Re: streams & truename

[Sam S. <sd...@gn...>]

Bruno,

We have a problem, yet another case where the CL universe is different
from UNIX (and, probably, Windows, but I don't have access to that, so,
thankfully, I can excuse myself):

* CL assumes that (truename open-file-stream) works

* on unix, "/dev/fd/0" resolves to "/proc/<pid>/fd/0" which is a symlink
  to "pipe:[123456789]" when the process is run like "clisp | cat".
  (and the "/proc/<pid>/fd/pipe:[...]" file does not exist).
  IOW, on unix one can do i/o on a non-existent path (sometimes).

What to do about it?

* We can detect that "/proc/<pid>/fd/0" is on "/proc" and refuse to
  follow symlinks there.
  This is fairly arbitrary, but we already use this sort of magic when
  deciding the default value for the :buffered argument.
  This would also prevent users from detecting that the stdout is a
  path (not good).
  [btw, shouldn't we treat /proc and /dev identically? neither is a real
  file system].

* We can defer computing strm_file_truename until necessary, leading to
  various special cases for (open (make-stream :input)) (which will call
  truename) &c.

I don't particularly like either approach; but I think I dislike the
first one less.

Other ideas?

> * Bruno Haible <oe...@py...t> [2017-02-27 22:25:59 +0100]:
>
> $ ./clisp -K boot  -E UTF-8 -Emisc 1:1 -Epathname 1:1 -norc --version 2>/dev/null | \
>   hexdump -e '"%06.6_ax  " 16/1 "%02X "' -e '"  " 16/1 "%_p" "\n"' "$@"
> 000000  0A 2A 2A 2A 20 2D 20 54 52 55 45 4E 41 4D 45 3A  .*** - TRUENAME:
> 000010  20 54 68 65 20 76 61 6C 75 65 20 6F 66 20 2A 54   The value of *T
> 000020  45 52 4D 49 4E 41 4C 2D 49 4F 2A 20 77 61 73 20  ERMINAL-IO* was 
> 000030  6E 6F 74 20 61 6E 20 61 70 70 72 6F 70 72 69 61  not an appropria
> 000040  74 65 20 73 74 72 65 61 6D 3A 20 23 3C 43 4C 4F  te stream: #<CLO
> 000050  53 45 44 20 49 4F 20 54 45 52 4D 49 4E 41 4C 2D  SED IO TERMINAL-
> 000060  53 54 52 45 41 4D 3E 2E 20 49 74 20 68 61 73 20  STREAM>. It has 
> 000070  62 65 65 6E 20 63 68 61 6E 67 65 64 20 74 6F 0A  been changed to.
> 000080  20 20 20 20 20 20 23 3C 49 4F 20 54 45 52 4D 49        #<IO TERMI
> 000090  4E 41 4C 2D 53 54 52 45 41 4D 3E 2E 0A 45 78 69  NAL-STREAM>..Exi
> 0000a0  74 69 6E 67 20 6F 6E 20 73 69 67 6E 61 6C 20 36  ting on signal 6
> 0000b0  0A                                               .
>
> Sam, your turn, I guess.

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1504
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