Understanding streams in php

　Streams is a powerful tool provided by PHP. We often use it inadvertently. If we make good use of it, it will greatly improve the productivity of PHP. Harnessing the power of Streams will take your applications to the next level.

The following is a description of Streams in the PHP manual:

Streams was introduced in PHP version 4.3.0. It is used to unify the operation methods of files, networks, data compression and other types of files, and provides File operations provide a common set of function interfaces. In short, a stream is a resource object with streaming behavior. In other words, we can read and write to the stream in a linear manner. And you can use fseek() to jump to any position within the stream.

　Each Streams object has a wrapper class, in which relevant code for handling special protocols and encodings can be added. Some commonly used packaging classes have been built into PHP, and we can also create and register custom packaging classes. We can even modify and enhance the wrapper class using existing context and filters.

　Stream Basics

　Stream can be referenced through ://. Among them, is the name of the packaging class, and the content in is specified by the syntax of the packaging class. The syntax of different packaging classes will be different.

　 PHP’s default packaging class is file://, which means that when we access the file system, we are actually using a stream. We can read the contents of the file in the following two ways, readfile('/path/to/somefile.txt') or readfile('file:///path/to/somefile.txt'). The methods are equivalent. If you use readfile('http://google.com/'), then PHP will select the HTTP stream wrapper class to operate.

　As mentioned above, PHP provides many built-in package classes, protocols and filters. According to the method described below, you can query the packaging classes supported by this machine:

<?php
print_r(stream_get_transports());
print_r(stream_get_wrappers());
print_r(stream_get_filters());

The output result on my machine is:

Array
(
    [0] => tcp
    [1] => udp
    [2] => unix
    [3] => udg
    [4] => ssl
    [5] => sslv3
    [6] => sslv2
    [7] => tls
)
Array
(
    [0] => https
    [1] => ftps
    [2] => compress.zlib
    [3] => compress.bzip2
    [4] => php
    [5] => file
    [6] => glob
    [7] => data
    [8] => http
    [9] => ftp
    [10] => zip
    [11] => phar
)
Array
(
    [0] => zlib.*
    [1] => bzip2.*
    [2] => convert.iconv.*
    [3] => string.rot13
    [4] => string.toupper
    [5] => string.tolower
    [6] => string.strip_tags
    [7] => convert.*
    [8] => consumed
    [9] => dechunk
    [10] => mcrypt.*
    [11] => mdecrypt.*
)

There are many functions provided, does it look good?

In addition to the above built-in Streams, we can also write more third-party Streams for Amazon S3, MS Excel, Google Storage, Dropbox and even Twitter.

　php:// wrapper class

　 PHP has a built-in wrapper class for processing I/O streams in this language. It can be divided into several categories. The basic ones are php://stdin, php://stdout, and php://stderr. These three streams are mapped to default I/O resources respectively. At the same time, PHP also provides php://input, through which the raw body in the POST request can be accessed in a read-only manner. This is a very useful feature, especially when dealing with remote services that embed data payloads into POST requests.

　Now we use the cURL tool to do a simple test:

curl -d "Hello World" -d "foo=bar&#038;name=John" <a href="http://localhost/dev/streams/php_input.php">http://localhost/dev/streams/php_input.php</a>

The test results of using print_r($_POST) in the PHP script are as follows:

Array
(
    [foo] => bar
    [name] => John
)

We note that the first item in the $_POST array cannot be accessed data. But if we use readfile('php://input'), the result is different:

Hello World&foo=bar&name=John

PHP 5.1 has added two package conversion classes, php://memory and php://tempstream, for reading and writing Temporary data. As the name of the wrapper class implies, this data is stored in memory or temporary files in the underlying system.

php://filter is a meta-packaging class used to add filter functionality to the stream. The filter will be enabled when opening a stream using readfile() or file_get_contents()/stream_get_contents(). Here is an example:

<?php
// Write encoded data
file_put_contents("php://filter/write=string.rot13/resource=file:///path/to/somefile.txt","Hello World");
 
// Read data and encode/decode
readfile("php://filter/read=string.toupper|string.rot13/resource=http://www.google.com");

In the first example, a filter is used to encode the data saved to disk. In the second example, two cascaded filters are used to read from the remote URL. Get data. Using filters can bring extremely powerful functionality to your application.

　Stream context

　Context is a set of stream-related parameters or options. Use context to modify or enhance the behavior of the wrapper class. For example, using context to modify the HTTP wrapper is a commonly used usage scenario. In this way, we can complete some simple network operations without using the cURL tool. Here is an example:

<?php
$opts = array(
  &#39;http&#39;=>array(
    &#39;method&#39;=>"POST",
    &#39;header&#39;=> "Auth: SecretAuthTokenrn" .
        "Content-type: application/x-www-form-urlencodedrn" .
              "Content-length: " . strlen("Hello World"),
    &#39;content&#39; => &#39;Hello World&#39;
  )
);
$default = stream_context_get_default($opts);
readfile(&#39;http://localhost/dev/streams/php_input.php&#39;);

首先要定义一个options array,这是个二位数组，可以通过$array['wrapper']['option_name']的形式来访问其中的参数。（注意每个包装类中context的options是不同的）。然后调用stream_context_get_default()来设置这些option,stream_context_get_default()同时还会将默认的context作为结果返回回来。设置完成后，接下来调用readfile()，就会应用刚才设置好的context来抓取内容。

　　在上面的例子中，内容被嵌入到request的body中，这样远端的脚本就可以使用php://input来读取这些内容。同时，我们还能使用apache_request_headers()来获取request的header，如下所示：

Array
(
    [Host] => localhost
    [Auth] => SecretAuthToken
    [Content-type] => application/x-www-form-urlencoded
    [Content-length] => 11
)

在上面的例子中是修改默认context的参数，当然我们也可以创建一个新的context,进行交替使用。

<?php
$alternative = stream_context_create($other_opts);
readfile(&#39;http://localhost/dev/streams/php_input.php&#39;, false, $alternative);

　结论

　　我们怎样在现实世界中驾驭stream的强大力量呢？使用stream能为我们的程序带来什么现实的好处？ 正如前文介绍的那样，stream对所有文件系统相关的功能进行了抽象，所以我第一个想到的应用场景是使用虚拟文件系统的包装类来访问PaaS供应商提供的服务，比如说访问HeroKu或者AppFog，它们实际上都没有真正文件系统。 使用stream只要对我们的应用程序稍作修改，就可以将其移植到云端。 接下来--在我的下一篇文章中--我将介绍如何编写自定义的包装类以实现对特殊文件格式和编码格式的操作。