从资源创建流

Question

我知道我可以创建一个 PHP stream from a filename (a real one, or an URL), by using the fopen 函数：

$stream = fopen('php://temp', 'r');

结果流 ($stream) 然后是资源类型 “流”，从 URL php://temp.

但是我如何从资源创建像上面这样的流？

我为什么要问这个？

我正在研究 PSR-7 library and I implemented the PSR-7 StreamInterface with a Stream class. In order to create Stream instances, I decided to implement a StreamFactory too. Its interface, StreamFactoryInterface, is defined in PSR-17: HTTP Factories。

StreamFactoryInterface 定义了一个名为 createStreamFromResource 的方法，根据其官方评论，该方法应该：

Create a new stream from an existing resource.

The stream MUST be readable and may be writable.

因此工厂方法接收资源作为参数。并且，在其具体实现中，创建了一个新的 Stream 对象——它也接收一个资源作为参数。

问题是：

为了简单起见，假设 Stream class 仅适用于流，例如资源类型为 "stream"。如果它收到的资源不是 "stream" 类型，它会拒绝它。

那么，如果 createStreamFromResource 的资源参数还不是 "stream" 类型的资源怎么办？我怎样才能把它变成一个流，例如放入类型为 "stream" 的资源中，以便我可以将它进一步传递给使用它创建新的 Stream 对象的调用？有没有办法（一个 PHP 方法、一个函数，或者一个转换函数）来完成这个任务？

备注：

为清楚起见，我准备了一个完整的示例 (testStream.php) 来说明如何创建流，例如一个 Stream 实例，以三种方式：一次直接，两次使用流工厂。
我也post工厂接口的具体实现：classStreamFactory和方法createStreamFromResource。调用此方法应该是我在 testStream.php.
此外，我提供了 classes Stream 和 Response，以便您可以直接测试所有内容，如果您愿意的话。这两个 classes 是我的真实代码的一个非常简化的版本。
在我的代码中，我用 "@asking".

非常感谢您的时间和耐心等待！

testStream.php（测试页）：

<?php

use Tests\Stream;
use Tests\Response;
use Tests\StreamFactory;

/*
 * ================================================
 * Option 1: Create a stream by a stream name
 * (like "php://temp") with read and write rights.
 * ================================================
 */
$stream = new Stream('php://temp', 'w+b');

$response = new Response($stream);
$response->getBody()->write(
        'Stream 1: Created directly.<br/><br/>'
);
echo $response->getBody();

/*
 * ================================================
 * Option 2: Create a stream by a stream name
 * (like "php://temp"), using a stream factory.
 * ================================================
 */
$streamFactory = new StreamFactory();
$stream = $streamFactory->createStreamFromFile('php://temp', 'w+b');

$response = new Response($stream);
$response->getBody()->write(
        'Stream 2: Created by a stream name, with a stream factory.<br/><br/>'
);
echo $response->getBody();

/*
 * ================================================
 * Option 3: Create a stream from a string, using a
 * stream factory.
 * ================================================
 */
$streamFactory = new StreamFactory();
$stream = $streamFactory->createStream(
        'Stream 3: Created from a string, with a stream factory.<br/><br/>'
);

$response = new Response($stream);
echo $response->getBody();

/*
 * ================================================
 * Option 4: Create a stream from an existing
 * resource, using a stream factory.
 * ================================================
 * 
 * @asking How can I create a stream by calling the
 * the factory method ServerFactory::createStreamFromResource
 * with a resource which is not of type "stream"?
 */
//...

