Raw content of Error # Error.pm # # Copyright (c) 1997-8 Graham Barr <gbarr@ti.com>. All rights reserved. # This program is free software; you can redistribute it and/or # modify it under the same terms as Perl itself. # # Based on my original Error.pm, and Exceptions.pm by Peter Seibel # <peter@weblogic.com> and adapted by Jesse Glick <jglick@sig.bsh.com>. # # but modified ***significantly*** package Error; use strict; use vars qw($VERSION); use 5.004; $VERSION = "0.13"; # $Id: Error.pm,v 1.1 2002/08/27 18:17:15 bosborne Exp $ use overload ( '""' => 'stringify', '0+' => 'value', 'fallback' => 1 ); $Error::Depth = 0; # Depth to pass to caller() $Error::Debug = 0; # Generate verbose stack traces @Error::STACK = (); # Clause stack for try $Error::THROWN = undef; # last error thrown, a workaround until die $ref works my $LAST; # Last error created my %ERROR; # Last error associated with package # Exported subs are defined in Error::subs sub import { shift; local $Exporter::ExportLevel = $Exporter::ExportLevel + 1; Error::subs->import(@_); } # I really want to use last for the name of this method, but it is a keyword # which prevent the syntax last Error sub prior { shift; # ignore return $LAST unless @_; my $pkg = shift; return exists $ERROR{$pkg} ? $ERROR{$pkg} : undef unless ref($pkg); my $obj = $pkg; my $err = undef; if($obj->isa('HASH')) { $err = $obj->{'__Error__'} if exists $obj->{'__Error__'}; } elsif($obj->isa('GLOB')) { $err = ${*$obj}{'__Error__'} if exists ${*$obj}{'__Error__'}; } $err; } # Return as much information as possible about where the error # happened. The -stacktrace element only exists if $Error::DEBUG # was set when the error was created sub stacktrace { my $self = shift; return $self->{'-stacktrace'} if exists $self->{'-stacktrace'}; my $text = exists $self->{'-text'} ? $self->{'-text'} : "Died"; $text .= sprintf(" at %s line %d.\n", $self->file, $self->line) unless($text =~ /\n$/s); $text; } # Allow error propagation, ie # # $ber->encode(...) or # return Error->prior($ber)->associate($ldap); sub associate { my $err = shift; my $obj = shift; return unless ref($obj); if($obj->isa('HASH')) { $obj->{'__Error__'} = $err; } elsif($obj->isa('GLOB')) { ${*$obj}{'__Error__'} = $err; } $obj = ref($obj); $ERROR{ ref($obj) } = $err; return; } sub new { my $self = shift; my($pkg,$file,$line) = caller($Error::Depth); my $err = bless { '-package' => $pkg, '-file' => $file, '-line' => $line, @_ }, $self; $err->associate($err->{'-object'}) if(exists $err->{'-object'}); # To always create a stacktrace would be very inefficient, so # we only do it if $Error::Debug is set if($Error::Debug) { require Carp; local $Carp::CarpLevel = $Error::Depth; my $text = defined($err->{'-text'}) ? $err->{'-text'} : "Error"; my $trace = Carp::longmess($text); # Remove try calls from the trace $trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog; $err->{'-stacktrace'} = $trace } $@ = $LAST = $ERROR{$pkg} = $err; } # Throw an error. this contains some very gory code. sub throw { my $self = shift; local $Error::Depth = $Error::Depth + 1; # if we are not rethrow-ing then create the object to throw $self = $self->new(@_) unless ref($self); die $Error::THROWN = $self; } # syntactic sugar for # # die with Error( ... ); sub with { my $self = shift; local $Error::Depth = $Error::Depth + 1; $self->new(@_); } # syntactic sugar for # # record Error( ... ) and return; sub record { my $self = shift; local $Error::Depth = $Error::Depth + 1; $self->new(@_); } # catch clause for # # try { ... } catch CLASS with { ... } sub catch { my $pkg = shift; my $code = shift; my $clauses = shift || {}; my $catch = $clauses->{'catch'} ||= []; unshift @$catch, $pkg, $code; $clauses; } # Object query methods sub object { my $self = shift; exists $self->{'-object'} ? $self->{'-object'} : undef; } sub file { my $self = shift; exists $self->{'-file'} ? $self->{'-file'} : undef; } sub line { my $self = shift; exists $self->{'-line'} ? $self->{'-line'} : undef; } sub text { my $self = shift; exists $self->{'-text'} ? $self->{'-text'} : undef; } # overload methods sub stringify { my $self = shift; defined $self->{'-text'} ? $self->{'-text'} : "Died"; } sub value { my $self = shift; exists $self->{'-value'} ? $self->{'-value'} : undef; } package Error::Simple; @Error::Simple::ISA = qw(Error); sub new { my $self = shift; my $text = "" . shift; my $value = shift; my(@args) = (); local $Error::Depth = $Error::Depth + 1; @args = ( -file => $1, -line => $2) if($text =~ s/ at (\S+) line (\d+)(\.\n)?$//s); push(@args, '-value', 0 + $value) if defined($value); $self->SUPER::new(-text => $text, @args); } sub stringify { my $self = shift; my $text = $self->SUPER::stringify; $text .= sprintf(" at %s line %d.\n", $self->file, $self->line) unless($text =~ /\n$/s); $text; } ########################################################################## ########################################################################## # Inspired by code from Jesse Glick <jglick@sig.bsh.com> and # Peter Seibel <peter@weblogic.com> package Error::subs; use Exporter (); use vars qw(@EXPORT_OK @ISA %EXPORT_TAGS); @EXPORT_OK = qw(try with finally except otherwise); %EXPORT_TAGS = (try => \@EXPORT_OK); @ISA = qw(Exporter); sub run_clauses ($$$\@) { my($clauses,$err,$wantarray,$result) = @_; my $code = undef; $err = new Error::Simple($err) unless ref($err); CATCH: { # catch my $catch; if(defined($catch = $clauses->{'catch'})) { my $i = 0; CATCHLOOP: for( ; $i < @$catch ; $i += 2) { my $pkg = $catch->[$i]; unless(defined $pkg) { #except splice(@$catch,$i,2,$catch->[$i+1]->()); $i -= 2; next CATCH; } elsif($err->isa($pkg)) { $code = $catch->[$i+1]; while(1) { my $more = 0; local($Error::THROWN); my $ok = eval { if($wantarray) { @{$result} = $code->($err,\$more); } elsif(defined($wantarray)) { @{$result} = (); $result->[0] = $code->($err,\$more); } else { $code->($err,\$more); } 1; }; if( $ok ) { next CATCHLOOP if $more; undef $err; } else { $err = defined($Error::THROWN) ? $Error::THROWN : $@; $err = new Error::Simple($err) unless ref($err); } last CATCH; }; } } } # otherwise my $owise; if(defined($owise = $clauses->{'otherwise'})) { my $code = $clauses->{'otherwise'}; my $more = 0; my $ok = eval { if($wantarray) { @{$result} = $code->($err,\$more); } elsif(defined($wantarray)) { @{$result} = (); $result->[0] = $code->($err,\$more); } else { $code->($err,\$more); } 1; }; if( $ok ) { undef $err; } else { $err = defined($Error::THROWN) ? $Error::THROWN : $@; $err = new Error::Simple($err) unless ref($err); } } } $err; } sub try (&;$) { my $try = shift; my $clauses = @_ ? shift : {}; my $ok = 0; my $err = undef; my @result = (); unshift @Error::STACK, $clauses; do { local $Error::THROWN = undef; $ok = eval { if(wantarray) { @result = $try->(); } elsif(defined wantarray) { $result[0] = $try->(); } else { $try->(); } 1; }; $err = defined($Error::THROWN) ? $Error::THROWN : $@ unless $ok; }; shift @Error::STACK; $err = run_clauses($clauses,$err,wantarray,@result) unless($ok); $clauses->{'finally'}->() if(defined($clauses->{'finally'})); throw $err if defined($err); wantarray ? @result : $result[0]; } # Each clause adds a sub to the list of clauses. The finally clause is # always the last, and the otherwise clause is always added just before # the finally clause. # # All clauses, except the finally clause, add a sub which takes one argument # this argument will be the error being thrown. The sub will return a code ref # if that clause can handle that error, otherwise undef is returned. # # The otherwise clause adds a sub which unconditionally returns the users # code reference, this is why it is forced to be last. # # The catch clause is defined in Error.pm, as the syntax causes it to # be called as a method sub with (&;$) { @_ } sub finally (&) { my $code = shift; my $clauses = { 