Implement better user agent support (#837)

* Expose transport.NewUserAgent

This allows you to supply a customer user agent string that will be
prepended before the go-containerregistry portion.

This uses go module build info to determine the version of
go-containerregistry that you have pulled in, which will be included in
the user agent as "go-containerregistry/${VERSION}". If we cannot get
the version, this is just "go-containerregistry".

* Expose remote.WithUserAgent

* Expose crane.WithUserAgent

* Supply useragent from crane CLI

cmd/crane/cmd/root.go

@@ -13,8 +13,10 @@
 package cmd
 
 import (
+	"fmt"
 	"net/http"
 	"os"
+	"path/filepath"
 
 	"github.com/docker/cli/cli/config"
 	"github.com/google/go-containerregistry/pkg/crane"
@@ -49,6 +51,13 @@ func New(use, short string, options []crane.Option) *cobra.Command {
 			if insecure {
 				options = append(options, crane.Insecure)
 			}
+			if Version != "" {
+				binary := "crane"
+				if len(os.Args[0]) != 0 {
+					binary = filepath.Base(os.Args[0])
+				}
+				options = append(options, crane.WithUserAgent(fmt.Sprintf("%s/%s", binary, Version)))
+			}
 
 			options = append(options, crane.WithPlatform(platform.platform))
 

cmd/crane/cmd/version.go

@@ -11,6 +11,16 @@ import (
 // -ldflags="-X 'github.com/google/go-containerregistry/cmd/crane/cmd.Version=$TAG'"
 var Version string
 
+func init() {
+	if Version == "" {
+		i, ok := debug.ReadBuildInfo()
+		if !ok {
+			return
+		}
+		Version = i.Main.Version
+	}
+}
+
 // NewCmdVersion creates a new cobra.Command for the version subcommand.
 func NewCmdVersion() *cobra.Command {
 	return &cobra.Command{
@@ -23,14 +33,10 @@ This could also be the go module version, if built with go modules (often "(deve
 		Args: cobra.NoArgs,
 		Run: func(_ *cobra.Command, _ []string) {
 			if Version == "" {
-				i, ok := debug.ReadBuildInfo()
-				if !ok {
-					fmt.Println("could not determine build information")
-					return
-				}
-				Version = i.Main.Version
+				fmt.Println("could not determine build information")
+			} else {
+				fmt.Println(Version)
 			}
-			fmt.Println(Version)
 		},
 	}
 }

pkg/crane/options.go

@@ -89,3 +89,11 @@ func WithAuth(auth authn.Authenticator) Option {
 		o.remote[0] = remote.WithAuth(auth)
 	}
 }
+
+// WithUserAgent adds the given string to the User-Agent header for any HTTP
+// requests.
+func WithUserAgent(ua string) Option {
+	return func(o *options) {
+		o.remote = append(o.remote, remote.WithUserAgent(ua))
+	}
+}

pkg/v1/remote/options.go

@@ -35,6 +35,7 @@ type options struct {
 	platform  v1.Platform
 	context   context.Context
 	jobs      int
+	userAgent string
 }
 
 var defaultPlatform = v1.Platform{
@@ -80,6 +81,11 @@ func makeOptions(target authn.Resource, opts ...Option) (*options, error) {
 	// Wrap the transport in something that can retry network flakes.
 	o.transport = transport.NewRetry(o.transport)
 
+	// Wrap this last to prevent transport.New from double-wrapping.
+	if o.userAgent != "" {
+		o.transport = transport.NewUserAgent(o.transport, o.userAgent)
+	}
+
 	return o, nil
 }
 
@@ -156,3 +162,14 @@ func WithJobs(jobs int) Option {
 		return nil
 	}
 }
+
+// WithUserAgent adds the given string to the User-Agent header for any HTTP
+// requests. This header will also include "go-containerregistry/${version}".
+//
+// If you want to completely overwrite the User-Agent header, use WithTransport.
+func WithUserAgent(ua string) Option {
+	return func(o *options) error {
+		o.userAgent = ua
+		return nil
+	}
+}

pkg/v1/remote/transport/basic.go

@@ -58,6 +58,5 @@ func (bt *basicTransport) RoundTrip(in *http.Request) (*http.Response, error) {
 			}
 		}
 	}
-	in.Header.Set("User-Agent", transportName)
 	return bt.inner.RoundTrip(in)
 }

