c99

Problem:

A common pattern is:

GUARD(s2n_stuffer_skip_write(stuffer, bytes_to_write));
uint8_t* ptr = suffer->blob.data + stuffer->write_cursor - bytes_to_write;

which could be simplified.

Solution:

*ptr could be an *out parameter to s2n_stuffer_skip_write

• Does this change what S2N sends over the wire? No.
• Does this change any public APIs? No.

While meson appears to support miniz, CMake (which I unfortunately have to use as my IDE doesn't support meson) requires zlib and cannot fall back to miniz. I am on windows and don't have zlib installed, so making this use miniz would be appreciated. Thanks.