I was running into problems with the lack of documentation in streams, and started writing some documentation. 
But it didn’t meet @jan’s quality standards, and I haven’t got around to rewriting it.
Some of my questions and @jan 's answers are here: (foreign functions) Safe release of resources during cleanup
(streams are a kind of blob, although they have somewhat different interfaces.)
The library(archive) code makes extensive use of streams (and streams that wrap blobs). I’m in the process of cleaning it up (lots of memory leaks, use-after-free, etc.) and have almost got things to the point of being able to submit a PR. If you can wait a few days, there might be some useful things there.
(I’ll let @jan answer your questions … we’ve had some offline discussions, which maybe should have been public)