Currently if an external command returns error exit code, a generic exception
is thrown and there is no chance for the caller to retrieve the command's
output.
This patch introduces a Git::Error::Command exception class which is thrown
in this case and contains both the error code and the captured command output.
You can use the new git_cmd_try statement to fatally catch the exception
while producing a user-friendly message.
It also adds command_close_pipe() for easier checking of exit status of
a command we have just a pipe handle of. It has partial forward dependency
on the next patch, but basically only in the area of documentation.
Signed-off-by: Petr Baudis <pasky@xxxxxxx>
---
git-fmt-merge-msg.perl | 13 +++
perl/Git.pm | 192 +++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 183 insertions(+), 22 deletions(-)
diff --git a/git-fmt-merge-msg.perl b/git-fmt-merge-msg.perl
index be2a48c..f86231e 100755
--- a/git-fmt-merge-msg.perl
+++ b/git-fmt-merge-msg.perl
@@ -7,6 +7,7 @@ # by grouping branches and tags together
use strict;
use Git;
+use Error qw(:try);
my $repo = Git->repository();
@@ -31,7 +32,17 @@ sub andjoin {
}
sub repoconfig {
- my ($val) = $repo->command_oneline('repo-config', '--get', 'merge.summary');
+ my $val;
+ try {
+ $val = $repo->command_oneline('repo-config', '--get', 'merge.summary');
+ } catch Git::Error::Command with {
+ my ($E) = shift;
+ if ($E->value() == 1) {
+ return undef;
+ } else {
+ throw $E;
+ }
+ };
return $val;
}
diff --git a/perl/Git.pm b/perl/Git.pm
index 733fec9..4205ac5 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -24,16 +24,17 @@ # Totally unstable API.
my $version = Git::command_oneline('version');
- Git::command_noisy('update-server-info');
+ git_cmd_try { Git::command_noisy('update-server-info') }
+ '%s failed w/ code %d';
my $repo = Git->repository (Directory => '/srv/git/cogito.git');
my @revs = $repo->command('rev-list', '--since=last monday', '--all');
- my $fh = $repo->command_pipe('rev-list', '--since=last monday', '--all');
+ my ($fh, $c) = $repo->command_pipe('rev-list', '--since=last monday', '--all');
my $lastrev = <$fh>; chomp $lastrev;
- close $fh; # You may want to test rev-list exit status here
+ $repo->command_close_pipe($fh, $c);
my $lastrev = $repo->command_oneline('rev-list', '--all');
@@ -44,11 +45,11 @@ require Exporter;
@ISA = qw(Exporter);
-@EXPORT = qw();
+@EXPORT = qw(git_cmd_try);
# Methods which can be called as standalone functions as well:
@EXPORT_OK = qw(command command_oneline command_pipe command_noisy
- version exec_path hash_object);
+ version exec_path hash_object git_cmd_try);
=head1 DESCRIPTION
@@ -88,7 +89,7 @@ increate nonwithstanding).
=cut
-use Carp qw(carp); # croak is bad - throw instead
+use Carp qw(carp croak); # but croak is bad - throw instead
use Error qw(:try);
require XSLoader;
@@ -193,21 +194,35 @@ In both cases, the command's stdin and s
=cut
sub command {
- my $fh = command_pipe(@_);
+ my ($fh, $ctx) = command_pipe(@_);
if (not defined wantarray) {
- _cmd_close($fh);
+ # Nothing to pepper the possible exception with.
+ _cmd_close($fh, $ctx);
} elsif (not wantarray) {
local $/;
my $text = <$fh>;
- _cmd_close($fh);
+ try {
+ _cmd_close($fh, $ctx);
+ } catch Git::Error::Command with {
+ # Pepper with the output:
+ my $E = shift;
+ $E->{'-outputref'} = \$text;
+ throw $E;
+ };
return $text;
} else {
my @lines = <$fh>;
- _cmd_close($fh);
chomp @lines;
+ try {
+ _cmd_close($fh, $ctx);
+ } catch Git::Error::Command with {
+ my $E = shift;
+ $E->{'-outputref'} = \@lines;
+ throw $E;
+ };
return @lines;
}
}
@@ -222,12 +237,18 @@ of the command's standard output.
=cut
sub command_oneline {
- my $fh = command_pipe(@_);
+ my ($fh, $ctx) = command_pipe(@_);
my $line = <$fh>;
- _cmd_close($fh);
-
chomp $line;
+ try {
+ _cmd_close($fh, $ctx);
+ } catch Git::Error::Command with {
+ # Pepper with the output:
+ my $E = shift;
+ $E->{'-outputref'} = \$line;
+ throw $E;
+ };
return $line;
}
@@ -251,7 +272,32 @@ sub command_pipe {
} elsif ($pid == 0) {
_cmd_exec($self, $cmd, @args);
}
- return $fh;
+ return wantarray ? ($fh, join(' ', $cmd, @args)) : $fh;
+}
+
+
+=item command_close_pipe ( PIPE [, CTX ] )
+
+Close the C<PIPE> as returned from C<command_pipe()>, checking
+whether the command finished successfuly. The optional C<CTX> argument
+is required if you want to see the command name in the error message,
+and it is the second value returned by C<command_pipe()> when
+called in array context. The call idiom is:
+
+ my ($fh, $ctx) = $r->command_pipe('status');
+ while (<$fh>) { ... }
+ $r->command_close_pipe($fh, $ctx);
+
+Note that you should not rely on whatever actually is in C<CTX>;
+currently it is simply the command name but in future the context might
+have more complicated structure.
