From 6ce8f052d3c827cc227c0a145cba6ef85a360bcd Mon Sep 17 00:00:00 2001
From: Nick Mohoric <nmohoric@hearst.com>
Date: Sun, 15 Oct 2017 22:52:58 -0400
Subject: [PATCH] Initial commit

---
 .gitignore                     |  5 ++
 .travis.yml                    |  5 ++
 LICENSE.txt                    | 21 +++++++++
 README.md                      | 41 +++++++++++++++++
 config/config.exs              | 24 ++++++++++
 lib/plug_opentracing.ex        | 84 ++++++++++++++++++++++++++++++++++
 mix.exs                        | 43 +++++++++++++++++
 mix.lock                       |  4 ++
 test/plug_opentracing_test.exs | 53 +++++++++++++++++++++
 test/test_helper.exs           | 28 ++++++++++++
 10 files changed, 308 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 .travis.yml
 create mode 100644 LICENSE.txt
 create mode 100644 README.md
 create mode 100644 config/config.exs
 create mode 100644 lib/plug_opentracing.ex
 create mode 100644 mix.exs
 create mode 100644 mix.lock
 create mode 100644 test/plug_opentracing_test.exs
 create mode 100644 test/test_helper.exs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..12d32ce
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+/_build
+/deps
+erl_crash.dump
+*.ez
+/doc
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..9b1923f
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,5 @@
+language: elixir
+elixir:
+  - 1.5.1
+otp_release:
+  - 20.0
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..c35425b
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 Nick Mohoric
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..eb98ef4
--- /dev/null
+++ b/README.md
@@ -0,0 +1,41 @@
+# PlugOpenTracing
+
+[![Build Status](https://travis-ci.org/nmohoric/plug_opentracing.svg?branch=master)](https://travis-ci.org/nmohoric/plug_opentracing)
+
+An Elixir Plug for adding OpenTracing instrumentation.
+
+## Usage
+
+Update your `mix.exs` file and run `mix deps.get`.
+```elixir
+defp deps do
+  [{:plug_opentracing, "~> 0.1"}]
+end
+```
+
+Add the plug to a pipeline. In this case we will look for the
+`uber-trace-id` header to exist. If so, it is split on `:` and
+the first and second values are used as the trace_id and parent_id
+when creating the span.
+
+```elixir
+defmodule MyPhoenixApp.MyController do
+  use MyPhoenixApp.Web, :controller
+  alias Plug.Conn.Status
+
+  plug PlugOpenTracing, trace_id: 'uber-trace-id'
+  plug :action
+
+  def index(conn, _params) do
+    conn
+    |> put_status(Status.code :ok)
+  end
+end
+
+```
+The created span can be accessed using `conn.assigns[:trace_span]`. This is useful
+when you want to use this span as the parent of another span in your request, or
+if you want to add tags/logs to the span before it is finished.
+
+The request span will be finished at the end of your request using a callback,
+which will send it to the Jaeger or Zipkin endpoint you've set up in your config.
diff --git a/config/config.exs b/config/config.exs
new file mode 100644
index 0000000..6dfa82f
--- /dev/null
+++ b/config/config.exs
@@ -0,0 +1,24 @@
+# This file is responsible for configuring your application
+# and its dependencies with the aid of the Mix.Config module.
+use Mix.Config
+
+# This configuration is loaded before any dependency and is restricted
+# to this project. If another project depends on this project, this
+# file won't be loaded nor affect the parent project. For this reason,
+# if you want to provide default values for your application for third-
+# party users, it should be done in your mix.exs file.
+
+# Sample configuration:
+#
+#     config :logger, :console,
+#       level: :info,
+#       format: "$date $time [$level] $metadata$message\n",
+#       metadata: [:user_id]
+
+# It is also possible to import configuration files, relative to this
+# directory. For example, you can emulate configuration per environment
+# by uncommenting the line below and defining dev.exs, test.exs and such.
+# Configuration from the imported file will override the ones defined
+# here (which is why it is important to import them last).
+#
+#     import_config "#{Mix.env}.exs"
diff --git a/lib/plug_opentracing.ex b/lib/plug_opentracing.ex
new file mode 100644
index 0000000..47d395d
--- /dev/null
+++ b/lib/plug_opentracing.ex
@@ -0,0 +1,84 @@
+defmodule PlugOpenTracing do
+  @moduledoc """
+  A plug for adding OpenTracing instrumentation to requests.
