HTTP消息接口

此文档描述了 RFC 7230 和
RFC 7231 HTTP 消息传递的接口，还有 RFC 3986 里对 HTTP 消息的 URIs 使用。

HTTP 消息是 Web 技术发展的基础。浏览器或 HTTP 客户端如 curl 生成发送 HTTP 请求消息到 Web 服务器，Web 服务器响应 HTTP 请求。服务端的代码接受 HTTP 请求消息后返回 HTTP 响应消息。

通常 HTTP 消息对于终端用户来说是不可见的，但是作为 Web 开发者，我们需要知道 HTTP 机制，如何发起、构建、取用还有操纵 HTTP 消息，知道这些原理，以助我们刚好的完成开发任务，无论这个任务是发起一个 HTTP 请求，或者处理传入的请求。

每一个 HTTP 请求都有专属的格式：

POST /path HTTP/1.1
Host: example.com

foo=bar&baz=bat

按照顺序，第一行的各个字段意义为： HTTP 请求方法、请求的目标地址（通常是一个绝对路径的 URI 或
者路径），HTTP 协议。

接下来是 HTTP 头信息，在这个例子中：目的主机。接下来是空行，然后是消息内容。

HTTP 返回消息有类似的结构：

HTTP/1.1 200 OK
Content-Type: text/plain

这是返回的消息内容

按照顺序，第一行为状态行，包括 HTTP 协议版本，HTTP 状态码，描述文本。

和 HTTP 请求类似的，接下来是 HTTP 头信息，在这个例子中：内容类型。接下来是空行，然后是消息内容。

此文档探讨的是 HTTP 请求消息接口，和构建 HTTP 消息需要的元素数据定义。

参考资料

• RFC 2119
• RFC 3986
• RFC 7230
• RFC 7231

关于「能愿动词」的使用

为了避免歧义，文档大量使用了「能愿动词」，对应的解释如下：

• 必须 (MUST)：绝对，严格遵循，请照做，无条件遵守；
• 一定不可 (MUST NOT)：禁令，严令禁止；
• 应该 (SHOULD) ：强烈建议这样做，但是不强求；
• 不该 (SHOULD NOT)：强烈不建议这样做，但是不强求；
• 可以 (MAY) 和 可选 (OPTIONAL) ：选择性高一点，在这个文档内，此词语使用较少；

参见：RFC 2119

1. 规范详情

1.1 消息

一个 HTTP 消息，指定是一个从客户端发往服务器端的请求，或者是服务器端返回客户端的响应。对应的两
个消息接口：Psr\Http\Message\RequestInterface 和 Psr\Http\Message\ResponseInterface。

这个两个接口都继承于 Psr\Http\Message\MessageInterface。虽然你 可以 实现
Psr\Http\Message\MessageInterface 接口，但是，最重要的，你 必须 实现
Psr\Http\Message\RequestInterface 和 Psr\Http\Message\ResponseInterface
接口。

从现在开始，为了行文的方便，我们提到这些接口的时候，都会把命名空间 Psr\Http\Message 去除掉。

1.2 HTTP 头信息

大小写不敏感的字段名字

HTTP 消息包含大小写不敏感头信息。使用 MessageInterface 接口来设置和获取头信息，大小写
不敏感的定义在于，如果你设置了一个 Foo 的头信息，foo 的值会被重写，你也可以通过 foo 来
拿到 FoO 头对应的值。

$message = $message->withHeader('foo', 'bar');

echo $message->getHeaderLine('foo');
// 输出: bar

echo $message->getHeaderLine('FOO');
// 输出: bar

$message = $message->withHeader('fOO', 'baz');
echo $message->getHeaderLine('foo');
// 输出: baz

虽然头信息可以用大小写不敏感的方式取出，但是接口实现类 必须 保持自己的大小写规范，特别是用 getHeaders() 方法输出的内容。

因为一些非标准的 HTTP 应用程序，可能会依赖于大小写敏感的头信息，所有在此我们把主宰 HTTP 大小写的权利开放出来，以适用不同的场景。

对应多条数组的头信息

为了适用一个 HTTP 「键」可以对应多条数据的情况，我们使用字符串配合数组来实现，你可以从一个 MessageInterface 取出数组或字符串，使用 getHeaderLine($name) 方法可以获取通过逗号分割的不区分大小写的字符串形式的所有值。也可以通过 getHeader($name) 获取数组形式头信息的所有值。

$message = $message
    ->withHeader('foo', 'bar')
    ->withAddedHeader('foo', 'baz');

$header = $message->getHeaderLine('foo');
// $header 包含: 'bar, baz'

$header = $message->getHeader('foo');
// ['bar', 'baz']

