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php debugging the really really hard way

Bash, Business, CLI, Linux, PHP, Random Thoughts, SRSLY, Software Development, WTF, Web Stuff | Posted by apokalyptik

Oct 06 2009

If you’re ever in a situation where something is only happening intermittently, and only on a live server, and only while it’s under load… Lets say its not generating any error_log or stderr output, and you cant run it manually to reproduce… (we’ve all been in this situation) How do you get any debugging output at all?

Step 1: add this to the top of your entry point php file

if ( $_SERVER['REMOTE_ADDR'] == '127.0.0.1' ) {
       error_log( ' :: ' . getmypid() );
       sleep( 10 );
}

Step 2: use curl on the localhost to make the request

Step 3: (this assumes your error log is /tmp/php-error-output) run the following command in a second (root) terminal window

strace -p $(tail -n 1000 /tmp/php-error-output | grep ' :: ' | tail -n 1 | sed -r s/'^.+ :: '//g) -s 10240 2>&1

Good luck…

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Quality Time With Your JPEGs

API, Blogging, Business, CLI, Linux, PHP, SRSLY, Software Development, WTF, Web Stuff | Posted by apokalyptik

Sep 16 2009

When working with user provided images in PHP you run into a problem. Lets say that you want to generate thumbnails of uploaded JPEGs for users. This is a fairly common use case where you would employ PHP and GD (the most prevalent php image extension.) But when you generate the new, smaller, image what quality setting do you use? If your quality setting is too low then the image is distorted unacceptably. Likewise if your quality setting is too high then you produce a dimensionally smaller image with a larger size in bytes than the original. So what do you do when you want to satisfy all cases? Well the obvious answer is that you should use the same JPEG quality setting that the image had when it was uploading. Now… Using PHP and GD tell me how you accomplish this.

Go ahead

I’ll wait

You can’t, can you? If you’re really sneaky you might be thinking about just pulling the data out of the binary stream, and if you’re a linux nut you’re probably sitting there muttering “just use identify (a la imagemagick)”. Of course if you try that under heavy traffic you’ll soon discover that it kills your servers. Just for reference I’ll share that code with you (not everyone is serving 2g/sec in dynamic image traffic after all). We already have the binary data in ram in the $rval variable, in case you were curious.

// define how we will deal with stdin, stdout, and stderr 
$descriptorspec = array( 0 => array( "pipe", "r" ), 1 => array( "pipe", "w" ), 2 => array( "pipe", "a" ) );
// run identify, -verbose required, - means read file from stdin
$process = proc_open( IDENTIFY . ' -verbose -', $descriptorspec, $pipes );
if ( false !== $process ) {
	// pipe the image data through it to its stdin
	fwrite( $pipes[0], $rval );
	// close stdin to allow identify to process
	fclose( $pipes[0] );
	// read the results of the program execution
	$results = stream_get_contents($pipes[1]);
	// clean up open file handles
	fclose( $pipes[1] );
	fclose( $pipes[2] );
	// Unix return value of 0 means success
	if ( 0 == proc_close($process) ) {
		// pull out the image quality from identify output
		if ( preg_match( '#Quality: ([0-9]+)[^0-9]#', $results, $m ) )
			$origin_quality = intval($m[1]);
		// detect when something goes wrong above
		if ( $origin_quality == 0 )
			$origin_quality = 100;
	}
}

So, since this consumes too much of our available resources (especially ram and cpu usage since identify fully decompresses and reads the image into a raw state for processing… hundreds of MB of ram, which you can limit but then it becomes unbearably slow…) that’s out. What now? If you’re really extra sneaky you’re thinking that you should be able to read the setting out of the binary data… there should be a header after all, right? Well… Yes there is a header but “quality” is not a “setting” its more a measure of how compressed the image is… which isn’t exactly recorded either… at least… not as an integer value. The compression matrix used to preform JPEGs lossy compression *IS* stored in a header.. and it turns out this is what the ImageMagick code uses to give us that quality setting. So I set out to reproduce this in PHP.

I know… I’m a masochist.

Thanks to some serious google-fu (and possibly a note in a php online doc manual relating to IPC, I don’t remember which of the two led me to the package first) I found that there’s already some code out there which deals with the nasty bits of reading raw JPEG headers (though not doing what I want with the header that I want) in the PHP JPEG Metadata Toolkit And the instructions for evaluating the header we can then pull is in the ImageMagick source code (coders/jpeg.c)

When we put the two together and modify it a bit to suite our needs (i.e. reading from the in-memory buffer, pulling just the right header from the jpeg file, etc) we get this code… and finally the ability to call $quality = get_jpeg_quality( $rval ); In my test (yea just one or two… very scientific like), this over 100 times faster than using the proc_open and executable method, uses less ram (a lot lot lot lot lot less ram) and generally just doesn’t suck as much.

