PSR-7: HTTP message interfaces

HTTP message interfaces

This document describes common interfaces for representing HTTP messages as described in RFC 7230 and RFC 7231, and URIs for use with HTTP messages as described in RFC 3986.

HTTP messages are the foundation of web development. Web browsers and HTTP clients such as cURL create HTTP request messages that are sent to a web server, which provides an HTTP response message. Server-side code receives an HTTP request message, and returns an HTTP response message.

HTTP messages are typically abstracted from the end-user consumer, but as developers, we typically need to know how they are structured and how to access or manipulate them in order to perform our tasks, whether that might be making a request to an HTTP API, or handling an incoming request.

Every HTTP request message has a specific form:

POST /path HTTP/1.1
Host: example.com

foo=bar&baz=bat

The first line of a request is the "request line", and contains, in order, the HTTP request method, the request target (usually either an absolute URI or a path on the web server), and the HTTP protocol version. This is followed by one or more HTTP headers, an empty line, and the message body.

HTTP response messages have a similar structure:

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

This is the response body

The first line is the "status line", and contains, in order, the HTTP protocol version, the HTTP status code, and a "reason phrase," a human-readable description of the status code. Like the request message, this is then followed by one or more HTTP headers, an empty line, and the message body.

The interfaces described in this document are abstractions around HTTP messages and the elements composing them.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

References

1. Specification

1.1 Messages

An HTTP message is either a request from a client to a server or a response from a server to a client. This specification defines interfaces for the HTTP messages Psr\Http\Message\RequestInterface and Psr\Http\Message\ResponseInterface respectively.

Both Psr\Http\Message\RequestInterface and Psr\Http\Message\ResponseInterface extend Psr\Http\Message\MessageInterface. While Psr\Http\Message\MessageInterface MAY be implemented directly, implementors SHOULD implement Psr\Http\Message\RequestInterface and Psr\Http\Message\ResponseInterface.

From here forward, the namespace Psr\Http\Message will be omitted when referring to these interfaces.

1.2 HTTP Headers

Case-insensitive header field names

HTTP messages include case-insensitive header field names. Headers are retrieved by name from classes implementing the MessageInterface in a case-insensitive manner. For example, retrieving the foo header will return the same result as retrieving the FoO header. Similarly, setting the Foo header will overwrite any previously set foo header value.

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

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

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

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

Despite that headers may be retrieved case-insensitively, the original case MUST be preserved by the implementation, in particular when retrieved with getHeaders().

Non-conforming HTTP applications may depend on a certain case, so it is useful for a user to be able to dictate the case of the HTTP headers when creating a request or response.

Headers with multiple values

In order to accommodate headers with multiple values yet still provide the convenience of working with headers as strings, headers can be retrieved from an instance of a MessageInterface as an array or a string. Use the getHeaderLine() method to retrieve a header value as a string containing all header values of a case-insensitive header by name concatenated with a comma. Use getHeader() to retrieve an array of all the header values for a particular case-insensitive header by name.

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

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

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

Note: Not all header values can be concatenated using a comma (e.g., Set-Cookie). When working with such headers, consumers of MessageInterface-based classes SHOULD rely on the getHeader() method for retrieving such multi-valued headers.

Host header

In requests, the Host header typically mirrors the host component of the URI, as well as the host used when establishing the TCP connection. However, the HTTP specification allows the Host header to differ from each of the two.

During construction, implementations MUST attempt to set the Host header from a provided URI if no Host header is provided.

RequestInterface::withUri() will, by default, replace the returned request's Host header with a Host header matching the host component of the passed UriInterface.

You can opt-in to preserving the original state of the Host header by passing true for the second ($preserveHost) argument. When this argument is set to true, the returned request will not update the Host header of the returned message -- unless the message contains no Host header.

This table illustrates what getHeaderLine('Host') will return for a request returned by withUri() with the $preserveHost argument set to true for various initial requests and URIs.

Request Host header1 Request host component2 URI host component3 Result
'' '' '' ''
'' foo.com '' foo.com
'' foo.com bar.com foo.com
foo.com '' bar.com foo.com
foo.com bar.com baz.com foo.com
  • 1 Host header value prior to operation.
  • 2 Host component of the URI composed in the request prior to the operation.
  • 3 Host component of the URI being injected via withUri().