注意：并不是所有的头信息都可以适用逗号分割（例如 Set-Cookie），当处理这种头信息时候， MessageInterace 的继承类 应该 使用 getHeader($name) 方法来获取这种多值的情况。

主机信息

在请求中，Host 头信息通常和 URI 的 host 信息，还有建立起 TCP 连接使用的 Host 信息一致。
然而，HTTP 标准规范允许主机 host 信息与其他两个不一样。

在构建请求的时候，如果 host 头信息未提供的话，实现类库 必须 尝试着从 URI 中提取 host
信息。

RequestInterface::withUri() 会默认的，从传参的 UriInterface 实例中提取 host ，
并替代请求中原有的 host 信息。

你可以提供传参第二个参数为 true 来保证返回的消息实例中，原有的 host 头信息不会被替代掉。

以下表格说明了当 withUri() 的第二个参数被设置为 true 的时，返回的消息实例中调用
getHeaderLine('Host') 方法会返回的内容：

• <sup id="rhh">1 当前请求的 Host 头信息。
• <sup id="rhc">2 当前请求 URI 中的 Host 信息。
• <sup id="uhc">3 通过 withUri() 传参进入的 URI 中的 host 信息。

1.3 数据流

HTTP 消息包含开始的一行、头信息、还有消息的内容。HTTP 的消息内容有时候可以很小，有时候确是
非常巨大。尝试使用字符串的形式来展示消息内容，会消耗大量的内存，使用数据流的形式来读取消息
可以解决此问题。StreamInterface 接口用来隐藏具体的数据流读写实现。在一些情况下，消息
类型的读取方式为字符串是能容许的，可以使用 php://memory 或者 php://temp。

StreamInterface 暴露出来几个接口，这些接口允许你读取、写入，还有高效的遍历内容。

数据流使用这个三个接口来阐明对他们的操作能力：isReadable()、isWritable() 和
isSeekable()。这些方法可以让数据流的操作者得知数据流能否能提供他们想要的功能。

每一个数据流的实例，都会有多种功能：可以只读、可以只写、可以读和写，可以随机读取，可以按顺序读取等。

最终，StreamInterface 定义了一个 __toString() 的方法，用来一次性以字符串的形式输出
所有消息内容。

与请求和响应的接口不同的是，StreamInterface 并不强调不可修改性。因为在 PHP 的实现内，基
本上没有办法保证不可修改性，因为指针的指向，内容的变更等状态，都是不可控的。作为读取者，可以
调用只读的方法来返回数据流，以最大程度上保证数据流的不可修改性。使用者要时刻明确的知道数据
流的可修改性，建议把数据流附加到消息实例中，来强迫不可修改的特性。

1.4 请求目标和 URI

翻译到此先告一段落，此规范篇幅有点过长，需要消耗的时间挺长的，暂且翻译至此，他日再战。

Per RFC 7230, request messages contain a "request-target" as the second segment
of the request line. The request target can be one of the following forms:

• origin-form, which consists of the path, and, if present, the query
  string; this is often referred to as a relative URL. Messages as transmitted
  over TCP typically are of origin-form; scheme and authority data are usually
  only present via CGI variables.
• absolute-form, which consists of the scheme, authority
  ("[user-info@]host[:port]", where items in brackets are optional), path (if
  present), query string (if present), and fragment (if present). This is often
  referred to as an absolute URI, and is the only form to specify a URI as
  detailed in RFC 3986. This form is commonly used when making requests to
  HTTP proxies.
• authority-form, which consists of the authority only. This is typically
  used in CONNECT requests only, to establish a connection between an HTTP
  client and a proxy server.
• asterisk-form, which consists solely of the string *, and which is used
  with the OPTIONS method to determine the general capabilities of a web server.

Aside from these request-targets, there is often an 'effective URL' which is
separate from the request target. The effective URL is not transmitted within
an HTTP message, but it is used to determine the protocol (http/https), port
and hostname for making the request.

The effective URL is represented by UriInterface. UriInterface models HTTP
and HTTPS URIs as specified in RFC 3986 (the primary use case). The interface
provides methods for interacting with the various URI parts, which will obviate
the need for repeated parsing of the URI. It also specifies a __toString()
method for casting the modeled URI to its string representation.

When retrieving the request-target with getRequestTarget(), by default this
method will use the URI object and extract all the necessary components to
construct the origin-form. The origin-form is by far the most common
request-target.

If it's desired by an end-user to use one of the other three forms, or if the
user wants to explicitly override the request-target, it is possible to do so
with withRequestTarget().

Calling this method does not affect the URI, as it is returned from getUri().

