NAME
    Data::URIEncode - Allow complex data structures to be encoded using flat
    URIs.

SYNOPSIS
        use Data::URIEncode qw(flat_to_complex complex_to_flat);

        my $data = {
            foo => {
                bar => 'bing',
            },
            baz => [123],
        };

        my $flat  = complex_to_flat($data);
        my $query = complex_to_query($data);

        # $flat looks like:
        $flat = {
           'foo.bar' => 'bing',
           'baz:0'   => 123,
        };

        # $query looks like:
        $query = "foo.bar=bing&baz:0=123"

        ################################################

        # put data back to how it was
        $data = flat_to_complex($flat);

        $data = query_to_complex($query);

        ################################################

        ### some html form somewhere
        <form>
        <input type="text" name="foo.bar.baz" value="brum">
        <input type="text" name="bing:2" value="blang">
        <input type="text" name="'key with :, ., and \''.red" value="blue">
        </form>

        ### when the form is submitted to the following code
        use CGI;
        use Data::URIEncode qw(query_to_complex);

        my $q = CGI->new;
        my $data = query_to_complex($q);

        ### data will look like
        $data = {
            foo => {
                bar => {
                   baz = "brum",
                },
            },
            bing => [
                undef,
                undef,
                "blang",
            ],
            "key with :, ., and '" => {
                red = "blue",
            },
        };

DESCRIPTION
    The world of the web works off of URI's. The Query string portion of
    URIs already support encoding of key/value paired data - they just don't
    natively allow for for complex data structures.

    There are modules or encodings that do support arbitrarily complex data
    structures. JSON, YAML and Data::Dumper all have their own way of
    encoding complex structures. But then to pass them across the web, you
    usually still have to URL encode them and pass them via a form
    parameter.

    Data::URIEncode allows for encoding and decoding complex (multi level
    datastructures) using native Query String manipulators (such as CGI.pm).
    It takes complex data and turns it into a flat hashref which can then be
    turned into a URI query string using URL encoding. It also takes a flat
    hashref of data passed in and translates it back to a complex structure.

    One benefit of using Data::URIEncode is that a standard submission from
    a standard html form can automatically be translated into complex data
    even though it arrived in a "flat" form. This somewhat mimics the
    abilities of XForms without introducing the complexity of XForms.

    Another benefit is that sparse data can be represented in a more compact
    form than JSON or YAML are able to provide. However, complex data with
    long key names will be more verbose as the full data hierarchy must be
    repeated for each value.

RULES
    For each of the following rules, the $data can be translated to $flat
    and $query by calling complex_to_flat and complex_to_query respectively.
    The $flat and $query can be translated back into $data using
    flat_to_complex and query_to_complex respectively.

    Simple values stay simple
            $data  =   {key => "val", key2 => "val2"};
            $flat  === {key => "val", key2 => "val2"};
            $query eq  "key=val&key2=val2"

    Nested hashes use a dot to modify the key.
            $data  =   {key => {key2 => "val"}};
            $flat  === {"key.key2" => "val"};
            $query eq  "key.key2=val

            ########

            $data  =   {foo => {bar => {baz => "bling"}}};
            $flat  === {"foo.bar.baz" = "bling"};
            $query eq  "foo.bar.baz=bling"

    Nested arrays use a colon to modify the key.
            $data  =   {key => ["val1", "val2"]};
            $flat  === {"key:0" => "val1", "key:1" => "val2"};
            $query eq  "key:0=val1&key:1=val2"

            ########

            $data  =   {key => [ [ ["val"] ] ]};
            $flat  === {"key:0:0" => "val"}
            $query eq  "key:0:0=val"

    Data structures can have an arrayref as the top level
        A leading colon is used to indicate the top level node is an
        arrayref.

            $data  =   ["val1", "val2"]
            $flat  === {":0" => "val1", ":1" => "val2"}
            $query eq  ":0=>val1&:1=>val2"

            ########

            $data  =   [ [ ["val"] ] ];
            $flat  === {":0:0:0" => "val"}
            $query eq  ":0:0:0=val"

    Keys in flat hashrefs MAY begin with a leading dot
        A leading dot may disambiguate some cases.

            $query =   ".foo=bar"
            $flat  =   {".foo" => "bar"}
            $data  === {foo => "bar"}

    Single quotes may be used to enclose complex strings.
        Any key containing a colon ":", a dot ".", or a single quote "'"
        must be quoted with single quotes and have enclosed single quotes
        escaped.

            $data  =   {"foo.bar"   => "baz"}
            $flat  === {"'foo.bar'" => "baz"}
            $query eq  "'foo.bar'=baz"  # the ' will be swapped with %27

            ########

            $data  =   {"foo:bar"   => "baz"}
            $flat  === {"'foo:bar'" => "baz"}
            $query eq  "'foo:bar'=baz"  # the ' will be swapped with %27

            ########

            $data  =   {""   => "baz"}
            $flat  === {"''" => "baz"}
            $query eq  "''=baz"  # the ' will be swapped with %27

            ########

            $data  =   {"'"     => "baz"}
            $flat  === {"'\\''" => "baz"}
            $query eq  "'\\''=baz"  # the ' will be swapped with %27 and the \ will be replaced with %5C

        Single quotes were chosen as double quotes are most commonly used in
        HTML forms, thus allowing escaped single quotes more easily inside
        the double quoted name.