< ?php
 
function get_jpeg_header_data( &$buff, $want=null ) { 
	$data = buffer_read( $buff, 2, true ); // Read the first two characters
	// Check that the first two characters are 0xFF 0xDA  (SOI - Start of image)
	if ( $data != "\xFF\xD8" ) {
		// No SOI (FF D8) at start of file - This probably isn't a JPEG file - close file and return;
		return false;
	}
	$data = buffer_read( $buff, 2 ); // Read the third character
	// Check that the third character is 0xFF (Start of first segment header)
	if ( $data{0} != "\xFF" ) {
		// NO FF found - close file and return - JPEG is probably corrupted
		return false;
	}
	// Cycle through the file until, one of: 
	//   1) an EOI (End of image) marker is hit,
	//   2) we have hit the compressed image data (no more headers are allowed after data)
	//   3) or end of file is hit
	$hit_compressed_image_data = FALSE;
	while ( ( $data{1} != "\xD9" ) && ( !$hit_compressed_image_data) && ( $data != '' ) ) { 
		// Found a segment to look at.
		// Check that the segment marker is not a Restart marker - restart markers don't have size or data after them
		if (  ( ord($data{1}) < 0xD0 ) || ( ord($data{1}) > 0xD7 ) ) {
			// Segment isn't a Restart marker
			$sizestr = buffer_read( $buff, 2 ); // Read the next two bytes (size)
			$decodedsize = unpack ("nsize", $sizestr); // convert the size bytes to an integer
			// Read the segment data with length indicated by the previously read size
			$segdata = buffer_read( $buff, $decodedsize['size'] - 2 );
			// Store the segment information in the output array
			if ( !$want || $want == ord($data{1}) ) {
				$headerdata[] = (object)array(  
					"SegType" => ord($data{1}),
					"SegName" => $GLOBALS[ "JPEG_Segment_Names" ][ ord($data{1}) ],
					"SegDesc" => $GLOBALS[ "JPEG_Segment_Descriptions" ][ ord($data{1}) ],
					"SegData" => $segdata 
				);
			}
		}
		// If this is a SOS (Start Of Scan) segment, then there is no more header data - the compressed image data follows
		if ( $data{1} == "\xDA" ) {
			$hit_compressed_image_data = true;
		} else {
			// Not an SOS - Read the next two bytes - should be the segment marker for the next segment
			$data = buffer_read( $buff, 2 );
			// Check that the first byte of the two is 0xFF as it should be for a marker
			if ( $data{0} != "\xFF" ) {
				// NO FF found - close file and return - JPEG is probably corrupted
				return false;
			}
		}
	}
	return $headerdata;
}
 
function buffer_read( &$buff, $len, $new=false ) {
	static $pointer = 0;
	if ( $new )
		$pointer = 0;
	if ( $pointer + $len > strlen( $buff ) ) {
		$len = strlen( $buff ) - $pointer;
		if ( $len < 1 )
			return null;
	}
	$data = substr( $buff, $pointer, $len );
	$pointer += $len;
	return $data;
}
 
