Context.SetUsername takes precedence (#973)

* Context.SetUsername takes precedence

If Context.SetUsername is called explicitly,
don't automatically set the username based on
HTTP user info (which may or may not exist.)

* Update CHANGELOG.asciidoc

CHANGELOG.asciidoc

@@ -24,6 +24,7 @@ endif::[]
 https://github.com/elastic/apm-agent-go/compare/v1.12.0...master[View commits]
 
 - Prefer w3c traceparent header over legacy elastic-apm-traceparent {pull}963[#(963)]
+- Context.SetUsername now takes precedence over HTTP user info from Context.SetHTTPRequest {pull}973[#(973)]
 
 [[release-notes-1.x]]
 === Go Agent version 1.x

context.go

@@ -159,7 +159,8 @@ func (c *Context) SetFramework(name, version string) {
 // If the request contains HTTP Basic Authentication, the username
 // from that will be recorded in the context. Otherwise, if the
 // request contains user info in the URL (i.e. a client-side URL),
-// that will be used.
+// that will be used. An explicit call to SetUsername always takes
+// precedence.
 func (c *Context) SetHTTPRequest(req *http.Request) {
 	// Special cases to avoid calling into fmt.Sprintf in most cases.
 	var httpVersion string
@@ -203,13 +204,15 @@ func (c *Context) SetHTTPRequest(req *http.Request) {
 		c.request.Socket = &c.requestSocket
 	}
 
-	username, _, ok := req.BasicAuth()
-	if !ok && req.URL.User != nil {
-		username = req.URL.User.Username()
-	}
-	c.user.Username = truncateString(username)
-	if c.user.Username != "" {
-		c.model.User = &c.user
+	if c.model.User == nil {
+		username, _, ok := req.BasicAuth()
+		if !ok && req.URL.User != nil {
+			username = req.URL.User.Username()
+		}
+		c.user.Username = truncateString(username)
+		if c.user.Username != "" {
+			c.model.User = &c.user
+		}
 	}
 }
 

context_test.go

@@ -19,6 +19,8 @@ package apm_test
 
 import (
 	"context"
+	"net/http"
+	"net/url"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -119,6 +121,18 @@ func TestContextCustom(t *testing.T) {
 	}, tx.Context.Custom)
 }
 
+func TestContextSetUsernamePrecedence(t *testing.T) {
+	tx := testSendTransaction(t, func(tx *apm.Transaction) {
+		tx.Context.SetUsername("frieda")
+		req, _ := http.NewRequest("GET", "/", nil)
+		req.URL.User = url.User("fred")
+		tx.Context.SetHTTPRequest(req)
+	})
+	require.NotNil(t, tx.Context)
+	require.NotNil(t, "", tx.Context.User)
+	assert.Equal(t, "frieda", tx.Context.User.Username)
+}
+
 func testSendTransaction(t *testing.T, f func(tx *apm.Transaction)) model.Transaction {
 	transaction, _, _ := apmtest.WithTransaction(func(ctx context.Context) {
 		f(apm.TransactionFromContext(ctx))