For example, a user may want to make an asterisk-form request to a server:

$request = $request
    ->withMethod('OPTIONS')
    ->withRequestTarget('*')
    ->withUri(new Uri('https://example.org/'));

This example may ultimately result in an HTTP request that looks like this:

OPTIONS * HTTP/1.1

But the HTTP client will be able to use the effective URL (from getUri()),
to determine the protocol, hostname and TCP port.

An HTTP client MUST ignore the values of Uri::getPath() and Uri::getQuery(),
and instead use the value returned by getRequestTarget(), which defaults
to concatenating these two values.

Clients that choose to not implement 1 or more of the 4 request-target forms,
MUST still use getRequestTarget(). These clients MUST reject request-targets
they do not support, and MUST NOT fall back on the values from getUri().

RequestInterface provides methods for retrieving the request-target or
creating a new instance with the provided request-target. By default, if no
request-target is specifically composed in the instance, getRequestTarget()
will return the origin-form of the composed URI (or "/" if no URI is composed).
withRequestTarget($requestTarget) creates a new instance with the
specified request target, and thus allows developers to create request messages
that represent the other three request-target forms (absolute-form,
authority-form, and asterisk-form). When used, the composed URI instance can
still be of use, particularly in clients, where it may be used to create the
connection to the server.

1.5 Server-side Requests

RequestInterface provides the general representation of an HTTP request
message. However, server-side requests need additional treatment, due to the
nature of the server-side environment. Server-side processing needs to take into
account Common Gateway Interface (CGI), and, more specifically, PHP's
abstraction and extension of CGI via its Server APIs (SAPI). PHP has provided
simplification around input marshaling via superglobals such as:

• $_COOKIE, which deserializes and provides simplified access for HTTP
  cookies.
• $_GET, which deserializes and provides simplified access for query string
  arguments.
• $_POST, which deserializes and provides simplified access for urlencoded
  parameters submitted via HTTP POST; generically, it can be considered the
  results of parsing the message body.
• $_FILES, which provides serialized metadata around file uploads.
• $_SERVER, which provides access to CGI/SAPI environment variables, which
  commonly include the request method, the request scheme, the request URI, and
  headers.

ServerRequestInterface extends RequestInterface to provide an abstraction
around these various superglobals. This practice helps reduce coupling to the
superglobals by consumers, and encourages and promotes the ability to test
request consumers.

The server request provides one additional property, "attributes", to allow
consumers the ability to introspect, decompose, and match the request against
application-specific rules (such as path matching, scheme matching, host
matching, etc.). As such, the server request can also provide messaging between
multiple request consumers.

1.6 Uploaded files

ServerRequestInterface specifies a method for retrieving a tree of upload
files in a normalized structure, with each leaf an instance of
UploadedFileInterface.

The $_FILES superglobal has some well-known problems when dealing with arrays
of file inputs. As an example, if you have a form that submits an array of files
— e.g., the input name "files", submitting files[0] and files[1] — PHP will
represent this as:

array(
    'files' => array(
        'name' => array(
            0 => 'file0.txt',
            1 => 'file1.html',
        ),
        'type' => array(
            0 => 'text/plain',
            1 => 'text/html',
        ),
        /* etc. */
    ),
)

instead of the expected:

array(
    'files' => array(
        0 => array(
            'name' => 'file0.txt',
            'type' => 'text/plain',
            /* etc. */
        ),
        1 => array(
            'name' => 'file1.html',
            'type' => 'text/html',
            /* etc. */
        ),
    ),
)

The result is that consumers need to know this language implementation detail,
and write code for gathering the data for a given upload.

Additionally, scenarios exist where $_FILES is not populated when file uploads
occur:

• When the HTTP method is not POST.
• When unit testing.
• When operating under a non-SAPI environment, such as ReactPHP.

In such cases, the data will need to be seeded differently. As examples:

• A process might parse the message body to discover the file uploads. In such
  cases, the implementation may choose not to write the file uploads to the
  file system, but instead wrap them in a stream in order to reduce memory,
  I/O, and storage overhead.
• In unit testing scenarios, developers need to be able to stub and/or mock the
  file upload metadata in order to validate and verify different scenarios.

getUploadedFiles() provides the normalized structure for consumers.
Implementations are expected to:

• Aggregate all information for a given file upload, and use it to populate a
  Psr\Http\Message\UploadedFileInterface instance.
• Re-create the submitted tree structure, with each leaf being the appropriate
  Psr\Http\Message\UploadedFileInterface instance for the given location in
  the tree.

The tree structure referenced should mimic the naming structure in which files
were submitted.

