# Specification

RingPHP applications consist of handlers, requests, responses, and middleware.

## Handlers

Handlers are implemented as a PHP `callable` that accept a request array and return a response array (`GuzzleHttp\Ring\Future\FutureArrayInterface`).

For example:

    use GuzzleHttp\Ring\Future\CompletedFutureArray;

    $mockHandler = function (array $request) {
        return new CompletedFutureArray([
            'status'  => 200,
            'headers' => ['X-Foo' => ['Bar']],
            'body'    => 'Hello!'
         ]);
    };

This handler returns the same response each time it is invoked. All RingPHP handlers must return a `GuzzleHttp\Ring\Future\FutureArrayInterface`. Use `GuzzleHttp\Ring\Future\CompletedFutureArray` when returning a response that has already completed.

## Requests

A request array is a PHP associative array that contains the configuration settings need to send a request.

    $request = [
        'http_method' => 'GET',
        'scheme'      => 'http',
        'uri'         => '/',
        'body'        => 'hello!',
        'client'      => ['timeout' => 1.0],
        'headers'     => [
            'host'  => ['httpbin.org'],
            'X-Foo' => ['baz', 'bar']
        ]
    ];

The request array contains the following key value pairs:

request_method
  (string, required) The HTTP request method, must be all caps corresponding to a HTTP request method, such as `GET` or `POST`.
scheme
  (string) The transport protocol, must be one of `http` or `https`. Defaults to `http`.
uri
  (string, required) The request URI excluding the query string. Must start with “/”.
query_string
  (string) The query string, if present (e.g., `foo=bar`).
version
  (string) HTTP protocol version. Defaults to `1.1`.
headers
  (required, array) Associative array of headers. Each key represents the header name. Each value contains an array of strings where each entry of the array SHOULD be sent over the wire on a separate header line.
body
  (string, fopen resource, `Iterator`, `GuzzleHttp\Stream\StreamInterface`) The body of the request, if present. Can be a string, resource returned from fopen, an `Iterator` that yields chunks of data, an object that implemented `__toString`, or a `GuzzleHttp\Stream\StreamInterface`.
future

  (bool, string) Controls the asynchronous behavior of a response.

  Set to `true` or omit the `future` option to request that a request will be completed asynchronously. Keep in mind that your request might not necessarily be completed asynchronously based on the handler you are using. Set the `future` option to `false` to request that a synchronous response be provided.

  You can provide a string value to specify fine-tuned future behaviors that may be specific to the underlying handlers you are using. There are, however, some common future options that handlers should implement if possible.

  lazy
    Requests that the handler does not open and send the request immediately, but rather only opens and sends the request once the future is dereferenced. This option is often useful for sending a large number of requests concurrently to allow handlers to take better advantage of non-blocking transfers by first building up a pool of requests.

  If an handler does not implement or understand a provided string value, then the request MUST be treated as if the user provided `true` rather than the string value.

  Future responses created by asynchronous handlers MUST attempt to complete any outstanding future responses when they are destructed. Asynchronous handlers MAY choose to automatically complete responses when the number of outstanding requests reaches an handler-specific threshold.

### Client Specific Options

The following options are only used in ring client handlers.

client

  (array) Associative array of client specific transfer options. The `client` request key value pair can contain the following keys:

  cert
    (string, array) Set to a string to specify the path to a file containing a PEM formatted SSL client side certificate. If a password is required, then set `cert` to an array containing the path to the PEM file in the first array element followed by the certificate password in the second array element.
  connect_timeout
    (float) Float describing the number of seconds to wait while trying to connect to a server. Use `0` to wait indefinitely (the default behavior).
  debug

    (bool, fopen() resource) Set to true or set to a PHP stream returned by fopen() to enable debug output with the handler used to send a request. If set to `true`, the output is written to PHP’s STDOUT. If a PHP `fopen` resource handle is provided, the output is written to the stream.

    “Debug output” is handler specific: different handlers will yield different output and various various level of detail. For example, when using cURL to transfer requests, cURL’s CURLOPT_VERBOSE will be used. When using the PHP stream wrapper, stream notifications will be emitted.

  decode_content
    (bool) Specify whether or not `Content-Encoding` responses (gzip, deflate, etc.) are automatically decoded. Set to `true` to automatically decode encoded responses. Set to `false` to not decode responses. By default, content is not decoded automatically.
  delay
    (int) The number of milliseconds to delay before sending the request. This is often used for delaying before retrying a request. Handlers SHOULD implement this if possible, but it is not a strict requirement.
  progress

    (function) Defines a function to invoke when transfer progress is made. The function accepts the following arguments:

    1. The total number of bytes expected to be downloaded
    2. The number of bytes downloaded so far
    3. The number of bytes expected to be uploaded
    4. The number of bytes uploaded so far
  proxy

    (string, array) Pass a string to specify an HTTP proxy, or an associative array to specify different proxies for different protocols where the scheme is the key and the value is the proxy address.