StreamFactoryclass（因为我有，所以没有简化）：

<?php

namespace Tests;

use Tests\Stream;
use Psr\Http\Message\StreamInterface;
use Psr\Http\Message\StreamFactoryInterface;

class StreamFactory implements StreamFactoryInterface {

    /**
     * Create a new stream from an existing resource.
     *
     * The stream MUST be readable and may be writable.
     *
     * @param resource $resource
     *
     * @return StreamInterface
     * @throws \InvalidArgumentException
     */
    public function createStreamFromResource($resource) {
        /*
         * @asking What if $resource is not already a resource of type *"stream"*? 
         * How can I transform it into a stream, e.g. into a resource of type *"stream"*, 
         * so that I can pass it further, to the call for creating a new `Stream` object 
         * with it? Is there a way (a PHP method, a function, or maybe a casting function) 
         * of achieving this task?
         */
         //...

        return new Stream($resource, 'w+b');
    }

    /**
     * Create a new stream from a string.
     *
     * The stream SHOULD be created with a temporary resource.
     *
     * @param string $content
     *
     * @return StreamInterface
     * @throws \InvalidArgumentException
     */
    public function createStream($content = '') {
        if (!isset($content) || !is_string($content)) {
            throw new \InvalidArgumentException('For creating a stream, a content string must be provided!');
        }

        $stream = $this->createStreamFromFile('php://temp', 'w+b');

        $stream->write($content);

        return $stream;
    }

    /**
     * Create a stream from an existing file.
     *
     * The file MUST be opened using the given mode, which may be any mode
     * supported by the `fopen` function.
     *
     * The `$filename` MAY be any string supported by `fopen()`.
     *
     * @param string $filename
     * @param string $mode
     *
     * @return StreamInterface
     */
    public function createStreamFromFile($filename, $mode = 'r') {
        return new Stream($filename, $mode);
    }

}

流class（非常简化）：

<?php

namespace Tests;

use Psr\Http\Message\StreamInterface;

class Stream implements StreamInterface {

    /**
     * Stream (resource).
     *
     * @var resource
     */
    private $stream;

    /**
     *
     * @param string|resource $stream Stream name, or resource.
     * @param string $accessMode (optional) Access mode.
     * @throws \InvalidArgumentException
     */
    public function __construct($stream, string $accessMode = 'r') {
        if (
                !isset($stream) ||
                (!is_string($stream) && !is_resource($stream))
        ) {
            throw new \InvalidArgumentException(
                'The provided stream must be a filename, or an opened resource of type "stream"!'
            );
        }

        if (is_string($stream)) {
            $this->stream = fopen($stream, $accessMode);
        } elseif (is_resource($stream)) {
            if ('stream' !== get_resource_type($stream)) {
                throw new \InvalidArgumentException('The provided resource must be of type "stream"!');
            }
            
            $this->stream = $stream;
        }
    }

    /**
     * Write data to the stream.
     *
     * @param string $string The string that is to be written.
     * @return int Returns the number of bytes written to the stream.
     * @throws \RuntimeException on failure.
     */
    public function write($string) {
        return fwrite($this->stream, $string);
    }

    /**
     * Reads all data from the stream into a string, from the beginning to end.
     *
     * @return string
     */
    public function __toString() {
        try {
            // Rewind the stream.
            fseek($this->stream, 0);

            // Get the stream contents as string.
            $contents = stream_get_contents($this->stream);

            return $contents;
        } catch (\RuntimeException $exc) {
            return '';
        }
    }

    public function close() {}
    public function detach() {}
    public function eof() {}
    public function getContents() {}
    public function getMetadata($key = null) {}
    public function getSize() {}
    public function isReadable() {}
    public function isSeekable() {}
    public function isWritable() {}
    public function read($length) {}
    public function rewind() {}
    public function seek($offset, $whence = SEEK_SET) {}
    public function tell() {}

}

响应class（非常简单）：

<?php

namespace Tests;

use Psr\Http\Message\StreamInterface;
use Psr\Http\Message\ResponseInterface;

class Response implements ResponseInterface {

    /**
     *
     * @param StreamInterface $body Message body.
     */
    public function __construct(StreamInterface $body) {
        $this->body = $body;
    }

    /**
     * Gets the body of the message.
     *
     * @return StreamInterface Returns the body as a stream.
     */
    public function getBody() {
        return $this->body;
    }

    public function getHeader($name) {}
    public function getHeaderLine($name) {}
    public function getHeaders() {}
    public function getProtocolVersion() {}
    public function hasHeader($name) {}
    public function withAddedHeader($name, $value) {}
    public function withBody(StreamInterface $body) {}
    public function withHeader($name, $value) {}
    public function withProtocolVersion($version) {}
    public function withoutHeader($name) {}
    public function getReasonPhrase() {}
    public function getStatusCode() {}
    public function withStatus($code, $reasonPhrase = '') {}

