[pgit]

A cancelled operation now promises one thing on both runtimes: it completes right away, with operation_canceled, and a write reports how much of its buffer it has taken, so that the body can still be finished where the message is still usable.

Changes

• Only terminal cancellation cancels a parked operation on ASIO (65febe7). on_cancel() ignores a request for partial or total alone, which is what Asio asks of an operation that can't guarantee what those types promise, and what its own coroutines do by default. cancel_after sends terminal and || sends all three, so neither is affected.

• A write says how much of its buffer it has taken (f82a6d7). API change: Write is void(error_code, size_t), and write() / write_eof() yield IoTask<size_t>. On success that is all of the buffer; after a cancellation it is what the protocol has taken:

  • nghttp2 v1: what it has copied
  • nghttp2 v2 and HTTP/3: what is staged, or handed over by reference
  • HTTP/1.1: the body bytes that reached the connection

  On HTTP/2, cancelling write_eof() before nghttp2 has seen the end now takes the end back, as HTTP/3 already did. So write_eof(buffer + n) finishes the body after any cancelled write, on every protocol.

• Tests for what a cancelled operation promises (c9c53c4):

  • partial/total alone leave a read running, and terminal completes it
  • a cancelled read_some() can be followed by reading the rest of the body
  • an 8 MiB write cancelled while the server isn't reading reports n, and write_eof(buffer + n) then gets the whole body across intact (HTTP/1.1 skips this one, because a cancelled write there ends the connection)

• docs/cancellation.rst (14556f7): a page on cancelling, abandoning and draining. It covers what a cancelled operation promises, what each operation leaves behind, how writes differ by protocol, and how to finish a body after a cancelled write. The programmer's guide and end-of-body.rst now link to it.

• test/test_runtime.cpp (df5c9dd): delay() can be cancelled on both runtimes, when_either() doesn't wait for the delay it cancels, and on ASIO partial/total alone don't reach the timer.

Testing

build/ (ASIO) and build-corosio/ pass the new runtime tests. CI runs the full matrix.

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