+
+  If a request already has a trace-id, the parts will be split
+  out and added as trace-id and parent-id in the new span. Otherwise,
+  a new span will be created.
+
+  The default header is "uber-trace-id" but this can be set at compile time.
+
+  At any point in the request you can access the span using conn.assigns[:trace].
+  This can then be used to either add tags onto it or use the span as a parent span
+  for other requests.
+
+  To use it, just plug it into your module:
+
+      plug PlugOpenTracing
+
+  ## Options
+
+    * `:trace_id` - An incoming trace-id. This should be hex and in the
+      form `trace-id:span-id` plus any optional bits that will be removed.
+
+        plug PlugOpenTracing, trace_id: "my-trace-header"
+  """
+
+  alias Plug.Conn
+  alias :otter, as: Otter
+  @behaviour Plug
+
+  def init(opts) do
+    Keyword.get(opts, :trace_header, "uber-trace-id")
+  end
+
+  def call(conn, trace_id_header) do
+    conn
+    |> get_trace_id(trace_id_header)
+    |> start_span()
+    |> tag_span()
+    |> register_span()
+  end
+
+  defp get_trace_id(conn, header) do
+    case Conn.get_req_header(conn, header) do
+      []      -> {conn, nil}
+      [val|_] -> {conn, extract_id(String.split(val, ":"))}
+    end
+  end
+
+  defp start_span({conn, [nil, _]}), do: start_span({conn, nil})
+  defp start_span({conn, [_, nil]}), do: start_span({conn, nil})
+  defp start_span({conn, [trace_id, span_id]}) do
+    {conn, Otter.start(conn.method, trace_id, span_id)}
+  end
+  defp start_span({conn, _}), do: {conn, Otter.start(conn.method)}
+
+  defp tag_span({conn, span}) do
+    span = span
+         |> Otter.tag("path", Enum.join(Enum.map(conn.path_info, &URI.decode/1), "/"))
+         |> Otter.tag("method", conn.method)
+    conn |> Conn.assign(:trace_span, span)
+  end
+
+  defp register_span(conn) do
+    Conn.register_before_send(conn, fn c ->
+      c.assigns[:trace_span]
+      |> Otter.finish()
+      c
+    end)
+  end
+
+  defp extract_id(vals) when length(vals) >= 2 do
+      vals
+      |> Enum.take(2)
+      |> Enum.map(fn(s) -> s
+                        |> Integer.parse(16)
+                        |> case do
+                          :error -> nil
+                          i      -> elem(i,0)
+                        end
+                     end)
+  end
+  defp extract_id(_), do: nil
+end
diff --git a/mix.exs b/mix.exs
new file mode 100644
index 0000000..9f0dd91
--- /dev/null
+++ b/mix.exs
@@ -0,0 +1,43 @@
+defmodule PlugOpenTracing.Mixfile do
+  use Mix.Project
+
+  def project do
+    [
+      app: :plug_opentracing,
+      version: "0.0.1",
+      name: "PlugOpenTracing",
+      source_url: "https://github.com/nmohoric/plug_opentracing",
+      elixir: "~> 1.0",
+      deps: deps(),
+      description: description(),
+      package: package()
+    ]
+  end
+
+  defp description do
+    """
+    An Elixir Plug for adding opentracing instrumentation.