}

Answer 1

您可以按照自己喜欢的任何方式实现它，但此方法本质上只是 pre-generated 资源的包装器。

在大多数情况下，您的 Stream 可能会接收一个字符串，也可能是一个 settings/options 数组，并根据信息创建一个流（可能在某个地方使用 fopen('http://...')。

createStreamFromResource($resource) 将接收 pre-generated 资源（例如 fopen 中的 return 资源值，而不是执行 fopen 的数据):

class Stream implements StreamInterface {

    // ...

    public function __construct($url, $opt = null) {

        // ...

        if( is_resource( $url ) ) {

            /*
             * Check that the $resource is a valid resource
             * (e.g. an http request from an fopen call vs a mysql resource.)
             * or possibly a stream context that still needs to create a
             * request...
             */

            if( !$isValid ) {
                return false;
            }

            $this->resource = $resource;

        } else {

            // ...

            $this->resource = fopen($url, $modifiedOpt);

            // ...

        }

    }

    // ...

    /* createStreamFromResource would call Stream::fromResource($r)
     * or possibly Stream($resource) directly, your call.
     */
    static function fromResource($resource) {
        return new static($resource);
    }

}

您的工厂方法可以像这样简单：

public function createStreamFromResource($resource) {
    return Stream::fromResource($resource);
}

Answer 2

有很多非常好的 PSR-7 实现 StreamInterface 我建议先看一下。您可能会对需要执行的验证和逻辑类型有所了解。

guzzle/psr7 - PSR-7 的 Guzzle 实现 StreamInterface
reactphp/stream - This one doesn't implement PSR-7, but the guys put a lot of thoughts into their implementation and code is very well documented. Look at ReadableResourceStream and WritableResourceStream.
zendframework/zend-diactoros
slimphp/Slim

更新：查看所有这些链接后，我发现了您当前代码的一些问题：

您必须在构造函数中检查资源类型。例如，它可能是 MySQL 资源，而您不想写入它：

public function __construct($stream, string $accessMode = 'r') {

    if (is_string($stream)) {
        $stream = fopen($stream, $accessMode);
    }

    if (! is_resource($stream) || 'stream' !== get_resource_type($stream)) {
        throw new InvalidArgumentException(
            'Invalid stream provided; must be a string stream identifier or stream resource'
        );
    }

    $this->stream = $stream;
}

当您写入流时检查流是否真的可写。您必须先实现 isWritable 方法并在 write 函数中调用它。此示例取自 zend-diactoros 库：

public function isWritable()
{
    if (! $this->resource) {
        return false;
    }
    $meta = stream_get_meta_data($this->resource);
    $mode = $meta['mode'];
    return (
        strstr($mode, 'x')
        || strstr($mode, 'w')
        || strstr($mode, 'c')
        || strstr($mode, 'a')
        || strstr($mode, '+')
    );
}

与read和seek功能相同，您必须先实现isSeekable和isReadable。

__toString 还应检查流是否可读和可查找：

public function __toString()
{
    if (! $this->isReadable()) {
        return '';
    }
    try {
        if ($this->isSeekable()) {
            $this->rewind();
        }
        return $this->getContents();
    } catch (RuntimeException $e) {
        return '';
    }
}

希望这对您有所帮助。祝你的新图书馆好运。

Answer 3

您如何处理传递的参数取决于您的最终实现。如果您的代码需要一个流参数，那么它应该在没有检测到这样的东西时停止。但是，如果您的代码有望处理该问题，那么您可以尝试创建一个流。

编辑

一开始没弄明白，但看起来问题是是否可以转换资源变量。根据 documentation 这是不可能的，没有意义。

从资源创建流

Create a stream from a resource

php

stream

fopen

psr-7

php-stream-wrappers