stream_wrapper_register()

(PHP 4 >= 4.3.2, PHP 5, PHP 7)

注册一个用 PHP 类实现的 URL 封装协议

说明

stream_wrapper_register(string $protocol,string $classname[,int $flags= 0]): bool

允许用户实现自定义的协议处理器和流，用于所有其它的文件系统函数中（例如fopen()，fread()等）。

参数

$protocol: 待注册的封装的名字。
$classname: 实现了$protocol的类名。
$flags: Should be set toSTREAM_IS_URLif$protocolis a URL protocol. Default is 0, local stream.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

当$protocol已经有处理者时，stream_wrapper_register()将返回FALSE

更新日志

版本	说明
5.2.4	添加`$flags`参数.

范例

如何注册一个 stream wrapper

<?php
$existed = in_array("var", stream_get_wrappers());
if ($existed) {
    stream_wrapper_unregister("var");
}
stream_wrapper_register("var", "VariableStream");
$myvar = "";
$fp = fopen("var://myvar", "r+");
fwrite($fp, "line1\n");
fwrite($fp, "line2\n");
fwrite($fp, "line3\n");
rewind($fp);
while (!feof($fp)) {
    echo fgets($fp);
}
fclose($fp);
var_dump($myvar);
if ($existed) {
    stream_wrapper_restore("var");
}
?>

以上例程会输出：

line1
line2
line3
string(18) "line1
line2
line3
"

参见

ThestreamWrapperprototype class
Example class registered as stream wrapper
stream_wrapper_unregister()Unregister a URL wrapper
stream_wrapper_restore()Restores a previously unregistered built-in wrapper
stream_get_wrappers() 获取已注册的流类型

If you plan to use your wrapper in a require_once you need to define stream_stat(). If you plan to allow any other tests like is_file()/is_dir(), you have to define url_stat().
stream_stat() must define the size of the file, or it will never be included. url_stat() must define mode, or is_file()/is_dir()/is_executable(), and any of those functions affected by clearstatcache() simply won't work.
It's not documented, but directories must be a mode like 040777 (octal), and files a mode like 0100666. If you wish the file to be executable, use 7s instead of 6s. The last 3 digits are exactly the same thing as what you pass to chmod. 040000 defines a directory, and 0100000 defines a file. It would be really helpful to add this to the official manual!

Updated for PHP 5, and optimized for readability, low line count, and minimum memory use:
<?php
class VariableStream {
  private $position;
  private $varname;
  public function stream_open($path, $mode, $options, &$opened_path) {
    $url = parse_url($path);
    $this->varname = $url["host"];
    $this->position = 0; 
    return true;
  }
  public function stream_read($count) {
    $p=&$this->position;
    $ret = substr($GLOBALS[$this->varname], $p, $count);
    $p += strlen($ret);
    return $ret;
  }
  public function stream_write($data){
    $v=&$GLOBALS[$this->varname];
    $l=strlen($data);
    $p=&$this->position;
    $v = substr($v, 0, $p) . $data . substr($v, $p += $l);
    return $l;
  }
  public function stream_tell() {
    return $this->position;
  }
  public function stream_eof() {
    return $this->position >= strlen($GLOBALS[$this->varname]);
  }
  public function stream_seek($offset, $whence) {
    $l=strlen(&$GLOBALS[$this->varname]);
    $p=&$this->position;
    switch ($whence) {
      case SEEK_SET: $newPos = $offset; break;
      case SEEK_CUR: $newPos = $p + $offset; break;
      case SEEK_END: $newPos = $l + $offset; break;
      default: return false;
    }
    $ret = ($newPos >=0 && $newPos <=$l);
    if ($ret) $p=$newPos;
    return $ret;
  }
}
stream_wrapper_register("var", "VariableStream") 
or die("Failed to register protocol");
$myvar = "";
  