pkg/v1/remote/transport/bearer.go

@@ -233,7 +233,7 @@ func (bt *bearerTransport) refreshOauth(ctx context.Context) ([]byte, error) {
 	v := url.Values{}
 	v.Set("scope", strings.Join(bt.scopes, " "))
 	v.Set("service", bt.service)
-	v.Set("client_id", transportName)
+	v.Set("client_id", defaultUserAgent)
 	if auth.IdentityToken != "" {
 		v.Set("grant_type", "refresh_token")
 		v.Set("refresh_token", auth.IdentityToken)

pkg/v1/remote/transport/transport.go

@@ -55,14 +55,16 @@ func NewWithContext(ctx context.Context, reg name.Registry, auth authn.Authentic
 		return nil, err
 	}
 
-	// Wrap the given transport in transports that use an appropriate scheme,
-	// (based on the ping response) and set the user agent.
-	t = &useragentTransport{
-		inner: &schemeTransport{
-			scheme:   pr.scheme,
-			registry: reg,
-			inner:    t,
-		},
+	// Wrap t with a useragent transport unless we already have one.
+	if _, ok := t.(*userAgentTransport); !ok {
+		t = NewUserAgent(t, "")
+	}
+
+	// Wrap t in a transport that selects the appropriate scheme based on the ping response.
+	t = &schemeTransport{
+		scheme:   pr.scheme,
+		registry: reg,
+		inner:    t,
 	}
 
 	switch pr.challenge.Canonical() {

pkg/v1/remote/transport/transport_test.go

@@ -64,9 +64,6 @@ func TestTransportSelectionAnonymous(t *testing.T) {
 	if got, want := recorded.URL.Scheme, "https"; got != want {
 		t.Errorf("wrong scheme, want %s got %s", want, got)
 	}
-	if want, got := recorded.Header.Get("User-Agent"), transportName; want != got {
-		t.Errorf("wrong useragent, want %s got %s", want, got)
-	}
 }
 
 func TestTransportSelectionBasic(t *testing.T) {

pkg/v1/remote/transport/useragent.go

@@ -14,19 +14,70 @@
 
 package transport
 
-import "net/http"
+import (
+	"fmt"
+	"net/http"
+	"runtime/debug"
+)
 
 const (
-	transportName = "go-containerregistry"
+	defaultUserAgent = "go-containerregistry"
+	moduleName       = "github.com/google/go-containerregistry"
 )
 
-type useragentTransport struct {
-	// Wrapped by useragentTransport.
+var ggcrVersion = defaultUserAgent
+
+type userAgentTransport struct {
 	inner http.RoundTripper
+	ua    string
+}
+
+func init() {
+	if v := version(); v != "" {
+		ggcrVersion = fmt.Sprintf("%s/%s", defaultUserAgent, v)
+	}
+}
+
+func version() string {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return ""
+	}
+
+	// Happens for crane and gcrane.
+	if info.Main.Path == moduleName {
+		return info.Main.Version
+	}
+
+	// Anything else.
+	for _, dep := range info.Deps {
+		if dep.Path == moduleName {
+			return dep.Version
+		}
+	}
+
+	return ""
+}
+
+// NewUserAgent returns an http.Roundtripper that sets the user agent to
+// The provided string plus additional go-containerregistry information,
+// e.g. if provided "crane/v0.1.4" and this modules was built at v0.1.4:
+//
+// User-Agent: crane/v0.1.4 go-containerregistry/v0.1.4
+func NewUserAgent(inner http.RoundTripper, ua string) http.RoundTripper {
+	if ua == "" {
+		ua = ggcrVersion
+	} else {
+		ua = fmt.Sprintf("%s %s", ua, ggcrVersion)
+	}
+	return &userAgentTransport{
+		inner: inner,
+		ua:    ua,
+	}
 }
 
 // RoundTrip implements http.RoundTripper
-func (ut *useragentTransport) RoundTrip(in *http.Request) (*http.Response, error) {
-	in.Header.Set("User-Agent", transportName)
+func (ut *userAgentTransport) RoundTrip(in *http.Request) (*http.Response, error) {
+	in.Header.Set("User-Agent", ut.ua)
 	return ut.inner.RoundTrip(in)
 }