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=head1 NAME |
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|
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IO::FDPass - pass a file descriptor over a socket |
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|
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=head1 SYNOPSIS |
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|
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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: $!"; |
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|
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=head1 DESCRIPTION |
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|
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This small low-level module only has one purpose: pass a file descriptor |
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to another process, using a (streaming) unix domain socket (on POSIX |
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systems) or any (streaming) socket (on WIN32 systems). The ability to pass |
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file descriptors on windows is currently the unique selling point of this |
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module. Have I mentioned that it is really small, too? |
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|
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=head1 FUNCTIONS |
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|
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=over 4 |
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|
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=cut |
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|
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package IO::FDPass; |
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|
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BEGIN { |
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$VERSION = 1.3; |
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|
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require XSLoader; |
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XSLoader::load (__PACKAGE__, $VERSION); |
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} |
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|
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=item $bool = IO::FDPass::send $socket_fd, $fd_to_pass |
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|
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Sends the file descriptor given by C<$fd_to_pass> over the socket |
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C<$socket_fd>. Return true if it worked, false otherwise. |
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|
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Note that I<both> parameters must be file descriptors, not handles. |
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|
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When used on non-blocking sockets, this function might fail with C<$!> |
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set to C<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 (e.g. via |
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C<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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=item $fd = IO::FDPass::recv $socket_fd |
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|
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Receive a file descriptor from the socket and return it if successful. On |
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errors, return C<-1>. |
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|
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Note that I<both> C<$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 C<$!> set |
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to C<EAGAIN> or equivalent, in which case you are free to try again. It |
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should succeed if called on a socket that indicates readability (e.g. via |
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C<select>). |
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|
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Example: receive a file descriptor from a blocking socket and convert it |
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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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=back |
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|
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=head1 PORTABILITY NOTES |
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|
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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 and |
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5.0, DragonFly BSD, FreeBSD 7, 8 and 9, Windows 7 + ActivePerl 5.16.3 32 |
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and 64 bit and Strawberry Perl 5.16.3 32 and 64 bit, and found to work, |
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although ActivePerl 32 bit needed a newer MinGW version (that supports XP |
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and higher). |
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|
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However, windows doesn't support asynchronous file descriptor passing, so |
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the source process must still be around when the destination process wants |
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to receive the file handle. Also, if the target process fails to fetch the |
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handle for any reason (crashes, fails to call C<recv> etc.), the handle |
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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 no |
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(working) method of opening a handle as fd. That is, it has one, but that |
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one isn't exposed to programs, and only used for stdin/out/err. Sigh. |
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|
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=head1 OTHER MODULES |
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|
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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: L<File::FDPasser> and |
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L<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 on |
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many 64 bit machines. It does, however, support a number of pre-standard |
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unices, basically everything of relevance at the time it 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 |
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part, doesn't support mixing data and file descriptors, and requires |
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AnyEvent. Presumably that makes it much more user friendly than this |
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module (skimming the manpage shows that a lot of thought has gone into |
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it, and 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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=head1 AUTHOR |
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|
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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|
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=cut |
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|
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1 |
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