'finally' => $code }; $clauses; } # The except clause is a block which returns a hashref or a list of # key-value pairs, where the keys are the classes and the values are subs. sub except (&;$) { my $code = shift; my $clauses = shift || {}; my $catch = $clauses->{'catch'} ||= []; my $sub = sub { my $ref; my(@array) = $code->($_[0]); if(@array == 1 && ref($array[0])) { $ref = $array[0]; $ref = [ %$ref ] if(UNIVERSAL::isa($ref,'HASH')); } else { $ref = \@array; } @$ref }; unshift @{$catch}, undef, $code; $clauses; } sub otherwise (&;$) { my $code = shift; my $clauses = shift || {}; if(exists $clauses->{'otherwise'}) { require Carp; Carp::croak("Multiple otherwise clauses"); } $clauses->{'otherwise'} = $code; $clauses; } 1; __END__ =head1 NAME Error - Error/exception handling in an OO-ish way =head1 SYNOPSIS use Error qw(:try); throw Error::Simple( "A simple error"); sub xyz { ... record Error::Simple("A simple error") and return; } unlink($file) or throw Error::Simple("$file: $!",$!); try { do_some_stuff(); die "error!" if $condition; throw Error::Simple -text => "Oops!" if $other_condition; } catch Error::IO with { my $E = shift; print STDERR "File ", $E->{'-file'}, " had a problem\n"; } except { my $E = shift; my $general_handler=sub {send_message $E->{-description}}; return { UserException1 => $general_handler, UserException2 => $general_handler }; } otherwise { print STDERR "Well I don't know what to say\n"; } finally { close_the_garage_door_already(); # Should be reliable }; # Don't forget the trailing ; or you might be surprised =head1 DESCRIPTION The C<Error> package provides two interfaces. Firstly C<Error> provides a procedural interface to exception handling. Secondly C<Error> is a base class for errors/exceptions that can either be thrown, for subsequent catch, or can simply be recorded. Errors in the class C<Error> should not be thrown directly, but the user should throw errors from a sub-class of C<Error>. =head1 PROCEDURAL INTERFACE C<Error> exports subroutines to perform exception handling. These will be exported if the C<:try> tag is used in the C<use> line. =over 4 =item try BLOCK CLAUSES C<try> is the main subroutine called by the user. All other subroutines exported are clauses to the try subroutine. The BLOCK will be evaluated and, if no error is throw, try will return the result of the block. C<CLAUSES> are the subroutines below, which describe what to do in the event of an error being thrown within BLOCK. =item catch CLASS with BLOCK This clauses will cause all errors that satisfy C<$err-E<gt>isa(CLASS)> to be caught and handled by evaluating C<BLOCK>. C<BLOCK> will be passed two arguments. The first will be the error being thrown. The second is a reference to a scalar variable. If this variable is set by the catch block then, on return from the catch block, try will continue processing as if the catch block was never found. To propagate the error the catch block may call C<$err-E<gt>throw> If the scalar reference by the second argument is not set, and the error is not thrown. Then the current try block will return with the result from the catch block. =item except BLOCK When C<try> is looking for a handler, if an except clause is found C<BLOCK> is evaluated. The return value from this block should be a HASHREF or a list of key-value pairs, where the keys are class names and the values are CODE references for the handler of errors of that type. =item otherwise BLOCK Catch any error by executing the code in C<BLOCK> When evaluated C<BLOCK> will be passed one argument, which will be the error being processed. Only one otherwise block may be specified per try block =item finally BLOCK Execute the code in C<BLOCK> either after the code in the try block has successfully completed, or if the try block throws an error then C<BLOCK> will be executed after the handler has completed. If the handler throws an error then the error will be caught, the