1NAME
2 IO::FDPass - pass a file descriptor over a socket
3
4SYNOPSIS
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
13DESCRIPTION
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
20FUNCTIONS
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
57PORTABILITY 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
80OTHER 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
102AUTHOR
103 Marc Lehmann <schmorp@schmorp.de>
104 http://home.schmorp.de/
105
106