Add support for Responses that produce a HTTP/1.1 chunked stream

[weierophinney]

HTTP/1.1 provides 'Transfer-encoding: chunked' for sending a stream of data from the server.

Zend Diactoros currently doesn't seem to provide out-of-the-box support for this.

• There's no existing Response that sets the required headers for you.
• There's no existing implementation of StreamInterface that supports dynamic content and is compatible with the requirements of SapiStreamEmitter.

Possible solution for out-of-the-box support could be:

• Add a DynamicStreamInterface interface that extends StreamInterface, for type-hinting in a moment
• Add a GeneratorStream class that implements DynamicStreamInterface, and its read() method gets the required data from a PHP generator
• Add another class that implements DynamicStreamInterface, and its read() method gets the required data from a PHP callback
• Add a StreamResponse class that requires a DynamicStreamInterface in the constructor, sets the necessary headers for chunked stream delivery

It leaves questions around handling $maxBufferLength, and where the code goes to write the actual chunked blocks (trait? helper class?).

I have to build a solution for this, and I'm happy to contribute it back to Diactoros, if we can agree a design :)

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Originally posted by @stuartherbert at zendframework/zend-diactoros#261

[weierophinney]

Honestly, this looks like a combination of:

• A stream type
• A custom emitter type

As such, it may make sense as a bridge package between Diactoros and zend-httphandlerrunner that provides the stream and the associated emitter. We would definitely promote it, and potentially offer to bring it into the zendframework organization if you wished.

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Originally posted by @weierophinney at zendframework/zend-diactoros#261 (comment)