dns_erlang

#!/usr/bin/env escript
%% -*- erlang -*-
%% Extract RFC references from the codebase and generate a markdown list.
%%
%% This script extracts RFC references from anywhere in the source files.
%% Only uppercase "RFC" is matched (e.g., "RFC 1035" or "RFC1035").
%% Lowercase "rfc" is NOT matched, which naturally filters out identifiers
%% like rfc3597_data, parse_rfc3597_token, calendar:system_time_to_rfc3999/2.
%%
%% Usage:
%%     # Generate RFC list to stdout
%%     escript scripts/generate_rfc_list.escript
%%
%%     # Generate RFC list and save to file
%%     escript scripts/generate_rfc_list.escript --output RFC_LIST.md
%%
%% To update the README.md:
%%     1. Run: escript scripts/generate_rfc_list.escript > /tmp/rfc_list.md
%%     2. Copy the output and replace the "## Supported RFCs" section in README.md
%%     3. Or use: escript scripts/generate_rfc_list.escript --output /tmp/rfc_list.md

-mode(compile).

-define(RFC_TITLES, #{
    ~"1034" => ~"Domain Names - Concepts and Facilites",
    ~"1035" => ~"Domain Names - Implementation and Specification",
    ~"3596" => ~"DNS Extensions to Support IP Version 6",
    ~"1183" => ~"New DNS RR Definitions",
    ~"1876" => ~"A Means for Expressing Location Information in the Domain Name System",
    ~"2230" => ~"Key Exchange Delegation Record for the DNS",
    ~"2782" => ~"A DNS RR for specifying the location of services (DNS SRV)",
    ~"3403" =>
        ~"Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database",
    ~"2308" => ~"Negative Caching of DNS Queries (DNS NCACHE)",
    ~"3597" => ~"Handling of Unknown DNS Resource Record (RR) Types",
    ~"4025" => ~"A Method for Storing IPsec Keying Material in DNS",
    ~"4255" => ~"Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints",
    ~"4398" => ~"Storing Certificates in the Domain Name System (DNS)",
    ~"4408" =>
        ~"Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1",
    ~"4701" =>
        ~"A DNS Resource Record (RR) for Encoding Dynamic Host Configuration Protocol (DHCP) Information (DHCID RR)",
    ~"6672" => ~"DNAME Redirection in the DNS",
    ~"6698" =>
        ~"The DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA",
    ~"6844" => ~"DNS Certification Authority Authorization (CAA) Resource Record",
    ~"9460" =>
        ~"Service Binding and Parameter Specification via the DNS (DNS SVCB and HTTPS Resource Records)",
    ~"2535" => ~"Domain Name System Security Extensions",
    ~"4034" => ~"Resource Records for the DNS Security Extensions",
    ~"4431" => ~"The DNSSEC Lookaside Validation (DLV) DNS Resource Record",
    ~"5155" => ~"DNS Security (DNSSEC) Hashed Authenticated Denial of Existence",
    ~"6605" => ~"Elliptic Curve Digital Signature Algorithm (DSA) for DNSSEC",
    ~"7344" => ~"Automating DNSSEC Delegation Trust Maintenance",
    ~"8080" => ~"Ed25519 and Ed448 for DNSSEC",
    ~"9077" => ~"NSEC and NSEC3 TTL Values",
    ~"7553" => ~"The Uniform Resource Identifier (URI) DNS Resource Record",
    ~"7043" => ~"Resource Records for EUI-48 and EUI-64 Addresses in the DNS",
    ~"8162" => ~"Using Secure DNS to Associate Certificates with Domain Names for S/MIME",
    ~"9606" => ~"DNS Resolver Information",
    ~"7929" => ~"DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP",
    ~"2845" => ~"Secret Key Transaction Authentication for DNS (TSIG)",
    ~"7477" => ~"Child-to-Parent Synchronization in DNS",
    ~"9859" => ~"Generalized DNS Notifications",
    ~"6891" => ~"Extension Mechanisms for DNS (EDNS(0))",
    ~"8976" => ~"Message Digest for DNS Zones",
    ~"5001" => ~"DNS Name Server Identifier (NSID) Option",
    ~"7871" => ~"Client Subnet in DNS Queries",
    ~"7873" => ~"Domain Name System (DNS) Cookies",
    ~"8764" => ~"DNS Long-Lived Queries (LLQ)",
    ~"8914" => ~"Extended DNS Errors",
    ~"9619" => ~"In the DNS, QDCOUNT Is (Usually) One"
}).

