(Includes fixes from Yichen Gu)
Currently the incoming ebuf is always replaced to point to either a whole
buflist segment, or up to the (pt_serv_buf - LWS_PRE) length in the pt_serv_buf.
This is called on path for handling http read... some user code reasonably wants to
restrict the read size to what it can handle.
Change the other lws_buflist_aware_read() callers to zero ebuf before calling, and for
those have it keep the current behaviour; but if non-NULL ebuf.token on incoming, as
in http read path case, restrict both reported len of buflist content and the read length
to the incoming ebuf.len so the user code can control what it will get at one time.
Additionally muxed protocol wsi have no choice but to read what was sent to them
since it's HOL-blocking for other streams and its own WINDOW_UPDATEs. So add an
internal param to lws_buflist_aware_read() forcing read even if buflist content
is available.
Refactor everything around ping / pong handling in ws and h2, so there
is instead a protocol-independent validity lws_sul tracking how long it
has been since the last exchange that confirms the operation of the
network connection in both directions.
Clean out periodic role callback and replace the last two role users
with discrete lws_sul for each pt.
With http, the protocol doesn't indicate where the headers end and the
next transaction or body begin. Until now, we handled that for client
header response parsing by reading from the tls buffer bytewise.
This modernizes the code to read in up to 256-byte chunks and parse
the chunks in one hit (the parse API is already set up for doing this
elsewhere).
Now we have a generic input buflist, adapt the parser loop to go through
that and arrange that any leftovers are placed on there.
Improve the code around stash, getting rid of the strdups for a net
code reduction. Remove the special destroy helper for stash since
it becomes a one-liner.
Trade several stack allocs in the client reset function for a single
sized brief heap alloc to reduce peak stack alloc by around 700 bytes.
