1FDPass(3) User Contributed Perl Documentation FDPass(3)
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6 IO::FDPass - pass a file descriptor over a socket
7
9 use IO::FDPass;
10 IO::FDPass::send fileno $socket, fileno $fh_to_pass
12 or die "send failed: $!";
13 my $fd = IO::FDPass::recv fileno $socket;
15 $fd >= 0 or die "recv failed: $!";
16
18 This small low-level module only has one purpose: pass a file
19 descriptor to another process, using a (streaming) unix domain socket
20 (on POSIX systems) or any (streaming) socket (on WIN32 systems). The
21 ability to pass file descriptors on windows is currently the unique
22 selling point of this module. Have I mentioned that it is really small,
23 too?
24
26 $bool = IO::FDPass::send $socket_fd, $fd_to_pass
27 Sends the file descriptor given by $fd_to_pass over the socket
28 $socket_fd. Return true if it worked, false otherwise.
29 Note that both parameters must be file descriptors, not handles.
31 When used on non-blocking sockets, this function might fail with $!
33 set to "EAGAIN" or equivalent, in which case you are free to try.
34 It should succeed if called on a socket that indicates writability
35 (e.g. via "select").
36 Example: pass a file handle over an open socket.
38 IO::FDPass::send fileno $socket, fileno $fh
40 or die "unable to pass file handle: $!";
41 $fd = IO::FDPass::recv $socket_fd
43 Receive a file descriptor from the socket and return it if
44 successful. On errors, return "-1".
45 Note that both $socket_fd and the returned file descriptor are, in
47 fact, file descriptors, not handles.
48 When used on non-blocking sockets, this function might fail with $!
50 set to "EAGAIN" or equivalent, in which case you are free to try
51 again. It should succeed if called on a socket that indicates
52 readability (e.g. via "select").
53 Example: receive a file descriptor from a blocking socket and
55 convert it to a file handle.
56 my $fd = IO::FDPass::recv fileno $socket;
58 $fd >= 0 or die "unable to receive file handle: $!";
59 open my $fh, "+<&=$fd"
60 or die "unable to convert file descriptor to handle: $!";
61
63 This module has been tested on GNU/Linux x86 and amd64, NetBSD 6, OS X
64 10.5, Windows 2000 ActivePerl 5.10, Solaris 10, OpenBSD 4.4, 4.5, 4.8
65 and 5.0, DragonFly BSD, FreeBSD 7, 8 and 9, Windows 7 + ActivePerl
66 5.16.3 32 and 64 bit and Strawberry Perl 5.16.3 32 and 64 bit, and
67 found to work, although ActivePerl 32 bit needed a newer MinGW version
68 (that supports XP and higher).
69 However, windows doesn't support asynchronous file descriptor passing,
71 so the source process must still be around when the destination process
72 wants to receive the file handle. Also, if the target process fails to
73 fetch the handle for any reason (crashes, fails to call "recv" etc.),
74 the handle will leak, so never do that.
75 Also, on windows, the receiving process must have the
77 PROCESS_DUP_HANDLE access right on the sender process for this module
78 to work.
79 Cygwin is not supported at the moment, as file descriptor passing in
81 cygwin is not supported, and cannot be rolled on your own as cygwin has
82 no (working) method of opening a handle as fd. That is, it has one, but
83 that one isn't exposed to programs, and only used for stdin/out/err.
84 Sigh.
85
87 At the time of this writing, the author of this module was aware of two
88 other file descriptor passing modules on CPAN: File::FDPasser and
89 AnyEvent::FDPasser.
90 The former hasn't seen any release for over a decade, isn't 64 bit
92 clean and it's author didn't respond to my mail with the fix, so
93 doesn't work on many 64 bit machines. It does, however, support a
94 number of pre-standard unices, basically everything of relevance at the
95 time it was written.
96 The latter seems to have similar support for antique unices, and
98 doesn't seem to suffer from 64 bit bugs, but inexplicably has a large
99 perl part, doesn't support mixing data and file descriptors, and
100 requires AnyEvent. Presumably that makes it much more user friendly
101 than this module (skimming the manpage shows that a lot of thought has
102 gone into it, and you are well advised to read it and maybe use it
103 before trying a low-level module such as this one). In fact, the
104 manpage discusses even more file descriptor passing modules on CPAN.
105 Neither seems to support native win32 perls.
107
109 Marc Lehmann <schmorp@schmorp.de>
110 http://home.schmorp.de/
111perl v5.34.0 2021-07-22 FDPass(3)