// The names of the JPEG segment markers, indexed by their marker number
$GLOBALS[ "JPEG_Segment_Names" ] = array(
	0xC0 =>  "SOF0",  0xC1 =>  "SOF1",  0xC2 =>  "SOF2",  0xC3 =>  "SOF4",
	0xC5 =>  "SOF5",  0xC6 =>  "SOF6",  0xC7 =>  "SOF7",  0xC8 =>  "JPG",
	0xC9 =>  "SOF9",  0xCA =>  "SOF10", 0xCB =>  "SOF11", 0xCD =>  "SOF13",
	0xCE =>  "SOF14", 0xCF =>  "SOF15",
	0xC4 =>  "DHT",   0xCC =>  "DAC",
	0xD0 =>  "RST0",  0xD1 =>  "RST1",  0xD2 =>  "RST2",  0xD3 =>  "RST3",
	0xD4 =>  "RST4",  0xD5 =>  "RST5",  0xD6 =>  "RST6",  0xD7 =>  "RST7",
	0xD8 =>  "SOI",   0xD9 =>  "EOI",   0xDA =>  "SOS",   0xDB =>  "DQT",
	0xDC =>  "DNL",   0xDD =>  "DRI",   0xDE =>  "DHP",   0xDF =>  "EXP",
	0xE0 =>  "APP0",  0xE1 =>  "APP1",  0xE2 =>  "APP2",  0xE3 =>  "APP3",
	0xE4 =>  "APP4",  0xE5 =>  "APP5",  0xE6 =>  "APP6",  0xE7 =>  "APP7",
	0xE8 =>  "APP8",  0xE9 =>  "APP9",  0xEA =>  "APP10", 0xEB =>  "APP11",
	0xEC =>  "APP12", 0xED =>  "APP13", 0xEE =>  "APP14", 0xEF =>  "APP15",
	0xF0 =>  "JPG0",  0xF1 =>  "JPG1",  0xF2 =>  "JPG2",  0xF3 =>  "JPG3",
	0xF4 =>  "JPG4",  0xF5 =>  "JPG5",  0xF6 =>  "JPG6",  0xF7 =>  "JPG7",
	0xF8 =>  "JPG8",  0xF9 =>  "JPG9",  0xFA =>  "JPG10", 0xFB =>  "JPG11",
	0xFC =>  "JPG12", 0xFD =>  "JPG13",
	0xFE =>  "COM",   0x01 =>  "TEM",   0x02 =>  "RES",
);
 
 
// The descriptions of the JPEG segment markers, indexed by their marker number
$GLOBALS[ "JPEG_Segment_Descriptions" ] = array(
	/* JIF Marker byte pairs in JPEG Interchange Format sequence */
	0xC0 => "Start Of Frame (SOF) Huffman  - Baseline DCT",
	0xC1 =>  "Start Of Frame (SOF) Huffman  - Extended sequential DCT",
	0xC2 =>  "Start Of Frame Huffman  - Progressive DCT (SOF2)",
	0xC3 =>  "Start Of Frame Huffman  - Spatial (sequential) lossless (SOF3)",
	0xC5 =>  "Start Of Frame Huffman  - Differential sequential DCT (SOF5)",
	0xC6 =>  "Start Of Frame Huffman  - Differential progressive DCT (SOF6)",
	0xC7 =>  "Start Of Frame Huffman  - Differential spatial (SOF7)",
	0xC8 =>  "Start Of Frame Arithmetic - Reserved for JPEG extensions (JPG)",
	0xC9 =>  "Start Of Frame Arithmetic - Extended sequential DCT (SOF9)",
	0xCA =>  "Start Of Frame Arithmetic - Progressive DCT (SOF10)",
	0xCB =>  "Start Of Frame Arithmetic - Spatial (sequential) lossless (SOF11)",
	0xCD =>  "Start Of Frame Arithmetic - Differential sequential DCT (SOF13)",
	0xCE =>  "Start Of Frame Arithmetic - Differential progressive DCT (SOF14)",
	0xCF =>  "Start Of Frame Arithmetic - Differential spatial (SOF15)",
	0xC4 =>  "Define Huffman Table(s) (DHT)",
	0xCC =>  "Define Arithmetic coding conditioning(s) (DAC)",
	0xD0 =>  "Restart with modulo 8 count 0 (RST0)",
	0xD1 =>  "Restart with modulo 8 count 1 (RST1)",
	0xD2 =>  "Restart with modulo 8 count 2 (RST2)",
	0xD3 =>  "Restart with modulo 8 count 3 (RST3)",
	0xD4 =>  "Restart with modulo 8 count 4 (RST4)",
	0xD5 =>  "Restart with modulo 8 count 5 (RST5)",
	0xD6 =>  "Restart with modulo 8 count 6 (RST6)",
	0xD7 =>  "Restart with modulo 8 count 7 (RST7)",
	0xD8 =>  "Start of Image (SOI)",
	0xD9 =>  "End of Image (EOI)",
	0xDA =>  "Start of Scan (SOS)",
	0xDB =>  "Define quantization Table(s) (DQT)",
	0xDC =>  "Define Number of Lines (DNL)",
	0xDD =>  "Define Restart Interval (DRI)",
	0xDE =>  "Define Hierarchical progression (DHP)",
	0xDF =>  "Expand Reference Component(s) (EXP)",
	0xE0 =>  "Application Field 0 (APP0) - usually JFIF or JFXX",
	0xE1 =>  "Application Field 1 (APP1) - usually EXIF or XMP/RDF",
	0xE2 =>  "Application Field 2 (APP2) - usually Flashpix",
	0xE3 =>  "Application Field 3 (APP3)",
	0xE4 =>  "Application Field 4 (APP4)",
	0xE5 =>  "Application Field 5 (APP5)",
	0xE6 =>  "Application Field 6 (APP6)",
	0xE7 =>  "Application Field 7 (APP7)",
	0xE8 =>  "Application Field 8 (APP8)",
	0xE9 =>  "Application Field 9 (APP9)",
	0xEA =>  "Application Field 10 (APP10)",
	0xEB =>  "Application Field 11 (APP11)",
	0xEC =>  "Application Field 12 (APP12) - usually [picture info]",
	0xED =>  "Application Field 13 (APP13) - usually photoshop IRB / IPTC",
	0xEE =>  "Application Field 14 (APP14)",
	0xEF =>  "Application Field 15 (APP15)",
	0xF0 =>  "Reserved for JPEG extensions (JPG0)",
	0xF1 =>  "Reserved for JPEG extensions (JPG1)",
	0xF2 =>  "Reserved for JPEG extensions (JPG2)",
	0xF3 =>  "Reserved for JPEG extensions (JPG3)",
	0xF4 =>  "Reserved for JPEG extensions (JPG4)",
	0xF5 =>  "Reserved for JPEG extensions (JPG5)",
	0xF6 =>  "Reserved for JPEG extensions (JPG6)",
	0xF7 =>  "Reserved for JPEG extensions (JPG7)",
	0xF8 =>  "Reserved for JPEG extensions (JPG8)",
	0xF9 =>  "Reserved for JPEG extensions (JPG9)",
	0xFA =>  "Reserved for JPEG extensions (JPG10)",
	0xFB =>  "Reserved for JPEG extensions (JPG11)",
	0xFC =>  "Reserved for JPEG extensions (JPG12)",
	0xFD =>  "Reserved for JPEG extensions (JPG13)",
	0xFE =>  "Comment (COM)",
	0x01 =>  "For temp private use arith code (TEM)",
	0x02 =>  "Reserved (RES)",
);
 
