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+Guzzle Upgrade Guide
+====================
+
+5.0 to 6.0
+----------
+
+Guzzle now uses [PSR-7](http://www.php-fig.org/psr/psr-7/) for HTTP messages.
+Due to the fact that these messages are immutable, this prompted a refactoring
+of Guzzle to use a middleware based system rather than an event system. Any
+HTTP message interaction (e.g., `GuzzleHttp\Message\Request`) need to be
+updated to work with the new immutable PSR-7 request and response objects. Any
+event listeners or subscribers need to be updated to become middleware
+functions that wrap handlers (or are injected into a
+`GuzzleHttp\HandlerStack`).
+
+- Removed `GuzzleHttp\BatchResults`
+- Removed `GuzzleHttp\Collection`
+- Removed `GuzzleHttp\HasDataTrait`
+- Removed `GuzzleHttp\ToArrayInterface`
+- The `guzzlehttp/streams` dependency has been removed. Stream functionality
+  is now present in the `GuzzleHttp\Psr7` namespace provided by the
+  `guzzlehttp/psr7` package.
+- Guzzle no longer uses ReactPHP promises and now uses the
+  `guzzlehttp/promises` library. We use a custom promise library for three
+  significant reasons:
+  1. React promises (at the time of writing this) are recursive. Promise
+     chaining and promise resolution will eventually blow the stack. Guzzle
+     promises are not recursive as they use a sort of trampolining technique.
+     Note: there has been movement in the React project to modify promises to
+     no longer utilize recursion.
+  2. Guzzle needs to have the ability to synchronously block on a promise to
+     wait for a result. Guzzle promises allows this functionality (and does
+     not require the use of recursion).
+  3. Because we need to be able to wait on a result, doing so using React
+     promises requires wrapping react promises with RingPHP futures. This
+     overhead is no longer needed, reducing stack sizes, reducing complexity,
+     and improving performance.
+- `GuzzleHttp\Mimetypes` has been moved to a function in
+  `GuzzleHttp\Psr7\mimetype_from_extension` and
+  `GuzzleHttp\Psr7\mimetype_from_filename`.
+- `GuzzleHttp\Query` and `GuzzleHttp\QueryParser` have been removed. Query
+  strings must now be passed into request objects as strings, or provided to
+  the `query` request option when creating requests with clients. The `query`
+  option uses PHP's `http_build_query` to convert an array to a string. If you
+  need a different serialization technique, you will need to pass the query
+  string in as a string. There are a couple helper functions that will make
+  working with query strings easier: `GuzzleHttp\Psr7\parse_query` and
+  `GuzzleHttp\Psr7\build_query`.
+- Guzzle no longer has a dependency on RingPHP. Due to the use of a middleware
+  system based on PSR-7, using RingPHP and it's middleware system as well adds
+  more complexity than the benefits it provides. All HTTP handlers that were
+  present in RingPHP have been modified to work directly with PSR-7 messages
+  and placed in the `GuzzleHttp\Handler` namespace. This significantly reduces
+  complexity in Guzzle, removes a dependency, and improves performance. RingPHP
+  will be maintained for Guzzle 5 support, but will no longer be a part of
+  Guzzle 6.
+- As Guzzle now uses a middleware based systems the event system and RingPHP
+  integration has been removed. Note: while the event system has been removed,
+  it is possible to add your own type of event system that is powered by the
+  middleware system.
+  - Removed the `Event` namespace.
+  - Removed the `Subscriber` namespace.
+  - Removed `Transaction` class
+  - Removed `RequestFsm`
+  - Removed `RingBridge`
+  - `GuzzleHttp\Subscriber\Cookie` is now provided by
+    `GuzzleHttp\Middleware::cookies`
+  - `GuzzleHttp\Subscriber\HttpError` is now provided by
+    `GuzzleHttp\Middleware::httpError`
+  - `GuzzleHttp\Subscriber\History` is now provided by
+    `GuzzleHttp\Middleware::history`
+  - `GuzzleHttp\Subscriber\Mock` is now provided by
+    `GuzzleHttp\Handler\MockHandler`
+  - `GuzzleHttp\Subscriber\Prepare` is now provided by
+    `GuzzleHttp\PrepareBodyMiddleware`
+  - `GuzzleHttp\Subscriber\Redirect` is now provided by
+    `GuzzleHttp\RedirectMiddleware`
+- Guzzle now uses `Psr\Http\Message\UriInterface` (implements in
+  `GuzzleHttp\Psr7\Uri`) for URI support. `GuzzleHttp\Url` is now gone.
+- Static functions in `GuzzleHttp\Utils` have been moved to namespaced
+  functions under the `GuzzleHttp` namespace. This requires either a Composer
+  based autoloader or you to include functions.php.
+- `GuzzleHttp\ClientInterface::getDefaultOption` has been renamed to
+  `GuzzleHttp\ClientInterface::getConfig`.
+- `GuzzleHttp\ClientInterface::setDefaultOption` has been removed.
+- The `json` and `xml` methods of response objects has been removed. With the
+  migration to strictly adhering to PSR-7 as the interface for Guzzle messages,
+  adding methods to message interfaces would actually require Guzzle messages
+  to extend from PSR-7 messages rather then work with them directly.
+
+## Migrating to middleware
+
+The change to PSR-7 unfortunately required significant refactoring to Guzzle
+due to the fact that PSR-7 messages are immutable. Guzzle 5 relied on an event
+system from plugins. The event system relied on mutability of HTTP messages and
+side effects in order to work. With immutable messages, you have to change your
+workflow to become more about either returning a value (e.g., functional
+middlewares) or setting a value on an object. Guzzle v6 has chosen the
+functional middleware approach.
+
+Instead of using the event system to listen for things like the `before` event,
+you now create a stack based middleware function that intercepts a request on
+the way in and the promise of the response on the way out. This is a much
+simpler and more predictable approach than the event system and works nicely
+with PSR-7 middleware. Due to the use of promises, the middleware system is
+also asynchronous.
+
+v5:
+
+```php
+use GuzzleHttp\Event\BeforeEvent;
+$client = new GuzzleHttp\Client();
+// Get the emitter and listen to the before event.
+$client->getEmitter()->on('before', function (BeforeEvent $e) {
+    // Guzzle v5 events relied on mutation
+    $e->getRequest()->setHeader('X-Foo', 'Bar');
+});
+```
+
+v6:
+
+In v6, you can modify the request before it is sent using the `mapRequest`
+middleware. The idiomatic way in v6 to modify the request/response lifecycle is
+to setup a handler middleware stack up front and inject the handler into a
+client.
