Multiple general improvements to http2 internals for
readability and efficiency

[This backport applied to v10.x cleanly but had several
merge conflicts on v8.x.]

PR-URL: nodejs#23984
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Ujjwal Sharma <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>

Key new feature: RFC 8441 `:protocol` support

PR-URL: nodejs#23284
Reviewed-By: Refael Ackermann <[email protected]>
Reviewed-By: Gus Caplan <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>

PR-URL: nodejs#26990
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>

PR-URL: nodejs#27295
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Yongsheng Zhang <[email protected]>
Reviewed-By: Masashi Hirano <[email protected]>

PR-URL: nodejs#28448
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>

This includes mitigations for CVE-2019-9512/CVE-2019-9515.

DRY up the `debug()` calls, and in particular, avoid building template
strings before we know whether we need to.

For some JS events, it only makes sense to call into JS when there
are listeners for the event in question.

The overhead is noticeable if a lot of these events are emitted during
the lifetime of a session. To reduce this overhead, keep track of
whether any/how many JS listeners are present, and if there are none,
skip calls into JS altogether.

This is part of performance improvements to mitigate CVE-2019-9513.

Lazily allocate `ArrayBuffer`s for the contents of DATA frames.
Creating `ArrayBuffer`s is, sadly, not a cheap operation with V8.

This is part of performance improvements to mitigate CVE-2019-9513.

Together with the previous commit, these changes improve throughput
in the adversarial case by about 100 %, and there is little more
that we can do besides artificially limiting the rate of incoming
metadata frames (i.e. after this patch, CPU usage is virtually
exclusively in libnghttp2).

[This backport also applies changes from 83e1b97 and required
some manual work due to the lack of `AllocatedBuffer` on v10.x.
More work was necessary for v8.x, including copying utilities
for `util.h` from more recent Node.js versions.]

Refs: nodejs#26201

Limit the number of streams that are rejected upon creation. Since
each such rejection is associated with an `NGHTTP2_ENHANCE_YOUR_CALM`
error that should tell the peer to not open any more streams,
continuing to open streams should be read as a sign of a misbehaving
peer. The limit is currently set to 100 but could be changed or made
configurable.

This is intended to mitigate CVE-2019-9514.

Limit the number of invalid input frames, as they may be pointing towards a
misbehaving peer. The limit is currently set to 1000 but could be changed or
made configurable.

This is intended to mitigate CVE-2019-9514.

[This commit differs from the v12.x one due to the lack of
libuv/libuv@ee24ce900e5714c950b248da2b.
See the comment in the test for more details.]

Ignore headers with 0-length names and track memory for headers
the way we track it for other HTTP/2 session memory too.

This is intended to mitigate CVE-2019-9516.

Allocating memory upfront comes with overhead, and in particular,
`std::vector` implementations do not necessarily return memory
to the system when one might expect that (e.g. after shrinking the
vector).

This is intended to mitigate CVE-2019-9518.

If a write to the underlying socket finishes asynchronously, that
means that we cannot write any more data at that point without waiting
for it to finish. If this happens, we should also not be producing any
more input.

This is part of mitigating CVE-2019-9511/CVE-2019-9517.

If we are waiting for the ability to send more output, we should not
process more input. This commit a) makes us send output earlier,
during processing of input, if we accumulate a lot and b) allows
interrupting the call into nghttp2 that processes input data
and resuming it at a later time, if we do find ourselves in a position
where we are waiting to be able to send more output.

This is part of mitigating CVE-2019-9511/CVE-2019-9517.

nghttp2 has updated its limit for outstanding Ping/Settings ACKs
to 1000. This commit allows reverting to the old default of 10000.

The associated CVEs are CVE-2019-9512/CVE-2019-9515.

Refs: nodejs#27914