This was originally changed so that flush_flight could forward BIO_write
errors as-is, but we can and probably should still map BIO_flush errors.
This is unlikely to matter (every relevant BIO likely just has a no-op
flush which returns one), but, e.g., our file BIO returns 0, not -1, on
error.
We possibly should also be mapping BIO_write errors, but I'll leave that
alone for now. It's primarily BIO_read where the BIO return value must
be preserved due to error vs. EOF.
(We probably can just remove the BIO_flush calls altogether, but since
the buffer BIO forwarded the flush signal it would be a user-visible
behavior change to confirm.)
Change-Id: Ib495cc5d043867cf964f99b7ee4535114f7b2230
Reviewed-on: https://boringssl-review.googlesource.com/13367
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>