http2: fix session memory accounting after pausing

[mikelehen]

The ability to pause input processing was added in 8a4a193 but
introduced a session memory accounting mismatch leading to potential
NGHTTP2_ENHANCE_YOUR_CALM errors.

After pausing
(

node/src/node_http2.cc

Line 871 in f36331c

// Mark the remainder of the data as available for later consumption.

),
the early return on line 873 skips the
DecrementCurrentSessionMemory(stream_buf_.len) call below (line 878).

When we later finished processing the input chunk
(

node/src/node_http2.cc

Line 1858 in f36331c

if (UNLIKELY(stream_buf_offset_ > 0)) {

),
we were calling DecrementCurrentSessionMemory(stream_buf_offset_) [line
1875] which was a no-op since we just set stream_buf_offset_ to 0 [line
1873].

The correct amount to decrement by is still stream_buf_.len, since
that's the amount we skipped previously (line 878).

Fixes: #29223
Refs: 164ac5b

Checklist

• make -j4 test (UNIX)
• tests and/or benchmarks are included
• commit message follows commit guidelines