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NAME |
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IO::FDPass - pass a file descriptor over a socket |
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|
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SYNOPSIS |
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use IO::FDPass; |
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|
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IO::FDPass::send fileno $socket, fileno $fh_to_pass |
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or die "send failed: $!"; |
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|
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my $fd = IO::FDPass::recv fileno $socket; |
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$fd >= 0 or die "recv failed: $!"; |
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|
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DESCRIPTION |
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This small low-level module only has one purpose: pass a file descriptor |
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to another process, using a (streaming) unix domain socket (on POSIX |
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systems) or any (streaming) socket (on WIN32 systems). The ability to |
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pass file descriptors on windows is currently the unique selling point |
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of this module. Have I mentioned that it is really small, too? |
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|
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FUNCTIONS |
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$bool = IO::FDPass::send $socket_fd, $fd_to_pass |
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Sends the file descriptor given by $fd_to_pass over the socket |
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$socket_fd. Return true if it worked, false otherwise. |
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|
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Note that *both* parameters must be file descriptors, not handles. |
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|
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When used on non-blocking sockets, this function might fail with $! |
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set to "EAGAIN" or equivalent, in which case you are free to try. It |
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should succeed if called on a socket that indicates writability |
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(e.g. via "select"). |
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|
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Example: pass a file handle over an open socket. |
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|
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IO::FDPass::send fileno $socket, fileno $fh |
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or die "unable to pass file handle: $!"; |
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|
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$fd = IO::FDPass::recv $socket_fd |
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Receive a file descriptor from the socket and return it if |
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successful. On errors, return -1. |
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|
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Note that *both* $socket_fd and the returned file descriptor are, in |
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fact, file descriptors, not handles. |
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|
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When used on non-blocking sockets, this function might fail with $! |
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set to "EAGAIN" or equivalent, in which case you are free to try |
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again. It should succeed if called on a socket that indicates |
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readability (e.g. via "select"). |
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|
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Example: receive a file descriptor from a blocking socket and |
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convert it to a file handle. |
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|
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my $fd = IO::FDPass::recv fileno $socket; |
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$fd >= 0 or die "unable to receive file handle: $!"; |
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open my $fh, "+<&=$fd" |
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or die "unable to convert file descriptor to handle: $!"; |
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|
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PORTABILITY NOTES |
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This module has been tested on GNU/Linux x86 and amd64, NetBSD 6, OS X |
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10.5, Windows 2000 ActivePerl 5.10, Solaris 10, OpenBSD 4.4, 4.5, 4.8 |
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and 5.0, DragonFly BSD, FreeBSD 7, 8 and 9, Windows 7 + ActivePerl |
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5.16.3 32 and 64 bit and Strawberry Perl 5.16.3 32 and 64 bit, and found |
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to work, although ActivePerl 32 bit needed a newer MinGW version (that |
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supports XP and higher). |
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|
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However, windows doesn't support asynchronous file descriptor passing, |
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so the source process must still be around when the destination process |
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wants to receive the file handle. Also, if the target process fails to |
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fetch the handle for any reason (crashes, fails to call "recv" etc.), |
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the handle will leak, so never do that. |
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|
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Also, on windows, the receiving process must have the PROCESS_DUP_HANDLE |
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access right on the sender process for this module to work. |
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|
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Cygwin is not supported at the moment, as file descriptor passing in |
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cygwin is not supported, and cannot be rolled on your own as cygwin has |
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no (working) method of opening a handle as fd. That is, it has one, but |
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that one isn't exposed to programs, and only used for stdin/out/err. |
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Sigh. |
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|
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OTHER MODULES |
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At the time of this writing, the author of this module was aware of two |
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other file descriptor passing modules on CPAN: File::FDPasser and |
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AnyEvent::FDPasser. |
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|
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The former hasn't seen any release for over a decade, isn't 64 bit clean |
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and it's author didn't respond to my mail with the fix, so doesn't work |
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on many 64 bit machines. It does, however, support a number of |
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pre-standard unices, basically everything of relevance at the time it |
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was written. |
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|
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The latter seems to have similar support for antique unices, and doesn't |
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seem to suffer from 64 bit bugs, but inexplicably has a large perl part, |
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doesn't support mixing data and file descriptors, and requires AnyEvent. |
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Presumably that makes it much more user friendly than this module |
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(skimming the manpage shows that a lot of thought has gone into it, and |
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you are well advised to read it and maybe use it before trying a |
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low-level module such as this one). In fact, the manpage discusses even |
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more file descriptor passing modules on CPAN. |
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|
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Neither seems to support native win32 perls. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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