+
+```php
+use GuzzleHttp\Middleware;
+// Create a handler stack that has all of the default middlewares attached
+$handler = GuzzleHttp\HandlerStack::create();
+// Push the handler onto the handler stack
+$handler->push(Middleware::mapRequest(function (RequestInterface $request) {
+    // Notice that we have to return a request object
+    return $request->withHeader('X-Foo', 'Bar');
+}));
+// Inject the handler into the client
+$client = new GuzzleHttp\Client(['handler' => $handler]);
+```
+
+## POST Requests
+
+This version added the [`form_params`](http://guzzle.readthedocs.org/en/latest/request-options.html#form_params)
+and `multipart` request options. `form_params` is an associative array of
+strings or array of strings and is used to serialize an
+`application/x-www-form-urlencoded` POST request. The
+[`multipart`](http://guzzle.readthedocs.org/en/latest/request-options.html#multipart)
+option is now used to send a multipart/form-data POST request.
+
+`GuzzleHttp\Post\PostFile` has been removed. Use the `multipart` option to add
+POST files to a multipart/form-data request.
+
+The `body` option no longer accepts an array to send POST requests. Please use
+`multipart` or `form_params` instead.
+
+The `base_url` option has been renamed to `base_uri`.
+
+4.x to 5.0
+----------
+
+## Rewritten Adapter Layer
+
+Guzzle now uses [RingPHP](http://ringphp.readthedocs.org/en/latest) to send
+HTTP requests. The `adapter` option in a `GuzzleHttp\Client` constructor
+is still supported, but it has now been renamed to `handler`. Instead of
+passing a `GuzzleHttp\Adapter\AdapterInterface`, you must now pass a PHP
+`callable` that follows the RingPHP specification.
+
+## Removed Fluent Interfaces
+
+[Fluent interfaces were removed](http://ocramius.github.io/blog/fluent-interfaces-are-evil)
+from the following classes:
+
+- `GuzzleHttp\Collection`
+- `GuzzleHttp\Url`
+- `GuzzleHttp\Query`
+- `GuzzleHttp\Post\PostBody`
+- `GuzzleHttp\Cookie\SetCookie`
+
+## Removed functions.php
+
+Removed "functions.php", so that Guzzle is truly PSR-4 compliant. The following
+functions can be used as replacements.
+
+- `GuzzleHttp\json_decode` -> `GuzzleHttp\Utils::jsonDecode`
+- `GuzzleHttp\get_path` -> `GuzzleHttp\Utils::getPath`
+- `GuzzleHttp\Utils::setPath` -> `GuzzleHttp\set_path`
+- `GuzzleHttp\Pool::batch` -> `GuzzleHttp\batch`. This function is, however,
+  deprecated in favor of using `GuzzleHttp\Pool::batch()`.
+
+The "procedural" global client has been removed with no replacement (e.g.,
+`GuzzleHttp\get()`, `GuzzleHttp\post()`, etc.). Use a `GuzzleHttp\Client`
+object as a replacement.
+
+## `throwImmediately` has been removed
+
+The concept of "throwImmediately" has been removed from exceptions and error
+events. This control mechanism was used to stop a transfer of concurrent
+requests from completing. This can now be handled by throwing the exception or
+by cancelling a pool of requests or each outstanding future request
+individually.
+
+## headers event has been removed
+
+Removed the "headers" event. This event was only useful for changing the
+body a response once the headers of the response were known. You can implement
+a similar behavior in a number of ways. One example might be to use a
+FnStream that has access to the transaction being sent. For example, when the
+first byte is written, you could check if the response headers match your
+expectations, and if so, change the actual stream body that is being
+written to.
+
+## Updates to HTTP Messages
+
+Removed the `asArray` parameter from
+`GuzzleHttp\Message\MessageInterface::getHeader`. If you want to get a header
+value as an array, then use the newly added `getHeaderAsArray()` method of
+`MessageInterface`. This change makes the Guzzle interfaces compatible with
+the PSR-7 interfaces.
+
+3.x to 4.0
+----------
+
+## Overarching changes:
+
+- Now requires PHP 5.4 or greater.
+- No longer requires cURL to send requests.
+- Guzzle no longer wraps every exception it throws. Only exceptions that are
+  recoverable are now wrapped by Guzzle.
+- Various namespaces have been removed or renamed.
+- No longer requiring the Symfony EventDispatcher. A custom event dispatcher
+  based on the Symfony EventDispatcher is
+  now utilized in `GuzzleHttp\Event\EmitterInterface` (resulting in significant
+  speed and functionality improvements).
+
+Changes per Guzzle 3.x namespace are described below.
+
+## Batch
+
+The `Guzzle\Batch` namespace has been removed. This is best left to
+third-parties to implement on top of Guzzle's core HTTP library.
+
+## Cache
+
+The `Guzzle\Cache` namespace has been removed. (Todo: No suitable replacement
+has been implemented yet, but hoping to utilize a PSR cache interface).
+
+## Common
+
+- Removed all of the wrapped exceptions. It's better to use the standard PHP
+  library for unrecoverable exceptions.
+- `FromConfigInterface` has been removed.
+- `Guzzle\Common\Version` has been removed. The VERSION constant can be found
+  at `GuzzleHttp\ClientInterface::VERSION`.
+
+### Collection
+
+- `getAll` has been removed. Use `toArray` to convert a collection to an array.
+- `inject` has been removed.
+- `keySearch` has been removed.
+- `getPath` no longer supports wildcard expressions. Use something better like
+  JMESPath for this.
+- `setPath` now supports appending to an existing array via the `[]` notation.
+
+### Events
+
+Guzzle no longer requires Symfony's EventDispatcher component. Guzzle now uses
+`GuzzleHttp\Event\Emitter`.
+
+- `Symfony\Component\EventDispatcher\EventDispatcherInterface` is replaced by
+  `GuzzleHttp\Event\EmitterInterface`.
+- `Symfony\Component\EventDispatcher\EventDispatcher` is replaced by
+  `GuzzleHttp\Event\Emitter`.
+- `Symfony\Component\EventDispatcher\Event` is replaced by
+  `GuzzleHttp\Event\Event`, and Guzzle now has an EventInterface in
+  `GuzzleHttp\Event\EventInterface`.
+- `AbstractHasDispatcher` has moved to a trait, `HasEmitterTrait`, and
+  `HasDispatcherInterface` has moved to `HasEmitterInterface`. Retrieving the
+  event emitter of a request, client, etc. now uses the `getEmitter` method
+  rather than the `getDispatcher` method.
+
+#### Emitter
+
+- Use the `once()` method to add a listener that automatically removes itself
+  the first time it is invoked.