$fp = fopen("var://myvar", "r+");
fwrite($fp, "line1\n");
fwrite($fp, "line2\n");
fwrite($fp, "line3\n");
rewind($fp);
while (!feof($fp)) {
  echo fgets($fp);
}
fclose($fp);
var_dump($myvar);
?>

In response to Anonymouse at Coward dot com:
The manual says "Reading stops when up to length bytes have been read, [...] or (after opening userspace stream) when 8192 bytes have been read whichever comes first."
I tested it and fread($filehandle, 4096) returns 4096 bytes, so it's working as the manual says it should. You're right when you say "8192 bytes is always passed to stream_read as count", but that doesn't mean fread will return 8192 bytes. If you call fread twice with length 4096, PHP calls stream_read passing 8192 as count on the first fread, and doesn't call it on second fread. On both cases, fread returns the correct amount of bytes.
<?php
class VariableStream {
  var $position;
  var $varname;
 
  function stream_open($path, $mode, $options, &$opened_path)
  {
    $url = parse_url($path);
    $this->varname = $url["host"];
    $this->position = 0;
    
    return true;
  }
  function stream_read($count)
  {
    echo "stream_read called asking for $count bytes\n";
    $ret = substr($GLOBALS[$this->varname], $this->position, $count);
    $this->position += strlen($ret);
    return $ret;
  }
  function stream_eof()
  {
    return $this->position >= strlen($GLOBALS[$this->varname]);
  }
}
stream_wrapper_register("var", "VariableStream")
  or die("Failed to register protocol");
$myvar = "";
$l=range('a','z');
for($i=0;$i<65536;$i++) {
  $myvar .= $l[array_rand($l)];
}
  
$fp = fopen("var://myvar", "r+");
while (!feof($fp)) {
  $out = fread($fp,1000);
  echo "fread returned ",strlen($out)," bytes\n";
}
fclose($fp);
?>

Actually, I don't know if there's a better way to figure out if stream_read() was called by fgets() or e.g. fread() than this one:
  public function stream_read($count)
  {
    $bt = debug_backtrace();
    if(($bt[0]['function'] == 'stream_read') &&
      ($bt[1]['function'] == 'fgets'))
    {
        $pos = strpos($GLOBALS[$this->varname], "\n", $this->position);
        $retval = substr($GLOBALS[$this->varname], $this->position, ($pos > $count) ? $count : $pos+1);
    }
    else
    {
        $retval = substr($GLOBALS[$this->varname], $this->position, $count);
    }
        $this->position += strlen($retval);
        return (string)$retval;
  }

on using dir_opendir on PHP5 make sure you not return a resource object on success. A resource object is diferent from false but php make a cast to bool to dir_opendir return value and modify the value of your resource to 1. 
example:
class myclass{
 private $mysqlHandler;
 public function dir_opendir(....)
 {
  $this->mysqlHandler = mysql_connect(....);
  return $this->mysqlHandler; //this is wrong, next
                     //time you use 
                     //$this->mysqlHandler
                     // the value is 1
 }
}

Updated. I figured there's no need to store the variable name if we're dereferenceing; we can just store the pointer and not have to dereference in each function for brevity.
Also, I added the assertion that the stream is a string, since we're behaving basically like it has to be, and I changed the name to GlobalStream and global://, as that's a more descriptive moniker than VariableName/var://.
<?php
class GlobalStream {
  private $pos;
  private $stream;
  public function stream_open($path, $mode, $options, &$opened_path) {
    $url = parse_url($path);
    $this->stream = &$GLOBALS[$url["host"]];
    $this->pos = 0; 
    if (!is_string($this->stream)) return false;
    return true;
  }
  public function stream_read($count) {
    $p=&$this->pos;
    $ret = substr($this->stream, $this->pos, $count);
    $this->pos += strlen($ret);
    return $ret;
  }
  public function stream_write($data){
    $l=strlen($data);
    $this->stream = 
      substr($this->stream, 0, $this->pos) . 
      $data . 
      substr($this->stream, $this->pos += $l);
    return $l;
  }
  public function stream_tell() {
    return $this->pos;
  }
  public function stream_eof() {
    return $this->pos >= strlen($this->stream);
  }
  public function stream_seek($offset, $whence) {
    $l=strlen($this->stream);
    switch ($whence) {
      case SEEK_SET: $newPos = $offset; break;
      case SEEK_CUR: $newPos = $this->pos + $offset; break;
      case SEEK_END: $newPos = $l + $offset; break;
      default: return false;
    }
    $ret = ($newPos >=0 && $newPos <=$l);
    if ($ret) $this->pos=$newPos;
    return $ret;
  }
}
stream_wrapper_register('global', 'GlobalStream') or die('Failed to register protocol global://');
$myvar = "";
  
