/ 
MultiValuedHash-1.0703
/ CGI::MultiValuedHash

NAME

CGI::MultiValuedHash - Store and manipulate url-encoded data.

DEPENDENCIES

Perl Version

5.004

Standard Modules

I<none>

Nonstandard Modules

Data::MultiValuedHash 1.06 (parent class)

SYNOPSIS

use CGI::MultiValuedHash;

my $case_insensitive = 1;
my $complementry_set = 1;

my $params = CGI::MultiValuedHash->new( $case_insensitive, 
	$ENV{'HTTP_COOKIE'} || $ENV{'COOKIE'}, '; ', '&' );

my $form_data;
read( STDIN, $form_data, $ENV{'CONTENT_LENGTH'} );
chomp( $form_data );
$params->from_url_encoded_string( $form_data );
$params->trim_bounding_whitespace();  # clean up user input

foreach my $key ($params->keys()) {
	my @values = $params->fetch( $key );
	print "Field '$key' contains: '".join( "','", @values )."'\n";
}

my @record_list = ();

open( FH, "+<guestbook.txt" ) or die "can't open file: $!\n";
flock( FH, 2 );
seek( FH, 0, 2 );
$params->to_file( \*FH );
seek( FH, 0, 0 );
@record_list = 
	@{CGI::MultiValuedHash->batch_from_file( \*FH, $case_insensitive )};
flock( FH, 8 );
close( FH );
	
foreach my $record (@record_list) {
	print "\nSubmitted by:".$record->fetch_value( 'name' )."\n";
	print "\nTracking cookie:".$record->fetch_value( 'track' )."\n";
	my %Qs_and_As = $record->fetch_all( ['name', 'track'], $complementary_set );
	foreach my $key (keys %Qs_and_As) {
		my @values = @{$Qs_and_As{$key}};
		print "Question: '$key'\n";
		print "Answers: '".join( "','", @values )."'\n";
	}
}

DESCRIPTION

This Perl 5 object class extends the functionality of Data::MultiValuedHash with new methods that are especially useful in a CGI environment. Please read the POD for the latter to see what the preexisting features are. New functionality includes importing and exporting of url-encoded data. This process is customizable and can handle such formats as http query or cookie strings, or newline-delimited text files. Similarly, this class can import from or export to a file stream. Other new features include exporting to html-encoded hidden form fields, for the purpose of having persistant form data that is too large for a query string. New manipulation features include trimming of whitespace from values so that when users type only enter such the field reads as empty. Useful inherited features include optional case-insensitive keys and the ability to export subsets of data when only some is needed (separate "other" form fields from special ones that you previously used).

SYNTAX

This class does not export any functions or methods, so you need to call them using object notation. This means using Class->function() for functions and $object->method() for methods. If you are inheriting this class for your own modules, then that often means something like $self->method().

This class is a subclass of Data::MultiValuedHash and inherits all of the latter's functionality and behaviour. Please read the POD for the latter to see how to use the preexisting methods.

FUNCTIONS AND METHODS

initialize([ CASE[, SOURCE[, *]] ])

The above method in Data::MultiValuedHash has hooks which allow subclasses to add more data types to be used for SOURCE; the hook is called if SOURCE is not a Hash ref (normal or of arrays) or an MVH object, which are already handled. This class adds the ability to use filehandles and url-encoded strings as SOURCE. If SOURCE is a valid file handle then from_file( SOURCE, * ) is used. Otherwise, the method from_url_encoded_string( SOURCE, * ) is used.

to_url_encoded_string([ DELIM[, VALSEP] ])

This method returns a scalar containing all of this object's keys and values encoded in an url-escaped "query string" format. The escaping format specifies that any characters which aren't in [a-zA-Z0-9_ .-] are replaced with a triplet containing a "%" followed by the two-hex-digit representation of the ascii value for the character. Also, any " " (space) is replaced with a "+". Each key and value pair is delimited by a "=". If a key has multiple values, then there are that many "key=value" pairs. The optional argument, DELIM, is a scalar specifying what to use as a delimiter between pairs. This is "&" by default. If a "\n" is given for DELIM, the resulting string would be suitable for writing to a file where each key=value pair is on a separate line. The second optional argument, VALSEP, is a scalar that specifies the delimiter between multiple consecutive values which share a common key, and that key only appears once. For example, SOURCE could be "key1=val1&val2; key2=val3&val4", as is the case with "cookie" strings (DELIM is "; " and VALSEP is "&") or "isindex" queries.

from_url_encoded_string( SOURCE[, DELIM[, VALSEP]] )