    Undefined values are not included in the flattened data
            $data  =   {foo => undef, bar => 1}
            $flat  === {bar => 1}
            $query eq  "bar=1"

            ########

            $data  =   ["val1", undef, "val2"]
            $flat  === {":0" => "val1", ":2" => "val2"}
            $query eq  ":0=val1&:2=val2"

    Blessed hashes and arrayrefs are dumped by default.
        Changing the default value of the global $DUMP_BLESSED_DATA variable
        changes the behavior.

            $Data::URIEncode::DUMP_BLESSED_DATA = 1; # default
            $data  =   {foo => bless({bar => "baz"}, "main"), one => "two"}
            $flat  === {"foo.bar" => "baz", one => "two"}
            $query eq  "foo.bar=baz&one=two"

            ########

            $Data::URIEncode::DUMP_BLESSED_DATA = 0;
            $data  =   {foo => bless({bar => "baz"}, "main"), one => "two"}
            $flat  === {one => "two"}
            $query eq  "one=two"

    Arrays created by flat_to_complex and query_to_complex must obey the
    value of the $MAX_ARRAY_EXPAND variable.

FUNCTIONS
    flat_to_complex
        Takes a hashref of simple key value pairs. Returns a data structure
        based on the the parsed key value pairs. The parsing proceeds
        according to the rules listed in RULES.

            my $data = flat_to_complex({"foo.bar.baz:2" => "bling"});
            # $data = {foo => {bar => {baz => [undef, undef, "bling"]}}};

    complex_to_flat
        Takes a complex data structure and turns it into a flat hashref
        (single level key/value pairs only). The parsing proceeds according
        to the rules listed in RULES.

            my $flat = complex_to_flat({foo => ['a','b']});
            # $flat = {"foo:0" => "a", "foo:1" => "b"});

    complex_to_query
        Similar to complex_to_flat, except that the flattened hashref is
        then translated into query string suitable for use in a URI.

            my $str = complex_to_query({foo => ['a','b']});
            # $str eq "foo:0=a&foo:1=b"

    query_to_complex
        Takes one of a string, a reference to a string, a hash, or a CGI.pm
        compatible object and translates it into a complex data structure.
        Similar to flat_to_complex, exempt that a first step is taken to
        access the query parameters from the CGI compatible object or
        string. If a string or string ref is given, the CGI module is used
        to parse the string into an initial flat hash of key value pairs
        (using the param method). If another module is desired over, CGI.pm
        you must initialize it with the data to be parsed prior to passing
        the object to the query_to_complex function.

            my $data = query_to_complex("foo.bar:0=baz");

            my $data = query_to_complex(\ "foo.bar:0=baz");

            my $data = query_to_complex({"foo.bar:0" => "baz"}); # same as flat_to_complex

            my $cgi  = CGI->new(\ "foo.bar:0=baz");
            my $data = query_to_complex($cgi);

            my $cgi  = CGI->new; # use the values passed in from STDIN
            my $data = query_to_complex($cgi);

VARIABLES
    $MAX_ARRAY_EXPAND
        Default value is 100. This variable is used to determine how large
        flat_to_complex will allow an array to be expanded beyond its
        current size. An array can grow as large as you have memory, but
        intermediate values must exist.

        Without this value, somebody could specify foo:1000000000000=bar and
        your server would attempt to set the 1000000000000th index of the
        foo value to bar.

        The string "foo:101=bar" would die, but the string
        "foo:50=bar&foo:101=baz" would not die because the intermediate
        foo->[50] increments the foo arrayref by 51 and the subsequent
        foo->[101] call increments the foo arrayref by only 51.

    $DUMP_BLESSED_DATA
        Default is true. If true, blessed hashrefs and arrayrefs will also
        be added to the flat data returned by complex_to_flat. If false,
        bless hashrefs and arrayrefs will be skipped.

BUGS
    Circular refs are not detected. Any attempt to dump a struture with
    cirular refs will result in an infinite loop. There is no immediate plan
    to add circular ref tracking.

SEE ALSO
    All of the following have attempted to solve the same problem as
    Data::URIEncode. All of them (including Data::URIEncode) suffer from the
    problem of being hard to find for the specific purpose. Hash::Flatten is
    probably the only suitable replacement for Data::URIEncode.

    Hash::Flatten

    CGI::Expand

    HTTP::Rollup

    CGI::State

AUTHOR
    Paul Seamons perlspam at seamons dot com

LICENSE
    This library may be distributed under the same terms as Perl itself.