Support context propagation. (#5)

lib/http_client_builder.ex

@@ -38,6 +38,8 @@ defmodule HttpClientBuilder do
         raise ":runtime_headers_getter option is not a nullary anonymous function or function capture "
     end
 
+    otel_headers? = Keyword.get(client_opts, :otel_headers?, true)
+
     quote do
       def child_spec(opts) do
         default_pools = %{:default => [size: 50]}
@@ -102,6 +104,8 @@ defmodule HttpClientBuilder do
             compile_time_headers
           end
 
+        headers = otel_headers(headers)
+
         method
         |> Finch.build(url, headers, body)
         |> Finch.request(__MODULE__, request_opts)
@@ -121,6 +125,15 @@ defmodule HttpClientBuilder do
         |> Map.to_list()
       end
 
+      # https://github.com/open-telemetry/opentelemetry-erlang-contrib/blob/main/instrumentation/opentelemetry_finch/README.md
+      if Code.ensure_loaded?(:otel_propagator_text_map) && unquote(otel_headers?) do
+        defp otel_headers(headers) when is_list(headers) do
+          :otel_propagator_text_map.inject([]) ++ headers
+        end
+      end
+
+      defp otel_headers(headers), do: headers
+
       defoverridable get: 2, post: 2, put: 2, delete: 2, patch: 2, do_request: 3, build_url: 2
     end
   end

mix.exs

@@ -27,6 +27,7 @@ defmodule HttpClientBuilder.MixProject do
       {:finch, "~> 0.9"},
       # for encode plug compat query string
       {:plug, "~> 1.12"},
+      {:opentelemetry_api, "~> 1.3", optional: true},
       {:jason, "~> 1.2", only: [:test]}
     ]
   end

mix.lock

@@ -7,6 +7,8 @@
   "mint": {:hex, :mint, "1.4.2", "50330223429a6e1260b2ca5415f69b0ab086141bc76dc2fbf34d7c389a6675b2", [:mix], [{:castore, "~> 0.1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:hpax, "~> 0.1.1", [hex: :hpax, repo: "hexpm", optional: false]}], "hexpm", "ce75a5bbcc59b4d7d8d70f8b2fc284b1751ffb35c7b6a6302b5192f8ab4ddd80"},
   "nimble_options": {:hex, :nimble_options, "0.4.0", "c89babbab52221a24b8d1ff9e7d838be70f0d871be823165c94dd3418eea728f", [:mix], [], "hexpm", "e6701c1af326a11eea9634a3b1c62b475339ace9456c1a23ec3bc9a847bca02d"},
   "nimble_pool": {:hex, :nimble_pool, "0.2.6", "91f2f4c357da4c4a0a548286c84a3a28004f68f05609b4534526871a22053cde", [:mix], [], "hexpm", "1c715055095d3f2705c4e236c18b618420a35490da94149ff8b580a2144f653f"},
+  "opentelemetry_api": {:hex, :opentelemetry_api, "1.3.1", "83b4713593f80562d9643c4ab0b6f80f3c5fa4c6d0632c43e11b2ccb6b04dfa7", [:mix, :rebar3], [{:opentelemetry_semantic_conventions, "~> 0.2", [hex: :opentelemetry_semantic_conventions, repo: "hexpm", optional: false]}], "hexpm", "9e8a5cc38671e3ac61be48abe5f6b3afdbbb50a1dc08b7950c56f169611505c1"},
+  "opentelemetry_semantic_conventions": {:hex, :opentelemetry_semantic_conventions, "0.2.0", "b67fe459c2938fcab341cb0951c44860c62347c005ace1b50f8402576f241435", [:mix, :rebar3], [], "hexpm", "d61fa1f5639ee8668d74b527e6806e0503efc55a42db7b5f39939d84c07d6895"},
   "plug": {:hex, :plug, "1.13.6", "187beb6b67c6cec50503e940f0434ea4692b19384d47e5fdfd701e93cadb4cc2", [:mix], [{:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:plug_crypto, "~> 1.1.1 or ~> 1.2", [hex: :plug_crypto, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4.3 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "02b9c6b9955bce92c829f31d6284bf53c591ca63c4fb9ff81dfd0418667a34ff"},
   "plug_crypto": {:hex, :plug_crypto, "1.2.3", "8f77d13aeb32bfd9e654cb68f0af517b371fb34c56c9f2b58fe3df1235c1251a", [:mix], [], "hexpm", "b5672099c6ad5c202c45f5a403f21a3411247f164e4a8fab056e5cd8a290f4a2"},
   "telemetry": {:hex, :telemetry, "1.1.0", "a589817034a27eab11144ad24d5c0f9fab1f58173274b1e9bae7074af9cbee51", [:rebar3], [], "hexpm", "b727b2a1f75614774cff2d7565b64d0dfa5bd52ba517f16543e6fc7efcc0df48"},