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<?php
/**
* Index - provides an 'index' object for packfile indexes
*
* PHP version 5.3
*
* @category Git
* @package Granite
* @author Craig Roberts <craig0990@googlemail.com>
* @license http://www.opensource.org/licenses/mit-license.php MIT License
* @link http://craig0990.github.com/Granite/
*/
namespace Granite\Git\Object;
use \UnexpectedValueException as UnexpectedValueException;
/**
* Index represents a packfile index
*
* @category Git
* @package Granite
* @author Craig Roberts <craig0990@googlemail.com>
* @license http://www.opensource.org/licenses/mit-license.php MIT License
* @link http://craig0990.github.com/Granite/
*/
class Index
{
const INDEX_MAGIC = "\377tOc";
/**
* The full path to the packfile index
*/
private $path;
/**
* The offset at which the fanout begins, version 2+ indexes have a 2-byte header
*/
private $offset = 8;
/**
* The size of the SHA-1 entries, version 1 stores 4-byte offsets alongside to
* total 24 bytes, version 2+ stores offsets separately
*/
private $size = 20;
/**
* The version of the index file format, versions 1 and 2 are in use and
* currently supported
*/
private $version;
/**
* Fetches a raw Git object and parses the result
*
* @param string $path The path to the repository root
* @param string $packname The name of the packfile index to read
*/
public function __construct($path, $packname)
{
$this->path = $path
. 'objects'
. DIRECTORY_SEPARATOR
. 'pack'
. DIRECTORY_SEPARATOR
. 'pack-' . $packname . '.idx';
$this->version = $this->_readVersion();
if ($this->version !== 1 && $this->version !== 2) {
throw new UnexpectedValueException(
"Unsupported index version (version $version)"
);
}
if ($this->version == 1) {
$this->offset = 0; // Version 1 index has no header/version
$this->size = 24; // Offsets + SHA-1 ids are stored together
}
}
/**
* Returns the offset of the object stored in the index
*
* @param string $sha The SHA-1 id of the object being requested
*
* @return int The offset of the object in the packfile
*/
public function find($sha)
{
$index = fopen($this->path, 'rb');
$offset = false; // Offset for object in packfile not found by default
// Read the fanout to skip to the start char in the sorted SHA-1 list
list($start, $after) = $this->_readFanout($index, $sha);
if ($start == $after) {
fclose($index);
return false; // Object is apparently located in a 0-length section
}
// Seek $offset + 255 4-byte fanout entries and read 256th entry
fseek($index, $this->offset + 4 * 255);
$totalObjects = $this->_uint32($index);
// Look up the SHA-1 id of the object
// TODO: Binary search
fseek($index, $this->offset + 1024 + $this->size * $start);
for ($i = $start; $i < $after; $i++) {
if ($this->version == 1) {
$offset = $this->_uint32($index);
}
$name = fread($index, 20);
if ($name == pack('H40', $sha)) {
break; // Found it
}
}
if ($i == $after) {
fclose($index);
return false; // Scanned entire section, couldn't find it
}
if ($this->version == 2) {
// Jump to the offset location and read it
fseek($index, 1032 + 24 * $totalObjects + 4 * $i);
$offset = $this->_uint32($index);
if ($offset & 0x80000000) {
// Offset is a 64-bit integer; packfile is larger than 2GB
fclose($index);
throw new UnexpectedValueException(
"Packfile larger than 2GB, currently unsupported"
);
}
}
fclose($index);
return $offset;
}
/**
* Converts a binary string into a 32-bit unsigned integer
*
* @param handle $file Binary string to convert
*
* @return int Integer value
*/
private function _uint32($file)
{
$val = unpack('Nx', fread($file, 4));
return $val['x'];
}
/**
* Reads the fanout for a particular SHA-1 id
*
* Largely modified from Glip, with some reference to Grit - largely because I
* can't see how to re-implement this in PHP
*
* @param handle $file File handle to the index file
* @param string $sha The SHA-1 id to search for
* @param int $offset The offset at which the fanout begins
*
* @return array Array containing integer 'start' and
* 'past-the-end' locations
*/
private function _readFanout($file, $sha)
{
$sha = pack('H40', $sha);
fseek($file, $this->offset);
if ($sha{0} == "\00") {
/**
* First character is 0, read first fanout entry to provide
* 'past-the-end' location (since first fanout entry provides start
* point for '1'-prefixed SHA-1 ids)
*/
$start = 0;
fseek($file, $this->offset); // Jump to start of fanout, $offset bytes in
$after = $this->_uint32($file);
} else {
/**
* Take ASCII value of first character, minus one to get the fanout
* position of the offset (minus one because the fanout does not
* contain an entry for "\00"), multiplied by four bytes per entry
*/
fseek($file, $this->offset + (ord($sha{0}) - 1) * 4);
$start = $this->_uint32($file);
$after = $this->_uint32($file);
}
return array($start, $after);
}
/**
* Returns the version number of the index file, or 1 if there is no version
* information
*
* @return int
*/
private function _readVersion()
{
$file = fopen($this->path, 'rb');
$magic = fread($file, 4);
$version = $this->_uint32($file);
if ($magic !== self::INDEX_MAGIC) {
$version = 1;
}
fclose($file);
return $version;
}
}
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