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|
open Base
let policy = {|<?xml version="1.0" encoding="UTF-8"?>
<Policy
xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17
http://docs.oasis-open.org/xacml/3.0/xacml-core-v3-schema-wd-17.xsd"
PolicyId="urn:oasis:names:tc:xacml:3.0:example:SimplePolicy1"
Version="1.0"
RuleCombiningAlgId="urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:deny-overrides">
<Description>
Medi Corp access control policy
</Description>
<Target/>
<Rule
RuleId= "urn:oasis:names:tc:xacml:3.0:example:SimpleRule1"
Effect="Permit">
<Description>
Any subject with an e-mail name in the med.example.com domain
can perform any action on any resource.
</Description>
<Target>
<AnyOf>
<AllOf>
<Match
MatchId="urn:oasis:names:tc:xacml:1.0:function:rfc822Name-match">
<AttributeValue
DataType="http://www.w3.org/2001/XMLSchema#string"
>med.example.com</AttributeValue>
<AttributeDesignator
MustBePresent="false"
Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject"
AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id"
DataType="urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name"/>
</Match>
</AllOf>
</AnyOf>
</Target>
</Rule>
</Policy>
|}
type xml_element = (string * (string * string) list * Xml.xml list)
type lean_expression = Identifier of string
| Bool of bool
| String of string
| Number of int
| List of lean_expression list
| Tuple of lean_expression list
| Application of lean_expression * lean_expression list
let rec fmt_lean_expression : lean_expression -> string = function
| Identifier s -> s
| Bool b -> if b then "True" else "False"
| String s -> Printf.sprintf "\"%s\"" s
| Number n -> Int.to_string n
| List xs -> Printf.sprintf "[%s]" (String.concat ~sep:", " (List.map ~f:fmt_lean_expression xs))
| Tuple xs -> Printf.sprintf "(%s)" (String.concat ~sep:", " (List.map ~f:fmt_lean_expression xs))
| Application (head, args) -> Printf.sprintf "(%s %s)" (fmt_lean_expression head) (String.concat ~sep:" " (List.map ~f:fmt_lean_expression args))
let rec get_attr (needle : string) : (string * string) list -> string option = function
| (k, v) :: xs -> if String.equal k needle then Some v else get_attr needle xs
| _ -> None
let rec get_children (kind : string) : Xml.xml list -> xml_element list = function
| (Element ((tag_name, _, _) as x)) :: xs ->
if String.equal tag_name kind
then x :: get_children kind xs
else get_children kind xs
| PCData s :: xs -> get_children kind xs
| _ -> []
let get_child kind xs = List.nth (get_children kind xs) 0
let xml_element_of_children (children : Xml.xml list) : xml_element list =
List.map children ~f:(function
| Element x -> x
| _ -> failwith "called on element with non-element children")
let compile_rule_combinator_algorithm : string -> lean_expression = function
| "urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:deny-overrides" ->
(Identifier "RuleCombinatorAlgorithm.deny_overrides")
| "urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:ordered-deny-overrides" ->
(Identifier "RuleCombinatorAlgorithm.ordered_deny_overrides")
| "urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:permit-overrides" ->
(Identifier "RuleCombinatorAlgorithm.ordered_deny_overrides")
| "urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:ordered-permit-overrides" ->
(Identifier "RuleCombinatorAlgorithm.ordered_permit_overrides")
| "urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:deny-unless-permit" ->
(Identifier "RuleCombinatorAlgorithm.deny_unless_permit")
| "urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:permit-unless-deny" ->
(Identifier "RuleCombinatorAlgorithm.permit_unless_deny")
| "urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:first-applicable" ->
(Identifier "RuleCombinatorAlgorithm.first_applicable")
| "urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:deny-overrides" ->
(Identifier "RuleCombinatorAlgorithm.legacy_deny_overrides")
| "urn:oasis:names:tc:xacml:1.1:rule-combining-algorithm:ordered-deny-overrides" ->