In the simplest example, this might be a single named form element submitted as:

<input type="file" name="avatar" />

In this case, the structure in $_FILES would look like:

array(
    'avatar' => array(
        'tmp_name' => 'phpUxcOty',
        'name' => 'my-avatar.png',
        'size' => 90996,
        'type' => 'image/png',
        'error' => 0,
    ),
)

The normalized form returned by getUploadedFiles() would be:

array(
    'avatar' => /* UploadedFileInterface instance */
)

In the case of an input using array notation for the name:

<input type="file" name="my-form[details][avatar]" />

$_FILES ends up looking like this:

array(
    'my-form' => array(
        'details' => array(
            'avatar' => array(
                'tmp_name' => 'phpUxcOty',
                'name' => 'my-avatar.png',
                'size' => 90996,
                'type' => 'image/png',
                'error' => 0,
            ),
        ),
    ),
)

And the corresponding tree returned by getUploadedFiles() should be:

array(
    'my-form' => array(
        'details' => array(
            'avatar' => /* UploadedFileInterface instance */
        ),
    ),
)

In some cases, you may specify an array of files:

Upload an avatar: <input type="file" name="my-form[details][avatars][]" />
Upload an avatar: <input type="file" name="my-form[details][avatars][]" />

(As an example, JavaScript controls might spawn additional file upload inputs to
allow uploading multiple files at once.)

In such a case, the specification implementation must aggregate all information
related to the file at the given index. The reason is because $_FILES deviates
from its normal structure in such cases:

array(
    'my-form' => array(
        'details' => array(
            'avatars' => array(
                'tmp_name' => array(
                    0 => '...',
                    1 => '...',
                    2 => '...',
                ),
                'name' => array(
                    0 => '...',
                    1 => '...',
                    2 => '...',
                ),
                'size' => array(
                    0 => '...',
                    1 => '...',
                    2 => '...',
                ),
                'type' => array(
                    0 => '...',
                    1 => '...',
                    2 => '...',
                ),
                'error' => array(
                    0 => '...',
                    1 => '...',
                    2 => '...',
                ),
            ),
        ),
    ),
)

The above $_FILES array would correspond to the following structure as
returned by getUploadedFiles():

array(
    'my-form' => array(
        'details' => array(
            'avatars' => array(
                0 => /* UploadedFileInterface instance */,
                1 => /* UploadedFileInterface instance */,
                2 => /* UploadedFileInterface instance */,
            ),
        ),
    ),
)

Consumers would access index 1 of the nested array using:

$request->getUploadedFiles()['my-form']['details']['avatars'][1];

Because the uploaded files data is derivative (derived from $_FILES or the
request body), a mutator method, withUploadedFiles(), is also present in the
interface, allowing delegation of the normalization to another process.

In the case of the original examples, consumption resembles the following:

$file0 = $request->getUploadedFiles()['files'][0];
$file1 = $request->getUploadedFiles()['files'][1];

printf(
    "Received the files %s and %s",
    $file0->getClientFilename(),
    $file1->getClientFilename()
);

// "Received the files file0.txt and file1.html"

This proposal also recognizes that implementations may operate in non-SAPI
environments. As such, UploadedFileInterface provides methods for ensuring
operations will work regardless of environment. In particular:

• moveTo($targetPath) is provided as a safe and recommended alternative to calling
  move_uploaded_file() directly on the temporary upload file. Implementations
  will detect the correct operation to use based on environment.
• getStream() will return a StreamInterface instance. In non-SAPI
  environments, one proposed possibility is to parse individual upload files
  into php://temp streams instead of directly to files; in such cases, no
  upload file is present. getStream() is therefore guaranteed to work
  regardless of environment.

As examples:

// Move a file to an upload directory
$filename = sprintf(
    '%s.%s',
    create_uuid(),
    pathinfo($file0->getClientFilename(), PATHINFO_EXTENSION)
);
$file0->moveTo(DATA_DIR . '/' . $filename);

// Stream a file to Amazon S3.
// Assume $s3wrapper is a PHP stream that will write to S3, and that
// Psr7StreamWrapper is a class that will decorate a StreamInterface as a PHP
// StreamWrapper.
$stream = new Psr7StreamWrapper($file1->getStream());
stream_copy_to_stream($stream, $s3wrapper);

2. Package

上面讨论的接口和类库已经整合成为扩展包：
psr/http-message。

3. Interfaces

3.1 Psr\Http\Message\MessageInterface

<?php
namespace Psr\Http\Message;