+- Use the `listeners()` method to retrieve a list of event listeners rather than
+  the `getListeners()` method.
+- Use `emit()` instead of `dispatch()` to emit an event from an emitter.
+- Use `attach()` instead of `addSubscriber()` and `detach()` instead of
+  `removeSubscriber()`.
+
+```php
+$mock = new Mock();
+// 3.x
+$request->getEventDispatcher()->addSubscriber($mock);
+$request->getEventDispatcher()->removeSubscriber($mock);
+// 4.x
+$request->getEmitter()->attach($mock);
+$request->getEmitter()->detach($mock);
+```
+
+Use the `on()` method to add a listener rather than the `addListener()` method.
+
+```php
+// 3.x
+$request->getEventDispatcher()->addListener('foo', function (Event $event) { /* ... */ } );
+// 4.x
+$request->getEmitter()->on('foo', function (Event $event, $name) { /* ... */ } );
+```
+
+## Http
+
+### General changes
+
+- The cacert.pem certificate has been moved to `src/cacert.pem`.
+- Added the concept of adapters that are used to transfer requests over the
+  wire.
+- Simplified the event system.
+- Sending requests in parallel is still possible, but batching is no longer a
+  concept of the HTTP layer. Instead, you must use the `complete` and `error`
+  events to asynchronously manage parallel request transfers.
+- `Guzzle\Http\Url` has moved to `GuzzleHttp\Url`.
+- `Guzzle\Http\QueryString` has moved to `GuzzleHttp\Query`.
+- QueryAggregators have been rewritten so that they are simply callable
+  functions.
+- `GuzzleHttp\StaticClient` has been removed. Use the functions provided in
+  `functions.php` for an easy to use static client instance.
+- Exceptions in `GuzzleHttp\Exception` have been updated to all extend from
+  `GuzzleHttp\Exception\TransferException`.
+
+### Client
+
+Calling methods like `get()`, `post()`, `head()`, etc. no longer create and
+return a request, but rather creates a request, sends the request, and returns
+the response.
+
+```php
+// 3.0
+$request = $client->get('/');
+$response = $request->send();
+
+// 4.0
+$response = $client->get('/');
+
+// or, to mirror the previous behavior
+$request = $client->createRequest('GET', '/');
+$response = $client->send($request);
+```
+
+`GuzzleHttp\ClientInterface` has changed.
+
+- The `send` method no longer accepts more than one request. Use `sendAll` to
+  send multiple requests in parallel.
+- `setUserAgent()` has been removed. Use a default request option instead. You
+  could, for example, do something like:
+  `$client->setConfig('defaults/headers/User-Agent', 'Foo/Bar ' . $client::getDefaultUserAgent())`.
+- `setSslVerification()` has been removed. Use default request options instead,
+  like `$client->setConfig('defaults/verify', true)`.
+
+`GuzzleHttp\Client` has changed.
+
+- The constructor now accepts only an associative array. You can include a
+  `base_url` string or array to use a URI template as the base URL of a client.
+  You can also specify a `defaults` key that is an associative array of default
+  request options. You can pass an `adapter` to use a custom adapter,
+  `batch_adapter` to use a custom adapter for sending requests in parallel, or
+  a `message_factory` to change the factory used to create HTTP requests and
+  responses.
+- The client no longer emits a `client.create_request` event.
+- Creating requests with a client no longer automatically utilize a URI
+  template. You must pass an array into a creational method (e.g.,
+  `createRequest`, `get`, `put`, etc.) in order to expand a URI template.
+
+### Messages
+
+Messages no longer have references to their counterparts (i.e., a request no
+longer has a reference to it's response, and a response no loger has a
+reference to its request). This association is now managed through a
+`GuzzleHttp\Adapter\TransactionInterface` object. You can get references to
+these transaction objects using request events that are emitted over the
+lifecycle of a request.
+
+#### Requests with a body
+
+- `GuzzleHttp\Message\EntityEnclosingRequest` and
+  `GuzzleHttp\Message\EntityEnclosingRequestInterface` have been removed. The
+  separation between requests that contain a body and requests that do not
+  contain a body has been removed, and now `GuzzleHttp\Message\RequestInterface`
+  handles both use cases.
+- Any method that previously accepts a `GuzzleHttp\Response` object now accept a
+  `GuzzleHttp\Message\ResponseInterface`.
+- `GuzzleHttp\Message\RequestFactoryInterface` has been renamed to
+  `GuzzleHttp\Message\MessageFactoryInterface`. This interface is used to create
+  both requests and responses and is implemented in
+  `GuzzleHttp\Message\MessageFactory`.
+- POST field and file methods have been removed from the request object. You
+  must now use the methods made available to `GuzzleHttp\Post\PostBodyInterface`
+  to control the format of a POST body. Requests that are created using a
+  standard `GuzzleHttp\Message\MessageFactoryInterface` will automatically use
+  a `GuzzleHttp\Post\PostBody` body if the body was passed as an array or if
+  the method is POST and no body is provided.
+
+```php
+$request = $client->createRequest('POST', '/');
+$request->getBody()->setField('foo', 'bar');
+$request->getBody()->addFile(new PostFile('file_key', fopen('/path/to/content', 'r')));
+```
+
+#### Headers
+
+- `GuzzleHttp\Message\Header` has been removed. Header values are now simply
+  represented by an array of values or as a string. Header values are returned
+  as a string by default when retrieving a header value from a message. You can
+  pass an optional argument of `true` to retrieve a header value as an array
+  of strings instead of a single concatenated string.
+- `GuzzleHttp\PostFile` and `GuzzleHttp\PostFileInterface` have been moved to
+  `GuzzleHttp\Post`. This interface has been simplified and now allows the
+  addition of arbitrary headers.
+- Custom headers like `GuzzleHttp\Message\Header\Link` have been removed. Most
+  of the custom headers are now handled separately in specific
+  subscribers/plugins, and `GuzzleHttp\Message\HeaderValues::parseParams()` has
+  been updated to properly handle headers that contain parameters (like the
+  `Link` header).
+
+#### Responses
+
+- `GuzzleHttp\Message\Response::getInfo()` and
+  `GuzzleHttp\Message\Response::setInfo()` have been removed. Use the event
+  system to retrieve this type of information.
+- `GuzzleHttp\Message\Response::getRawHeaders()` has been removed.
+- `GuzzleHttp\Message\Response::getMessage()` has been removed.
+- `GuzzleHttp\Message\Response::calculateAge()` and other cache specific
+  methods have moved to the CacheSubscriber.
+- Header specific helper functions like `getContentMd5()` have been removed.
+  Just use `getHeader('Content-MD5')` instead.