+
+=cut
+
+sub command_close_pipe {
+ my ($self, $fh, $ctx) = _maybe_self(@_);
+ $ctx ||= '<unknown>';
+ _cmd_close($fh, $ctx);
}
@@ -280,9 +326,8 @@ sub command_noisy {
} elsif ($pid == 0) {
_cmd_exec($self, $cmd, @args);
}
- if (waitpid($pid, 0) > 0 and $? != 0) {
- # This is the best candidate for a custom exception class.
- throw Error::Simple("exit status: $?");
+ if (waitpid($pid, 0) > 0 and $?>>8 != 0) {
+ throw Git::Error::Command(join(' ', $cmd, @args), $? >> 8);
}
}
@@ -340,12 +385,117 @@ are involved.
# Implemented in Git.xs.
+
=back
=head1 ERROR HANDLING
All functions are supposed to throw Perl exceptions in case of errors.
-See L<Error>.
+See the L<Error> module on how to catch those. Most exceptions are mere
+L<Error::Simple> instances.
+
+However, the C<command()>, C<command_oneline()> and C<command_noisy()>
+functions suite can throw C<Git::Error::Command> exceptions as well: those are
+thrown when the external command returns an error code and contain the error
+code as well as access to the captured command's output. The exception class
+provides the usual C<stringify> and C<value> (command's exit code) methods and
+in addition also a C<cmd_output> method that returns either an array or a
+string with the captured command output (depending on the original function
+call context; C<command_noisy()> returns C<undef>) and $<cmdline> which
+returns the command and its arguments (but without proper quoting).
+
+Note that the C<command_pipe()> function cannot throw this exception since
+it has no idea whether the command failed or not. You will only find out
+at the time you C<close> the pipe; if you want to have that automated,
+use C<command_close_pipe()>, which can throw the exception.
+
+=cut
+
+{
+ package Git::Error::Command;
+
+ @Git::Error::Command::ISA = qw(Error);
+
+ sub new {
+ my $self = shift;
+ my $cmdline = '' . shift;
+ my $value = 0 + shift;
+ my $outputref = shift;
+ my(@args) = ();
+
+ local $Error::Depth = $Error::Depth + 1;
+
+ push(@args, '-cmdline', $cmdline);
+ push(@args, '-value', $value);
+ push(@args, '-outputref', $outputref);
+
+ $self->SUPER::new(-text => 'command returned error', @args);
+ }
+
+ sub stringify {
+ my $self = shift;
+ my $text = $self->SUPER::stringify;
+ $self->cmdline() . ': ' . $text . ': ' . $self->value() . "\n";
+ }
+
+ sub cmdline {
+ my $self = shift;
+ $self->{'-cmdline'};
+ }
+
+ sub cmd_output {
+ my $self = shift;
+ my $ref = $self->{'-outputref'};
+ defined $ref or undef;
+ if (ref $ref eq 'ARRAY') {
+ return @$ref;
+ } else { # SCALAR
+ return $$ref;
+ }
+ }
+}
+
+=over 4
+
+=item git_cmd_try { CODE } ERRMSG
+
+This magical statement will automatically catch any C<Git::Error::Command>
+exceptions thrown by C<CODE> and make your program die with C<ERRMSG>
+on its lips; the message will have %s substituted for the command line
+and %d for the exit status. This statement is useful mostly for producing
+more user-friendly error messages.
+
+In case of no exception caught the statement returns C<CODE>'s return value.
+
+Note that this is the only auto-exported function.
+
+=cut
+
+sub git_cmd_try(&$) {
+ my ($code, $errmsg) = @_;
+ my @result;
+ my $err;
+ my $array = wantarray;
+ try {
+ if ($array) {
+ @result = &$code;
+ } else {
+ $result[0] = &$code;
+ }
+ } catch Git::Error::Command with {
+ my $E = shift;
+ $err = $errmsg;
+ $err =~ s/\%s/$E->cmdline()/ge;
+ $err =~ s/\%d/$E->value()/ge;
+ # We can't croak here since Error.pm would mangle
+ # that to Error::Simple.
+ };
+ $err and croak $err;
+ return $array ? @result : $result[0];
+}
+
+
+=back
=head1 COPYRIGHT
@@ -384,14 +534,14 @@ # _execv_git_cmd(), implemented in Git.x
# Close pipe to a subprocess.
sub _cmd_close {
- my ($fh) = @_;
+ my ($fh, $ctx) = @_;
if (not close $fh) {
if ($!) {
# It's just close, no point in fatalities
carp "error closing pipe: $!";
} elsif ($? >> 8) {
- # This is the best candidate for a custom exception class.
- throw Error::Simple("exit status: ".($? >> 8));
+ # The caller should pepper this.
+ throw Git::Error::Command($ctx, $? >> 8);
}
# else we might e.g. closed a live stream; the command
# dying of SIGPIPE would drive us here.
-
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