[PHP] 使用ftell和fseek函数直接定位文件位置获取部分数据

对于大文件只获取部分数据很有用

1.使用ftell函数可以获取当前指针的字节位置
2.使用fseek函数可以直接定位到指定的位置
3.读取指定字节的数据就可以部分获取文件内容了

<?php
class FileStream
{
    private $fp = null;
    private $mode = 'r';
    private $context = null;
    private $readonly = false;
    private $writeonly = false;
    private $appendMode = false;

    public function __construct($file, $mode = 'r', $context = null)
    {
        $mode = trim($mode);
        if (isset($mode[0])) {
            $this->mode = strtolower($mode);
        }

        if ($context) {
            $this->context = $context;
            $this->fp = fopen($file, $mode, false, $this->context);
        } else {
            $this->fp = fopen($file, $mode);
        }

        if (!$this->fp) {
            throw new Exception('can not open ' . $file);
        }
        
        if ($this->mode == 'r') {
            $this->readonly = true;
        } elseif ($this->mode == 'w') {
            $this->writeonly = true;
        } elseif ($this->mode[0] == 'a') {
            $this->appendMode = true;
        }
    }

    public function __destruct()
    {
        $this->close();
    }

    public function close()
    {
        if (!$this->fp) {
            fclose($this->fp);
            $this->fp = null;
        }
    }

    public function read($size)
    {
        if ($this->writeonly) {
            throw new Exception('write only');
        }

        if (!$this->fp) {
            throw new Exception('stream already closed');
        }

        $buf = fread($this->fp, $size);
        if ($buf === false) {
            throw new Exception('read failed');
        }

        return $buf;
    }

    public function readLine()
    {
        if ($this->writeonly) {
            throw new Exception('write only');
        }

        if (!$this->fp) {
            throw new Exception('stream already closed');
        }
                
        return fgets($this->fp);
    }

    public function readAll()
    {
        if ($this->writeonly) {
            throw new Exception('write only');
        }

        if (!$this->fp) {
            throw new Exception('stream already closed');
        }

        $buf = '';

        while (true) {
            $s = fread($this->fp, 8192);
            if ($s === false) {
                throw new Exception('read failed');
            }

            if (!isset($s[0])) {
                break;
            }

            $buf .= $s;
        }

        return $buf;
    }

    public function write($data)
    {
        if ($this->readonly) {
            throw new Exception('read only');
        }

        if (!$this->fp) {
            throw new Exception('stream already closed');
        }

        if (fwrite($this->fp, $data) === false) {
            throw new Exception('write failed');
        }
    }
    
    public function tell()
    {
        if ($this->appendMode) {
            throw new Exception('tell can not work on appendmode');
        }

        if (!$this->fp) {
            throw new Exception('stream already closed');
        }

        $p = ftell($this->fp);
        if ($p === false) {
            throw new Exception('tell failed');
        }

        return $p;
    }

    public function seek($position)
    {
        if ($this->appendMode) {
            throw new Exception('seek can not work on seekmode');
        }

        if (!$this->fp) {
            throw new Exception('stream already closed');
        }

        if (fseek($this->fp, $position) !== 0) {
            throw new Exception('seek failed');
        }
    }
}

$stream=new FileStream("1.log");
$start=0;
$end=0;
//获取开始和结束的字节位置
while($ln=$stream->readLine()){
    if($ln=="3333333333333
"){
        $start=$stream->tell();
    }
    if($ln=="5555555555555
"){
       $end=$stream->tell();
    }
}
var_dump($start,$end);

//直接定位到开始的字节位置
$stream->seek($start);
//读取指定字节数的数据
$res=$stream->read($end - $start);

var_dump($res);

1.log的内容

2.获取部分结果