There seems to be some disagreement on where the file position indicator
(cursor) ends up upon the creation of a Stream instance. I have done some
minor testing and put the results on GitHub
<https://github.com/Zegnat/php-psr17-test-cursor>. This can lead to
incompatibilities when doing something like:
echo (new StreamFactory)->createStream('Hello!')->read(6);
- createStream() seems to be the most contested. The cursor goes at the
start or end of the string. Even more surprising (to me) is that Diactoros
will result in a different state depending on whether you use its own
factory or the tuupola one. (Again showing how compatibility may be an
issue here!)
- createStreamFromResource() seems to be agreed upon by all
implementations: keep the cursor wherever it was at in the original
resource. Even without specifically being defined by the PSR this makes a
lot of sense to me, and I will propose adding a test for this to the
(official) unit tests.
- createStreamFromFile() has one of the tested implementations do its
own thing: berlioz/http-message copies the contents of the file into a new
stream and puts the cursor at the end. Every other implementations puts the
cursor at the start, matching where it would be if fopen() is called on a
file.
Of course the (official) unit tests
<https://github.com/http-interop/http-factory-tests> that go with the
PSR-17 interfaces do not have tests for any of this as it isn’t covered by
the PSR itself.
The default for createStream() is a coin toss to me. I see no clear
argument for either position. But I do think the PSR should define a
location. This does not sound like something that can just be errata’d in,
and defining behaviour now will lead to breaking changes in implementations
:( Not sure what the way is to start addressing this.
For *FromResource() there seem to be good reasons to just leave the cursor
be where it is, and I believe this can be mentioned by the PSR. As all
implementations do this already, maybe this can be an errata of some kind?
For *FromFile() I don’t know what can be defined, other than saying it
should follow what fopen() does by default. For files this will mean the
cursor position is set to the start of the stream, I am not sure what the
cursor does for other protocols/wrappers/schemes.
Ideas?
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