PNGImageBaker Class Reference

Php library to Bake the PNG Images. More...

Collaboration diagram for PNGImageBaker:

Public Member Functions
	__construct ($contents)
	Prepares file for handling metadata. More...
	checkChunks ($type, $check)
	Checks if a key already exists in the chunk of said type. More...
	addChunk ($chunkType, $key, $value)
	Add a chunk by type with given key and text. More...
	removeChunks ($chunkType, $key, $png)
	removes a chunk by type with given key and text More...
	extractBadgeInfo ($png, $key='openbadges')
	Extracts the baked PNG info by the Key. More...

Private Attributes
	$_contents
	$_size
	$_chunks

Detailed Description

Php library to Bake the PNG Images.

Definition at line 7 of file baker.lib.php.

Constructor & Destructor Documentation

__construct()

PNGImageBaker::__construct

(

$contents

)

Prepares file for handling metadata.

Verifies that this file is a valid PNG file. Unpacks file chunks and reads them into an array.

Parameters

string

$contents

File content as a string

Definition at line 20 of file baker.lib.php.

References $contents, $header, and array.

                                           {
        $this->_contents = $contents;
        $png_signature = pack("C8", 137, 80, 78, 71, 13, 10, 26, 10);
        // Read 8 bytes of PNG header and verify.
        $header = substr($this->_contents, 0, 8);
        if ($header != $png_signature) {
            echo 'This is not a valid PNG image';
        }
        $this->_size = strlen($this->_contents);
        $this->_chunks = array();
        // Skip 8 bytes of IHDR image header.
        $position = 8;
        do {
            $chunk = @unpack('Nsize/a4type', substr($this->_contents, $position, 8));
            $this->_chunks[$chunk['type']][] = substr($this->_contents, $position + 8, $chunk['size']);
            // Skip 12 bytes chunk overhead.
            $position += $chunk['size'] + 12;
        } while ($position < $this->_size);
    }

Member Function Documentation

addChunk()

PNGImageBaker::addChunk	(		$chunkType,
			$key,
			$value
	)

Add a chunk by type with given key and text.

Parameters

string	$chunkType	Chunk type, like iTXt, tEXt, etc.
string	$key	Keyword that needs to be added.
string	$value	Currently an assertion URL that is added to an image metadata.

Returns

string $result File content with a new chunk as a string.

Definition at line 71 of file baker.lib.php.

References $result.

                                                       {
        
        $chunkData = $key . "\0" . $value;
        $crc = pack("N", crc32($chunkType . $chunkData));
        $len = pack("N", strlen($chunkData));
        
        $newChunk = $len . $chunkType . $chunkData . $crc;
        $result = substr($this->_contents, 0, $this->_size - 12)
                . $newChunk
                . substr($this->_contents, $this->_size - 12, 12);
        return $result;
    }

checkChunks()

PNGImageBaker::checkChunks	(		$type,
			$check
	)

Checks if a key already exists in the chunk of said type.

We need to avoid writing same keyword into file chunks.

Parameters

string	$type	Chunk type, like iTXt, tEXt, etc.
string	$check	Keyword that needs to be checked.

Returns

boolean (true|false) True if file is safe to write this keyword, false otherwise.

Definition at line 49 of file baker.lib.php.

References $data.

                                               {
        if (array_key_exists($type, $this->_chunks)) {
            foreach (array_keys($this->_chunks[$type]) as $typekey) {
                list($key, $data) = explode("\0", $this->_chunks[$type][$typekey]);
                if (strcmp($key, $check) == 0) {
                    echo 'Key "' . $check . '" already exists in "' . $type . '" chunk.';
                    return false;
                }
            }
        }
        return true;
    }

extractBadgeInfo()

PNGImageBaker::extractBadgeInfo	(		$png,
			$key = 'openbadges'
	)

Extracts the baked PNG info by the Key.

Parameters

string	$png	the png image
string	$key	Keyword that needs to be searched.

Returns

mixed - If there is an error - boolean false is returned If there is PNG information that matches the key an array is returned

Definition at line 134 of file baker.lib.php.

References $data.

                                                              {
        // Read the magic bytes and verify
        $retval = substr($png,0,8);
        $ipos = 8;
        if ($retval != "\x89PNG\x0d\x0a\x1a\x0a") {
            return false;
        }

        // Loop through the chunks. Byte 0-3 is length, Byte 4-7 is type
        $chunkHeader = substr($png,$ipos,8);
        $ipos = $ipos + 8;
        while ($chunkHeader) {
            // Extract length and type from binary data
            $chunk = @unpack('Nsize/a4type', $chunkHeader);
            $skip = false;
            if ($chunk['type'] == 'tEXt') {
                $data = substr($png,$ipos,$chunk['size']);
                $sections = explode("\0", $data);
                if ($sections[0] == $key) {
                   return $sections;
                }
            }
            // Extract the data and the CRC
            $data = substr($png,$ipos,$chunk['size']+4);
            $ipos = $ipos + $chunk['size'] + 4;

            // Read next chunk header
            $chunkHeader = substr($png,$ipos,8);
            $ipos = $ipos + 8;
        }
    }

removeChunks()

PNGImageBaker::removeChunks	(		$chunkType,
			$key,
			$png
	)

removes a chunk by type with given key and text

Parameters

string	$chunkType	Chunk type, like iTXt, tEXt, etc.
string	$key	Keyword that needs to be deleted.
string	$png	the png image.

Returns

string $result New File content.

Definition at line 93 of file baker.lib.php.

References $data.

                                                         {
        // Read the magic bytes and verify
        $retval = substr($png,0,8);
        $ipos = 8;
        if ($retval != "\x89PNG\x0d\x0a\x1a\x0a")
            throw new Exception('Is not a valid PNG image');
        // Loop through the chunks. Byte 0-3 is length, Byte 4-7 is type
        $chunkHeader = substr($png,$ipos,8);
        $ipos = $ipos + 8;
        while ($chunkHeader) {
            // Extract length and type from binary data
            $chunk = @unpack('Nsize/a4type', $chunkHeader);
            $skip = false;
            if ( $chunk['type'] == $chunkType ) {
                $data = substr($png,$ipos,$chunk['size']);
                $sections = explode("\0", $data);
                print_r($sections);
                if ( $sections[0] == $key ) $skip = true;
            }
            // Extract the data and the CRC
            $data = substr($png,$ipos,$chunk['size']+4);
            $ipos = $ipos + $chunk['size'] + 4;
            // Add in the header, data, and CRC
            if ( ! $skip ) $retval = $retval . $chunkHeader . $data;
            // Read next chunk header
            $chunkHeader = substr($png,$ipos,8);
            $ipos = $ipos + 8;
        }
        return $retval;
    }

Field Documentation

$_chunks

PNGImageBaker::$_chunks

private

Definition at line 11 of file baker.lib.php.

$_contents

PNGImageBaker::$_contents

private

Definition at line 9 of file baker.lib.php.

$_size

PNGImageBaker::$_size

private

Definition at line 10 of file baker.lib.php.

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The documentation for this class was generated from the following file:

• Services/Badge/lib/baker.lib.php