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contrib/long-running-filter: add long running filter example

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Add a simple pass-thru filter as example implementation for the Git
filter protocol version 2. See Documentation/gitattributes.txt, section
"Filter Protocol" for more info.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Lars Schneider 2016-10-16 16:20:38 -07:00 committed by Junio C Hamano
parent edcc85814c
commit 0f71fa273f
2 changed files with 131 additions and 1 deletions
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4
Documentation/gitattributes.txt
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@ -516,7 +516,9 @@ the command pipe on exit. The filter is expected to detect EOF
and exit gracefully on its own. Git will wait until the filter
process has stopped.
If you develop your own long running filter
A long running filter demo implementation can be found in
`contrib/long-running-filter/example.pl` located in the Git
core repository. If you develop your own long running filter
process then the `GIT_TRACE_PACKET` environment variables can be
very helpful for debugging (see linkgit:git[1]).

128
contrib/long-running-filter/example.pl Executable file
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@ -0,0 +1,128 @@
#!/usr/bin/perl
#
# Example implementation for the Git filter protocol version 2
# See Documentation/gitattributes.txt, section "Filter Protocol"
#
# Please note, this pass-thru filter is a minimal skeleton. No proper
# error handling was implemented.
#
use strict;
use warnings;
my $MAX_PACKET_CONTENT_SIZE = 65516;
sub packet_bin_read {
my $buffer;
my $bytes_read = read STDIN, $buffer, 4;
if ( $bytes_read == 0 ) {
# EOF - Git stopped talking to us!
exit();
}
elsif ( $bytes_read != 4 ) {
die "invalid packet: '$buffer'";
}
my $pkt_size = hex($buffer);
if ( $pkt_size == 0 ) {
return ( 1, "" );
}
elsif ( $pkt_size > 4 ) {
my $content_size = $pkt_size - 4;
$bytes_read = read STDIN, $buffer, $content_size;
if ( $bytes_read != $content_size ) {
die "invalid packet ($content_size bytes expected; $bytes_read bytes read)";
}
return ( 0, $buffer );
}
else {
die "invalid packet size: $pkt_size";
}
}
sub packet_txt_read {
my ( $res, $buf ) = packet_bin_read();
unless ( $buf =~ s/\n$// ) {
die "A non-binary line MUST be terminated by an LF.";
}
return ( $res, $buf );
}
sub packet_bin_write {
my $buf = shift;
print STDOUT sprintf( "%04x", length($buf) + 4 );
print STDOUT $buf;
STDOUT->flush();
}
sub packet_txt_write {
packet_bin_write( $_[0] . "\n" );
}
sub packet_flush {
print STDOUT sprintf( "%04x", 0 );
STDOUT->flush();
}
( packet_txt_read() eq ( 0, "git-filter-client" ) ) || die "bad initialize";
( packet_txt_read() eq ( 0, "version=2" ) ) || die "bad version";
( packet_bin_read() eq ( 1, "" ) ) || die "bad version end";
packet_txt_write("git-filter-server");
packet_txt_write("version=2");
packet_flush();
( packet_txt_read() eq ( 0, "capability=clean" ) ) || die "bad capability";
( packet_txt_read() eq ( 0, "capability=smudge" ) ) || die "bad capability";
( packet_bin_read() eq ( 1, "" ) ) || die "bad capability end";
packet_txt_write("capability=clean");
packet_txt_write("capability=smudge");
packet_flush();
while (1) {
my ($command) = packet_txt_read() =~ /^command=([^=]+)$/;
my ($pathname) = packet_txt_read() =~ /^pathname=([^=]+)$/;
packet_bin_read();
my $input = "";
{
binmode(STDIN);
my $buffer;
my $done = 0;
while ( !$done ) {
( $done, $buffer ) = packet_bin_read();
$input .= $buffer;
}
}
my $output;
if ( $command eq "clean" ) {
### Perform clean here ###
$output = $input;
}
elsif ( $command eq "smudge" ) {
### Perform smudge here ###
$output = $input;
}
else {
die "bad command '$command'";
}
packet_txt_write("status=success");
packet_flush();
while ( length($output) > 0 ) {
my $packet = substr( $output, 0, $MAX_PACKET_CONTENT_SIZE );
packet_bin_write($packet);
if ( length($output) > $MAX_PACKET_CONTENT_SIZE ) {
$output = substr( $output, $MAX_PACKET_CONTENT_SIZE );
}
else {
$output = "";
}
}
packet_flush(); # flush content!
packet_flush(); # empty list, keep "status=success" unchanged!
}