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When a writable HANDLE is managed by the handle-io.c system, you ask to send EOF on the handle by calling handle_write_eof. That waits until all buffered data has been written, and then sends an EOF event by simply closing the handle. That is, of course, the only way to send an EOF signal on a handle at all. And yet, it's a bug, because the handle_output system does not take ownership of the handle you give it: the client of handle_output retains ownership, keeps its own copy of the handle, and will expect to close it itself. In most cases, the extra close will harmlessly fail, and return ERROR_INVALID_HANDLE (which the caller didn't notice anyway). But if you're unlucky, in conditions of frantic handle opening and closing (e.g. with a lot of separate named-pipe-style agent forwarding connections being constantly set up and torn down), the handle value might have been reused between the two closes, so that the second CloseHandle closes an unrelated handle belonging to some other part of the program. We can't fix this by giving handle_output permanent ownership of the handle, because it really _is_ necessary for copies of it to survive elsewhere: in particular, for a bidirectional file such as a serial port or named pipe, the reading side also needs a copy of the same handle! And yet, we can't replace the handle_write_eof call in the client with a direct CloseHandle, because that won't wait until buffered output has been drained. The solution is that the client still calls handle_write_eof to register that it _wants_ an EOF sent; the handle_output system will wait until it's ready, but then, instead of calling CloseHandle, it will ask its _client_ to close the handle, by calling the provided 'sentdata' callback with the new 'close' flag set to true. And then the client can not only close the handle, but do whatever else it needs to do to record that that has been done.
This is the README for PuTTY, a free Windows and Unix Telnet and SSH
client.
PuTTY is built using CMake <https://cmake.org/>. To compile in the
simplest way (on any of Linux, Windows or Mac), run these commands in
the source directory:
cmake .
cmake --build .
Documentation (in various formats including Windows Help and Unix
`man' pages) is built from the Halibut (`.but') files in the `doc'
subdirectory using `doc/Makefile'. If you aren't using one of our
source snapshots, you'll need to do this yourself. Halibut can be
found at <https://www.chiark.greenend.org.uk/~sgtatham/halibut/>.
The PuTTY home web site is
https://www.chiark.greenend.org.uk/~sgtatham/putty/
If you want to send bug reports or feature requests, please read the
Feedback section of the web site before doing so. Sending one-line
reports saying `it doesn't work' will waste your time as much as
ours.
See the file LICENCE for the licence conditions.