(Identifier "RuleCombinatorAlgorithm.legacy_ordered_deny_overrides")
| "urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:permit-overrides" ->
(Identifier "RuleCombinatorAlgorithm.legacy_permit_overrides")
| "urn:oasis:names:tc:xacml:1.1:rule-combining-algorithm:ordered-permit-overrides" ->
(Identifier "RuleCombinatorAlgorithm.legacy_ordered_permit_overrides")
| _ -> failwith "unknown rule combinator"
open Option.Let_syntax
(* let (tag_name, attributes, children) = elt in *)
let compile_attribute_value (elt : xml_element) : lean_expression option =
let (tag_name, attrs, children) = elt in
assert (String.equal tag_name "AttributeValue");
let%bind kind = get_attr "DataType" attrs in
match List.nth_exn children 0 with
| PCData s -> Some (Tuple [(String kind); (String s)])
| _ -> failwith "invalid value expression"
let compile_attribute_designator (elt : xml_element) : lean_expression option =
let (tag_name, attrs, children) = elt in
assert (String.equal tag_name "AttributeDesignator");
let%bind category = get_attr "Category" attrs in
let%bind identifier = get_attr "AttributeId" attrs in
let%bind kind = get_attr "DataType" attrs in
let%bind must_be_present = get_attr "MustBePresent" attrs in
let issuer = (match get_attr "Issuer" attrs with
| Some s -> (Application ((Identifier "some"), [(String s)]))
| _ -> (Application ((Identifier "none"), [])))
in
Some (Application
((Identifier "AttributeDesignator.mk"),
[(String category);
(String identifier);
(Identifier kind);
issuer;
(Bool (Bool.of_string must_be_present))]))
let compile_match (elt : xml_element) : lean_expression option =
(* TODO: Can the match contain multiple value/designator pairs? *)
let (tag_name, attrs, children) = elt in
assert (String.equal tag_name "Match");
let%bind alg_id = get_attr "MatchId" attrs in
let%bind value = get_child "AttributeValue" children in
let%bind value = compile_attribute_value value in
let%bind designator = get_child "AttributeDesignator" children in
let%bind designator = compile_attribute_designator designator in
Some (Application
((Identifier "Match.mk"),
[(String alg_id);
designator;
value]))
let compile_all_of (elt : xml_element) : lean_expression option =
let (tag_name, _, children) = elt in
assert (String.equal tag_name "AllOf");
if phys_equal (List.length children) 0
then failwith "empty <AllOf>"
else failwith "unimplemented"
let compile_any_of (elt : xml_element) : lean_expression option =
let (tag_name, _, children) = elt in
assert (String.equal tag_name "AnyOf");
if phys_equal (List.length children) 0
then failwith "empty <AnyOf>"
else failwith "unimplemented"
let rec option_of_maybe_list : 'a option list -> 'a list option = function
| Some x :: xs -> (match option_of_maybe_list xs with
| Some xs' -> Some (x::xs')
| None -> None)
| [] -> Some []
| _ -> None
let compile_target (elt : xml_element) : lean_expression option =
let (tag_name, _, children) = elt in
assert (String.equal tag_name "Target");
let%bind xs = List.map ~f:compile_any_of (xml_element_of_children children)
|> option_of_maybe_list in
Some (List xs)
(* failwith "unimplemented" *)
let compile_policy (attrs : (string * string) list) (children : Xml.xml list) : lean_expression option =
let%bind alg_id = get_attr "RuleCombiningAlgId" attrs in
let%bind target = get_child "Target" children in
let%bind target = compile_target target in
Some (Application
((Identifier "Policy.mk"),
[(compile_rule_combinator_algorithm alg_id);
target;
(List []); (* TODO: Compile obligation expressions *)
(List []) (* TODO: Compile advice expressions *)
]))
let compile : Xml.xml -> lean_expression option = function
| Element (tag_name, attributes, children) ->
(match tag_name with
| "Policy" -> compile_policy attributes children
| _ -> failwith (Printf.sprintf "(%s)" tag_name))
| PCData s -> failwith s
let () =
match compile @@ Xml.parse_string policy with
| Some ast ->
ast
|> fmt_lean_expression
|> Caml.print_endline
| _ -> failwith "compilation failed!"
|