/**
 * Most of this function is taken directly from the source code for imagemagick
 * and how it handles identify -verbose $filename to present you with a Quality
 * number.  This number should be considered approximate.  It's essentially
 * based upon the numbers used to perform compression on the original image
 * data... 
 *
 * See: http://www.obrador.com/essentialjpeg/headerinfo.htm
 * See: http://www.impulseadventure.com/photo/jpeg-quantization.html
 * See: http://www.impulseadventure.com/photo/jpeg-huffman-coding.html
 */
function get_jpeg_quality( &$buff ) {
	$tables = array(
		'multi' => array(
			'hash' => array(
				 1020, 1015,  932,  848,  780,  735,  702,  679,  660,  645,
				  632,  623,  613,  607,  600,  594,  589,  585,  581,  571,
				  555,  542,  529,  514,  494,  474,  457,  439,  424,  410,
				  397,  386,  373,  364,  351,  341,  334,  324,  317,  309,
				  299,  294,  287,  279,  274,  267,  262,  257,  251,  247,
				  243,  237,  232,  227,  222,  217,  213,  207,  202,  198,
				  192,  188,  183,  177,  173,  168,  163,  157,  153,  148,
				  143,  139,  132,  128,  125,  119,  115,  108,  104,   99,
				   94,   90,   84,   79,   74,   70,   64,   59,   55,   49,
				   45,   40,   34,   30,   25,   20,   15,   11,    6,    4,
					0	
			), // hash
			'sums' => array (
				 32640, 32635, 32266, 31495, 30665, 29804, 29146, 28599, 28104,
				 27670, 27225, 26725, 26210, 25716, 25240, 24789, 24373, 23946,
				 23572, 22846, 21801, 20842, 19949, 19121, 18386, 17651, 16998,
				 16349, 15800, 15247, 14783, 14321, 13859, 13535, 13081, 12702,
				 12423, 12056, 11779, 11513, 11135, 10955, 10676, 10392, 10208,
				  9928,  9747,  9564,  9369,  9193,  9017,  8822,  8639,  8458,
				  8270,  8084,  7896,  7710,  7527,  7347,  7156,  6977,  6788,
				  6607,  6422,  6236,  6054,  5867,  5684,  5495,  5305,  5128,
				  4945,  4751,  4638,  4442,  4248,  4065,  3888,  3698,  3509,
				  3326,  3139,  2957,  2775,  2586,  2405,  2216,  2037,  1846,
				  1666,  1483,  1297,  1109,   927,   735,   554,   375,   201,
				   128,     0
			 ), // sums
		), // multi
		'single' => array(
			'hash' => array(
               510,  505,  422,  380,  355,  338,  326,  318,  311,  305,
               300,  297,  293,  291,  288,  286,  284,  283,  281,  280,
               279,  278,  277,  273,  262,  251,  243,  233,  225,  218,
               211,  205,  198,  193,  186,  181,  177,  172,  168,  164,
               158,  156,  152,  148,  145,  142,  139,  136,  133,  131,
               129,  126,  123,  120,  118,  115,  113,  110,  107,  105,
               102,  100,   97,   94,   92,   89,   87,   83,   81,   79,
                76,   74,   70,   68,   66,   63,   61,   57,   55,   52,
                50,   48,   44,   42,   39,   37,   34,   31,   29,   26,
                24,   21,   18,   16,   13,   11,    8,    6,    3,    2,
                 0
			), // hash
			'sums' => array(
               16320, 16315, 15946, 15277, 14655, 14073, 13623, 13230, 12859,
               12560, 12240, 11861, 11456, 11081, 10714, 10360, 10027,  9679,
                9368,  9056,  8680,  8331,  7995,  7668,  7376,  7084,  6823,
                6562,  6345,  6125,  5939,  5756,  5571,  5421,  5240,  5086,
                4976,  4829,  4719,  4616,  4463,  4393,  4280,  4166,  4092,
                3980,  3909,  3835,  3755,  3688,  3621,  3541,  3467,  3396,
                3323,  3247,  3170,  3096,  3021,  2952,  2874,  2804,  2727,
                2657,  2583,  2509,  2437,  2362,  2290,  2211,  2136,  2068,
                1996,  1915,  1858,  1773,  1692,  1620,  1552,  1477,  1398,
                1326,  1251,  1179,  1109,  1031,   961,   884,   814,   736,
                 667,   592,   518,   441,   369,   292,   221,   151,    86,
                  64,     0
			), // sums
		), // single
	); // tables
 