1.3 Streams

HTTP messages consist of a start-line, headers, and a body. The body of an HTTP message can be very small or extremely large. Attempting to represent the body of a message as a string can easily consume more memory than intended because the body must be stored completely in memory. Attempting to store the body of a request or response in memory would preclude the use of that implementation from being able to work with large message bodies. StreamInterface is used in order to hide the implementation details when a stream of data is read from or written to. For situations where a string would be an appropriate message implementation, built-in streams such as php://memory and php://temp may be used.

StreamInterface exposes several methods that enable streams to be read from, written to, and traversed effectively.

Streams expose their capabilities using three methods: isReadable(), isWritable(), and isSeekable(). These methods can be used by stream collaborators to determine if a stream is capable of their requirements.

Each stream instance will have various capabilities: it can be read-only, write-only, or read-write. It can also allow arbitrary random access (seeking forwards or backwards to any location), or only sequential access (for example in the case of a socket, pipe, or callback-based stream).

Finally, StreamInterface defines a __toString() method to simplify retrieving or emitting the entire body contents at once.

Unlike the request and response interfaces, StreamInterface does not model immutability. In situations where an actual PHP stream is wrapped, immutability is impossible to enforce, as any code that interacts with the resource can potentially change its state (including cursor position, contents, and more). Our recommendation is that implementations use read-only streams for server-side requests and client-side responses. Consumers should be aware of the fact that the stream instance may be mutable, and, as such, could alter the state of the message; when in doubt, create a new stream instance and attach it to a message to enforce state.

1.4 Request Targets and URIs

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 to HTTP cookies.
  • $_GET, which deserializes and provides simplified access to 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

The interfaces and classes described are provided as part of the psr/http-message package.

3. Interfaces

3.1 Psr\Http\Message\MessageInterface

<?php
namespace Psr\Http\Message;

/**
 * HTTP messages consist of requests from a client to a server and responses
 * from a server to a client. This interface defines the methods common to
 * each.
 *
 * Messages 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.
 *
 * @see http://www.ietf.org/rfc/rfc7230.txt
 * @see http://www.ietf.org/rfc/rfc7231.txt
 */
interface MessageInterface
{
    /**
     * Retrieves the HTTP protocol version as a string.
     *
     * The string MUST contain only the HTTP version number (e.g., "1.1", "1.0").
     *
     * @return string HTTP protocol version.
     */
    public function getProtocolVersion();

    /**
     * Return an instance with the specified HTTP protocol version.
     *
     * The version string MUST contain only the HTTP version number (e.g.,
     * "1.1", "1.0").
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * new protocol version.
     *
     * @param string $version HTTP protocol version
     * @return static
     */
    public function withProtocolVersion($version);

    /**
     * Retrieves all message header values.
     *
     * The keys represent the header name as it will be sent over the wire, and
     * each value is an array of strings associated with the header.
     *
     *     // Represent the headers as a string
     *     foreach ($message->getHeaders() as $name => $values) {
     *         echo $name . ': ' . implode(', ', $values);
     *     }
     *
     *     // Emit headers iteratively:
     *     foreach ($message->getHeaders() as $name => $values) {
     *         foreach ($values as $value) {
     *             header(sprintf('%s: %s', $name, $value), false);
     *         }
     *     }
     *
     * While header names are not case-sensitive, getHeaders() will preserve the
     * exact case in which headers were originally specified.
     *
     * @return string[][] Returns an associative array of the message's headers.
     *     Each key MUST be a header name, and each value MUST be an array of
     *     strings for that header.
     */
    public function getHeaders();

    /**
     * Checks if a header exists by the given case-insensitive name.
     *
     * @param string $name Case-insensitive header field name.
     * @return bool Returns true if any header names match the given header
     *     name using a case-insensitive string comparison. Returns false if
     *     no matching header name is found in the message.
     */
    public function hasHeader($name);

    /**
     * Retrieves a message header value by the given case-insensitive name.
     *
     * This method returns an array of all the header values of the given
     * case-insensitive header name.
     *
     * If the header does not appear in the message, this method MUST return an
     * empty array.
     *
     * @param string $name Case-insensitive header field name.
     * @return string[] An array of string values as provided for the given
     *    header. If the header does not appear in the message, this method MUST
     *    return an empty array.
     */
    public function getHeader($name);

