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libraries/vendor/psr/http-message/docs/PSR7-Usage.md

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+### PSR-7 Usage
+
+All PSR-7 applications comply with these interfaces 
+They were created to establish a standard between middleware implementations.
+
+> `RequestInterface`, `ServerRequestInterface`, `ResponseInterface` extend `MessageInterface`  because the `Request` and the `Response` are `HTTP Messages`.
+> When using `ServerRequestInterface`, both `RequestInterface` and `Psr\Http\Message\MessageInterface` methods are considered.
+
+
+The following examples will illustrate how basic operations are done in PSR-7.
+
+##### Examples
+
+
+For this examples to work (at least) a PSR-7 implementation package is required. (eg: zendframework/zend-diactoros, guzzlehttp/psr7, slim/slim, etc)
+All PSR-7 implementations should have the same behaviour.
+
+The following will be assumed: 
+`$request` is an object of `Psr\Http\Message\RequestInterface` and
+
+`$response` is an object implementing `Psr\Http\Message\RequestInterface`
+
+
+### Working with HTTP Headers
+
+#### Adding headers to response:
+
+```php
+$response->withHeader('My-Custom-Header', 'My Custom Message');
+```
+
+#### Appending values to headers
+
+```php
+$response->withAddedHeader('My-Custom-Header', 'The second message');
+```
+
+#### Checking if header exists:
+
+```php
+$request->hasHeader('My-Custom-Header'); // will return false
+$response->hasHeader('My-Custom-Header'); // will return true
+```
+
+> Note: My-Custom-Header was only added in the Response
+
+#### Getting comma-separated values from a header (also applies to request)
+
+```php
+// getting value from request headers
+$request->getHeaderLine('Content-Type'); // will return: "text/html; charset=UTF-8"
+// getting value from response headers
+$response->getHeaderLine('My-Custom-Header'); // will return:  "My Custom Message; The second message"
+```
+
+#### Getting array of value from a header (also applies to request)
+```php
+// getting value from request headers
+$request->getHeader('Content-Type'); // will return: ["text/html", "charset=UTF-8"]
+// getting value from response headers
+$response->getHeader('My-Custom-Header'); // will return:  ["My Custom Message",  "The second message"]
+```
+
+#### Removing headers from HTTP Messages
+```php
+// removing a header from Request, removing deprecated "Content-MD5" header
+$request->withoutHeader('Content-MD5'); 
+
+// removing a header from Response
+// effect: the browser won't know the size of the stream
+// the browser will download the stream till it ends
+$response->withoutHeader('Content-Length');
+```
+
+### Working with HTTP Message Body
+
+When working with the PSR-7 there are two methods of implementation:
+#### 1. Getting the body separately
+
+> This method makes the body handling easier to understand and is useful when repeatedly calling body methods. (You only call `getBody()` once). Using this method mistakes like `$response->write()` are also prevented.
+
+```php
+$body = $response->getBody();
+// operations on body, eg. read, write, seek
+// ...
+// replacing the old body
+$response->withBody($body); 
+// this last statement is optional as we working with objects
+// in this case the "new" body is same with the "old" one
+// the $body variable has the same value as the one in $request, only the reference is passed
+```
+
+#### 2. Working directly on response
+
+> This method is useful when only performing few operations as the `$request->getBody()` statement fragment is required
+
+```php
+$response->getBody()->write('hello');
+```
+
+### Getting the body contents
+
+The following snippet gets the contents of a stream contents.
+> Note: Streams must be rewinded, if content was written into streams, it will be ignored when calling `getContents()` because the stream pointer is set to the last character, which is `\0` - meaning end of stream.
+```php 
+$body = $response->getBody();
+$body->rewind(); // or $body->seek(0);
+$bodyText = $body->getContents();
+```
+> Note: If `$body->seek(1)` is called before `$body->getContents()`, the first character will be ommited as the starting pointer is set to `1`, not `0`. This is why using `$body->rewind()` is recommended.
+
+### Append to body
+
+```php
+$response->getBody()->write('Hello'); // writing directly
+$body = $request->getBody(); // which is a `StreamInterface`
+$body->write('xxxxx');
+```
+
+### Prepend to body
+Prepending is different when it comes to streams. The content must be copied before writing the content to be prepended.
+The following example will explain the behaviour of streams.
+
+```php
+// assuming our response is initially empty
+$body = $repsonse->getBody();
+// writing the string "abcd"
+$body->write('abcd');
+
+// seeking to start of stream
+$body->seek(0);
+// writing 'ef'
+$body->write('ef'); // at this point the stream contains "efcd"
+```
+
+#### Prepending by rewriting separately
+
+```php
+// assuming our response body stream only contains: "abcd"
+$body = $response->getBody();
+$body->rewind();
+$contents = $body->getContents(); // abcd
+// seeking the stream to beginning
+$body->rewind();
+$body->write('ef'); // stream contains "efcd"
+$body->write($contents); // stream contains "efabcd"
+```
+
+> Note: `getContents()` seeks the stream while reading it, therefore if the second `rewind()` method call was not present the stream would have resulted in `abcdefabcd` because the `write()` method appends to stream if not preceeded by `rewind()` or `seek(0)`.
+
+#### Prepending by using contents as a string
+```php
+$body = $response->getBody();
+$body->rewind();
+$contents = $body->getContents(); // efabcd
+$contents = 'ef'.$contents;
+$body->rewind();
+$body->write($contents);
+```