Fix implementation of __toString()

[mxr576]

"This method MUST attempt to seek to the beginning of the stream before reading data and read the stream until the end is reached."

https://github.com/php-fig/http-message/blob/master/src/StreamInterface.php#L28

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no

What's in this PR?

This is a followup on this bug reported for the client-common package: php-http/client-common#98

[xabbuh]

might be a good idea to even add a test for this

[joelwurtz]

Thanks for this PR.

Problem is that it will always be false, we use a decorator here but we should have implemented directly this interface as a FilteredStream cannot be seekable.

As an example, a deflate stream will build it's deflate "table" (how to decode this string) on the fly, which means reseeking at the begin of the stream will produce a different response if using the same table. (You need to reset the table also)

IMO, the correct way would be to override isSeekable, seek and rewind functions to not allow those method (return false / throw exception), and an optional buffer option on top of plugin using the BufferedStream implementation.

[joelwurtz]

We can close this if #100 is merged

[dbu]

#100 has been merged