    /**
     * Retrieves a comma-separated string of the values for a single header.
     *
     * This method returns all of the header values of the given
     * case-insensitive header name as a string concatenated together using
     * a comma.
     *
     * NOTE: Not all header values may be appropriately represented using
     * comma concatenation. For such headers, use getHeader() instead
     * and supply your own delimiter when concatenating.
     *
     * If the header does not appear in the message, this method MUST return
     * an empty string.
     *
     * @param string $name Case-insensitive header field name.
     * @return string A string of values as provided for the given header
     *    concatenated together using a comma. If the header does not appear in
     *    the message, this method MUST return an empty string.
     */
    public function getHeaderLine($name);

    /**
     * Return an instance with the provided value replacing the specified header.
     *
     * While header names are case-insensitive, the casing of the header will
     * be preserved by this function, and returned from getHeaders().
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * new and/or updated header and value.
     *
     * @param string $name Case-insensitive header field name.
     * @param string|string[] $value Header value(s).
     * @return static
     * @throws \InvalidArgumentException for invalid header names or values.
     */
    public function withHeader($name, $value);

    /**
     * Return an instance with the specified header appended with the given value.
     *
     * Existing values for the specified header will be maintained. The new
     * value(s) will be appended to the existing list. If the header did not
     * exist previously, it will be added.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * new header and/or value.
     *
     * @param string $name Case-insensitive header field name to add.
     * @param string|string[] $value Header value(s).
     * @return static
     * @throws \InvalidArgumentException for invalid header names.
     * @throws \InvalidArgumentException for invalid header values.
     */
    public function withAddedHeader($name, $value);

    /**
     * Return an instance without the specified header.
     *
     * Header resolution MUST be done without case-sensitivity.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that removes
     * the named header.
     *
     * @param string $name Case-insensitive header field name to remove.
     * @return static
     */
    public function withoutHeader($name);

    /**
     * Gets the body of the message.
     *
     * @return StreamInterface Returns the body as a stream.
     */
    public function getBody();

    /**
     * Return an instance with the specified message body.
     *
     * The body MUST be a StreamInterface object.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return a new instance that has the
     * new body stream.
     *
     * @param StreamInterface $body Body.
     * @return static
     * @throws \InvalidArgumentException When the body is not valid.
     */
    public function withBody(StreamInterface $body);
}

3.2 Psr\Http\Message\RequestInterface

<?php
namespace Psr\Http\Message;

/**
 * Representation of an outgoing, client-side request.
 *
 * Per the HTTP specification, this interface includes properties for
 * each of the following:
 *
 * - Protocol version
 * - HTTP method
 * - URI
 * - Headers
 * - Message body
 *
 * During construction, implementations MUST attempt to set the Host header from
 * a provided URI if no Host header is provided.
 *
 * Requests 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.
 */
interface RequestInterface extends MessageInterface
{
    /**
     * Retrieves the message's request target.
     *
     * Retrieves the message's request-target either as it will appear (for
     * clients), as it appeared at request (for servers), or as it was
     * specified for the instance (see withRequestTarget()).
     *
     * In most cases, this will be the origin-form of the composed URI,
     * unless a value was provided to the concrete implementation (see
     * withRequestTarget() below).
     *
     * If no URI is available, and no request-target has been specifically
     * provided, this method MUST return the string "/".
     *
     * @return string
     */
    public function getRequestTarget();

    /**
     * Return an instance with the specific request-target.
     *
     * If the request needs a non-origin-form request-target — e.g., for
     * specifying an absolute-form, authority-form, or asterisk-form —
     * this method may be used to create an instance with the specified
     * request-target, verbatim.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * changed request target.
     *
     * @see http://tools.ietf.org/html/rfc7230#section-5.3 (for the various
     *     request-target forms allowed in request messages)
     * @param mixed $requestTarget
     * @return static
     */
    public function withRequestTarget($requestTarget);

    /**
     * Retrieves the HTTP method of the request.
     *
     * @return string Returns the request method.
     */
    public function getMethod();