/**
 * 
 * HTTP 消息值得是客户端发起的「请求」和服务器端返回的「响应」，此接口
 * 定义了他们通用的方法。
 * 
 * HTTP 消息是被视为无法修改的，所有能修改状态的方法，都 **必须** 有一套
 * 机制，在内部保持好原有的内容，然后把修改状态后的信息返回。
 *
 * @see http://www.ietf.org/rfc/rfc7230.txt
 * @see http://www.ietf.org/rfc/rfc7231.txt
 */
interface MessageInterface
{
    /**
     * 获取字符串形式的 HTTP 协议版本信息
     *
     * 字符串必须包含 HTTP 版本数字，如："1.1", "1.0"。
     *
     * @return string HTTP 协议版本
     */
    public function getProtocolVersion();

    /**
     * 返回指定 HTTP 版本号的消息实例。
     *
     * 传参的版本号必须 **只** 包含 HTTP 版本数字，如："1.1", "1.0"。
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息对象，然后返回
     * 一个新的带有传参进去的 HTTP 版本的实例
     *
     * @param string $version HTTP 版本信息
     * @return self
     */
    public function withProtocolVersion($version);

    /**
     * 获取所有的头信息
     *
     * 返回的二维数组中，第一维数组的「键」代表单条头信息的名字，「值」是
     * 以数据形式返回的，见以下实例：
     *
     *     // 把「值」的数据当成字串打印出来
     *     foreach ($message->getHeaders() as $name => $values) {
     *         echo $name . ': ' . implode(', ', $values);
     *     }
     *
     *     // 迭代的循环二维数组
     *     foreach ($message->getHeaders() as $name => $values) {
     *         foreach ($values as $value) {
     *             header(sprintf('%s: %s', $name, $value), false);
     *         }
     *     }
     *
     * 虽然头信息是没有大小写之分，但是使用 `getHeaders()` 会返回保留了原本
     * 大小写形式的内容。
     *
     * @return string[][] 返回一个两维数组，第一维数组的「键」 **必须** 为单条头信息的
     *     名称，对应的是由字串组成的数组，请注意，对应的「值」 **必须** 是数组形式的。
     */
    public function getHeaders();

    /**
     * 检查是否头信息中包含有此名称的值，不区分大小写
     *
     * @param string $name 不区分大小写的头信息名称
     * @return bool 找到返回 true，未找到返回 false
     */
    public function hasHeader($name);

    /**
     * 根据给定的名称，获取一条头信息，不区分大小写，以数组形式返回
     *
     * 此方法以数组形式返回对应名称的头信息。
     *
     * 如果没有对应的头信息，**必须** 返回一个空数组。
     *
     * @param string $name 不区分大小写的头部字段名称。
     * @return string[] 返回头信息中，对应名称的，由字符串组成的数组值，如果没有对应
     *  的内容，**必须** 返回空数组。
     */
    public function getHeader($name);

    /**
     * 根据给定的名称，获取一条头信息，不区分大小写，以逗号分隔的形式返回
     * 
     * 此方法返回所有对应的头信息，并将其使用逗号分隔的方法拼接起来。
     *
     * 注意：不是所有的头信息都可使用逗号分隔的方法来拼接，对于那些头信息，请使用
     * `getHeader()` 方法来获取。
     * 
     * 如果没有对应的头信息，此方法 **必须** 返回一个空字符串。
     *
     * @param string $name 不区分大小写的头部字段名称。
     * @return string 返回头信息中，对应名称的，由逗号分隔组成的字串，如果没有对应
     *  的内容，**必须** 返回空字符串。
     */
    public function getHeaderLine($name);

    /**
     * 返回指定头信息「键/值」对的消息实例。
     *
     * 虽然头信息是不区分大小写的，但是此方法必须保留其传参时的大小写状态，并能够在
     * 调用 `getHeaders()` 的时候被取出。
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息对象，然后返回
     * 一个新的带有传参进去头信息的实例
     *
     * @param string $name Case-insensitive header field name.
     * @param string|string[] $value Header value(s).
     * @return self
     * @throws \InvalidArgumentException for invalid header names or values.
     */
    public function withHeader($name, $value);

    /**
     * 返回一个头信息增量的 HTTP 消息实例。
     *
     * 原有的头信息会被保留，新的值会作为增量加上，如果头信息不存在的话，会被加上。
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息对象，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @param string $name 不区分大小写的头部字段名称。
     * @param string|string[] $value 头信息对应的值。
     * @return self
     * @throws \InvalidArgumentException 头信息字段名称非法时会被抛出。
     * @throws \InvalidArgumentException 头信息的值非法的时候，会被抛出。
     */
    public function withAddedHeader($name, $value);

    /**
     * 返回被移除掉指定头信息的 HTTP 消息实例。
     *
     * 头信息字段在解析的时候，**必须** 保证是不区分大小写的。
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息对象，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @param string $name 不区分大小写的头部字段名称。
     * @return self
     */
    public function withoutHeader($name);