finally block will be executed and the error will be re-thrown. Only one finally block may be specified per try block =back =head1 CLASS INTERFACE =head2 CONSTRUCTORS The C<Error> object is implemented as a HASH. This HASH is initialized with the arguments that are passed to it's constructor. The elements that are used by, or are retrievable by the C<Error> class are listed below, other classes may add to these. -file -line -text -value -object If C<-file> or C<-line> are not specified in the constructor arguments then these will be initialized with the file name and line number where the constructor was called from. If the error is associated with an object then the object should be passed as the C<-object> argument. This will allow the C<Error> package to associate the error with the object. The C<Error> package remembers the last error created, and also the last error associated with a package. This could either be the last error created by a sub in that package, or the last error which passed an object blessed into that package as the C<-object> argument. =over 4 =item throw ( [ ARGS ] ) Create a new C<Error> object and throw an error, which will be caught by a surrounding C<try> block, if there is one. Otherwise it will cause the program to exit. C<throw> may also be called on an existing error to re-throw it. =item with ( [ ARGS ] ) Create a new C<Error> object and returns it. This is defined for syntactic sugar, eg die with Some::Error ( ... ); =item record ( [ ARGS ] ) Create a new C<Error> object and returns it. This is defined for syntactic sugar, eg record Some::Error ( ... ) and return; =back =head2 STATIC METHODS =over 4 =item prior ( [ PACKAGE ] ) Return the last error created, or the last error associated with C<PACKAGE> =back =head2 OBJECT METHODS =over 4 =item stacktrace If the variable C<$Error::Debug> was non-zero when the error was created, then C<stacktrace> returns a string created by calling C<Carp::longmess>. If the variable was zero the C<stacktrace> returns the text of the error appended with the filename and line number of where the error was created, providing the text does not end with a newline. =item object The object this error was associated with =item file The file where the constructor of this error was called from =item line The line where the constructor of this error was called from =item text The text of the error =back =head2 OVERLOAD METHODS =over 4 =item stringify A method that converts the object into a string. This method may simply return the same as the C<text> method, or it may append more information. For example the file name and line number. By default this method returns the C<-text> argument that was passed to the constructor, or the string C<"Died"> if none was given. =item value A method that will return a value that can be associated with the error. For example if an error was created due to the failure of a system call, then this may return the numeric value of C<$!> at the time. By default this method returns the C<-value> argument that was passed to the constructor. =back =head1 PRE-DEFINED ERROR CLASSES =over 4 =item Error::Simple This class can be used to hold simple error strings and values. It's constructor takes two arguments. The first is a text value, the second is a numeric value. These values are what will be returned by the overload methods. If the text value ends with C<at file line 1> as $@ strings do, then this infomation will be used to set the C<-file> and C<-line> arguments of the error object. This class is used internally if an eval'd block die's with an error that is a plain string. =back =head1 KNOWN BUGS None, but that does not mean there are not any. =head1 AUTHORS Graham Barr E<lt>gbarr@pobox.comE<gt> The code that inspired me to write this was originally written by Peter Seibel E<lt>peter@weblogic.comE<gt> and adapted by Jesse Glick E<lt>jglick@sig.bsh.comE<gt>. =cut