    /**
     * Return an instance with the provided HTTP method.
     *
     * While HTTP method names are typically all uppercase characters, HTTP
     * method names are case-sensitive and thus implementations SHOULD NOT
     * modify the given string.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * changed request method.
     *
     * @param string $method Case-sensitive method.
     * @return static
     * @throws \InvalidArgumentException for invalid HTTP methods.
     */
    public function withMethod($method);

    /**
     * Retrieves the URI instance.
     *
     * This method MUST return a UriInterface instance.
     *
     * @see http://tools.ietf.org/html/rfc3986#section-4.3
     * @return UriInterface Returns a UriInterface instance
     *     representing the URI of the request.
     */
    public function getUri();

    /**
     * Returns an instance with the provided URI.
     *
     * This method MUST update the Host header of the returned request by
     * default if the URI contains a host component. If the URI does not
     * contain a host component, any pre-existing Host header MUST be carried
     * over to the returned request.
     *
     * You can opt-in to preserving the original state of the Host header by
     * setting `$preserveHost` to `true`. When `$preserveHost` is set to
     * `true`, this method interacts with the Host header in the following ways:
     *
     * - If the Host header is missing or empty, and the new URI contains
     *   a host component, this method MUST update the Host header in the returned
     *   request.
     * - If the Host header is missing or empty, and the new URI does not contain a
     *   host component, this method MUST NOT update the Host header in the returned
     *   request.
     * - If a Host header is present and non-empty, this method MUST NOT update
     *   the Host header in the returned request.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * new UriInterface instance.
     *
     * @see http://tools.ietf.org/html/rfc3986#section-4.3
     * @param UriInterface $uri New request URI to use.
     * @param bool $preserveHost Preserve the original state of the Host header.
     * @return static
     */
    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 at 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.
 *
 * Requests 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.
 */
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.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * updated cookie values.
     *
     * @param array $cookies Array of key/value pairs representing cookies.
     * @return static
     */
    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.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * updated query string arguments.
     *
     * @param array $query Array of query string arguments, typically from
     *     $_GET.
     * @return static
     */
    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.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * updated body parameters.
     *
     * @param array $uploadedFiles An array tree of UploadedFileInterface instances.
     * @return static
     * @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.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * updated body parameters.
     *
     * @param null|array|object $data The deserialized body data. This will
     *     typically be in an array or object.
     * @return static
     * @throws \InvalidArgumentException if an unsupported argument type is
     *     provided.
     */
    public function withParsedBody($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().
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * updated attribute.
     *
     * @see getAttributes()
     * @param string $name The attribute name.
     * @param mixed $value The value of the attribute.
     * @return static
     */
    public function withAttribute($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().
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that removes
     * the attribute.
     *
     * @see getAttributes()
     * @param string $name The attribute name.
     * @return static
     */
    public function withoutAttribute($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.
 */
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.
     *
     * This method MUST be implemented in such a way as to retain the
     * immutability of the message, and MUST return an instance that has the
     * updated status and reason phrase.
     *
     * @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 $reasonPhrase The reason phrase to use with the
     *     provided status code; if none is provided, implementations MAY
     *     use the defaults as suggested in the HTTP specification.
     * @return static
     * @throws \InvalidArgumentException For invalid status code arguments.
     */
    public function withStatus($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();
}

3.4 Psr\Http\Message\StreamInterface

<?php
namespace Psr\Http\Message;

/**
 * Describes a data stream.
 *
 * Typically, an instance will wrap a PHP stream; this interface provides
 * a wrapper around the most common operations, including serialization of
 * the entire stream to a string.
 */
interface StreamInterface
{
    /**
     * Reads all data from the stream into a string, from the beginning to end.
     *
     * This method MUST attempt to seek to the beginning of the stream before
     * reading data and read the stream until the end is reached.
     *
     * Warning: This could attempt to load a large amount of data into memory.
     *
     * This method MUST NOT raise an exception in order to conform with PHP's
     * string casting operations.
     *
     * @see http://php.net/manual/en/language.oop5.magic.php#object.tostring
     * @return string
     */
    public function __toString();

    /**
     * Closes the stream and any underlying resources.
     *
     * @return void
     */
    public function close();

