Start with service description type and DNS data functions

Author: sbergen

.github/workflows/test.yml

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+name: test
+
+on:
+  push:
+    branches:
+      - master
+      - main
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: "28"
+          gleam-version: "1.13.0"
+          rebar3-version: "3"
+          # elixir-version: "1"
+      - run: gleam deps download
+      - run: gleam test
+      - run: gleam format --check src test

.gitignore

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+*.beam
+*.ez
+/build
+erl_crash.dump

README.md

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+# esdee
+
+[![Package Version](https://img.shields.io/hexpm/v/esdee)](https://hex.pm/packages/esdee)
+[![Hex Docs](https://img.shields.io/badge/hex-docs-ffaff3)](https://hexdocs.pm/esdee/)
+
+```sh
+gleam add esdee@1
+```
+```gleam
+import esdee
+
+pub fn main() -> Nil {
+  // TODO: An example of the project in use
+}
+```
+
+Further documentation can be found at <https://hexdocs.pm/esdee>.
+
+## Development
+
+```sh
+gleam run   # Run the project
+gleam test  # Run the tests
+```

gleam.toml

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+name = "esdee"
+version = "1.0.0"
+
+# Fill out these fields if you intend to generate HTML documentation or publish
+# your project to the Hex package manager.
+#
+# description = ""
+# licences = ["Apache-2.0"]
+# repository = { type = "github", user = "", repo = "" }
+# links = [{ title = "Website", href = "" }]
+#
+# For a full reference of all the available options, you can have a look at
+# https://gleam.run/writing-gleam/gleam-toml/.
+
+[dependencies]
+gleam_stdlib = ">= 0.44.0 and < 2.0.0"
+gleam_erlang = ">= 1.3.0 and < 2.0.0"
+
+[dev-dependencies]
+gleeunit = ">= 1.0.0 and < 2.0.0"
+

manifest.toml

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+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "gleam_erlang", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "1124AD3AA21143E5AF0FC5CF3D9529F6DB8CA03E43A55711B60B6B7B3874375C" },
+  { name = "gleam_stdlib", version = "0.65.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "7C69C71D8C493AE11A5184828A77110EB05A7786EBF8B25B36A72F879C3EE107" },
+  { name = "gleeunit", version = "1.7.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "CD701726CBCE5588B375D157B4391CFD0F2F134CD12D9B6998A395484DE05C58" },
+]
+
+[requirements]
+gleam_erlang = { version = ">= 1.3.0 and < 2.0.0" }
+gleam_stdlib = { version = ">= 0.44.0 and < 2.0.0" }
+gleeunit = { version = ">= 1.0.0 and < 2.0.0" }

src/esdee.gleam

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+import gleam/option
+
+pub type ServiceDescription {
+  ServiceDescription(
+    service_type: String,
+    instance_name: String,
+    target_name: String,
+    priority: Int,
+    weight: Int,
+    port: Int,
+    txt_values: List(String),
+    ipv4: option.Option(#(Int, Int, Int, Int)),
+    ipv6: option.Option(#(Int, Int, Int, Int, Int, Int, Int, Int)),
+  )
+}

src/esdee/internal/dns.gleam

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+//// Minimal implementation of DNS message encoding/decoding for DNS-SD
+
+/// Encodes a DNS-SD question for the given domain
+@external(erlang, "esdee_ffi", "encode_question")
+pub fn encode_question(domain: String) -> BitArray
+
+/// The minimal resource record data we require
+pub type ResourceRecord {
+  PtrRecord(service_type: String, instance_name: String)
+  SrvRecord(
+    instance_name: String,
+    priority: Int,
+    weight: Int,
+    port: Int,
+    target_name: String,
+  )
+  TxtRecord(instance_name: String, values: List(String))
+  ARecord(target_name: String, ip: #(Int, Int, Int, Int))
+  AaaaRecord(target_name: String, ip: #(Int, Int, Int, Int, Int, Int, Int, Int))
+}
+
+/// Decode the resource records out of a binary DNS record.
+/// We don't currently care about the header or other entries.
+@external(erlang, "esdee_ffi", "decode_records")
+pub fn decode_records(data: BitArray) -> Result(List(ResourceRecord), Nil)

src/esdee_ffi.erl

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+-module(esdee_ffi).
+
+-export([encode_question/1, decode_records/1]).
+
+-include_lib("kernel/src/inet_dns.hrl").
+
+encode_question(Domain) ->
+  Header = #dns_header{},
+  Question =
+    #dns_query{domain = unicode:characters_to_list(Domain),
+               type = ?T_ANY,
+               class = ?C_IN},
+  Record = #dns_rec{header = Header, qdlist = [Question]},
+  inet_dns:encode(Record, true).
+
+decode_records(Bits) ->
+  case inet_dns:decode(Bits) of
+    {ok, Record} ->
+      Header = Record#dns_rec.header,
+      case Header#dns_header.qr of
+        true ->
+          Answers = lists:filtermap(fun map_answer/1, Record#dns_rec.anlist),
+          Resources = lists:filtermap(fun map_resource/1, Record#dns_rec.arlist),
+          {ok, Answers ++ Resources};
+        _ ->
+          {ok, []}
+      end;
+    _ ->
+      {error, nil}
+  end.
+
+map_answer(Answer) ->
+  case Answer#dns_rr.type of
+    ?S_PTR ->
+      {true, map_ptr(Answer)};
+    _ ->
+      false
+  end.
+
+map_resource(Resource) ->
+  case Resource#dns_rr.type of
+    ?S_TXT ->
+      {true, map_txt(Resource)};
+    ?S_SRV ->
+      {true, map_srv(Resource)};
+    ?S_A ->
+      {true, map_a(Resource)};
+    ?S_AAAA ->
+      {true, map_aaaa(Resource)};
+    _ ->
+      false
+  end.
+
+map_ptr(Record) ->
+  ServiceType = unicode:characters_to_binary(Record#dns_rr.domain),
+  InstanceName = unicode:characters_to_binary(Record#dns_rr.data),
+  {ptr_record, ServiceType, InstanceName}.
+
+map_txt(Record) ->
+  InstanceName = unicode:characters_to_binary(Record#dns_rr.domain),
+  Values = lists:map(fun unicode:characters_to_binary/1, Record#dns_rr.data),
+  {txt_record, InstanceName, Values}.
+
+map_srv(Record) ->
+  InstanceName = unicode:characters_to_binary(Record#dns_rr.domain),
+  {Priority, Weight, Port, TargetName} = Record#dns_rr.data,
+  {srv_record,
+   InstanceName,
+   Priority,
+   Weight,
+   Port,
+   unicode:characters_to_binary(TargetName)}.
+
+map_a(Record) ->
+  TargetName = unicode:characters_to_binary(Record#dns_rr.domain),
+  Ip = Record#dns_rr.data,
+  {a_record, TargetName, Ip}.
+
+map_aaaa(Record) ->
+  TargetName = unicode:characters_to_binary(Record#dns_rr.domain),
+  Ip = Record#dns_rr.data,
+  {aaaa_record, TargetName, Ip}.