+- `GuzzleHttp\Message\Response::setRequest()` and
+  `GuzzleHttp\Message\Response::getRequest()` have been removed. Use the event
+  system to work with request and response objects as a transaction.
+- `GuzzleHttp\Message\Response::getRedirectCount()` has been removed. Use the
+  Redirect subscriber instead.
+- `GuzzleHttp\Message\Response::isSuccessful()` and other related methods have
+  been removed. Use `getStatusCode()` instead.
+
+#### Streaming responses
+
+Streaming requests can now be created by a client directly, returning a
+`GuzzleHttp\Message\ResponseInterface` object that contains a body stream
+referencing an open PHP HTTP stream.
+
+```php
+// 3.0
+use Guzzle\Stream\PhpStreamRequestFactory;
+$request = $client->get('/');
+$factory = new PhpStreamRequestFactory();
+$stream = $factory->fromRequest($request);
+$data = $stream->read(1024);
+
+// 4.0
+$response = $client->get('/', ['stream' => true]);
+// Read some data off of the stream in the response body
+$data = $response->getBody()->read(1024);
+```
+
+#### Redirects
+
+The `configureRedirects()` method has been removed in favor of a
+`allow_redirects` request option.
+
+```php
+// Standard redirects with a default of a max of 5 redirects
+$request = $client->createRequest('GET', '/', ['allow_redirects' => true]);
+
+// Strict redirects with a custom number of redirects
+$request = $client->createRequest('GET', '/', [
+    'allow_redirects' => ['max' => 5, 'strict' => true]
+]);
+```
+
+#### EntityBody
+
+EntityBody interfaces and classes have been removed or moved to
+`GuzzleHttp\Stream`. All classes and interfaces that once required
+`GuzzleHttp\EntityBodyInterface` now require
+`GuzzleHttp\Stream\StreamInterface`. Creating a new body for a request no
+longer uses `GuzzleHttp\EntityBody::factory` but now uses
+`GuzzleHttp\Stream\Stream::factory` or even better:
+`GuzzleHttp\Stream\create()`.
+
+- `Guzzle\Http\EntityBodyInterface` is now `GuzzleHttp\Stream\StreamInterface`
+- `Guzzle\Http\EntityBody` is now `GuzzleHttp\Stream\Stream`
+- `Guzzle\Http\CachingEntityBody` is now `GuzzleHttp\Stream\CachingStream`
+- `Guzzle\Http\ReadLimitEntityBody` is now `GuzzleHttp\Stream\LimitStream`
+- `Guzzle\Http\IoEmittyinEntityBody` has been removed.
+
+#### Request lifecycle events
+
+Requests previously submitted a large number of requests. The number of events
+emitted over the lifecycle of a request has been significantly reduced to make
+it easier to understand how to extend the behavior of a request. All events
+emitted during the lifecycle of a request now emit a custom
+`GuzzleHttp\Event\EventInterface` object that contains context providing
+methods and a way in which to modify the transaction at that specific point in
+time (e.g., intercept the request and set a response on the transaction).
+
+- `request.before_send` has been renamed to `before` and now emits a
+  `GuzzleHttp\Event\BeforeEvent`
+- `request.complete` has been renamed to `complete` and now emits a
+  `GuzzleHttp\Event\CompleteEvent`.
+- `request.sent` has been removed. Use `complete`.
+- `request.success` has been removed. Use `complete`.
+- `error` is now an event that emits a `GuzzleHttp\Event\ErrorEvent`.
+- `request.exception` has been removed. Use `error`.
+- `request.receive.status_line` has been removed.
+- `curl.callback.progress` has been removed. Use a custom `StreamInterface` to
+  maintain a status update.
+- `curl.callback.write` has been removed. Use a custom `StreamInterface` to
+  intercept writes.
+- `curl.callback.read` has been removed. Use a custom `StreamInterface` to
+  intercept reads.
+
+`headers` is a new event that is emitted after the response headers of a
+request have been received before the body of the response is downloaded. This
+event emits a `GuzzleHttp\Event\HeadersEvent`.
+
+You can intercept a request and inject a response using the `intercept()` event
+of a `GuzzleHttp\Event\BeforeEvent`, `GuzzleHttp\Event\CompleteEvent`, and
+`GuzzleHttp\Event\ErrorEvent` event.
+
+See: http://docs.guzzlephp.org/en/latest/events.html
+
+## Inflection
+
+The `Guzzle\Inflection` namespace has been removed. This is not a core concern
+of Guzzle.
+
+## Iterator
+
+The `Guzzle\Iterator` namespace has been removed.
+
+- `Guzzle\Iterator\AppendIterator`, `Guzzle\Iterator\ChunkedIterator`, and
+  `Guzzle\Iterator\MethodProxyIterator` are nice, but not a core requirement of
+  Guzzle itself.
+- `Guzzle\Iterator\FilterIterator` is no longer needed because an equivalent
+  class is shipped with PHP 5.4.
+- `Guzzle\Iterator\MapIterator` is not really needed when using PHP 5.5 because
+  it's easier to just wrap an iterator in a generator that maps values.
+
+For a replacement of these iterators, see https://github.com/nikic/iter
+
+## Log
+
+The LogPlugin has moved to https://github.com/guzzle/log-subscriber. The
+`Guzzle\Log` namespace has been removed. Guzzle now relies on
+`Psr\Log\LoggerInterface` for all logging. The MessageFormatter class has been
+moved to `GuzzleHttp\Subscriber\Log\Formatter`.
+
+## Parser
+
+The `Guzzle\Parser` namespace has been removed. This was previously used to
+make it possible to plug in custom parsers for cookies, messages, URI
+templates, and URLs; however, this level of complexity is not needed in Guzzle
+so it has been removed.
+
+- Cookie: Cookie parsing logic has been moved to
+  `GuzzleHttp\Cookie\SetCookie::fromString`.
+- Message: Message parsing logic for both requests and responses has been moved
+  to `GuzzleHttp\Message\MessageFactory::fromMessage`. Message parsing is only
+  used in debugging or deserializing messages, so it doesn't make sense for
+  Guzzle as a library to add this level of complexity to parsing messages.
+- UriTemplate: URI template parsing has been moved to
+  `GuzzleHttp\UriTemplate`. The Guzzle library will automatically use the PECL
+  URI template library if it is installed.
+- Url: URL parsing is now performed in `GuzzleHttp\Url::fromString` (previously
+  it was `Guzzle\Http\Url::factory()`). If custom URL parsing is necessary,
+  then developers are free to subclass `GuzzleHttp\Url`.
+
+## Plugin
+
+The `Guzzle\Plugin` namespace has been renamed to `GuzzleHttp\Subscriber`.
