http: allow custom `User-Agent` for outgoing HTTP requests

changelog/unreleased/issue-4768

@@ -0,0 +1,8 @@
+Enhancement: Allow custom User-Agent to be specified for outgoing requests
+
+Restic now permits setting a custom `User-Agent` for outgoing HTTP requests 
+using the global flag `--http-user-agent` or the `RESTIC_HTTP_USER_AGENT` 
+environment variable.
+
+https://github.com/restic/restic/issues/4768
+https://github.com/restic/restic/pull/4810

cmd/restic/global.go

@@ -135,6 +135,7 @@ func init() {
 	f.IntVar(&globalOptions.Limits.DownloadKb, "limit-download", 0, "limits downloads to a maximum `rate` in KiB/s. (default: unlimited)")
 	f.UintVar(&globalOptions.PackSize, "pack-size", 0, "set target pack `size` in MiB, created pack files may be larger (default: $RESTIC_PACK_SIZE)")
 	f.StringSliceVarP(&globalOptions.Options, "option", "o", []string{}, "set extended option (`key=value`, can be specified multiple times)")
+	f.StringVar(&globalOptions.HTTPUserAgent, "http-user-agent", "", "set a http user agent for outgoing http requests")
 	// Use our "generate" command instead of the cobra provided "completion" command
 	cmdRoot.CompletionOptions.DisableDefaultCmd = true
 
@@ -155,6 +156,10 @@ func init() {
 	// parse target pack size from env, on error the default value will be used
 	targetPackSize, _ := strconv.ParseUint(os.Getenv("RESTIC_PACK_SIZE"), 10, 32)
 	globalOptions.PackSize = uint(targetPackSize)
+
+	if os.Getenv("RESTIC_HTTP_USER_AGENT") != "" {
+		globalOptions.HTTPUserAgent = os.Getenv("RESTIC_HTTP_USER_AGENT")
+	}
 }
 
 func stdinIsTerminal() bool {

doc/manual_rest.rst

@@ -54,6 +54,7 @@ Usage help is available:
           --cleanup-cache              auto remove old cache directories
           --compression mode           compression mode (only available for repository format version 2), one of (auto|off|max) (default: $RESTIC_COMPRESSION) (default auto)
       -h, --help                       help for restic
+          --http-user-agent value      set a custom user agent for outgoing http requests
           --insecure-no-password       use an empty password for the repository, must be passed to every restic command (insecure)
           --insecure-tls               skip TLS certificate verification when connecting to the repository (insecure)
           --json                       set output mode to JSON for commands that support it
@@ -134,6 +135,7 @@ command:
           --cache-dir directory        set the cache directory. (default: use system default cache directory)
           --cleanup-cache              auto remove old cache directories
           --compression mode           compression mode (only available for repository format version 2), one of (auto|off|max) (default: $RESTIC_COMPRESSION) (default auto)
+          --http-user-agent value      set a custom user agent for outgoing http requests
           --insecure-no-password       use an empty password for the repository, must be passed to every restic command (insecure)
           --insecure-tls               skip TLS certificate verification when connecting to the repository (insecure)
           --json                       set output mode to JSON for commands that support it

internal/backend/http_transport.go

@@ -28,6 +28,9 @@ type TransportOptions struct {
 
 	// Skip TLS certificate verification
 	InsecureTLS bool
+
+	// Specify Custom User-Agent for the http Client
+	HTTPUserAgent string
 }
 
 // readPEMCertKey reads a file and returns the PEM encoded certificate and key
@@ -132,6 +135,13 @@ func Transport(opts TransportOptions) (http.RoundTripper, error) {
 	}
 
 	rt := http.RoundTripper(tr)
+
+	// if the userAgent is set in the Transport Options, wrap the
+	// http.RoundTripper
+	if opts.HTTPUserAgent != "" {
+		rt = newCustomUserAgentRoundTripper(rt, opts.HTTPUserAgent)
+	}
+
 	if feature.Flag.Enabled(feature.BackendErrorRedesign) {
 		rt = newWatchdogRoundtripper(rt, 120*time.Second, 128*1024)
 	}

internal/backend/httpuseragent_roundtripper.go

@@ -0,0 +1,25 @@
+package backend
+
+import "net/http"
+
+// httpUserAgentRoundTripper is a custom http.RoundTripper that modifies the User-Agent header
+// of outgoing HTTP requests.
+type httpUserAgentRoundTripper struct {
+	userAgent string
+	rt        http.RoundTripper
+}
+
+func newCustomUserAgentRoundTripper(rt http.RoundTripper, userAgent string) *httpUserAgentRoundTripper {
+	return &httpUserAgentRoundTripper{
+		rt:        rt,
+		userAgent: userAgent,
+	}
+}
+
+// RoundTrip modifies the User-Agent header of the request and then delegates the request
+// to the underlying RoundTripper.
+func (c *httpUserAgentRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	req = req.Clone(req.Context())
+	req.Header.Set("User-Agent", c.userAgent)
+	return c.rt.RoundTrip(req)
+}

internal/backend/httpuseragent_roundtripper_test.go

@@ -0,0 +1,50 @@
+package backend
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestCustomUserAgentTransport(t *testing.T) {
+	// Create a mock HTTP handler that checks the User-Agent header
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		userAgent := r.Header.Get("User-Agent")
+		if userAgent != "TestUserAgent" {
+			t.Errorf("Expected User-Agent: TestUserAgent, got: %s", userAgent)
+		}
+		w.WriteHeader(http.StatusOK)
+	})
+
+	// Create a test server with the mock handler
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	// Create a custom user agent transport
+	customUserAgent := "TestUserAgent"
+	transport := &httpUserAgentRoundTripper{
+		userAgent: customUserAgent,
+		rt:        http.DefaultTransport,
+	}
+
+	// Create an HTTP client with the custom transport
+	client := &http.Client{
+		Transport: transport,
+	}
+
+	// Make a request to the test server
+	resp, err := client.Get(server.URL)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer func() {
+		if err := resp.Body.Close(); err != nil {
+			t.Log("failed to close response body")
+		}
+	}()
+
+	// Check the response status code
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("Expected status code: %d, got: %d", http.StatusOK, resp.StatusCode)
+	}
+}