	$headers = get_jpeg_header_data( $buff, 0xDB );
	if ( !is_array( $headers ) || !count( $headers ) )
		return 100;
	$header = $headers[0];	
	$quality = 0;
	if ( strlen($header->SegData) > 128 ) {
		$entry = array( 0 => array(), 1 => array() );
		foreach ( str_split( substr( $header->SegData, 1, 64) ) as $chr ) 
			$entry[0][] = ord($chr);
		foreach ( str_split( substr( $header->SegData, -64) ) as $chr )
			$entry[1][] = ord($chr);
		$sum = array_sum( $entry[0] ) + array_sum( $entry[1] );
		$qvalue = $entry[0][2] + $entry[0][53] + $entry[1][0] + $entry[1][63];
		$table = "multi";
	} else if ( strlen($header->SegData) > 64 ) {
		$entry = array( 0 => array() );
		foreach ( str_split( substr( $header->SegData, 1, 64) ) as $chr )
			$entry[0][] = ord($chr);
		$sum = array_sum( $entry[0] );
		$qvalue = $entry[0][2] + $entry[0][53];
		$table = "single";
	} else {
		return 100; // go with a safe value
	}
	for( $i = 0; $i < 100; $i++ ) {
		if ( ( $qvalue < $tables[$table]['hash'][$i] ) && ( $sum < $tables[$table]['sums'][$i] ) )
			continue;
		// error_log( "$table >> $qvalue && $sum >> " . ( $i + 1 ) );
		return $i + 1;
	}
	return 100; // go with a safe value
}

Right… serious suckage. Which is why I’m sharing it here so that you don’t have to go through all that trouble. You can just steal my stolen code. Aren’t GPL compatible licenses fun?

Ok, finally, you… in the back… stop jumping up and down screaming about the Imagick PECL extension… In my testing getCompressionQuality() didnt work and getImageCompression() was unavailable (though I hear there is a newer version of the extension now… YMMV)

5 Comments »

Debian Lenny, Avahi, AFP… Linux Fileserver for OSX Clients

Apple, CLI, Linux, Personal, Random Thoughts, Software Development | Posted by apokalyptik

Feb 12 2009

If you’re like me you have an OSX computer or 3 at home, and a debian file server. If you’re like me you hate samba/nfs on principle and want your debian server to show up in finder. If you’re like me you arent using debian 3 which is what most of the walkthroughs seem to expect… This is how I did it… With Debian Lenny.