+Several plugins are shipping with the core Guzzle library under this namespace.
+
+- `GuzzleHttp\Subscriber\Cookie`: Replaces the old CookiePlugin. Cookie jar
+  code has moved to `GuzzleHttp\Cookie`.
+- `GuzzleHttp\Subscriber\History`: Replaces the old HistoryPlugin.
+- `GuzzleHttp\Subscriber\HttpError`: Throws errors when a bad HTTP response is
+  received.
+- `GuzzleHttp\Subscriber\Mock`: Replaces the old MockPlugin.
+- `GuzzleHttp\Subscriber\Prepare`: Prepares the body of a request just before
+  sending. This subscriber is attached to all requests by default.
+- `GuzzleHttp\Subscriber\Redirect`: Replaces the RedirectPlugin.
+
+The following plugins have been removed (third-parties are free to re-implement
+these if needed):
+
+- `GuzzleHttp\Plugin\Async` has been removed.
+- `GuzzleHttp\Plugin\CurlAuth` has been removed.
+- `GuzzleHttp\Plugin\ErrorResponse\ErrorResponsePlugin` has been removed. This
+  functionality should instead be implemented with event listeners that occur
+  after normal response parsing occurs in the guzzle/command package.
+
+The following plugins are not part of the core Guzzle package, but are provided
+in separate repositories:
+
+- `Guzzle\Http\Plugin\BackoffPlugin` has been rewritten to be much simpler
+  to build custom retry policies using simple functions rather than various
+  chained classes. See: https://github.com/guzzle/retry-subscriber
+- `Guzzle\Http\Plugin\Cache\CachePlugin` has moved to
+  https://github.com/guzzle/cache-subscriber
+- `Guzzle\Http\Plugin\Log\LogPlugin` has moved to
+  https://github.com/guzzle/log-subscriber
+- `Guzzle\Http\Plugin\Md5\Md5Plugin` has moved to
+  https://github.com/guzzle/message-integrity-subscriber
+- `Guzzle\Http\Plugin\Mock\MockPlugin` has moved to
+  `GuzzleHttp\Subscriber\MockSubscriber`.
+- `Guzzle\Http\Plugin\Oauth\OauthPlugin` has moved to
+  https://github.com/guzzle/oauth-subscriber
+
+## Service
+
+The service description layer of Guzzle has moved into two separate packages:
+
+- http://github.com/guzzle/command Provides a high level abstraction over web
+  services by representing web service operations using commands.
+- http://github.com/guzzle/guzzle-services Provides an implementation of
+  guzzle/command that provides request serialization and response parsing using
+  Guzzle service descriptions.
+
+## Stream
+
+Stream have moved to a separate package available at
+https://github.com/guzzle/streams.
+
+`Guzzle\Stream\StreamInterface` has been given a large update to cleanly take
+on the responsibilities of `Guzzle\Http\EntityBody` and
+`Guzzle\Http\EntityBodyInterface` now that they have been removed. The number
+of methods implemented by the `StreamInterface` has been drastically reduced to
+allow developers to more easily extend and decorate stream behavior.
+
+## Removed methods from StreamInterface
+
+- `getStream` and `setStream` have been removed to better encapsulate streams.
+- `getMetadata` and `setMetadata` have been removed in favor of
+  `GuzzleHttp\Stream\MetadataStreamInterface`.
+- `getWrapper`, `getWrapperData`, `getStreamType`, and `getUri` have all been
+  removed. This data is accessible when
+  using streams that implement `GuzzleHttp\Stream\MetadataStreamInterface`.
+- `rewind` has been removed. Use `seek(0)` for a similar behavior.
+
+## Renamed methods
+
+- `detachStream` has been renamed to `detach`.
+- `feof` has been renamed to `eof`.
+- `ftell` has been renamed to `tell`.
+- `readLine` has moved from an instance method to a static class method of
+  `GuzzleHttp\Stream\Stream`.
+
+## Metadata streams
+
+`GuzzleHttp\Stream\MetadataStreamInterface` has been added to denote streams
+that contain additional metadata accessible via `getMetadata()`.
+`GuzzleHttp\Stream\StreamInterface::getMetadata` and
+`GuzzleHttp\Stream\StreamInterface::setMetadata` have been removed.
+
+## StreamRequestFactory
+
+The entire concept of the StreamRequestFactory has been removed. The way this
+was used in Guzzle 3 broke the actual interface of sending streaming requests
+(instead of getting back a Response, you got a StreamInterface). Streaming
+PHP requests are now implemented through the `GuzzleHttp\Adapter\StreamAdapter`.
+
+3.6 to 3.7
+----------
+
+### Deprecations
+
+- You can now enable E_USER_DEPRECATED warnings to see if you are using any deprecated methods.:
+
+```php
+\Guzzle\Common\Version::$emitWarnings = true;
+```
+
+The following APIs and options have been marked as deprecated:
+
+- Marked `Guzzle\Http\Message\Request::isResponseBodyRepeatable()` as deprecated. Use `$request->getResponseBody()->isRepeatable()` instead.
+- Marked `Guzzle\Http\Message\Request::canCache()` as deprecated. Use `Guzzle\Plugin\Cache\DefaultCanCacheStrategy->canCacheRequest()` instead.
+- Marked `Guzzle\Http\Message\Request::canCache()` as deprecated. Use `Guzzle\Plugin\Cache\DefaultCanCacheStrategy->canCacheRequest()` instead.
+- Marked `Guzzle\Http\Message\Request::setIsRedirect()` as deprecated. Use the HistoryPlugin instead.
+- Marked `Guzzle\Http\Message\Request::isRedirect()` as deprecated. Use the HistoryPlugin instead.
+- Marked `Guzzle\Cache\CacheAdapterFactory::factory()` as deprecated
+- Marked `Guzzle\Service\Client::enableMagicMethods()` as deprecated. Magic methods can no longer be disabled on a Guzzle\Service\Client.
+- Marked `Guzzle\Parser\Url\UrlParser` as deprecated. Just use PHP's `parse_url()` and percent encode your UTF-8.
+- Marked `Guzzle\Common\Collection::inject()` as deprecated.
+- Marked `Guzzle\Plugin\CurlAuth\CurlAuthPlugin` as deprecated. Use
+  `$client->getConfig()->setPath('request.options/auth', array('user', 'pass', 'Basic|Digest|NTLM|Any'));` or
+  `$client->setDefaultOption('auth', array('user', 'pass', 'Basic|Digest|NTLM|Any'));`
+
+3.7 introduces `request.options` as a parameter for a client configuration and as an optional argument to all creational
+request methods. When paired with a client's configuration settings, these options allow you to specify default settings
+for various aspects of a request. Because these options make other previous configuration options redundant, several
+configuration options and methods of a client and AbstractCommand have been deprecated.
