>
> checking the code in as it is is also an option...it gets more eyeballs on
> the problem
>
I checked in the code for a Unix redirecting command handler.
It's still work-in-progress, not only because of some minor issues (e. g.
Ctrl+C handling), but because some severe restrictions, that I know no
solutions for.
1) in a scenario, where we feed redirected input to a command that really
doesn't consume it (e. g. echo), the command may finish before we can pipe
all stdin input. The spawned child exits, closing its stdin pipe read
end. On my test system, Ubuntu 16.04, the following write() operation
then, instead of failing with an errno indication, will exit the program.
No message, no segmentation fault, no indication at all.
I'm trying circumventing this issue by not closing the parent stdin pipe
read end (which normally isn't used at all and is suggested to be closed in
most sample code). This fixes the "exit" issue, but now, when the child
finishes, further writes to the pipe don't give an error indication (as it
is still valid because the parent read end is open) which leads to an
endless loop. This might be fixed if the handler checked whether the
commandchild was still alive upon each loop (adding another complication
that I wouldn't expect to be necessary)
2) when piping more than 64K (the default pipe size on Linux) to cat by
redirecting stdin and stdout cat typically issues an error an output will
miss lines. I've left debug trace statements in the handler to show the
issue.
Feeding 660 lines with 100 characters each (plus a newline)
the handler sees the correct 66660 total bytes, writes them in 4K blocks
(the size of PIP_BUF which ensures we have atomic writes)
at 64K the pipe is full, tha handler sees an EAGAIN error, tries to read
from stdout (nothing there yet), waits a little and loops.
loops #2 and #3 see the full stdin pipe, and an empty stdout pipe, but now
cat complains: "cat: -: Resource temporarily unavailable"
in loop #4 the handler is able to write the remaining bytes to stdin, and
also stdout can be read now, but not all expected output lines are there
With less than 64K input to stdin, things seem to work fine.
~~~
$ ./rexx -e "a = .Array~new; address io 'cat' with input using
(.Array~new(arg(1))~fill('-'~copies(100))) output stem o.; say o.0 o.1" 660
io args /bin/sh -c cat
io redirection requested
io input redirection requested
io output redirection requested
io spawned command
io input feed total buffer 66660 bytes
io loop #1, input:1 output:1 error:0
io input feed write offset 0, length 4096, written 4096 bytes
io input feed write offset 4096, length 4096, written 4096 bytes
io input feed write offset 8192, length 4096, written 4096 bytes
io input feed write offset 12288, length 4096, written 4096 bytes
io input feed write offset 16384, length 4096, written 4096 bytes
io input feed write offset 20480, length 4096, written 4096 bytes
io input feed write offset 24576, length 4096, written 4096 bytes
io input feed write offset 28672, length 4096, written 4096 bytes
io input feed write offset 32768, length 4096, written 4096 bytes
io input feed write offset 36864, length 4096, written 4096 bytes
io input feed write offset 40960, length 4096, written 4096 bytes
io input feed write offset 45056, length 4096, written 4096 bytes
io input feed write offset 49152, length 4096, written 4096 bytes
io input feed write offset 53248, length 4096, written 4096 bytes
io input feed write offset 57344, length 4096, written 4096 bytes
io input feed write offset 61440, length 4096, written 4096 bytes
io input feed write offset 65536, length 1124, written -1 bytes
io input feed write failure Resource temporarily unavailable
io output buffer -1 bytes read
io output retry: Resource temporarily unavailable
io loop wait 250 usec done
io loop #2, input:1 output:1 error:0
io input feed write offset 65536, length 1124, written -1 bytes
io input feed write failure Resource temporarily unavailable
io output buffer -1 bytes read
io output retry: Resource temporarily unavailable
io loop wait 250 usec done
io loop #3, input:1 output:1 error:0
io input feed write offset 65536, length 1124, written -1 bytes
io input feed write failure Resource temporarily unavailable
io output buffer -1 bytes read
io output retry: Resource temporarily unavailable
cat: -: Resource temporarily unavailable
io loop wait 250 usec done
io loop #4, input:1 output:1 error:0
io input feed write offset 65536, length 1124, written 1124 bytes
io input feed closed
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 4096 bytes read
io output buffer 0 bytes read
io output feed closed
io waitpid(12788) = 12788
io child ended with rc 1
io returning
649
----------------------------------------------------------------------------------------------------
~~~
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