    /**
     * 获取 HTTP 消息的内容。
     *
     * @return StreamInterface 以数据流的形式返回。
     */
    public function getBody();

    /**
     * 返回拼接了内容的 HTTP 消息实例。
     *
     * 内容 **必须** 是 StreamInterface 接口的实例。
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息对象，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @param StreamInterface $body 数据流形式的内容。
     * @return self
     * @throws \InvalidArgumentException 当消息内容不正确的时候。
     */
    public function withBody(StreamInterface $body);
}

3.2 Psr\Http\Message\RequestInterface

<?php
namespace Psr\Http\Message;

/**
 * 代表客户端请求的 HTTP 消息对象。
 *
 * 根据规范，每一个 HTTP 请求都包含以下信息：
 *
 * - HTTP 协议版本号 (Protocol version)
 * - HTTP 请求方法 (HTTP method)
 * - URI
 * - 头信息 (Headers)
 * - 消息内容 (Message body)
 *
 * 在构造 HTTP 请求对象的时候，实现类库 **必须** 从给出的 URI 中去提取 HOST 信息。
 *
 * HTTP 请求是被视为无法修改的，所有能修改状态的方法，都 **必须** 有一套机制，在内部保
 * 持好原有的内容，然后把修改状态后的，新的 HTTP 请求实例返回。
 */
interface RequestInterface extends MessageInterface
{
    /**
     * 获取消息请求的目标。
     *
     * 在大部分情况下，此方法会返回完整的 URI，除非 `withRequestTarget()` 被设置过。
     *
     * 如果没有提供 URI，并且没有提供任何的请求目标，此方法 **必须** 返回 "/"。
     *
     * @return string
     */
    public function getRequestTarget();

    /**
     * 返回一个指定目标的请求实例。
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 请求实例，然后返回
     * 一个新的修改过的 HTTP 请求实例。
     *
     * @see 关于请求目标的各种允许的格式，请见 http://tools.ietf.org/html/rfc7230#section-2.7 
     * 
     * @param mixed $requestTarget
     * @return self
     */
    public function withRequestTarget($requestTarget);

    /**
     * 获取当前请求使用的 HTTP 方法
     *
     * @return string HTTP 方法字符串
     */
    public function getMethod();

    /**
     * 返回更改了请求方法的消息实例。
     *
     * 虽然，在大部分情况下，HTTP 请求方法都是使用大写字母来标示的，但是，实现类库 **一定不可**
     * 修改用户传参的大小格式。
     * 
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 请求实例，然后返回
     * 一个新的修改过的 HTTP 请求实例。
     *
     * @param string $method 大小写敏感的方法名
     * @return self
     * @throws \InvalidArgumentException 当非法的 HTTP 方法名传入时会抛出异常。
     */
    public function withMethod($method);

    /**
     * 获取 URI 实例。
     *
     * 此方法必须返回 `UriInterface` 的 URI 实例。
     *
     * @see http://tools.ietf.org/html/rfc3986#section-4.3
     * @return UriInterface 返回与当前请求相关 `UriInterface` 类型的 URI 实例。
     */
    public function getUri();

    /**
     * 返回修改了 URI 的消息实例。
     *
     * 当传入的 `URI` 包含有 `HOST` 信息时，**必须** 更新 `HOST` 头信息，如果 `URI` 
     * 实例没有附带 `HOST` 信息，任何之前存在的 `HOST` 信息 **必须** 作为候补，应用
     * 更改到返回的消息实例里。
     * 
     * 你可以通过传入第二个参数来，来干预方法的处理，当 `$preserveHost` 设置为 `true` 
     * 的时候，会保留原来的 `HOST` 信息。
     * 
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 请求实例，然后返回
     * 一个新的修改过的 HTTP 请求实例。
     *
     * @see http://tools.ietf.org/html/rfc3986#section-4.3
     * @param UriInterface $uri `UriInterface` 类型的 URI 实例
     * @param bool $preserveHost 是否保留原有的 HOST 头信息
     * @return self
     */
    public function withUri(UriInterface $uri, $preserveHost = false);
}

3.2.1 Psr\Http\Message\ServerRequestInterface

<?php
namespace Psr\Http\Message;

