The Form BrokerIntroduction
The FormBroker package creates instances of
objects representing a form data description. These objects offer a
simple interface of methods meant to validate and control data
as typically posted through an HTML form,
thus data represented through the association of form variables
with their values as returned, for example,
by the ::rivet::load_response command
The FormBroker package is still experimental.
Basic functionalities and interface are not likely to change but
internal details and implementation could be redesigned
in future releases. More specifically the external validator mechanism
could be improved with the purpose of shielding the FormBroker
internals from a data validation procedure.
FormBroker
Form broker object creator
::FormBrokercreate...Description
The command returns a reference to a form broker object by creating
a representation of the form data using the list of variable
descriptors passed to create. Each descriptor
is a list of parameter or parameter-value pairs whose order has as only requirement
to begin with the {variable_name variable_type} pair.
A formbroker object handles natively integer, unsigned, string, boolean and email data types.
The programmer can defined new data type and provide in the descriptor a
reference to a validating procedure for that type.
The optional -quoting quoting_procedure switch assigns a procedure to
be called to quote the form response values. The quoting procedure is any
procedure accepting a single string argument and returning its quoted value. A most
basic example is the FormBroker default quoting procedure
proc force_quote {str} {
return "'$str'"
}
Other parameters of a descriptors are
type: the data type of the variablebounds: limits of a variable value. The
meanining of bounds depends on the variable type. For an integer is the
maximum absolute value for that variable (for an unsigned the lower
limit is invariably 0), for a string is the maximum length of the string. The
parameter bounds has no effect on an email data type
constrain: boolean value telling the variable has to be
forced to fulfill the constrain imposed by bounds. This field
is bidirectional in that it can be used by the validator to force the
variable value rewritingvalidator: name of the specialized validator for this variabledefault: default value of the variable if not set in a response array.
When a variable is given a default value the form validation will not fail on the fact that
this variable may be missing from the form response arrayquote: the variable value has to be quoted when written back in
the response arrayvalidator: name of the validator procedure. The procedure
can be any Tcl procedure accepting as argument the name of a dictionary
holding the variable internal representation.
An example of a form accepting four variable, one for each native type of a form broker object
% set fbroker [::FormBroker create {var1 integer} {var2 unsigned} {var3 string} {var4 integer bounds {-10 100}}]
::FormBroker::form0Form broker object methods
The central method of a form broker object is validateformBroker_objectvalidateresponseresponse copy
The method validate takes as argument the name of an array of variables
in the way this is produced by command ::rivet::load_response
returning a form response. The optional argument -forcequote causes the
variable values to be rewritten and quoted. If the optional argument response copy
is present the validated response is copied in this array instead of the input response
array.
If the form data have been validated the method validate returns true
Example of form data validation (assuming ::rivet::load_response is loading the array response
with data taken from a form non displayed here)
% set fbroker [::FormBroker create {var1 integer} {var2 unsigned} {var3 string} {var4 integer bounds {-10 100}}]
::FormBroker::form0
% ::rivet::load_response
% parray response
response(var1) = -10
response(var2) = 20
response(var3) = a string
response(var4) = 50
# let's keep a copy of the response
% array set response_copy [array get response]
# form data validation
% $fbroker validate response
true
% $fbroker validate -forcequote response
% parray response
response(var1) = '-10'
response(var2) = '20'
response(var3) = 'a string'
response(var4) = '50'
# restore response original value
% array set response [array get response_copy]
% $fbroker validate -forcequote response response_copy
true
% parray response
response(var1) = -10
response(var2) = 20
response(var3) = a string
response(var4) = 50
% parray response_copy
response_copy(var1) = '-10'
response_copy(var2) = '20'
response_copy(var3) = 'a string'
response_copy(var4) = '50'
# a form object has to be destroyed if it's not needed anymore
% $fbroker destroyformBroker_objectfailing
In case the validation fails method failing returns a list
of variable_name - error_condition pairs for each
variable whose value failed to validate and was impossible to fix. This list
is suitable to populate an array or used directly as a dictionary
% package require formbroker
1.0
% set fbroker [::FormBroker create {var1 integer} \
{var2 unsigned} \
{var3 string} \
{var4 integer}]
::FormBroker::form0
% ::rivet::load_response
# let's suppose we have an incomplete response
% parray response
response(var1) = '100'
response(var2) = '20'
response(var3) = 'a string'
% $fbroker validate response
false
$fbroker failing
var4 MISSING_VAR
# this can be prevented by assigning a variable a default value
% set fbroker [::FormBroker create {var1 integer} \
{var2 unsigned} \
{var3 string} \
{var4 integer default 0}]
::FormBroker::form1
% $fbroker validate response
true
% parray response
response(var1) = 100
response(var2) = 20
response(var3) = a string
response(var4) = 0
% set fbroker [::FormBroker create {var1 integer} \
{var2 unsigned} \
{var3 string length 10 constrain} \
{var4 integer bounds {-10 100}}]
::FormBroker::form2
% ::rivet::load_response
# this time the response has invalid data
% parray response
response(var1) = 'aaaaa'
response(var2) = '-20'
response(var3) = 'a longer string that breaks the 10 chars max limit imposed'
response(var4) = '150'
% $fbroker validate response
false
% $fbroker failing
var1 NOT_INTEGER var2 FB_OUT_OF_BOUNDS var4 FB_OUT_OF_BOUNDS
Notice that even though $response(var3) exceeds the 10 characters max length imposed to variable var3
this variable is not in the list returned by failing because
the 'constrain' attribute forced the truncation of the string.
