: multipart/x-mixed-replace; boundary=$boundary");

@ini_set('implicit_flush', 1);
for ($i = 0; $i < ob_get_level(); $i++)
ob_end_flush();
ob_implicit_flush(1);

stream_set_blocking($f2, false);

//Send data to client
while (connection_status() == CONNECTION_NORMAL)
{
    $chunk = fread($socketConn, 128);
    print $chunk;   
}

fclose($socketConn);

 Answers

13

tl;dr version

Do two things:

  1. Disable the userspace output buffer, either...

    • Globally, by either...

      • Turning off output_buffering in your php.ini, or
      • Turning off output_buffering in your Apache config using

        php_flag "output_buffering" Off
        
    • or for just the script you care about, by either...

      • calling ob_end_flush(), or
      • calling ob_end_clean()
  2. Also, disable the server-level output buffer as much as you possibly can, by either:

    • calling ob_implicit_flush() at the start of your script, or
    • calling flush() after every echo statement or other statement that adds output to the response body

Longer version

Confusingly, there are two layers of buffering that may be relevant and the PHP documentation does a poor job of distinguishing between the two.

The output buffer

The first layer is usually referred to by the PHP docs as the 'output buffer'. This layer of buffering only affects output to the body of the HTTP response, not the headers. You can turn on output buffering with ob_start(), and turn it off with ob_end_flush() or ob_end_clean(). You can also have all your scripts automatically start with output buffering on using the output_buffering option in php.ini.

The default value of this option for production versions of php.ini is 4096, which means that the first 4096 bytes of output will be buffered in the output buffer, at which point it will be flushed and output buffering is turned off.

You can disable this layer of buffering globally by setting output_buffering to Off in your php.ini file (or using

php_flag "output_buffering" Off

in your Apache config, if you're using Apache). Alternatively, you can disable it for a single script by calling ob_end_clean() or ob_end_flush() at the start of the script.

The write buffer, and the webserver buffer

Beyond the output buffer is what the PHP manual refers to as the 'write buffer', plus any buffering system your web server has. If you're using PHP with Apache through mod_php, and are not using mod_gzip, you can call flush() to flush these; with other backends, it might work too, although the manual is cagey about giving assurances:

Description

void flush ( void )

Flushes the write buffers of PHP and whatever backend PHP is using (CGI, a web server, etc). This attempts to push current output all the way to the browser with a few caveats.

flush() may not be able to override the buffering scheme of your web server and it has no effect on any client-side buffering in the browser. It also doesn't affect PHP's userspace output buffering mechanism. This means you will have to call both ob_flush() and flush() to flush the ob output buffers if you are using those.

There are also a couple of ways you can make PHP automatically call flush() every time you echo anything (or do anything else that echoes output to the response body).

The first is to call ob_implicit_flush(). Note that this function is deceptively named; given its ob_ prefix, any reasonable person would expect that it would affect the 'output buffer', as do ob_start, ob_flush etc. However, this is not the case; ob_implicit_flush(), like flush(), affects the server-level output buffer and does not interact in any way with the output buffer controlled by the other ob_ functions.

The second is to globally enable implicit flushing by setting the implicit_flush flag to On in your php.ini. This is equivalent to calling ob_implicit_flush() at the start of every script. Note that the manual advises against this, cryptically citing "serious performance implications", some of which I explore in this tangentially related answer.

Wednesday, March 31, 2021
 
nighter
answered 7 Months ago
96

Answered to help people who might stumble across this

As the the answer at Session lost when switching from HTTP to HTTPS in PHP has concluded, since you are using session.cookie_secure = 1 the cookie that contains the session ID is not transferred when the connection switches from HTTPS to HTTP. At HTTP connection, when you session_start(), PHP creates a new session id, which replaces the previous session id.

The answer also suggests a solution, pass the session id using query string, which is then picked up by the page. This smells of bad of security flaw. Don't forget the reason why we used HTTPS in the first place!

So the solution I suggest to you is that you redirect all http request to https counterparts. Use HTTPS for everything in your site, from css, images, to mundane static html pages. This is actually something that every application that is serious about security does. For example, visiting github page using HTTP will return:

HTTP/1.1 301 Moved Permanently
Server: nginx/0.7.67
Date: Sun, 08 May 2011 15:43:01 GMT
Content-Type: text/html
Content-Length: 185
Connection: close
Location: https://github.com/

<html>
<head><title>301 Moved Permanently</title></head>
<body bgcolor="white">
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx/0.7.67</center>
</body>
</html>

Remember why you used HTTPS in the first place, if you want to be totally secure, use HTTPS for everything.

Detect if the request is HTTPS or not (See this question) at bootstrap.

If the request is HTTP, either redirect all requests to HTTPS home page, or you can try parsing $_SERVER['REQUEST_URI'] and redirecting HTTP request to their HTTPS counterpart using parse_url and http_build_url.


Second Alternative Solution

If you really really don't want to use HTTPS for everything, then don't session_start() on pages that are accessed with HTTP. Secure cookies will be retained when you do this.


Third Alternative Solution

The other solution is to try and detect the user by IP addresses and user agent. This is not guaranteed to be accurate, so what I suggest is just use HTTPS for everything. Paypal, for example, always use HTTPS even for mundane static pages.

Wednesday, March 31, 2021
 
hakre
answered 7 Months ago
51

Use ob_get_clean() instead of ob_get_flush(). The former will remove the buffer without printing it and return its contents. The latter will do the same and print the contents of the buffer.

Wednesday, March 31, 2021
 
Extrakun
answered 7 Months ago
34

First php has to correctly flush everything :

@ob_end_flush();
@flush();

Then, I found two working solutions:

1) Via Nginx configuration:

fastcgi_buffering off;

2) Via HTTP header in the php code

header('X-Accel-Buffering: no');
Sunday, August 1, 2021
 
NewPHP
answered 3 Months ago
10

Well, if you want your client to see the mjpeg stream, you need to send the whole http response. HTTP client like browser or media player like VLC need a mjpeg stream that looks like :

HTTP/1.1 200 OK
Content-Type: multipart/x-mixed-replace; boundary=myboundary

--myboundary
Content-Type: image/jpeg
Content-length: 12345

[image 1 encoded jpeg data]


--myboundary
Content-Type: image/jpeg
Content-length: 45678

[image 2 encoded jpeg data]

...

NOTE: As Ergousha said in an answer, you must have an empty line after the Content-length field.

By the way, why not redirect your client directly to the mjpeg stream ?

You can use http://ipcam/mjpg/video.mjpg AXIS IP cameras for example.

If you just need the image through HTTP, you have to set the correct header and the MIME content-type image/jpeg. To decode the image, you have to get the byte data and you will get jpeg encoding. Then you will have to decode jpeg to get an image in a specific format (something like yuv420p I think). I've check on my ip camera, and its stream is not base64 encoded I think.

Precise your needs, I will try to help more.

my2c

EDIT:

Well, I suppose you do something like :

client    : connect to proxy, 
            get example.com/camera1.mjpg,
            while not the end
                recv


yourproxy : wait connection
            connect to camera,
            get 10.0.0.123/camera1.mjpg
            while not the end
                recv buffer
                copy buffer
                send buffer to client

That to say that you must send the correct header to your client. To be sure use a tool like wireshark to spy on the packet and be sure that after your client has issued a HTTP GET you send to him the correct MJPEG stream (like the one I describe at the beginning of my post ...)

m2c

Tuesday, September 21, 2021
 
Kaiepi
answered 1 Month ago
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