Exif を PHP で分解してみた (異常系は手抜き)

readexif.php

<?php

// ref) http://dsas.blog.klab.org/archives/52123322.html

class Exif {
    private $data;
    private $byteOrder; // 1:Big Endian, 2:Little Endian
    private $IFDs = array();
    private $cursol = 0;
    const IFD_OFFSET_BASE = 6;
    function parse($data) {
        $this->data = $data;
        $head6 = substr($data, 0, 6);
        if ($head6 != "Exif\0\0") {
            throw new Exception("Unknown head 6 byte: $head6");
            return false;
        }
        $byteOrderId = substr($data, 6, 2);
        switch ($byteOrderId) {
        case "MM": // Big Endian
            $this->byteOrder = 1;
                break;
        case "II": // Little Endian
            $this->byteOrder = 2;
                break;
        default:
            throw new Exception("Unknown byte order: $byteOrderId");
        }
        //$tiffVersion = substr($data, 8, 2);
        $this->setCursol(8);
        $tiffVersion = $this->getUI16();
        if ($tiffVersion !== 0x002A) {
            throw new Exception("Unknown tiff version:0x".dechex($tiffVersion));
        }
        $IFD0thOffset = $this->getUI32();
        $IFD0thTable = $this->makeIFDTable(self::IFD_OFFSET_BASE + $IFD0thOffset);
        $this->IDFs["0th"] = $IFD0thTable;
        $IFD1thOffset = $this->getUI32();
        if ($IFD1thOffset > 0) {
            $IFD1thTable = $this->makeIFDTable(self::IFD_OFFSET_BASE + $IFD1thOffset);
            while (($nextIFDOffset = $this->getUI32()) > 0) {
                $nextIFDTable = $this->makeIFDTable(self::IFD_OFFSET_BASE + $nextIFDOffset);
                $IFD1thTable = $IFD1thTable + $nextIFDTable;
            }
            $this->IDFs["1th"] = $IFD1thTable;
        }
    }
    private function setCursol($cursol) {
        $this->cursol = $cursol;
    }
    private function getCursol() {
        return $this->cursol;
    }
    private function incrCursol($incr) {
        $this->cursol += $incr;
    }
    private function getUI8() {
        $v = ord($this->data[$this->cursol]);
        $this->cursol += 1;
        return $v;
    }
    private function getUI16() {
        if ($this->byteOrder === 1) {
            $a = unpack("n", substr($this->data, $this->cursol, 4));
        } else {
            $a = unpack("v", substr($this->data, $this->cursol, 4));
        }
        $this->cursol += 2;
        return $a[1];
    }
    private function _getUI32() {
        if ($this->byteOrder === 1) {
            $a = unpack("N", substr($this->data, $this->cursol, 4));
        } else {
            $a = unpack("V", substr($this->data, $this->cursol, 4));
        }
        $this->cursol += 4;
        return $a[1];
    }
    private function getUI32() {
        $value = $this->_getUI32();
        if (PHP_INT_SIZE > 4) { // 64bit CPU
            return $value;
        }
        if ($value < 0x80000000) {
            return $value;
        }
        return $value + 0x100000000; // 2-negative
    }
    private function getSI32() {
        $value = $this->_getUI32();
        if (PHP_INT_SIZE <=  4) { // 32bit CPU
            return $value;
        }
        if ($value < 0x80000000) {
            return $value;
        }
        return $value - 0x100000000; // 2-negative

    }
    private function getData($length) {
        $v = substr($this->data, $this->cursol, $length);
        $this->cursol += $length;
        return $v;
    }
    private function makeIFDTable($offset) {
        $data = $this->data;
        $this->setCursol($offset);
        $nTags = $this->getUI16();
        $IFDTable = array();
        for ($i = 0 ; $i < $nTags ; $i++) {
            $tagNo    = $this->getUI16();
            $tagType  = $this->getUI16();
            $tagCount = $this->getUI32();
            // echo "tag: $tagNo $tagType $tagCount\n";
            $value = null;
            $nextCursol = $this->getCursol() + 4;
            switch ($tagType) {
            case 1: // BYTE
                if ($tagCount > 4) {
                    $tagOffset = $this->getUI32();
                    $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                }
                for ($j = 0 ; $j < $tagCount ; $j++) {
                    $value []= $this->getUI8();
                }
                break;
            case 2: // ASCII
            case 7: // UNDEFINED
                if ($tagCount > 4) {
                    $tagOffset = $this->getUI32();
                    $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                }
                $value = $this->getData($tagCount);
                break;
            case 3: // SHORT
                if ($tagCount > 2) {
                    $tagOffset = $this->getUI32();
                    $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                }
                for ($j = 0 ; $j < $tagCount ; $j++) {
                    $value []= $this->getUI16();
                }
                break;
            case 4: // LONG
                if ($tagCount > 1) {
                    $tagOffset = $this->getUI32();
                    $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                }
                for ($j = 0 ; $j < $tagCount ; $j++) {
                    $value []= $this->getUI32();
                }
                break;
            case 9: // SLONG
                if ($tagCount > 1) {
                    $tagOffset = $this->getUI32();
                    $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                }
                for ($j = 0 ; $j < $tagCount ; $j++) {
                    $value []= $this->getSI32();
                }
                break;
            case 5: // RATIONAL
                $tagOffset = $this->getUI32();
                $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                for ($j = 0 ; $j < $tagCount ; $j++) {
                    $numer = $this->getUI32();
                    $denom = $this->getUI32();
                    $value []= [$numer, $denom];
                }
                break;
            case 10: // RATIONAL
                $tagOffset = $this->getUI32();
                $this->setCursol(self::IFD_OFFSET_BASE +  $tagOffset);
                for ($j = 0 ; $j < $tagCount ; $j++) {
                    $numer = $this->getSI32();
                    $denom = $this->getSI32();
                    $value []= [$numer, $denom];
                }
                break;
            default:
                throw new Exception("Unknown tagType:$tagType");
            }
            $this->setCursol($nextCursol);
            $IFDTable[$tagNo] = $value;
        }
        $IFDTypes = [0x8769 => "Exif", 0x8769 => "GPSInfo", 0xA005 => "Interoperability"];
        foreach ($IFDTypes as $offset => $name) {
            if (isset($IFDTable[$offset])) {
                $o = $IFDTable[$offset][0];
                $table = $this->makeIFDTable(self::IFD_OFFSET_BASE + $o);
                $this->IDFs[$name] = $table;
            }
        }
        return $IFDTable;
    }

    function listIDFs() {
        return array_keys($this->IDFs);
    }
    function getIDF($key) {
        if (isset($this->IFDs[$key])) {
            return $this->IFDs[$key];
        }
        return false;
    }
}

$data = file_get_contents($argv[1]);

$exif = new Exif();
$exif->parse($data);

var_dump($exif->IDFs);