    /**
     * Separates any underlying resources from the stream.
     *
     * After the stream has been detached, the stream is in an unusable state.
     *
     * @return resource|null Underlying PHP stream, if any
     */
    public function detach();

    /**
     * Get the size of the stream if known.
     *
     * @return int|null Returns the size in bytes if known, or null if unknown.
     */
    public function getSize();

    /**
     * Returns the current position of the file read/write pointer
     *
     * @return int Position of the file pointer
     * @throws \RuntimeException on error.
     */
    public function tell();

    /**
     * Returns true if the stream is at the end of the stream.
     *
     * @return bool
     */
    public function eof();

    /**
     * Returns whether or not the stream is seekable.
     *
     * @return bool
     */
    public function isSeekable();

    /**
     * Seek to a position in the stream.
     *
     * @see http://www.php.net/manual/en/function.fseek.php
     * @param int $offset Stream offset
     * @param int $whence Specifies how the cursor position will be calculated
     *     based on the seek offset. Valid values are identical to the built-in
     *     PHP $whence values for `fseek()`.  SEEK_SET: Set position equal to
     *     offset bytes SEEK_CUR: Set position to current location plus offset
     *     SEEK_END: Set position to end-of-stream plus offset.
     * @throws \RuntimeException on failure.
     */
    public function seek($offset, $whence = SEEK_SET);

    /**
     * Seek to the beginning of the stream.
     *
     * If the stream is not seekable, this method will raise an exception;
     * otherwise, it will perform a seek(0).
     *
     * @see seek()
     * @see http://www.php.net/manual/en/function.fseek.php
     * @throws \RuntimeException on failure.
     */
    public function rewind();

    /**
     * Returns whether or not the stream is writable.
     *
     * @return bool
     */
    public function isWritable();

    /**
     * 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);

    /**
     * Returns whether or not the stream is readable.
     *
     * @return bool
     */
    public function isReadable();

    /**
     * Read data from the stream.
     *
     * @param int $length Read up to $length bytes from the object and return
     *     them. Fewer than $length bytes may be returned if underlying stream
     *     call returns fewer bytes.
     * @return string Returns the data read from the stream, or an empty string
     *     if no bytes are available.
     * @throws \RuntimeException if an error occurs.
     */
    public function read($length);

    /**
     * Returns the remaining contents in a string
     *
     * @return string
     * @throws \RuntimeException if unable to read.
     * @throws \RuntimeException if error occurs while reading.
     */
    public function getContents();

    /**
     * Get stream metadata as an associative array or retrieve a specific key.
     *
     * The keys returned are identical to the keys returned from PHP's
     * stream_get_meta_data() function.
     *
     * @see http://php.net/manual/en/function.stream-get-meta-data.php
     * @param string $key Specific metadata to retrieve.
     * @return array|mixed|null Returns an associative array if no key is
     *     provided. Returns a specific key value if a key is provided and the
     *     value is found, or null if the key is not found.
     */
    public function getMetadata($key = null);
}

3.5 Psr\Http\Message\UriInterface

<?php
namespace Psr\Http\Message;

/**
 * Value object representing a URI.
 *
 * This interface is meant to represent URIs according to RFC 3986 and to
 * provide methods for most common operations. Additional functionality for
 * working with URIs can be provided on top of the interface or externally.
 * Its primary use is for HTTP requests, but may also be used in other
 * contexts.
 *
 * Instances of this interface are considered immutable; all methods that
 * might change state MUST be implemented such that they retain the internal
 * state of the current instance and return an instance that contains the
 * changed state.
 *
 * Typically the Host header will also be present in the request message.
 * For server-side requests, the scheme will typically be discoverable in the
 * server parameters.
 *
 * @see http://tools.ietf.org/html/rfc3986 (the URI specification)
 */
interface UriInterface
{
    /**
     * Retrieve the scheme component of the URI.
     *
     * If no scheme is present, this method MUST return an empty string.
     *
     * The value returned MUST be normalized to lowercase, per RFC 3986
     * Section 3.1.
     *
     * The trailing ":" character is not part of the scheme and MUST NOT be
     * added.
     *
     * @see https://tools.ietf.org/html/rfc3986#section-3.1
     * @return string The URI scheme.
     */
    public function getScheme();

