Sergey Zhuk has posted another article to his site covering functionality provided in ReactPHP. In this latest tutorial he covers the PromiseStream handling of the library allowing for the translation from promise to stream (and back).

One of the patterns that are used to deal with streams is spooling: we need the entire resource data available before we start processing it. One approach is to collect each chunk of data received from the stream.

But, imagine that we have some client code that wants to process some data from a file. It doesn’t care about the streams, it only needs to receive the entire data from the file. With this approach, this code should be called inside the callback for the end event of the stream. So, the client code should now about streams, events, and callbacks. But sometimes it’s impossible.

Example code is included to illustrate the problem above and an answer is provided in the form of ReactPHP promises. This allows the data to move into the promise as the data is being read from the stream's source. The tutorial goes on to talk about the functionality behind this transition including the buffer method to create the promise with chunked data, the all method to build the promise from the full data in the stream and the first method that works with events on the stream. The article then covers the reverse, showing how to pull information from a promise and push it back out to a stream via the unwrapReadable and unwrapWritable methods.