In-depth understanding of the Streams tool in PHP, in-depth understanding of phpstreams_PHP tutorial

In-depth understanding of the Streams tool in PHP and phpstreams

Streams is a powerful tool provided by PHP. We often use it inadvertently. If we make good use of 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 a set of common function interfaces for these types of file operations. 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 wrapper classes, protocols and filters. According to the method described below, you can query the packaging classes supported by this machine:

<&#63;php
print_r(stream_get_transports());
print_r(stream_get_wrappers());
print_r(stream_get_filters());

The output 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.*
)

It provides a lot of functions. 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:// packaging class

PHP has built-in wrapper classes 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.

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

curl -d "Hello World" -d "foo=bar&name=John" http://localhost/dev/streams/php_input.php

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

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

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

Hello World&foo=bar&name=John

PHP 5.1 adds two package transfer 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:

<&#63;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 data from the remote URL. 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:

<&#63;php
$opts = array(
 'http'=>array(
  'method'=>"POST",
  'header'=> "Auth: SecretAuthTokenrn" .
    "Content-type: application/x-www-form-urlencodedrn" .
       "Content-length: " . strlen("Hello World"),
  'content' => 'Hello World'
 )
);
$default = stream_context_get_default($opts);
readfile('http://localhost/dev/streams/php_input.php');

First define an options array, which is a two-digit array. The parameters can be accessed in the form of $array['wrapper']['option_name']. (Note that the context options in each wrapper class are different). Then call stream_context_get_default() to set these options. stream_context_get_default() will also return the default context as a result. After the setting is completed, then call readfile(), and the context just set will be used to capture the content.

In the above example, the content is embedded in the request body so that remote scripts can use php://input to read the content. At the same time, we can also use apache_request_headers() to get the header of the request, as shown below:

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。

<&#63;php
$alternative = stream_context_create($other_opts);
readfile('http://localhost/dev/streams/php_input.php', 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。

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