+
+- Marked `Guzzle\Service\Client::getDefaultHeaders()` as deprecated. Use `$client->getDefaultOption('headers')`.
+- Marked `Guzzle\Service\Client::setDefaultHeaders()` as deprecated. Use `$client->setDefaultOption('headers/{header_name}', 'value')`.
+- Marked 'request.params' for `Guzzle\Http\Client` as deprecated. Use `$client->setDefaultOption('params/{param_name}', 'value')`
+- Marked 'command.headers', 'command.response_body' and 'command.on_complete' as deprecated for AbstractCommand. These will work through Guzzle 4.0
+
+        $command = $client->getCommand('foo', array(
+            'command.headers' => array('Test' => '123'),
+            'command.response_body' => '/path/to/file'
+        ));
+
+        // Should be changed to:
+
+        $command = $client->getCommand('foo', array(
+            'command.request_options' => array(
+                'headers' => array('Test' => '123'),
+                'save_as' => '/path/to/file'
+            )
+        ));
+
+### Interface changes
+
+Additions and changes (you will need to update any implementations or subclasses you may have created):
+
+- Added an `$options` argument to the end of the following methods of `Guzzle\Http\ClientInterface`:
+  createRequest, head, delete, put, patch, post, options, prepareRequest
+- Added an `$options` argument to the end of `Guzzle\Http\Message\Request\RequestFactoryInterface::createRequest()`
+- Added an `applyOptions()` method to `Guzzle\Http\Message\Request\RequestFactoryInterface`
+- Changed `Guzzle\Http\ClientInterface::get($uri = null, $headers = null, $body = null)` to
+  `Guzzle\Http\ClientInterface::get($uri = null, $headers = null, $options = array())`. You can still pass in a
+  resource, string, or EntityBody into the $options parameter to specify the download location of the response.
+- Changed `Guzzle\Common\Collection::__construct($data)` to no longer accepts a null value for `$data` but a
+  default `array()`
+- Added `Guzzle\Stream\StreamInterface::isRepeatable`
+- Made `Guzzle\Http\Client::expandTemplate` and `getUriTemplate` protected methods.
+
+The following methods were removed from interfaces. All of these methods are still available in the concrete classes
+that implement them, but you should update your code to use alternative methods:
+
+- Removed `Guzzle\Http\ClientInterface::setDefaultHeaders(). Use
+  `$client->getConfig()->setPath('request.options/headers/{header_name}', 'value')`. or
+  `$client->getConfig()->setPath('request.options/headers', array('header_name' => 'value'))` or
+  `$client->setDefaultOption('headers/{header_name}', 'value')`. or
+  `$client->setDefaultOption('headers', array('header_name' => 'value'))`.
+- Removed `Guzzle\Http\ClientInterface::getDefaultHeaders(). Use `$client->getConfig()->getPath('request.options/headers')`.
+- Removed `Guzzle\Http\ClientInterface::expandTemplate()`. This is an implementation detail.
+- Removed `Guzzle\Http\ClientInterface::setRequestFactory()`. This is an implementation detail.
+- Removed `Guzzle\Http\ClientInterface::getCurlMulti()`. This is a very specific implementation detail.
+- Removed `Guzzle\Http\Message\RequestInterface::canCache`. Use the CachePlugin.
+- Removed `Guzzle\Http\Message\RequestInterface::setIsRedirect`. Use the HistoryPlugin.
+- Removed `Guzzle\Http\Message\RequestInterface::isRedirect`. Use the HistoryPlugin.
+
+### Cache plugin breaking changes
+
+- CacheKeyProviderInterface and DefaultCacheKeyProvider are no longer used. All of this logic is handled in a
+  CacheStorageInterface. These two objects and interface will be removed in a future version.
+- Always setting X-cache headers on cached responses
+- Default cache TTLs are now handled by the CacheStorageInterface of a CachePlugin
+- `CacheStorageInterface::cache($key, Response $response, $ttl = null)` has changed to `cache(RequestInterface
+  $request, Response $response);`
+- `CacheStorageInterface::fetch($key)` has changed to `fetch(RequestInterface $request);`
+- `CacheStorageInterface::delete($key)` has changed to `delete(RequestInterface $request);`
+- Added `CacheStorageInterface::purge($url)`
+- `DefaultRevalidation::__construct(CacheKeyProviderInterface $cacheKey, CacheStorageInterface $cache, CachePlugin
+  $plugin)` has changed to `DefaultRevalidation::__construct(CacheStorageInterface $cache,
+  CanCacheStrategyInterface $canCache = null)`
+- Added `RevalidationInterface::shouldRevalidate(RequestInterface $request, Response $response)`
+
+3.5 to 3.6
+----------
+
+* Mixed casing of headers are now forced to be a single consistent casing across all values for that header.
+* Messages internally use a HeaderCollection object to delegate handling case-insensitive header resolution
+* Removed the whole changedHeader() function system of messages because all header changes now go through addHeader().
+  For example, setHeader() first removes the header using unset on a HeaderCollection and then calls addHeader().
+  Keeping the Host header and URL host in sync is now handled by overriding the addHeader method in Request.
+* Specific header implementations can be created for complex headers. When a message creates a header, it uses a
+  HeaderFactory which can map specific headers to specific header classes. There is now a Link header and
+  CacheControl header implementation.
+* Moved getLinks() from Response to just be used on a Link header object.
+
+If you previously relied on Guzzle\Http\Message\Header::raw(), then you will need to update your code to use the
+HeaderInterface (e.g. toArray(), getAll(), etc.).
+
+### Interface changes
+
+* Removed from interface: Guzzle\Http\ClientInterface::setUriTemplate
+* Removed from interface: Guzzle\Http\ClientInterface::setCurlMulti()
+* Removed Guzzle\Http\Message\Request::receivedRequestHeader() and implemented this functionality in
+  Guzzle\Http\Curl\RequestMediator
+* Removed the optional $asString parameter from MessageInterface::getHeader(). Just cast the header to a string.
+* Removed the optional $tryChunkedTransfer option from Guzzle\Http\Message\EntityEnclosingRequestInterface
+* Removed the $asObjects argument from Guzzle\Http\Message\MessageInterface::getHeaders()
+
+### Removed deprecated functions
+
+* Removed Guzzle\Parser\ParserRegister::get(). Use getParser()
+* Removed Guzzle\Parser\ParserRegister::set(). Use registerParser().
