From 586a0bb9122e875ec2d0ed772533abfdd9ea8ec0 Mon Sep 17 00:00:00 2001
From: Rachel Yang <rachel.yang@datadoghq.com>
Date: Fri, 8 Nov 2024 11:30:07 -0500
Subject: [PATCH] ddtrace/tracer: fix trace_agent_url on startup log (#2949)
MIME-Version: 1.0
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Co-authored-by: Dario Castañé <dario.castane@datadoghq.com>
---
 ddtrace/tracer/log.go      |  9 ++++-
 ddtrace/tracer/log_test.go | 75 ++++++++++++++++++++++++++++++++++++++
 ddtrace/tracer/option.go   |  4 ++
 3 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/ddtrace/tracer/log.go b/ddtrace/tracer/log.go
index f64d2dadee..79b538e958 100644
--- a/ddtrace/tracer/log.go
+++ b/ddtrace/tracer/log.go
@@ -105,6 +105,13 @@ func logStartup(t *tracer) {
 		injectorNames = "custom"
 		extractorNames = "custom"
 	}
+	// Determine the agent URL to use in the logs
+	var agentURL string
+	if t.config.originalAgentURL != nil && t.config.originalAgentURL.Scheme == "unix" {
+		agentURL = t.config.originalAgentURL.String()
+	} else {
+		agentURL = t.config.transport.endpoint()
+	}
 
 	info := startupInfo{
 		Date:                        time.Now().Format(time.RFC3339),
@@ -115,7 +122,7 @@ func logStartup(t *tracer) {
 		LangVersion:                 runtime.Version(),
 		Env:                         t.config.env,
 		Service:                     t.config.serviceName,
-		AgentURL:                    t.config.transport.endpoint(),
+		AgentURL:                    agentURL,
 		Debug:                       t.config.debug,
 		AnalyticsEnabled:            !math.IsNaN(globalconfig.AnalyticsRate()),
 		SampleRate:                  fmt.Sprintf("%f", t.rulesSampling.traces.globalRate),
diff --git a/ddtrace/tracer/log_test.go b/ddtrace/tracer/log_test.go
index 3bc2998569..a0c0d0597c 100644
--- a/ddtrace/tracer/log_test.go
+++ b/ddtrace/tracer/log_test.go
@@ -8,6 +8,7 @@ package tracer
 import (
 	"fmt"
 	"math"
+	"regexp"
 	"testing"
 
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
@@ -261,3 +262,77 @@ func setup(t *testing.T, customProp Propagator) string {
 	require.Len(t, tp.Logs(), 2)
 	return tp.Logs()[1]
 }
+
+func findLogEntry(logs []string, pattern string) (string, bool) {
+	for _, log := range logs {
+		if matched, _ := regexp.MatchString(pattern, log); matched {
+			return log, true
+		}
+	}
+	return "", false
+}
+
+func TestAgentURL(t *testing.T) {
+	assert := assert.New(t)
+	tp := new(log.RecordLogger)
+	tracer := newTracer(WithLogger(tp), WithUDS("var/run/datadog/apm.socket"))
+	defer tracer.Stop()
+	tp.Reset()
+	tp.Ignore("appsec: ", telemetry.LogPrefix)
+	logStartup(tracer)
+	logEntry, found := findLogEntry(tp.Logs(), `"agent_url":"unix://var/run/datadog/apm.socket"`)
+	if !found {
+		t.Fatal("Expected to find log entry")
+	}
+	assert.Regexp(`"agent_url":"unix://var/run/datadog/apm.socket"`, logEntry)
+}
+
+func TestAgentURLFromEnv(t *testing.T) {
+	assert := assert.New(t)
+	t.Setenv("DD_TRACE_AGENT_URL", "unix://var/run/datadog/apm.socket")
+	tp := new(log.RecordLogger)
+	tracer := newTracer(WithLogger(tp))
+	defer tracer.Stop()
+	tp.Reset()
+	tp.Ignore("appsec: ", telemetry.LogPrefix)
+	logStartup(tracer)
+	logEntry, found := findLogEntry(tp.Logs(), `"agent_url":"unix://var/run/datadog/apm.socket"`)
+	if !found {
+		t.Fatal("Expected to find log entry")
+	}
+	assert.Regexp(`"agent_url":"unix://var/run/datadog/apm.socket"`, logEntry)
+}
+
+func TestInvalidAgentURL(t *testing.T) {
+	assert := assert.New(t)
+	// invalid socket URL
+	t.Setenv("DD_TRACE_AGENT_URL", "var/run/datadog/apm.socket")
+	tp := new(log.RecordLogger)
+	tracer := newTracer(WithLogger(tp))
+	defer tracer.Stop()
+	tp.Reset()
+	tp.Ignore("appsec: ", telemetry.LogPrefix)
+	logStartup(tracer)
+	logEntry, found := findLogEntry(tp.Logs(), `"agent_url":"http://localhost:8126/v0.4/traces"`)
+	if !found {
+		t.Fatal("Expected to find log entry")
+	}
+	// assert that it is the default URL
+	assert.Regexp(`"agent_url":"http://localhost:8126/v0.4/traces"`, logEntry)
+}
+
+func TestAgentURLConflict(t *testing.T) {
+	assert := assert.New(t)
+	t.Setenv("DD_TRACE_AGENT_URL", "unix://var/run/datadog/apm.socket")
+	tp := new(log.RecordLogger)
+	tracer := newTracer(WithLogger(tp), WithUDS("var/run/datadog/apm.socket"), WithAgentAddr("localhost:8126"))
+	defer tracer.Stop()
+	tp.Reset()
+	tp.Ignore("appsec: ", telemetry.LogPrefix)
+	logStartup(tracer)
+	logEntry, found := findLogEntry(tp.Logs(), `"agent_url":"http://localhost:8126/v0.4/traces"`)
+	if !found {
+		t.Fatal("Expected to find log entry")
+	}
+	assert.Regexp(`"agent_url":"http://localhost:8126/v0.4/traces"`, logEntry)
+}
diff --git a/ddtrace/tracer/option.go b/ddtrace/tracer/option.go
index 8415b29ee5..e9bb4bf120 100644
--- a/ddtrace/tracer/option.go
+++ b/ddtrace/tracer/option.go
@@ -160,6 +160,9 @@ type config struct {
 	// agentURL is the agent URL that receives traces from the tracer.
 	agentURL *url.URL
 
+	// originalAgentURL is the agent URL that receives traces from the tracer and does not get changed.
+	originalAgentURL *url.URL
+
 	// serviceMappings holds a set of service mappings to dynamically rename services
 	serviceMappings map[string]string
 
@@ -457,6 +460,7 @@ func newConfig(opts ...StartOption) *config {
 	if c.agentURL == nil {
 		c.agentURL = internal.AgentURLFromEnv()
 	}
+	c.originalAgentURL = c.agentURL // Preserve the original agent URL for logging
 	if c.httpClient == nil {
 		if c.agentURL.Scheme == "unix" {
 			// If we're connecting over UDS we can just rely on the agent to provide the hostname