In fact this applies also to the integer and unsigned values
% set fbroker [::FormBroker create {var1 integer bounds 10 constrain} \
{var2 unsigned constrain} \
{var3 string length 10 constrain} \
{var4 integer bounds {-10 100} constrain}]
::FormBroker::form0
% ::rivet::load_response
% parray response
response(var1) = abcdef
response(var2) = -20
response(var3) = a longer string that breaks the 10 chars max limit imposed
response(var4) = 150
% $fbroker validate response response_copy
false
% $fbroker failing
var1 NOT_INTEGER
% parray response_copy
response_copy(var2) = 0
response_copy(var3) = a longer s
response_copy(var4) = 100
The variable var1 could not be constrained because the input
value "abcdef" is fundamentally incompatible
formBroker_objectresponse
The response method fills
the array whose name is passed as optional argument
with the last response processing. If this argument is omitted
the method creates an array named response.
This method can be called also if no form response validation has taken place: it
simply populates the array with the default values assigned to the form variables. As
such is a way to create form default arrays to initialize forms created with
the form package.
set fbroker [::FormBroker create {var1 integer default 0} \
{var2 unsigned default 1} \
{var3 string} \
{var4 integer default 0}]
% $fbroker response a
% parray a
a(var1) = 0
a(var2) = 1
a(var4) = 0formBroker_objectreset
The method resets the object to its initial defaults
Writing a custom variable validator
The form broker is by no means restricted to work only with its native
data types: you may define your own form variable types and have
them validated with their own variable validator.
A validator is a function accepting a dictionary as single argument and
must return either FB_OK, if the variable value is valid,
or any other used defined error code. The dictionary argument stores
the variable descriptor used internally by the form broker.
Suppose you're writing a form text entry that demands as input a network
interface MAC address.
A MAC address is represented by 6 hexadecimal octets separated by
either a - (Windows convention) or :
(Unix, Mac convention). The procedure validate_mac
checks the validity of the mac address and if validation is successful it
transforms its representation into the Unix form.
By setting the key constrain
in the dictionary mac_address_d the procedure
is telling the form broker to copy the transformed value back
in the input response array
proc validate_mac {_mac_address_d} {
upvar $_mac_address_d mac_address_d
dict with mac_address_d {
set var [string trim $var]
if {[regexp {^[[:xdigit:]]{2}([:-][[:xdigit:]]{2}){5}$} $var]} {
set var [string tolower $var]
# we normalize the mac address to the Unix form.
# The dash '-' characters in the windows representation
# are replaced by columns ':'
set var [regsub -all -- {-} $var :]
# the 'constrain' field is bidirectional:
# it tells the validator to curb/change the value
# within bonds/forms/representation. By setting it the
# validator tells the FormBroker to copy the value
# back in the response array
set constrain 1
return FB_OK
} else {
return FB_WRONG_MAC
}
}
}
% set fbroker [::FormBroker create {mac mac_address validator validate_mac}]
% ::rivet::load_response r
% parray r
r(mac) = 00-A1-B2-C3-D4-C5
% $fbroker validate r
true
% parray r
r(mac) = 00:a1:b2:c3:d4:c5