+
+### Deprecations
+
+* The ability to case-insensitively search for header values
+* Guzzle\Http\Message\Header::hasExactHeader
+* Guzzle\Http\Message\Header::raw. Use getAll()
+* Deprecated cache control specific methods on Guzzle\Http\Message\AbstractMessage. Use the CacheControl header object
+  instead.
+
+### Other changes
+
+* All response header helper functions return a string rather than mixing Header objects and strings inconsistently
+* Removed cURL blacklist support. This is no longer necessary now that Expect, Accept, etc. are managed by Guzzle
+  directly via interfaces
+* Removed the injecting of a request object onto a response object. The methods to get and set a request still exist
+  but are a no-op until removed.
+* Most classes that used to require a `Guzzle\Service\Command\CommandInterface` typehint now request a
+  `Guzzle\Service\Command\ArrayCommandInterface`.
+* Added `Guzzle\Http\Message\RequestInterface::startResponse()` to the RequestInterface to handle injecting a response
+  on a request while the request is still being transferred
+* `Guzzle\Service\Command\CommandInterface` now extends from ToArrayInterface and ArrayAccess
+
+3.3 to 3.4
+----------
+
+Base URLs of a client now follow the rules of http://tools.ietf.org/html/rfc3986#section-5.2.2 when merging URLs.
+
+3.2 to 3.3
+----------
+
+### Response::getEtag() quote stripping removed
+
+`Guzzle\Http\Message\Response::getEtag()` no longer strips quotes around the ETag response header
+
+### Removed `Guzzle\Http\Utils`
+
+The `Guzzle\Http\Utils` class was removed. This class was only used for testing.
+
+### Stream wrapper and type
+
+`Guzzle\Stream\Stream::getWrapper()` and `Guzzle\Stream\Stream::getStreamType()` are no longer converted to lowercase.
+
+### curl.emit_io became emit_io
+
+Emitting IO events from a RequestMediator is now a parameter that must be set in a request's curl options using the
+'emit_io' key. This was previously set under a request's parameters using 'curl.emit_io'
+
+3.1 to 3.2
+----------
+
+### CurlMulti is no longer reused globally
+
+Before 3.2, the same CurlMulti object was reused globally for each client. This can cause issue where plugins added
+to a single client can pollute requests dispatched from other clients.
+
+If you still wish to reuse the same CurlMulti object with each client, then you can add a listener to the
+ServiceBuilder's `service_builder.create_client` event to inject a custom CurlMulti object into each client as it is
+created.
+
+```php
+$multi = new Guzzle\Http\Curl\CurlMulti();
+$builder = Guzzle\Service\Builder\ServiceBuilder::factory('/path/to/config.json');
+$builder->addListener('service_builder.create_client', function ($event) use ($multi) {
+    $event['client']->setCurlMulti($multi);
+}
+});
+```
+
+### No default path
+
+URLs no longer have a default path value of '/' if no path was specified.
+
+Before:
+
+```php
+$request = $client->get('http://www.foo.com');
+echo $request->getUrl();
+// >> http://www.foo.com/
+```
+
+After:
+
+```php
+$request = $client->get('http://www.foo.com');
+echo $request->getUrl();
+// >> http://www.foo.com
+```
+
+### Less verbose BadResponseException
+
+The exception message for `Guzzle\Http\Exception\BadResponseException` no longer contains the full HTTP request and
+response information. You can, however, get access to the request and response object by calling `getRequest()` or
+`getResponse()` on the exception object.
+
+### Query parameter aggregation
+
+Multi-valued query parameters are no longer aggregated using a callback function. `Guzzle\Http\Query` now has a
+setAggregator() method that accepts a `Guzzle\Http\QueryAggregator\QueryAggregatorInterface` object. This object is
+responsible for handling the aggregation of multi-valued query string variables into a flattened hash.
+
+2.8 to 3.x
+----------
+
+### Guzzle\Service\Inspector
+
+Change `\Guzzle\Service\Inspector::fromConfig` to `\Guzzle\Common\Collection::fromConfig`
+
+**Before**
+
+```php
+use Guzzle\Service\Inspector;
+
+class YourClient extends \Guzzle\Service\Client
+{
+    public static function factory($config = array())
+    {
+        $default = array();
+        $required = array('base_url', 'username', 'api_key');
+        $config = Inspector::fromConfig($config, $default, $required);
+
+        $client = new self(
+            $config->get('base_url'),
+            $config->get('username'),
+            $config->get('api_key')
+        );
+        $client->setConfig($config);
+
+        $client->setDescription(ServiceDescription::factory(__DIR__ . DIRECTORY_SEPARATOR . 'client.json'));
+
+        return $client;
+    }
+```
+
+**After**
+
+```php
+use Guzzle\Common\Collection;
+
+class YourClient extends \Guzzle\Service\Client
+{
+    public static function factory($config = array())
+    {
+        $default = array();
+        $required = array('base_url', 'username', 'api_key');
+        $config = Collection::fromConfig($config, $default, $required);
+
+        $client = new self(
+            $config->get('base_url'),
+            $config->get('username'),
+            $config->get('api_key')
+        );
+        $client->setConfig($config);
+
+        $client->setDescription(ServiceDescription::factory(__DIR__ . DIRECTORY_SEPARATOR . 'client.json'));
+
+        return $client;
+    }
+```
+
+### Convert XML Service Descriptions to JSON
+
+**Before**
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<client>
+    <commands>
+        <!-- Groups -->
+        <command name="list_groups" method="GET" uri="groups.json">
+            <doc>Get a list of groups</doc>
+        </command>
+        <command name="search_groups" method="GET" uri='search.json?query="{{query}} type:group"'>
+            <doc>Uses a search query to get a list of groups</doc>
+            <param name="query" type="string" required="true" />
+        </command>
+        <command name="create_group" method="POST" uri="groups.json">
+            <doc>Create a group</doc>
+            <param name="data" type="array" location="body" filters="json_encode" doc="Group JSON"/>
+            <param name="Content-Type" location="header" static="application/json"/>
+        </command>
+        <command name="delete_group" method="DELETE" uri="groups/{{id}}.json">
+            <doc>Delete a group by ID</doc>
+            <param name="id" type="integer" required="true"/>
+        </command>
+        <command name="get_group" method="GET" uri="groups/{{id}}.json">
+            <param name="id" type="integer" required="true"/>
+        </command>
+        <command name="update_group" method="PUT" uri="groups/{{id}}.json">
+            <doc>Update a group</doc>
+            <param name="id" type="integer" required="true"/>