/**
 * Representation of an incoming, server-side HTTP request.
 *
 * Per the HTTP specification, this interface includes properties for
 * each of the following:
 *
 * - Protocol version
 * - HTTP method
 * - URI
 * - Headers
 * - Message body
 *
 * Additionally, it encapsulates all data as it has arrived to the
 * application from the CGI and/or PHP environment, including:
 *
 * - The values represented in $_SERVER.
 * - Any cookies provided (generally via $_COOKIE)
 * - Query string arguments (generally via $_GET, or as parsed via parse_str())
 * - Upload files, if any (as represented by $_FILES)
 * - Deserialized body parameters (generally from $_POST)
 *
 * $_SERVER values MUST be treated as immutable, as they represent application
 * state at the time of request; as such, no methods are provided to allow
 * modification of those values. The other values provide such methods, as they
 * can be restored from $_SERVER or the request body, and may need treatment
 * during the application (e.g., body parameters may be deserialized based on
 * content type).
 *
 * Additionally, this interface recognizes the utility of introspecting a
 * request to derive and match additional parameters (e.g., via URI path
 * matching, decrypting cookie values, deserializing non-form-encoded body
 * content, matching authorization headers to users, etc). These parameters
 * are stored in an "attributes" property.
 *
 * HTTP 请求是被视为无法修改的，所有能修改状态的方法，都 **必须** 有一套机制，在内部保
 * 持好原有的内容，然后把修改状态后的，新的 HTTP 请求实例返回。
 */
interface ServerRequestInterface extends RequestInterface
{
    /**
     * Retrieve server parameters.
     *
     * Retrieves data related to the incoming request environment,
     * typically derived from PHP's $_SERVER superglobal. The data IS NOT
     * REQUIRED to originate from $_SERVER.
     *
     * @return array
     */
    public function getServerParams();

    /**
     * Retrieve cookies.
     *
     * Retrieves cookies sent by the client to the server.
     *
     * The data MUST be compatible with the structure of the $_COOKIE
     * superglobal.
     *
     * @return array
     */
    public function getCookieParams();

    /**
     * Return an instance with the specified cookies.
     *
     * The data IS NOT REQUIRED to come from the $_COOKIE superglobal, but MUST
     * be compatible with the structure of $_COOKIE. Typically, this data will
     * be injected at instantiation.
     *
     * This method MUST NOT update the related Cookie header of the request
     * instance, nor related values in the server params.
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     * 
     * @param array $cookies Array of key/value pairs representing cookies.
     * @return self
     */
    public function withCookieParams(array $cookies);

    /**
     * Retrieve query string arguments.
     *
     * Retrieves the deserialized query string arguments, if any.
     *
     * Note: the query params might not be in sync with the URI or server
     * params. If you need to ensure you are only getting the original
     * values, you may need to parse the query string from `getUri()->getQuery()`
     * or from the `QUERY_STRING` server param.
     *
     * @return array
     */
    public function getQueryParams();

    /**
     * Return an instance with the specified query string arguments.
     *
     * These values SHOULD remain immutable over the course of the incoming
     * request. They MAY be injected during instantiation, such as from PHP's
     * $_GET superglobal, or MAY be derived from some other value such as the
     * URI. In cases where the arguments are parsed from the URI, the data
     * MUST be compatible with what PHP's parse_str() would return for
     * purposes of how duplicate query parameters are handled, and how nested
     * sets are handled.
     *
     * Setting query string arguments MUST NOT change the URI stored by the
     * request, nor the values in the server params.
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @param array $query Array of query string arguments, typically from
     *     $_GET.
     * @return self
     */
    public function withQueryParams(array $query);

    /**
     * Retrieve normalized file upload data.
     *
     * This method returns upload metadata in a normalized tree, with each leaf
     * an instance of Psr\Http\Message\UploadedFileInterface.
     *
     * These values MAY be prepared from $_FILES or the message body during
     * instantiation, or MAY be injected via withUploadedFiles().
     *
     * @return array An array tree of UploadedFileInterface instances; an empty
     *     array MUST be returned if no data is present.
     */
    public function getUploadedFiles();

    /**
     * Create a new instance with the specified uploaded files.
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @param array An array tree of UploadedFileInterface instances.
     * @return self
     * @throws \InvalidArgumentException if an invalid structure is provided.
     */
    public function withUploadedFiles(array $uploadedFiles);

    /**
     * Retrieve any parameters provided in the request body.
     *
     * If the request Content-Type is either application/x-www-form-urlencoded
     * or multipart/form-data, and the request method is POST, this method MUST
     * return the contents of $_POST.
     *
     * Otherwise, this method may return any results of deserializing
     * the request body content; as parsing returns structured content, the
     * potential types MUST be arrays or objects only. A null value indicates
     * the absence of body content.
     *
     * @return null|array|object The deserialized body parameters, if any.
     *     These will typically be an array or object.
     */
    public function getParsedBody();

