From 2288666f638b34ac60a48b4648fd6907b4ea4c04 Mon Sep 17 00:00:00 2001
From: Lucas Pimentel <lucas.pimentel@datadoghq.com>
Date: Mon, 3 Dec 2018 17:51:22 -0500
Subject: [PATCH] set "env" tag from DD_DEV environment variable (#225)

* add support for `DD_ENV` environment variable

* define constant `Tags.Env`

* add unit test

* fix comment

* fix comment
---
 src/Datadog.Trace/Tags.cs               |  5 +++++
 src/Datadog.Trace/Tracer.cs             | 10 ++++++++++
 test/Datadog.Trace.Tests/TracerTests.cs | 17 +++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/src/Datadog.Trace/Tags.cs b/src/Datadog.Trace/Tags.cs
index f9fb6d6f41a3..a10286edcdad 100644
--- a/src/Datadog.Trace/Tags.cs
+++ b/src/Datadog.Trace/Tags.cs
@@ -5,6 +5,11 @@ namespace Datadog.Trace
     /// </summary>
     public static class Tags
     {
+        /// <summary>
+        /// The environment of the profiled service.
+        /// </summary>
+        public const string Env = "env";
+
         /// <summary>
         /// The URL of an HTTP request
         /// </summary>
diff --git a/src/Datadog.Trace/Tracer.cs b/src/Datadog.Trace/Tracer.cs
index bd015462a4c2..f2a87d3f9f9b 100644
--- a/src/Datadog.Trace/Tracer.cs
+++ b/src/Datadog.Trace/Tracer.cs
@@ -17,6 +17,7 @@ public class Tracer : IDatadogTracer
         private const string UnknownServiceName = "UnknownService";
         private const string DefaultTraceAgentHost = "localhost";
         private const string DefaultTraceAgentPort = "8126";
+        private const string EnvVariableName = "DD_ENV";
 
         private static readonly string[] TraceAgentHostEnvironmentVariableNames =
         {
@@ -146,6 +147,15 @@ public Span StartSpan(string operationName, SpanContext childOf = null, string s
             }
 
             var span = new Span(this, childOf, operationName, serviceName, startTime);
+
+            var env = Environment.GetEnvironmentVariable(EnvVariableName);
+
+            // automatically add the "env" tag if environment variable is defined
+            if (!string.IsNullOrWhiteSpace(env))
+            {
+                span.SetTag(Tags.Env, env);
+            }
+
             span.TraceContext.AddSpan(span);
             return span;
         }
diff --git a/test/Datadog.Trace.Tests/TracerTests.cs b/test/Datadog.Trace.Tests/TracerTests.cs
index abfa77b00bb7..20ad65357fa3 100644
--- a/test/Datadog.Trace.Tests/TracerTests.cs
+++ b/test/Datadog.Trace.Tests/TracerTests.cs
@@ -276,5 +276,22 @@ public void SetHostAndPortEnvironmentVariables(string host, string port, string
             Environment.SetEnvironmentVariable("DD_AGENT_HOST", originalHost);
             Environment.SetEnvironmentVariable("DD_TRACE_AGENT_PORT", originalPort);
         }
+
+        [Theory]
+        [InlineData(null)]
+        [InlineData("test")]
+        public void SetEnvEnvironmentVariable(string env)
+        {
+            var name = "DD_ENV";
+            string originalEnv = Environment.GetEnvironmentVariable(name);
+
+            Environment.SetEnvironmentVariable(name, env);
+            Span span = Tracer.Instance.StartSpan("operation");
+
+            Assert.Equal(env, span.GetTag(Tags.Env));
+
+            // reset the environment variable to its original value (if any) when done
+            Environment.SetEnvironmentVariable(name, originalEnv);
+        }
     }
 }