What we’re using, and why:

Avahi handles zeroconf (making it show up in finder) (most howtos involve howl which is no longer in apt)
netatalk has afpd
afpd is the fileserver

From: http://blog.damontimm.com/how-to-install-netatalk-afp-on-ubuntu-with-encrypted-authentication/

apt-get update
mkdir -p ~/src/netatalk
cd ~/src/netatalk
apt-get install cracklib2-dev libssl-dev
apt-get source netatalk
apt-get build-dep netatalk
cd netatalk-2.0.3

From: http://www.sharedknowhow.com/2008/05/installing-netatalk-under-centos-5-with-leopard-support/

vim bin/cnid/cnid_index.c ## replace “ret = db->stat(db, &sp, 0);” with “ret = db->stat(db, NULL, &sp, 0);” line 277
vim etc/cnid_dbd/dbif.c ## replace “ret = db->stat(db, &sp, 0);” with “ret = db->stat(db, NULL, &sp, 0);” line 517

Mine

./configure –prefix=/usr/local/netatalk
make
make install
vim /etc/rc.local ## add “/usr/local/netatalk/sbin/afpd”
/usr/local/netatalk/sbin/afpd

From: http://www.disgruntled-dutch.com/2007/general/how-to-get-your-linux-based-afp-server-to-show-up-correctly-in-leopards-new-finder

apt-get install avahi-daemon
vim /etc/nsswitch.conf ## make the hosts line read “hosts: files dns mdns4″
cd /etc/avahi/services
wget http://www.disgruntled-dutch.com/media/afpd.service
/etc/init.d/avahi-daemon restart

in case that file drops off the face of the net, this is its contents (except “< ?” is “<?” and “< !” is “<!”) :

< ?xml version="1.0" standalone='no'?><!--*-nxml-*-->
< !DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service -group>
<name replace-wildcards="yes">%h</name>
</service><service>
<type>_afpovertcp._tcp</type>
<port>548</port>
</service>

At this point your server should show up under the network in your finder… and you should be able to connect with any system username/pw combo

6 Comments »

making munin-graph take advantage of multiple cpus/cores

Business, CLI, Linux, Software Development | Posted by apokalyptik

Jan 23 2009

I do a lot of things for Automattic, and many of the things I do are quite esoteric (for a php developer anyways.) Perl is not my language of choice, but I’ve never balked at a challenge…. just… did it have to be perl? Anyways. We have more than a thousand machines that we track with munin… which means a TON of graphs. munin-update is efficient, taking advantage of all cpus and getting done in the fastest time possible, but munin-graph started taking so long as to be useless (and munin-cgi-graph takes almost a minute to fully render the servers day/week summary page which is completely unacceptable when we’re trying to troubleshoot a sudden, urgent, problem.) So I got to dive in and make it faster…

Step 1: add in this function (which i borrowed from somewhere else)

sub afork (\@$&) {
  my ($data, $max, $code) = @_;
  my $c = 0;
  foreach my $data (@$data) {
    wait unless ++ $c < = $max;
    die "Fork failed: $!\n" unless defined (my $pid = fork);
    exit $code -> ($data) unless $pid;
  }
  1 until -1 == wait;
}

Step 2: replace this

for my $service (@$work_array) {
    process_service ($service);
}

with this

afork(@$work_array, 16, \&process_service);

I also have munin-html and munin-graph running side-by-side

( [ -x /usr/local/munin/lib/munin-graph  ] &&
    nice /usr/local/munin/lib/munin-graph --cron $@ 2>&1 |
    fgrep -v "*** attempt to put segment in horiz list twice" )& $waitgraph=$!
( [ -x /usr/local/munin/lib/munin-html   ] && nice /usr/local/munin/lib/munin-html $@; )& $waithtml=$!
wait $waitgraph
wait $waithtml

I did several other, more complicated hacks as well. Such as not generating month and year graphs via cron, letting those render on-demand with munin-cgi-graph

All said we’re doing in under 2.5 minutes what was taking 7 or 8 minutes previously

4 Comments »

Using wait, $!, and () for threading in bash

Bash, Business, CLI, Linux, Random Thoughts, Software Development, Web Stuff | Posted by apokalyptik