    /**
     * Retrieve the authority component of the URI.
     *
     * If no authority information is present, this method MUST return an empty
     * string.
     *
     * The authority syntax of the URI is:
     *
     * <pre>
     * [user-info@]host[:port]
     * </pre>
     *
     * If the port component is not set or is the standard port for the current
     * scheme, it SHOULD NOT be included.
     *
     * @see https://tools.ietf.org/html/rfc3986#section-3.2
     * @return string The URI authority, in "[user-info@]host[:port]" format.
     */
    public function getAuthority();

    /**
     * Retrieve the user information component of the URI.
     *
     * If no user information is present, this method MUST return an empty
     * string.
     *
     * If a user is present in the URI, this will return that value;
     * additionally, if the password is also present, it will be appended to the
     * user value, with a colon (":") separating the values.
     *
     * The trailing "@" character is not part of the user information and MUST
     * NOT be added.
     *
     * @return string The URI user information, in "username[:password]" format.
     */
    public function getUserInfo();

    /**
     * Retrieve the host component of the URI.
     *
     * If no host is present, this method MUST return an empty string.
     *
     * The value returned MUST be normalized to lowercase, per RFC 3986
     * Section 3.2.2.
     *
     * @see http://tools.ietf.org/html/rfc3986#section-3.2.2
     * @return string The URI host.
     */
    public function getHost();

    /**
     * Retrieve the port component of the URI.
     *
     * If a port is present, and it is non-standard for the current scheme,
     * this method MUST return it as an integer. If the port is the standard port
     * used with the current scheme, this method SHOULD return null.
     *
     * If no port is present, and no scheme is present, this method MUST return
     * a null value.
     *
     * If no port is present, but a scheme is present, this method MAY return
     * the standard port for that scheme, but SHOULD return null.
     *
     * @return null|int The URI port.
     */
    public function getPort();

    /**
     * Retrieve the path component of the URI.
     *
     * The path can either be empty or absolute (starting with a slash) or
     * rootless (not starting with a slash). Implementations MUST support all
     * three syntaxes.
     *
     * Normally, the empty path "" and absolute path "/" are considered equal as
     * defined in RFC 7230 Section 2.7.3. But this method MUST NOT automatically
     * do this normalization because in contexts with a trimmed base path, e.g.
     * the front controller, this difference becomes significant. It's the task
     * of the user to handle both "" and "/".
     *
     * The value returned MUST be percent-encoded, but MUST NOT double-encode
     * any characters. To determine what characters to encode, please refer to
     * RFC 3986, Sections 2 and 3.3.
     *
     * As an example, if the value should include a slash ("/") not intended as
     * delimiter between path segments, that value MUST be passed in encoded
     * form (e.g., "%2F") to the instance.
     *
     * @see https://tools.ietf.org/html/rfc3986#section-2
     * @see https://tools.ietf.org/html/rfc3986#section-3.3
     * @return string The URI path.
     */
    public function getPath();

    /**
     * Retrieve the query string of the URI.
     *
     * If no query string is present, this method MUST return an empty string.
     *
     * The leading "?" character is not part of the query and MUST NOT be
     * added.
     *
     * The value returned MUST be percent-encoded, but MUST NOT double-encode
     * any characters. To determine what characters to encode, please refer to
     * RFC 3986, Sections 2 and 3.4.
     *
     * As an example, if a value in a key/value pair of the query string should
     * include an ampersand ("&") not intended as a delimiter between values,
     * that value MUST be passed in encoded form (e.g., "%26") to the instance.
     *
     * @see https://tools.ietf.org/html/rfc3986#section-2
     * @see https://tools.ietf.org/html/rfc3986#section-3.4
     * @return string The URI query string.
     */
    public function getQuery();

    /**
     * Retrieve the fragment component of the URI.
     *
     * If no fragment is present, this method MUST return an empty string.
     *
     * The leading "#" character is not part of the fragment and MUST NOT be
     * added.
     *
     * The value returned MUST be percent-encoded, but MUST NOT double-encode
     * any characters. To determine what characters to encode, please refer to
     * RFC 3986, Sections 2 and 3.5.
     *
     * @see https://tools.ietf.org/html/rfc3986#section-2
     * @see https://tools.ietf.org/html/rfc3986#section-3.5
     * @return string The URI fragment.
     */
    public function getFragment();