        $request = [
            'http_method' => 'GET',
            'headers'     => ['host' => ['httpbin.org']],
            'client'      => [
                // Use different proxies for different URI schemes.
                'proxy' => [
                    'http'  => 'http://proxy.example.com:5100',
                    'https' => 'https://proxy.example.com:6100'
                ]
            ]
        ];

  ssl_key
    (string, array) Specify the path to a file containing a private SSL key in PEM format. If a password is required, then set to an array containing the path to the SSL key in the first array element followed by the password required for the certificate in the second element.
  save_to
    (string, fopen resource, `GuzzleHttp\Stream\StreamInterface`) Specifies where the body of the response is downloaded. Pass a string to open a local file on disk and save the output to the file. Pass an fopen resource to save the output to a PHP stream resource. Pass a `GuzzleHttp\Stream\StreamInterface` to save the output to a Guzzle StreamInterface. Omitting this option will typically save the body of a response to a PHP temp stream.
  stream
    (bool) Set to true to stream a response rather than download it all up-front. This option will only be utilized when the corresponding handler supports it.
  timeout
    (float) Float describing the timeout of the request in seconds. Use 0 to wait indefinitely (the default behavior).
  verify
    (bool, string) Describes the SSL certificate verification behavior of a request. Set to true to enable SSL certificate verification using the system CA bundle when available (the default). Set to false to disable certificate verification (this is insecure!). Set to a string to provide the path to a CA bundle on disk to enable verification using a custom certificate.
  version
    (string) HTTP protocol version to use with the request.

### Server Specific Options

The following options are only used in ring server handlers.

server_port
  (integer) The port on which the request is being handled. This is only used with ring servers, and is required.
server_name
  (string) The resolved server name, or the server IP address. Required when using a Ring server.
remote_addr
  (string) The IP address of the client or the last proxy that sent the request. Required when using a Ring server.

## Responses

A response is an array-like object that implements `GuzzleHttp\Ring\Future\FutureArrayInterface`. Responses contain the following key value pairs:

body
  (string, fopen resource, `Iterator`, `GuzzleHttp\Stream\StreamInterface`) The body of the response, if present. Can be a string, resource returned from fopen, an `Iterator` that yields chunks of data, an object that implemented `__toString`, or a `GuzzleHttp\Stream\StreamInterface`.
effective_url
  (string) The URL that returned the resulting response.
error
  (`\Exception`) Contains an exception describing any errors that were encountered during the transfer.
headers
  (Required, array) Associative array of headers. Each key represents the header name. Each value contains an array of strings where each entry of the array is a header line. The headers array MAY be an empty array in the event an error occurred before a response was received.
reason
  (string) Optional reason phrase. This option should be provided when the reason phrase does not match the typical reason phrase associated with the `status` code. See RFC 7231 for a list of HTTP reason phrases mapped to status codes.
status
  (Required, integer) The HTTP status code. The status code MAY be set to `null` in the event an error occurred before a response was received (e.g., a networking error).
transfer_stats
  (array) Provides an associative array of arbitrary transfer statistics if provided by the underlying handler.
version
  (string) HTTP protocol version. Defaults to `1.1`.

## Middleware

Ring middleware augments the functionality of handlers by invoking them in the process of generating responses. Middleware is typically implemented as a higher-order function that takes one or more handlers as arguments followed by an optional associative array of options as the last argument, returning a new handler with the desired compound behavior.

Here’s an example of a middleware that adds a Content-Type header to each request.

    use GuzzleHttp\Ring\Client\CurlHandler;
    use GuzzleHttp\Ring\Core;

    $contentTypeHandler = function(callable $handler, $contentType) {
        return function (array $request) use ($handler, $contentType) {
            return $handler(Core::setHeader('Content-Type', $contentType));
        };
    };

    $baseHandler = new CurlHandler();
    $wrappedHandler = $contentTypeHandler($baseHandler, 'text/html');
    $response = $wrappedHandler([/** request hash **/]);