Dec 11 2008

This is a simplistic use of the pattern that I wrote about in my last post to wait on multiple commands in bash. In essence I have a script which runs a command (like uptime or restarting a daemon) on a whole bunch of servers (think pssh). Anyways… this is how I modified the script to run the command on multiple hosts in parallel. This is a bit simplistic as it runs, say, 10 parallel ssh commands and then waits for all 10 to complete. I’m very confident that someone could easily adapt this to run at a constant concurrency level of $threads… but I didn’t need it just then so I didn’t go that far… As a side note, this is possibly the first time I’ve ever *needed* an array in a bash script… hah…

# $1 is the commandto run on the remote hosts
# $2 is used for something not important for this script
# $3 is the (optional) number of concurrent connections to use
 
if [ ! "$3" == "" ]
then
    threads=$3
else
    threads=1
fi
 
cthreads=0;
stack=()
for s in $servers
  do
    if [ $cthreads -eq $threads ]; then
        for job in ${stack[@]}; do
              wait $job
        done
        stack=()
        cthreads=0
    fi
    (
        for i in $(ssh root@$s "$1" )
            do
                echo -e "$s:\t$i"
        done
    )& stack[$cthreads]=$!
    let cthreads=$cthreads+1
done
for job in ${stack[@]}; do
    wait $job
done

1 Comment »

bash – collecting the return value of backgrounded processes

Bash, Business, CLI, Linux, Random Thoughts, Software Development | Posted by apokalyptik

Dec 05 2008

You know that you can run something in the background in a bash script with ( command )&, but a coworker recently wanted to run multiple commands, wait for all of them to complete, collect and decide what to do based on their return values… this proved much trickier. Luckily there is an answer

#!/bin/bash
 
(sleep 3; exit 1)& p1=$!
(sleep 2; exit 2)& p2=$!
(sleep 1; exit 3)& p3=$!
 
wait "$p1"; r1=$?
wait "$p2"; r2=$?
wait "$p3"; r3=$?
 
echo "$p1:$r1 $p2:$r2 $p3:$r3"

2 Comments »

a dumbed down version of wpdb for sqlite

API, Business, CLI, Linux, MySQL, PHP, Personal, Random Thoughts, Software Development, Web Stuff | Posted by apokalyptik

Nov 18 2008

I’ve been working, gradually, on a project using an sqlite3 database (for its convenience) and found myself missing the clean elegance of wpdb… so I implemented it. It was actually really easy to do, and I figured I would throw it up here for anyone else wishing to use it. The functionality that I build this around is obtainable here: http://php-sqlite3.sourceforge.net/pmwiki/pmwiki.php (don’t freak… its in apt…)

With this I can focus on the sql, which is different enough, and not fumble over function names and such… $db = new sqlite_wpdb($dbfile, 3); var_dump($db->get_results(“SELECT * FROM `mytable` LIMIT 5″));

the code is below… and hopefully not too mangled…

< ?php
 
class sqlite_wpdb {
 
        var $version = null;
        var $db = null;
        var $result = null;
        var $error = null;
 
        function sqwpdb($file, $version=3) { 
                return $this->__construct($file, $version); 
        }
 
        function __construct($file, $version=3) {
                $function = "sqlite{$version}_open";
                if ( !function_exists($function) )
                        return false;
                if ( !file_exists($file) )
                        return false;
                if ( !$this->db = @$function($file) )
                        return false;
                $this->version = $version;
                $this->fquery = "sqlite{$this->version}_query";
                $this->ferror = "sqlite{$this->version}_error";
                $this->farray = "sqlite{$this->version}_fetch_array";
                return $this;
        }
 
        function escape($string) {
                return str_replace("'", "''", $string);
        }
 
        function query($query) {
                if ( $this->result = call_user_func($this->fquery, $this->db, $query) )
                        return $this->result;
                $this->error = call_user_func($this->ferror, $this->db);
                return false;
        }
 
        function array_to_object($array) {
                if ( ! is_array($array) )
                        return $array;
 