This method takes a scalar, SOURCE, containing a set of keys and values encoded in an url-escaped "query string" format, and adds them to this object. The escaping format specifies that any characters which aren't in [a-zA-Z0-9_ .-] are replaced with a triplet containing a "%" followed by the two-hex-digit representation of the ascii value for the character. Also, any " " (space) is replaced with a "+". Each key and value pair is delimited by a "=". If a key has multiple values, then there are that many "key=value" pairs. The first optional argument, DELIM, is a scalar specifying what to use as a delimiter between pairs. This is "&" by default. If a "\n" is given for DELIM, the source string was likely read from a file where each key=value pair is on a separate line. The second optional argument, VALSEP, is a scalar that specifies the delimiter between multiple consecutive values which share a common key, and that key only appears once. For example, SOURCE could be "key1=val1&val2; key2=val3&val4", as is the case with "cookie" strings (DELIM is "; " and VALSEP is "&") or "isindex" queries.

to_file( FH[, DELIM[, VALSEP[, REC_DELIM[, EMPTY]]]]] )

This method encodes all of this object's keys and values using the to_url_encoded_string( DELIM, VALSEP ) method and writes it to the filehandle provided in FH. The optional argument REC_DELIM is a scalar value that will be written to FH before this encoded object, and serves to delimit multiple encoded objects of this class. The default values for [DELIM, VALSEP, REC_DELIM] are ["\n", undef, "\n=\n"]. If the boolean argument EMPTY is true then this object will be written to FH even if it is empty (has no keys), resulting in only a REC_DELIM actually being written. The default behaviour of false prevents this from happening, so only objects containing data are output. This method returns 1 on a successful write, 0 for an empty record that was skipped, and it returns undef on a file-system error.

from_file( FH[, DELIM[, VALSEP[, REC_DELIM[, EMPTY]]]]] )

This method adds keys and values to this object from an encoded record read from the filehandle provided in FH and parsed with from_url_encoded_string( ., DELIM, VALSEP ). The optional argument REC_DELIM is a scalar value that delimits encoded records in the file stream. The default values for [DELIM, VALSEP, REC_DELIM] are ["\n", undef, "\n=\n"]. If the boolean argument EMPTY is true then this object will be initialized to empty (has no keys) if the record delimiter is encountered in the file stream before any valid encoded record. The default behaviour of false prevents this from happening, so the file stream continues to be read until a valid record is found. This method returns 1 on a successful read, 0 for an empty record that was kept (may be end-of-file), and it returns undef on a file-system error.

to_html_encoded_table([ LINEBREAK ])

This method returns a scalar containing table html with all of this object's keys and values. The table has two columns, with keys on the left and values on the right, and each row is one key and its values. By default, the values appear comma-delimited, but if the optional boolean argument LINEBREAK is true, then the value list is delimited with <BR> tags instead, putting each value on its own line. All keys and values are html-escaped such that any occurances of [&,",<,>] are substitued with [&amp;,&quot;,&gt;,&lt;].

to_html_encoded_hidden_fields()

This method returns a scalar containing html text which defines a list of hidden form fields whose names and values are all of this object's keys and values. Each list element looks like '<INPUT TYPE="hidden" NAME="key" VALUE="value">'. Where a key has multiple values, a hidden field is made for each value. All keys and values are html-escaped such that any occurances of [&,",<,>] are substitued with [&amp;,&quot;,&gt;,&lt;]. In cases where this object was storing user input that was submitted using 'post', this method can generate the content of a self-referencing form, should the main program need to call itself. It would handle persistant data which is too big to put in a self-referencing query string.

trim_bounding_whitespace()

This method cleans up all of this object's values by trimming any leading or trailing whitespace. The keys are left alone. This would normally be done when the object is representing user input from a form, including when they entered nothing but whitespace, and the program should act like they left the field empty.

batch_to_file( FH, LIST[, DELIM[, VALSEP[, REC_DELIM[, EMPTY]]]]] )

This batch function writes encoded MVH objects to the filehandle provided in the first argument, FH. The second argument, LIST, is an array ref containing the MVH objects or hash refs to be written. Symantecs are similar to calling to_file( FH, * ) once on each MVH object; any remaining arguments are passed on as is to to_file(). If any array elements aren't MVHs or HASH refs, they are disregarded. This method returns 1 on success, even if there are no objects to write. It returns undef on a file-system error, even if some of the objects were written first.

batch_from_file( FH, CASE[, MAX[, DELIM[, VALSEP[, REC_DELIM[, EMPTY]]]]] )

This batch function reads encoded MVH objects from the filehandle provided in the first argument, FH, and returns them in a list. The second argument, CASE, specifies whether the new MVH objects are case-insensitive or not. The third optional argument, MAX, specifies the maximum number of objects to read. If that argument is undefined or less than 1, then all objects are read until the end-of-file is reached. Symantecs are similar to calling from_file( FH, * ) once on each MVH object; any remaining arguments are passed on as is to from_file(). This method returns an ARRAY ref containing the new records (as MVHs) on success, even if the end-of-file is reached before we find any records. It returns undef on a file-system error, even if some records were read first.