    /**
     * Return an instance with the specified scheme.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified scheme.
     *
     * Implementations MUST support the schemes "http" and "https" case
     * insensitively, and MAY accommodate other schemes if required.
     *
     * An empty scheme is equivalent to removing the scheme.
     *
     * @param string $scheme The scheme to use with the new instance.
     * @return static A new instance with the specified scheme.
     * @throws \InvalidArgumentException for invalid schemes.
     * @throws \InvalidArgumentException for unsupported schemes.
     */
    public function withScheme($scheme);

    /**
     * Return an instance with the specified user information.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified user information.
     *
     * Password is optional, but the user information MUST include the
     * user; an empty string for the user is equivalent to removing user
     * information.
     *
     * @param string $user The user name to use for authority.
     * @param null|string $password The password associated with $user.
     * @return static A new instance with the specified user information.
     */
    public function withUserInfo($user, $password = null);

    /**
     * Return an instance with the specified host.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified host.
     *
     * An empty host value is equivalent to removing the host.
     *
     * @param string $host The hostname to use with the new instance.
     * @return static A new instance with the specified host.
     * @throws \InvalidArgumentException for invalid hostnames.
     */
    public function withHost($host);

    /**
     * Return an instance with the specified port.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified port.
     *
     * Implementations MUST raise an exception for ports outside the
     * established TCP and UDP port ranges.
     *
     * A null value provided for the port is equivalent to removing the port
     * information.
     *
     * @param null|int $port The port to use with the new instance; a null value
     *     removes the port information.
     * @return static A new instance with the specified port.
     * @throws \InvalidArgumentException for invalid ports.
     */
    public function withPort($port);

    /**
     * Return an instance with the specified path.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified path.
     *
     * The path can either be empty or absolute (starting with a slash) or
     * rootless (not starting with a slash). Implementations MUST support all
     * three syntaxes.
     *
     * If an HTTP path is intended to be host-relative rather than path-relative
     * then it must begin with a slash ("/"). HTTP paths not starting with a slash
     * are assumed to be relative to some base path known to the application or
     * consumer.
     *
     * Users can provide both encoded and decoded path characters.
     * Implementations ensure the correct encoding as outlined in getPath().
     *
     * @param string $path The path to use with the new instance.
     * @return static A new instance with the specified path.
     * @throws \InvalidArgumentException for invalid paths.
     */
    public function withPath($path);

    /**
     * Return an instance with the specified query string.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified query string.
     *
     * Users can provide both encoded and decoded query characters.
     * Implementations ensure the correct encoding as outlined in getQuery().
     *
     * An empty query string value is equivalent to removing the query string.
     *
     * @param string $query The query string to use with the new instance.
     * @return static A new instance with the specified query string.
     * @throws \InvalidArgumentException for invalid query strings.
     */
    public function withQuery($query);

    /**
     * Return an instance with the specified URI fragment.
     *
     * This method MUST retain the state of the current instance, and return
     * an instance that contains the specified URI fragment.
     *
     * Users can provide both encoded and decoded fragment characters.
     * Implementations ensure the correct encoding as outlined in getFragment().
     *
     * An empty fragment value is equivalent to removing the fragment.
     *
     * @param string $fragment The fragment to use with the new instance.
     * @return static A new instance with the specified fragment.
     */
    public function withFragment($fragment);

    /**
     * Return the string representation as a URI reference.
     *
     * Depending on which components of the URI are present, the resulting
     * string is either a full URI or relative reference according to RFC 3986,
     * Section 4.1. The method concatenates the various components of the URI,
     * using the appropriate delimiters:
     *
     * - If a scheme is present, it MUST be suffixed by ":".
     * - If an authority is present, it MUST be prefixed by "//".
     * - The path can be concatenated without delimiters. But there are two
     *   cases where the path has to be adjusted to make the URI reference
     *   valid as PHP does not allow to throw an exception in __toString():
     *     - If the path is rootless and an authority is present, the path MUST
     *       be prefixed by "/".
     *     - If the path is starting with more than one "/" and no authority is
     *       present, the starting slashes MUST be reduced to one.
     * - If a query is present, it MUST be prefixed by "?".
     * - If a fragment is present, it MUST be prefixed by "#".
     *
     * @see http://tools.ietf.org/html/rfc3986#section-4.1
     * @return string
     */
    public function __toString();
}