                $object = new stdClass();
                foreach ( $array as $idx => $val ) {
                        $object->$idx = $val;
                }
                return $object;
        }
 
        function get_results($query) {
                if ( !$this->query($query) )
                        return false;
                $rval = array();
                while ( $row = $this->array_to_object(call_user_func($this->farray, $this->result)) ) {
                        $rval[] = $row;
                }
                return $rval;
        }
 
        function get_row($query) {
                if ( ! $results = $this->get_results($query) )
                        return false;
                return array_shift($results);
        }
 
        function get_var($query) {
                return $this->get_val($query);
        }
 
        function get_val($query) {
                if ( !$row = $this->get_row($query) )
                        return false;
                $row = get_object_vars($row);
                if ( !count($row) )
                        return false;
                return array_shift($row);
        }
 
        function get_col($query) {
                if ( !$results = $this->get_results($query) )
                        return false;
                $column = array();
                foreach ( $results as $row ) {
                        $row = get_object_vars($row);
                        if ( !count($row) )
                                continue;
                        $column[] = array_shift($row);
                }
                return $column;
        }
 
}
 
?>

1 Comment »

Postfix, DKIMproxy, Spamc

Business, CLI, Funny Stuff, Linux, Security, Software Development, Web Stuff | Posted by apokalyptik

Nov 14 2008

If you’re running any moderately busy mail server you’re probably using spamassassins spamc/spamd to check for spam because its tons more efficient than piping the mail through the spamassassin cli. Assuming that you do, and that you plan on adding DKIM proxy to the mix to verify and sign emails you need to put things in the right order, to save you some headache here’s what I did:

smtp|smtps => -o smtpd_proxy_filter=127.0.0.1:10035 # outgoing dkim verify port
127.0.0.1:10036 => -o content_filter=spamassassin
spamassassin => pipe user=nobody argv=/usr/bin/spamc -f -e /usr/sbin/sendmail -oi -f ${sender} ${recipient} # this delivers to the “pickup” service
pickup => -o content_filter=dksign:127.0.0.1:10037 # outgoing dkim signing port
127.0.0.1:10038 => -o content_filter= # the buck stops here

If you arent careful with these (which I wasnt) you’ll end up causing an infinite loop between your filters (which I did). Thus concludes our public service announcement.

No Comments »

Writing your own shell in php

API, Business, CLI, Linux, MySQL, PHP, Personal, Random Thoughts, Software Development, Web Stuff | Posted by apokalyptik

Aug 03 2008

I’ve always wanted to write my own simple shell in php. Call me a glutin for punishment, but it seems like something that a lot of people could use to be able to do… If your web app had a command line interface for various things… like looking up stats, or users, or suspending naughty accounts, or whatever…. wouldnt that be cool and useful? Talk about geek porn. Anyways this this morning I got around to tinkering with the idea, and here is what i came up with… It’s rough, and empty, but its REALLY easy to extend and plug into any php application.

apokalyptik:~/phpshell$ ./shell.php

/home/apokalyptik/phpshell > hello

hi there

/home/apokalyptik/phpshell > hello world

hi there world

/home/apokalyptik/phpshell > cd ..

/home/apokalyptik/ > cd phpshell

/home/apokalyptik/phpshell > ls

shell.php

/home/apokalyptik//phpshell > exit

apokalyptik:~/phpshell$ ./shell.php

See the source here: shell.phps

4 Comments »

Internally Caching Longer Than Externally Caching

Business, Linux, Random Thoughts, Web Stuff | Posted by apokalyptik

Jul 16 2008

We use varnish for a lot of our file caching needs, and recently we figured out how to do something rather important through a combination of technologies. Imagine you have backend servers generating dynamic content based on user input. So your users do something that fits the following categories:

is expensive to generate dynamically, and should be served from cache
many requests come in for the same objects, bandwidth should be conserved
doesnt change very often
once changed needs to take effect quickly

Now wish varnish we’ve been using the Expires header for a long time with great success, but for this we were having no luck. If we set the expires header to 3 weeks, then clients also cache the content for 3 weeks (violating requirement #3.) We can kill the Expires header in varnish at vcl_deliver, but then clients don’t cache at all (#2.) We can add Content-Control, overwrite the Age (otherwise reported Age: will be greater than max-age), and kill the Expires headers in the same place, but this isn’t pretty, and seems like a cheap hack. Ideally we could rewrite the Expires header in varnish, but that doesn’t seem doable.

So what we ended up doing, was header rewriting at the load balancer (nginx.) inside our location tag we added the following:

proxy_hide_header Age;
proxy_hide_header Expires;
proxy_hide_header Cache-Control;
add_header Source-Age $upstream_http_Age;
expires  300s;

Now nginx setsa proper Cache-Control: and Expires: headers for us, disregarding what varnish serves out. Web clients dont check back for 5 minutes (reusing the old object) and varnish can cache until judgment dat because we get wild card invalidation

Isn’t technology fun?!