$fp = fopen("global://myvar", "r+");
fwrite($fp, "line1\n");
fwrite($fp, "line2\n");
fwrite($fp, "line3\n");
rewind($fp);
while (!feof($fp)) {
  echo fgets($fp);
}
fclose($fp);
var_dump($myvar);
?>

Be aware that even when stream_wrapper_register won't fail, open_basedir will affect functionality of the class.

"for use with all the other filesystem functions"
"all" is not accurate. Unfortunately, zip_open(), and presumably others, will ignore your custom stream wrapper.

In case someone else starts scratching their head like I was, you should change the VariableStream::stream_eof() function to something like this:
  function stream_eof()
  {
    $eof = ($this->position >= strlen($GLOBALS[$this->varname]));
    if(version_compare(PHP_VERSION,'5.0','>=') && version_compare(PHP_VERSION,'5.1','<'))
    {
      $eof = !$eof;
    }
    return $eof;
  }
PHP 5.0 introduced a bug that wasn't fixed until 5.1

It is worth noting that if your wrapper supports stream_flush() then when you flcose() your stream this function will be called prior to closing the stream.

using streams to use the ever useful fgetcsv() on a variable where explode() would not work (and would otherwise require regex(though that may be easier;)))
$explode_this="yak, llama, 'big llama', 'wobmat, with a comma in it', bandycoot";
 
<?php 
class csvstream{ 
  var $position; 
  var $varname; 
  function stream_open($path, $mode, $options, &$opened_path){ 
    $url = parse_url($path); 
    $this->varname = $url['host'] ; 
    $this->position = 0; 
    return true; 
  } 
 function stream_read($count){ 
    $ret = substr($GLOBALS[$this->varname], $this->position, $count); 
    $this->position += strlen($ret); 
    return $ret; 
  } 
 function stream_eof(){ 
    return $this->position >= strlen($GLOBALS[$this->varname]); 
  } 
  function stream_tell(){ 
    return $this->position; 
  } 
} 
  stream_wrapper_register("csvstr", "csvstream") ; 
  $str="yak, llama, 'big llama', 'wobmat, with a comma in it', bandycoot"; 
  $fp = fopen("csvstr://str", "r+"); 
  print_r(fgetcsv($fp,100,",","'")); 
?>

Use caution with writing code that may use stream wrappers with fread, as fread behaviour is 'inconsistent' with normal file operations because of the 8192 bytes internal buffer used by PHP ( >= 5.0.5 IIRC ).
ie:
fread($filehandle, filesize($filename))
will not work correctly if the file is larger than 8KB, it will only get you the first 8192 bytes. Also, it seems that:
fread($filehandle, 4096)
will still give you 8KB (if the file is larger than 8KB) as 8192 bytes is always passed to stream_read as count.
This makes it somewhat impossible to just 'drop in' a stream where normally a file would be used without taking special care. 
Yes, it IS mentioned in the documentation here if you read it really well, but I for one spent some time scratching my head over it, and looking at the bug tracker, I am not the only one. The dev's say this inconsistancy is a feature though, even if it does make stream wrappers pretty much useless 'out of the box'.
file_get_contents and stream_get_contents seem to work ok though.

The current URL standard is RFC 3986 - available at www.ietf.org/rfc/rfc3986.txt