Merge pull request #489 from maxmind/wstorey/transport-change

Avoid mutating http.DefaultTransport in NewUpdater

Author: oschwald

CHANGELOG.md

@@ -5,6 +5,10 @@
 - BREAKING CHANGE: `geoipupdate` stops updating on the first error.
 - A config file can now be used to configure the Docker image. This was
   documented but was not functional. Fixed by Shizun Ge. GitHub #433.
+- `NewUpdater` in the unexported `internal/geoipupdate` package no longer
+  mutates `http.DefaultTransport` when a proxy is configured. The CLI is the
+  only caller, so there is no user-visible behavior change. Reported by B.
+  Conners. GitHub #488.
 
 ## 7.1.1 (2025-07-09)
 

internal/geoipupdate/geoip_updater.go

@@ -35,12 +35,12 @@ type Updater struct {
 
 // NewUpdater initialized a new Updater struct.
 func NewUpdater(config *Config) (*Updater, error) {
-	transport := http.DefaultTransport
+	httpClient := &http.Client{}
 	if config.Proxy != nil {
-		proxyFunc := http.ProxyURL(config.Proxy)
-		transport.(*http.Transport).Proxy = proxyFunc
+		transport := http.DefaultTransport.(*http.Transport).Clone()
+		transport.Proxy = http.ProxyURL(config.Proxy)
+		httpClient.Transport = transport
 	}
-	httpClient := &http.Client{Transport: transport}
 
 	updateClient, err := client.New(
 		config.AccountID,

internal/geoipupdate/geoip_updater_test.go

@@ -11,8 +11,10 @@ import (
 	"log"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
@@ -232,6 +234,35 @@ func TestRetryWhenWriting(t *testing.T) {
 	require.Contains(t, logOutput.String(), `"edition_id":"foo-db-name"`)
 }
 
+// TestNewUpdaterDoesNotMutateDefaultTransport verifies that NewUpdater does not
+// modify http.DefaultTransport when a proxy is configured. See issue #488.
+func TestNewUpdaterDoesNotMutateDefaultTransport(t *testing.T) {
+	defaultTransport := http.DefaultTransport.(*http.Transport)
+	originalProxy := defaultTransport.Proxy
+
+	proxyURL, err := url.Parse("http://proxy.example.com:8080")
+	require.NoError(t, err)
+
+	tempDir := t.TempDir()
+	config := &Config{
+		AccountID:         10,
+		LicenseKey:        "foo",
+		EditionIDs:        []string{"GeoLite2-City"},
+		DatabaseDirectory: tempDir,
+		LockFile:          filepath.Join(tempDir, ".geoipupdate.lock"),
+		Proxy:             proxyURL,
+	}
+
+	_, err = NewUpdater(config)
+	require.NoError(t, err)
+
+	require.Equal(
+		t,
+		reflect.ValueOf(originalProxy).Pointer(),
+		reflect.ValueOf(defaultTransport.Proxy).Pointer(),
+	)
+}
+
 type mockUpdateClient struct {
 	i       int
 	outputs []client.DownloadResponse