THE DEFAULT URL-ENCODED FORMAT

When the to_url_encoded_string() and from_url_encoded_string() methods and their derivatives are used with the fewest number of arguments, they default to an encoding format used in query strings, such as $ENV{QUERY_STRING}. Normal query strings look like this:

name=name&type=textfield&visible_title=What%27s+your+name%3f

Here's another example with a multi-valued field (it is actually a single line, but appears on two here for clarity:

name=color&type=popup_menu&values=red&values=green&values=blue&
values=chartreuse&visible_title=What%27s+your+favorite+colour%3f

Some query strings are the result of ISINDEX queries, and they look different:

tell&me&about&stuff

Cookie strings such as $ENV{HTTP_COOKIE} are different yet and look like:

name=color; type=popup_menu; values=red&green&blue&chartreuse

In the argument lists for the above methods, DELIM refers to the "&" in normal query strings and the "; " in cookies, whereas VALSEP is meaningless with normal query strings and is the "&" in "isindex" queries and cookie strings.

THE DEFAULT FILE FORMAT

When the to_file() and from_file() methods and their derivatives are used with the fewest number of arguments, they default to an encoding format that is quite easy for humans to read. This common format is capable of storing an ordered list of variable-length records where the fields of each record are stored in name=value pairs, one field value per line.

Each record can have different fields from the others, and each field can have either one or several values. In the latter case, the field name is repeated for each value. Records are delimited by lines that contain only a "=" and are otherwise empty. The order of individual fields in the file doesn't matter, but the order of parts of multivalued fields does; this order is preserved.

All field names and values are url-escaped, so we are capable of storing binary data without corrupting it.

The following example shows 4 MVH objects encoded in the default format:

=
name=name
type=textfield
visible_title=What%27s+your+name%3f
=
default=eenie
default=minie
name=words
type=checkbox_group
values=eenie
values=meenie
values=minie
values=moe
visible_title=What%27s+the+combination%3f
=
name=color
type=popup_menu
values=red
values=green
values=blue
values=chartreuse
visible_title=What%27s+your+favorite+colour%3f
=
type=submit

This file format is identical to that used by CGI.pm when saving its state, so such files could be used and manipulated by either that class or this one as you see fit. Furthermore, this format is identical to that used by the Whitehead Genome Center's data exchange format, and can be manipulated and even databased using Boulderio utilities. (That may not be url-escaped, however.) See "http://www.genome.wi.mit.edu/genome_software/other/boulder.html" for further details. However, this compatability does not extend to all of Boulderio's features, so Boulderio can store more complex data structures than this class.

SOME DEVELOPMENT HISTORY

The file default format in question became known to me during a programming exercise where I was given an example file containing usernames and passwords and had to parse it. I was informed at the time that this file format was common.

This functionality was created for my own use, as I stored html form descriptions and user input from my CGI scripts in the file format. Through independent development, my module gained the ability to store binary data safely through url-encoding (preserving white-space formatting among other benefits), and could store everything from multi-valued fields.

AUTHOR

Copyright (c) 1999-2001, Darren R. Duncan. All rights reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. However, I do request that this copyright information remain attached to the file. If you modify this module and redistribute a changed version then please attach a note listing the modifications.

I am always interested in knowing how my work helps others, so if you put this module to use in any of your own code then please send me the URL. Also, if you make modifications to the module because it doesn't work the way you need, please send me a copy so that I can roll desirable changes into the main release.

Address comments, suggestions, and bug reports to perl@DarrenDuncan.net.

CREDITS

Thanks to Johan Vromans <jvromans@squirrel.nl> for suggesting the split of my old module "CGI::HashOfArrays" into the two current ones, "Data::MultiValuedHash" and "CGI::MultiValuedHash". This took care of a longstanding logistical problem concerning whether the module was a generic data structure or a tool for encoding/decoding CGI data.

Thanks to Steve Benson <steve.benson@stanford.edu> for suggesting POD improvements in regards to the case-insensitivity feature, so the documentation is easier to understand.

Thanks to Geir Johannessen <geir.johannessen@nextra.com> for alerting me to several "ambiguous call" warnings.

Thanks to Jonathan Snyder <jonathan@mail.method.com> for alerting me to the fact that my file format comparison with Boulderio was difficult to understand.

SEE ALSO

perl(1), Data::MultiValuedHash, HTML::FormTemplate, CGI::Portable.