Feature: Save png to octet vector

[uint]

Would you be interested in adding a canvas function save-png-octet-vector or save-png-data that simply returns an octet vector with the entire png file for in-memory storage? Seems like a simple thing I'd be happy to make a PR for.

My use case: I want to be able to make a hunchentoot-based server that dynamically generates png's, stores them in memory and serves them when requested, without committing files to storage. Currently I use save-png-stream and a custom binary stream that writes to an octet vector I later retrieve, but this should be simpler.

[xach]

I use SAVE-PNG-STREAM too. I'd be happy to get a PR for save-png-octet-vector - as long as it includes an update to the docs, as well. Thanks!

[phoe]

It seems that (flex:with-output-to-sequence (stream) (vecto:save-png-stream stream)) solves this problem, albeit with an external dependency. It might be a bit heavy-weight to use as a dependency since it's a big library, but a Gray stream might be a proper abstraction since all of ZPNG internals are about writing to streams rather than assembling sequences in-memory.

Should Vecto depend on trivial-gray-streams and copy only the bare essentials from Flexi-Streams instead? Or just should it tell users to use flex:with-output-to-sequence?