1 |
NAME |
2 |
IO::FDPass - pass a file descriptor over a socket |
3 |
|
4 |
SYNOPSIS |
5 |
use IO::FDPass; |
6 |
|
7 |
IO::FDPass::send fileno $socket, fileno $fh_to_pass |
8 |
or die "send failed: $!"; |
9 |
|
10 |
my $fd = IO::FDPass::recv fileno $socket; |
11 |
$fd >= 0 or die "recv failed: $!"; |
12 |
|
13 |
DESCRIPTION |
14 |
This small low-level module only has one purpose: pass a file descriptor |
15 |
to another process, using a (streaming) unix domain socket (on POSIX |
16 |
systems) or any (streaming) socket (on WIN32 systems). The ability to |
17 |
pass file descriptors on windows is currently the unique selling point |
18 |
of this module. Have I mentioned that it is really small, too? |
19 |
|
20 |
FUNCTIONS |
21 |
$bool = IO::FDPass::send $socket_fd, $fd_to_pass |
22 |
Sends the file descriptor given by $fd_to_pass over the socket |
23 |
$socket_fd. Return true if it worked, false otherwise. |
24 |
|
25 |
Note that *both* parameters must be file descriptors, not handles. |
26 |
|
27 |
When used on non-blocking sockets, this function might fail with $! |
28 |
set to "EAGAIN" or equivalent, in which case you are free to try. It |
29 |
should succeed if called on a socket that indicates writability |
30 |
(e.g. via "select"). |
31 |
|
32 |
Example: pass a file handle over an open socket. |
33 |
|
34 |
IO::FDPass::send fileno $socket, fileno $fh |
35 |
or die "unable to pass file handle: $!"; |
36 |
|
37 |
$fd = IO::FDPass::recv $socket_fd |
38 |
Receive a file descriptor from the socket and return it if |
39 |
successful. On errors, return -1. |
40 |
|
41 |
Note that *both* $socket_fd and the returned file descriptor are, in |
42 |
fact, file descriptors, not handles. |
43 |
|
44 |
When used on non-blocking sockets, this function might fail with $! |
45 |
set to "EAGAIN" or equivalent, in which case you are free to try |
46 |
again. It should succeed if called on a socket that indicates |
47 |
readability (e.g. via "select"). |
48 |
|
49 |
Example: receive a file descriptor from a blocking socket and |
50 |
convert it to a file handle. |
51 |
|
52 |
my $fd = IO::FDPass::recv fileno $socket; |
53 |
$fd >= 0 or die "unable to receive file handle: $!"; |
54 |
open my $fh, "+<&=$fd" |
55 |
or die "unable to convert file descriptor to handle: $!"; |
56 |
|
57 |
PORTABILITY NOTES |
58 |
This module has been tested on GNU/Linux x86 and amd64, NetBSD 6, OS X |
59 |
10.5, Windows 2000 ActivePerl 5.10, Solaris 10, OpenBSD 4.4, 4.5, 4.8 |
60 |
and 5.0, DragonFly BSD, FreeBSD 7, 8 and 9, Windows 7 + ActivePerl |
61 |
5.16.3 32 and 64 bit and Strawberry Perl 5.16.3 32 and 64 bit, and found |
62 |
to work, although ActivePerl 32 bit needed a newer MinGW version (that |
63 |
supports XP and higher). |
64 |
|
65 |
However, windows doesn't support asynchronous file descriptor passing, |
66 |
so the source process must still be around when the destination process |
67 |
wants to receive the file handle. Also, if the target process fails to |
68 |
fetch the handle for any reason (crashes, fails to call "recv" etc.), |
69 |
the handle will leak, so never do that. |
70 |
|
71 |
Also, on windows, the receiving process must have the PROCESS_DUP_HANDLE |
72 |
access right on the sender process for this module to work. |
73 |
|
74 |
Cygwin is not supported at the moment, as file descriptor passing in |
75 |
cygwin is not supported, and cannot be rolled on your own as cygwin has |
76 |
no (working) method of opening a handle as fd. That is, it has one, but |
77 |
that one isn't exposed to programs, and only used for stdin/out/err. |
78 |
Sigh. |
79 |
|
80 |
OTHER MODULES |
81 |
At the time of this writing, the author of this module was aware of two |
82 |
other file descriptor passing modules on CPAN: File::FDPasser and |
83 |
AnyEvent::FDPasser. |
84 |
|
85 |
The former hasn't seen any release for over a decade, isn't 64 bit clean |
86 |
and it's author didn't respond to my mail with the fix, so doesn't work |
87 |
on many 64 bit machines. It does, however, support a number of |
88 |
pre-standard unices, basically everything of relevance at the time it |
89 |
was written. |
90 |
|
91 |
The latter seems to have similar support for antique unices, and doesn't |
92 |
seem to suffer from 64 bit bugs, but inexplicably has a large perl part, |
93 |
doesn't support mixing data and file descriptors, and requires AnyEvent. |
94 |
Presumably that makes it much more user friendly than this module |
95 |
(skimming the manpage shows that a lot of thought has gone into it, and |
96 |
you are well advised to read it and maybe use it before trying a |
97 |
low-level module such as this one). In fact, the manpage discusses even |
98 |
more file descriptor passing modules on CPAN. |
99 |
|
100 |
Neither seems to support native win32 perls. |
101 |
|
102 |
AUTHOR |
103 |
Marc Lehmann <schmorp@schmorp.de> |
104 |
http://home.schmorp.de/ |
105 |
|