main(Args) ->
    RootDir = get_root_dir(),
    Opts = parse_args(Args, []),
    %% Only match uppercase "RFC" (not lowercase "rfc")
    {ok, RfcPattern} = re:compile(~B"RFC[\s-]?(\d+)", [unicode]),
    io:format(standard_error, "Searching for RFC references in ~s...~n", [RootDir]),
    RfcRefs = find_rfc_references(RootDir, RfcPattern),
    RfcCount = maps:size(RfcRefs),
    io:format(standard_error, "Found ~p unique RFCs:~n", [RfcCount]),
    Markdown = generate_markdown(RfcRefs),
    case proplists:get_value(output, Opts, undefined) of
        undefined ->
            io:format("~s", [Markdown]);
        File ->
            file:write_file(File, Markdown),
            io:format(standard_error, "Generated RFC list: ~s~n", [File])
    end.

parse_args([], Acc) ->
    lists:reverse(Acc);
parse_args(["--output", File | Rest], Acc) ->
    parse_args(Rest, [{output, File} | Acc]);
parse_args([Unknown | Rest], Acc) ->
    io:format(standard_error, "Warning: Unknown option ~s~n", [Unknown]),
    parse_args(Rest, Acc).

get_root_dir() ->
    ScriptPath = escript:script_name(),
    ScriptDir = filename:dirname(filename:absname(ScriptPath)),
    filename:dirname(ScriptDir).

find_rfc_references(RootDir, RfcPattern) ->
    Dirs = [~"src", ~"include"],
    Extensions = ["*.erl", "*.hrl"],
    Files = [
        File
     || Ext <- Extensions,
        Dir <- Dirs,
        File <- filelib:wildcard(binary_to_list(filename:join([RootDir, Dir, "**", Ext])))
    ],
    lists:foldl(fun(File, Acc) -> scan_file(File, Acc, RfcPattern) end, #{}, Files).

scan_file(File, Acc, RfcPattern) ->
    case file:read_file(File) of
        {ok, Content} ->
            extract_rfc_numbers(Content, RfcPattern, File, Acc);
        {error, Reason} ->
            io:format(standard_error, "Warning: Could not read ~s: ~p~n", [File, Reason]),
            Acc
    end.

extract_rfc_numbers(Content, RfcPattern, File, Acc) ->
    %% Extract all RFC references from the content
    %% Only uppercase "RFC" is matched, so lowercase identifiers like rfc3597_data won't match
    case re:run(Content, RfcPattern, [global, {capture, all, binary}]) of
        {match, Matches} ->
            RfcNums = [RfcNum || [_, RfcNum] <- Matches],
            lists:foldl(
                fun(RfcNum, AccAcc) ->
                    maps:update_with(
                        RfcNum,
                        fun(Refs) -> [File | Refs] end,
                        [File],
                        AccAcc
                    )
                end,
                Acc,
                RfcNums
            );
        nomatch ->
            Acc
    end.

generate_markdown(RfcRefs) ->
    Header =
        ~"""
        # Supported RFCs

        This library implements encoding and decoding of DNS packets according to the following RFCs.
        Note that this library focuses on packet encoding/decoding only and does not implement DNS server
        functionality such as socket handling or query resolution.


        """,
    SortedRfcs = lists:sort(
        fun(A, B) -> binary_to_integer(A) < binary_to_integer(B) end, maps:keys(RfcRefs)
    ),
    RfcItems = lists:map(
        fun(RfcNum) ->
            Title = maps:get(RfcNum, ?RFC_TITLES, ~"Unknown"),
            RfcUrl = <<"https://tools.ietf.org/html/rfc", RfcNum/binary>>,
            <<"- **[RFC ", RfcNum/binary, "](", RfcUrl/binary, ")**: ", Title/binary, "\n">>
        end,
        SortedRfcs
    ),
    iolist_to_binary([Header | RfcItems]).