+            <param name="data" type="array" location="body" filters="json_encode" doc="Group JSON"/>
+            <param name="Content-Type" location="header" static="application/json"/>
+        </command>
+    </commands>
+</client>
+```
+
+**After**
+
+```json
+{
+    "name":       "Zendesk REST API v2",
+    "apiVersion": "2012-12-31",
+    "description":"Provides access to Zendesk views, groups, tickets, ticket fields, and users",
+    "operations": {
+        "list_groups":  {
+            "httpMethod":"GET",
+            "uri":       "groups.json",
+            "summary":   "Get a list of groups"
+        },
+        "search_groups":{
+            "httpMethod":"GET",
+            "uri":       "search.json?query=\"{query} type:group\"",
+            "summary":   "Uses a search query to get a list of groups",
+            "parameters":{
+                "query":{
+                    "location":   "uri",
+                    "description":"Zendesk Search Query",
+                    "type":       "string",
+                    "required":   true
+                }
+            }
+        },
+        "create_group": {
+            "httpMethod":"POST",
+            "uri":       "groups.json",
+            "summary":   "Create a group",
+            "parameters":{
+                "data":        {
+                    "type":       "array",
+                    "location":   "body",
+                    "description":"Group JSON",
+                    "filters":    "json_encode",
+                    "required":   true
+                },
+                "Content-Type":{
+                    "type":    "string",
+                    "location":"header",
+                    "static":  "application/json"
+                }
+            }
+        },
+        "delete_group": {
+            "httpMethod":"DELETE",
+            "uri":       "groups/{id}.json",
+            "summary":   "Delete a group",
+            "parameters":{
+                "id":{
+                    "location":   "uri",
+                    "description":"Group to delete by ID",
+                    "type":       "integer",
+                    "required":   true
+                }
+            }
+        },
+        "get_group":    {
+            "httpMethod":"GET",
+            "uri":       "groups/{id}.json",
+            "summary":   "Get a ticket",
+            "parameters":{
+                "id":{
+                    "location":   "uri",
+                    "description":"Group to get by ID",
+                    "type":       "integer",
+                    "required":   true
+                }
+            }
+        },
+        "update_group": {
+            "httpMethod":"PUT",
+            "uri":       "groups/{id}.json",
+            "summary":   "Update a group",
+            "parameters":{
+                "id":          {
+                    "location":   "uri",
+                    "description":"Group to update by ID",
+                    "type":       "integer",
+                    "required":   true
+                },
+                "data":        {
+                    "type":       "array",
+                    "location":   "body",
+                    "description":"Group JSON",
+                    "filters":    "json_encode",
+                    "required":   true
+                },
+                "Content-Type":{
+                    "type":    "string",
+                    "location":"header",
+                    "static":  "application/json"
+                }
+            }
+        }
+}
+```
+
+### Guzzle\Service\Description\ServiceDescription
+
+Commands are now called Operations
+
+**Before**
+
+```php
+use Guzzle\Service\Description\ServiceDescription;
+
+$sd = new ServiceDescription();
+$sd->getCommands();     // @returns ApiCommandInterface[]
+$sd->hasCommand($name);
+$sd->getCommand($name); // @returns ApiCommandInterface|null
+$sd->addCommand($command); // @param ApiCommandInterface $command
+```
+
+**After**
+
+```php
+use Guzzle\Service\Description\ServiceDescription;
+
+$sd = new ServiceDescription();
+$sd->getOperations();           // @returns OperationInterface[]
+$sd->hasOperation($name);
+$sd->getOperation($name);       // @returns OperationInterface|null
+$sd->addOperation($operation);  // @param OperationInterface $operation
+```
+
+### Guzzle\Common\Inflection\Inflector
+
+Namespace is now `Guzzle\Inflection\Inflector`
+
+### Guzzle\Http\Plugin
+
+Namespace is now `Guzzle\Plugin`. Many other changes occur within this namespace and are detailed in their own sections below.
+
+### Guzzle\Http\Plugin\LogPlugin and Guzzle\Common\Log
+
+Now `Guzzle\Plugin\Log\LogPlugin` and `Guzzle\Log` respectively.
+
+**Before**
+
+```php
+use Guzzle\Common\Log\ClosureLogAdapter;
+use Guzzle\Http\Plugin\LogPlugin;
+
+/** @var \Guzzle\Http\Client */
+$client;
+
+// $verbosity is an integer indicating desired message verbosity level
+$client->addSubscriber(new LogPlugin(new ClosureLogAdapter(function($m) { echo $m; }, $verbosity = LogPlugin::LOG_VERBOSE);
+```
+
+**After**
+
+```php
+use Guzzle\Log\ClosureLogAdapter;
+use Guzzle\Log\MessageFormatter;
+use Guzzle\Plugin\Log\LogPlugin;
+
+/** @var \Guzzle\Http\Client */
+$client;
+
+// $format is a string indicating desired message format -- @see MessageFormatter
+$client->addSubscriber(new LogPlugin(new ClosureLogAdapter(function($m) { echo $m; }, $format = MessageFormatter::DEBUG_FORMAT);
+```
+
+### Guzzle\Http\Plugin\CurlAuthPlugin
+
+Now `Guzzle\Plugin\CurlAuth\CurlAuthPlugin`.
+
+### Guzzle\Http\Plugin\ExponentialBackoffPlugin
+
+Now `Guzzle\Plugin\Backoff\BackoffPlugin`, and other changes.
+
+**Before**
+
+```php
+use Guzzle\Http\Plugin\ExponentialBackoffPlugin;
+
+$backoffPlugin = new ExponentialBackoffPlugin($maxRetries, array_merge(
+        ExponentialBackoffPlugin::getDefaultFailureCodes(), array(429)
+    ));
+
+$client->addSubscriber($backoffPlugin);
+```
+
+**After**
+
+```php
+use Guzzle\Plugin\Backoff\BackoffPlugin;
+use Guzzle\Plugin\Backoff\HttpBackoffStrategy;
+
+// Use convenient factory method instead -- see implementation for ideas of what
+// you can do with chaining backoff strategies
+$backoffPlugin = BackoffPlugin::getExponentialBackoff($maxRetries, array_merge(
+        HttpBackoffStrategy::getDefaultFailureCodes(), array(429)
+    ));
+$client->addSubscriber($backoffPlugin);
+```
+
+### Known Issues
+
+#### [BUG] Accept-Encoding header behavior changed unintentionally.
+
+(See #217) (Fixed in 09daeb8c666fb44499a0646d655a8ae36456575e)
+
+In version 2.8 setting the `Accept-Encoding` header would set the CURLOPT_ENCODING option, which permitted cURL to
+properly handle gzip/deflate compressed responses from the server. In versions affected by this bug this does not happen.
+See issue #217 for a workaround, or use a version containing the fix.