+    """
+  end
+
+  defp package do
+    [
+      maintainers: ["Nick Mohoric"],
+      files: ["lib", "mix.exs", "README*", "LICENSE*"],
+      licenses: ["MIT"],
+      links: %{"GitHub" => "https://github.com/nmohoric/plug_opentracing"}
+    ]
+  end
+
+  def application do
+    [applications: [:plug]]
+  end
+
+  defp deps do
+    [
+      {:plug, "~> 1.3"},
+      {:ibrowse, "~> 4.4"},
+      {:otter, "~> 0.2.0"},
+    ]
+  end
+end
diff --git a/mix.lock b/mix.lock
new file mode 100644
index 0000000..1da963d
--- /dev/null
+++ b/mix.lock
@@ -0,0 +1,4 @@
+%{"ibrowse": {:hex, :ibrowse, "4.4.0", "2d923325efe0d2cb09b9c6a047b2835a5eda69d8a47ed6ff8bc03628b764e991", [], [], "hexpm"},
+  "mime": {:hex, :mime, "1.1.0", "01c1d6f4083d8aa5c7b8c246ade95139620ef8effb009edde934e0ec3b28090a", [], [], "hexpm"},
+  "otter": {:hex, :otter, "0.2.0", "0ca08e94db43c9ef6bf22a9b803a776880841e9f7fbf7b9207ade0cdeb0c6251", [], [], "hexpm"},
+  "plug": {:hex, :plug, "1.4.3", "236d77ce7bf3e3a2668dc0d32a9b6f1f9b1f05361019946aae49874904be4aed", [], [{:cowboy, "~> 1.0.1 or ~> 1.1", [hex: :cowboy, repo: "hexpm", optional: true]}, {:mime, "~> 1.0", [hex: :mime, repo: "hexpm", optional: false]}], "hexpm"}}
diff --git a/test/plug_opentracing_test.exs b/test/plug_opentracing_test.exs
new file mode 100644
index 0000000..95e3fbe
--- /dev/null
+++ b/test/plug_opentracing_test.exs
@@ -0,0 +1,53 @@
+defmodule PlugOpenTracingTest do
+  use ExUnit.Case, async: true
+  use Plug.Test
+  alias Plug.Conn.Status
+
+  test "missing trace header results in new span" do
+    connection = conn(:get, "/test-path")
+    response = TestApp.call(connection, [])
+
+    assert response.status == Status.code(:ok)
+    assert response.resp_body != ""
+  end
+
+  test "bad trace header results in new span" do
+    connection = conn(:get, "/test-path") |> put_req_header("uber-trace-id", "1234")
+    response = TestApp.call(connection, [])
+
+    assert response.status == Status.code(:ok)
+    assert response.resp_body != ""
+  end
+
+  test "valid trace header results in span with those ids" do
+    connection = conn(:get, "/test-path") |> put_req_header("uber-trace-id", "6a5c63925e01051b:150b1b1adcde6f4:6a5c63925e01051b:1")
+    response = TestApp.call(connection, [])
+
+    assert response.status == Status.code(:ok)
+    assert response.resp_body == "7664110146171241755"
+  end
+
+  test "invalid hex trace header results in usable span" do
+    connection = conn(:get, "/test-path") |> put_req_header("uber-trace-id", "6a5x63925t01051b:150b1p1adcdq6f4:6a5c63925e01051b:1")
+    response = TestApp.call(connection, [])
+
+    assert response.status == Status.code(:ok)
+    assert response.resp_body == "1701"
+  end
+
+  test "empty trace header results in new span" do
+    connection = conn(:get, "/test-path") |> put_req_header("uber-trace-id", "")
+    response = TestApp.call(connection, [])
+
+    assert response.status == Status.code(:ok)
+    assert response.resp_body != ""
+  end
+
+  test "just some colons results in new span" do
+    connection = conn(:get, "/test-path") |> put_req_header("uber-trace-id", "::::")
+    response = TestApp.call(connection, [])
+
+    assert response.status == Status.code(:ok)
+    assert response.resp_body != ""
+  end
+end
diff --git a/test/test_helper.exs b/test/test_helper.exs
new file mode 100644
index 0000000..bd46c18
--- /dev/null
+++ b/test/test_helper.exs
@@ -0,0 +1,28 @@
+ExUnit.start()
+
+defmodule AppMaker do
+  defmacro __using__(options) do
+    quote do
+      use Plug.Router
+      alias Plug.Conn.Status
+
+      plug PlugOpenTracing, unquote(options)
+      plug :match
+      plug :dispatch
+    end
+  end
+end
+
+defmodule TestApp do
+  alias :otter, as: Otter
+  use AppMaker, trace_header: "uber-trace-id"
+
+  get "/test-path" do
+    send_resp(conn, Status.code(:ok), ids_to_string(conn))
+  end
+
+  defp ids_to_string(conn) do
+    {trace_id, _} = Otter.ids(conn.assigns[:trace_span])
+    "#{Integer.to_string(trace_id)}"
+  end
+end