    /**
     * Return an instance with the specified body parameters.
     *
     * These MAY be injected during instantiation.
     *
     * If the request Content-Type is either application/x-www-form-urlencoded
     * or multipart/form-data, and the request method is POST, use this method
     * ONLY to inject the contents of $_POST.
     *
     * The data IS NOT REQUIRED to come from $_POST, but MUST be the results of
     * deserializing the request body content. Deserialization/parsing returns
     * structured data, and, as such, this method ONLY accepts arrays or objects,
     * or a null value if nothing was available to parse.
     *
     * As an example, if content negotiation determines that the request data
     * is a JSON payload, this method could be used to create a request
     * instance with the deserialized parameters.
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @param null|array|object $data The deserialized body data. This will
     *     typically be in an array or object.
     * @return self
     * @throws \InvalidArgumentException if an unsupported argument type is
     *     provided.
     */
    public function withParsedBody($data);

    /**
     * Retrieve attributes derived from the request.
     *
     * The request "attributes" may be used to allow injection of any
     * parameters derived from the request: e.g., the results of path
     * match operations; the results of decrypting cookies; the results of
     * deserializing non-form-encoded message bodies; etc. Attributes
     * will be application and request specific, and CAN be mutable.
     *
     * @return mixed[] Attributes derived from the request.
     */
    public function getAttributes();

    /**
     * Retrieve a single derived request attribute.
     *
     * Retrieves a single derived request attribute as described in
     * getAttributes(). If the attribute has not been previously set, returns
     * the default value as provided.
     *
     * This method obviates the need for a hasAttribute() method, as it allows
     * specifying a default value to return if the attribute is not found.
     *
     * @see getAttributes()
     * @param string $name The attribute name.
     * @param mixed $default Default value to return if the attribute does not exist.
     * @return mixed
     */
    public function getAttribute($name, $default = null);

    /**
     * Return an instance with the specified derived request attribute.
     *
     * This method allows setting a single derived request attribute as
     * described in getAttributes().
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @see getAttributes()
     * @param string $name The attribute name.
     * @param mixed $value The value of the attribute.
     * @return self
     */
    public function withAttribute($name, $value);

    /**
     * Return an instance that removes the specified derived request attribute.
     *
     * This method allows removing a single derived request attribute as
     * described in getAttributes().
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @see getAttributes()
     * @param string $name The attribute name.
     * @return self
     */
    public function withoutAttribute($name);
}

3.3 Psr\Http\Message\ResponseInterface

<?php
namespace Psr\Http\Message;

/**
 * Representation of an outgoing, server-side response.
 *
 * Per the HTTP specification, this interface includes properties for
 * each of the following:
 *
 * - Protocol version
 * - Status code and reason phrase
 * - Headers
 * - Message body
 *
 * Responses are considered immutable; all methods that might change state MUST
 * be implemented such that they retain the internal state of the current
 * message and return an instance that contains the changed state.
 * 
 * HTTP 响应是被视为无法修改的，所有能修改状态的方法，都 **必须** 有一套机制，在内部保
 * 持好原有的内容，然后把修改状态后的，新的 HTTP 响应实例返回。
 */
interface ResponseInterface extends MessageInterface
{
    /**
     * Gets the response status code.
     *
     * The status code is a 3-digit integer result code of the server's attempt
     * to understand and satisfy the request.
     *
     * @return int Status code.
     */
    public function getStatusCode();

    /**
     * Return an instance with the specified status code and, optionally, reason phrase.
     *
     * If no reason phrase is specified, implementations MAY choose to default
     * to the RFC 7231 or IANA recommended reason phrase for the response's
     * status code.
     *
     * 此方法在实现的时候，**必须** 保留原有的不可修改的 HTTP 消息实例，然后返回
     * 一个新的修改过的 HTTP 消息实例。
     *
     * @see http://tools.ietf.org/html/rfc7231#section-6
     * @see http://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
     * @param int $code The 3-digit integer result code to set.
     * @param string $reasonPhrase The reason phrase to use with the
     *     provided status code; if none is provided, implementations MAY
     *     use the defaults as suggested in the HTTP specification.
     * @return self
     * @throws \InvalidArgumentException For invalid status code arguments.
     */
    public function withStatus($code, $reasonPhrase = '');

    /**
     * Gets the response reason phrase associated with the status code.
     *
     * Because a reason phrase is not a required element in a response
     * status line, the reason phrase value MAY be empty. Implementations MAY
     * choose to return the default RFC 7231 recommended reason phrase (or those
     * listed in the IANA HTTP Status Code Registry) for the response's
     * status code.
     *
     * @see http://tools.ietf.org/html/rfc7231#section-6
     * @see http://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
     * @return string Reason phrase; must return an empty string if none present.
     */
    public function getReasonPhrase();
}