3.6 Psr\Http\Message\UploadedFileInterface

<?php
namespace Psr\Http\Message;

/**
 * Value object representing a file uploaded through an HTTP request.
 *
 * Instances of this interface are considered immutable; all methods that
 * might change state MUST be implemented such that they retain the internal
 * state of the current instance and return an instance that contains the
 * changed state.
 */
interface UploadedFileInterface
{
    /**
     * Retrieve a stream representing the uploaded file.
     *
     * This method MUST return a StreamInterface instance, representing the
     * uploaded file. The purpose of this method is to allow utilizing native PHP
     * stream functionality to manipulate the file upload, such as
     * stream_copy_to_stream() (though the result will need to be decorated in a
     * native PHP stream wrapper to work with such functions).
     *
     * If the moveTo() method has been called previously, this method MUST raise
     * an exception.
     *
     * @return StreamInterface Stream representation of the uploaded file.
     * @throws \RuntimeException in cases when no stream is available.
     * @throws \RuntimeException in cases when no stream can be created.
     */
    public function getStream();

    /**
     * Move the uploaded file to a new location.
     *
     * Use this method as an alternative to move_uploaded_file(). This method is
     * guaranteed to work in both SAPI and non-SAPI environments.
     * Implementations must determine which environment they are in, and use the
     * appropriate method (move_uploaded_file(), rename(), or a stream
     * operation) to perform the operation.
     *
     * $targetPath may be an absolute path, or a relative path. If it is a
     * relative path, resolution should be the same as used by PHP's rename()
     * function.
     *
     * The original file or stream MUST be removed on completion.
     *
     * If this method is called more than once, any subsequent calls MUST raise
     * an exception.
     *
     * When used in an SAPI environment where $_FILES is populated, when writing
     * files via moveTo(), is_uploaded_file() and move_uploaded_file() SHOULD be
     * used to ensure permissions and upload status are verified correctly.
     *
     * If you wish to move to a stream, use getStream(), as SAPI operations
     * cannot guarantee writing to stream destinations.
     *
     * @see http://php.net/is_uploaded_file
     * @see http://php.net/move_uploaded_file
     * @param string $targetPath Path to which to move the uploaded file.
     * @throws \InvalidArgumentException if the $targetPath specified is invalid.
     * @throws \RuntimeException on any error during the move operation.
     * @throws \RuntimeException on the second or subsequent call to the method.
     */
    public function moveTo($targetPath);

    /**
     * Retrieve the file size.
     *
     * Implementations SHOULD return the value stored in the "size" key of
     * the file in the $_FILES array if available, as PHP calculates this based
     * on the actual size transmitted.
     *
     * @return int|null The file size in bytes or null if unknown.
     */
    public function getSize();

    /**
     * Retrieve the error associated with the uploaded file.
     *
     * The return value MUST be one of PHP's UPLOAD_ERR_XXX constants.
     *
     * If the file was uploaded successfully, this method MUST return
     * UPLOAD_ERR_OK.
     *
     * Implementations SHOULD return the value stored in the "error" key of
     * the file in the $_FILES array.
     *
     * @see http://php.net/manual/en/features.file-upload.errors.php
     * @return int One of PHP's UPLOAD_ERR_XXX constants.
     */
    public function getError();

    /**
     * Retrieve the filename sent by the client.
     *
     * Do not trust the value returned by this method. A client could send
     * a malicious filename with the intention to corrupt or hack your
     * application.
     *
     * Implementations SHOULD return the value stored in the "name" key of
     * the file in the $_FILES array.
     *
     * @return string|null The filename sent by the client or null if none
     *     was provided.
     */
    public function getClientFilename();

    /**
     * Retrieve the media type sent by the client.
     *
     * Do not trust the value returned by this method. A client could send
     * a malicious media type with the intention to corrupt or hack your
     * application.
     *
     * Implementations SHOULD return the value stored in the "type" key of
     * the file in the $_FILES array.
     *
     * @return string|null The media type sent by the client or null if none
     *     was provided.
     */
    public function getClientMediaType();
}