Support Warning header aggregation and reporting in crane

cmd/crane/cmd/root.go

@@ -20,6 +20,10 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"runtime"
+	"sort"
+	"strings"
+	"sync"
 
 	"github.com/docker/cli/cli/config"
 	"github.com/google/go-containerregistry/internal/cmd"
@@ -44,6 +48,8 @@ func New(use, short string, options []crane.Option) *cobra.Command {
 	ndlayers := false
 	platform := &platformValue{}
 
+	wt := &warnTransport{}
+
 	root := &cobra.Command{
 		Use:               use,
 		Short:             short,
@@ -90,8 +96,15 @@ func New(use, short string, options []crane.Option) *cobra.Command {
 				}
 			}
 
+			// Inject our warning-collecting transport.
+			wt.inner = rt
+			rt = wt
+
 			options = append(options, crane.WithTransport(rt))
 		},
+		PersistentPostRun: func(_ *cobra.Command, _ []string) {
+			wt.Report() // Report any collected warnings.
+		},
 	}
 
 	root.AddCommand(
@@ -146,3 +159,76 @@ func (ht *headerTransport) RoundTrip(in *http.Request) (*http.Response, error) {
 	}
 	return ht.inner.RoundTrip(in)
 }
+
+type warnTransport struct {
+	mu    sync.Mutex
+	warns map[string]struct{}
+	inner http.RoundTripper
+}
+
+func (wt *warnTransport) RoundTrip(in *http.Request) (*http.Response, error) {
+	resp, err := wt.inner.RoundTrip(in)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, wh := range resp.Header.Values("Warning") {
+		if !strings.HasPrefix(wh, "299 - ") {
+			// Warning response headers are supposed to have
+			// warn-code 299 and warn-agent "-"; discard these.
+			continue
+		}
+		start := strings.Index(wh, `"`)
+		end := strings.LastIndex(wh, `"`)
+		warn := wh[start+1 : end]
+		func() {
+			wt.mu.Lock()
+			defer wt.mu.Unlock()
+			if wt.warns == nil {
+				wt.warns = map[string]struct{}{}
+			}
+			wt.warns[warn] = struct{}{}
+		}()
+	}
+	return resp, nil
+}
+
+func (wt *warnTransport) Report() {
+	if wt.warns == nil {
+		return
+	}
+
+	warns := make([]string, 0, len(wt.warns))
+	for k := range wt.warns {
+		warns = append(warns, k)
+	}
+	sort.Strings(warns)
+	prefix := "\033[1;33m[WARNING]\033[0m:"
+	if nocolor() {
+		prefix = "[WARNING]:"
+	}
+	for _, w := range warns {
+		fmt.Fprintln(os.Stderr, prefix, w)
+	}
+}
+
+func nocolor() bool {
+	// These adapted from https://github.com/kubernetes/kubernetes/blob/fe91bc257b505eb6057eb50b9c550a7c63e9fb91/staging/src/k8s.io/kubectl/pkg/util/term/term.go
+
+	// https://en.wikipedia.org/wiki/Computer_terminal#Dumb_terminals
+	if os.Getenv("TERM") == "dumb" {
+		return true
+	}
+
+	// https://no-color.org/
+	if _, nocolor := os.LookupEnv("NO_COLOR"); nocolor {
+		return true
+	}
+
+	// On Windows WT_SESSION is set by the modern terminal component.
+	// Older terminals have poor support for UTF-8, VT escape codes, etc.
+	if runtime.GOOS == "windows" && os.Getenv("WT_SESSION") == "" {
+		return true
+	}
+	return false
+}

cmd/registry/main.go

@@ -38,7 +38,9 @@ func main() {
 	log.Printf("serving on port %d", porti)
 	s := &http.Server{
 		ReadHeaderTimeout: 5 * time.Second, // prevent slowloris, quiet linter
-		Handler:           registry.New(),
+		Handler: registry.New(
+			registry.WithWarning(.01, "Congratulations! You've won a lifetime's supply of free image pulls from this in-memory registry!"),
+		),
 	}
 	log.Fatal(s.Serve(listener))
 }

go.mod

@@ -21,7 +21,6 @@ require (
 require (
 	cloud.google.com/go/compute v1.18.0 // indirect
 	cloud.google.com/go/compute/metadata v0.2.3 // indirect
-	github.com/Azure/go-ansiterm v0.0.0-20210617225240-d185dfc1b5a1 // indirect
 	github.com/Microsoft/go-winio v0.6.0 // indirect
 	github.com/cpuguy83/go-md2man/v2 v2.0.2 // indirect
 	github.com/docker/docker-credential-helpers v0.7.0 // indirect
@@ -30,7 +29,7 @@ require (
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
-	github.com/moby/term v0.0.0-20210610120745-9d4ed1856297 // indirect
+	github.com/moby/term v0.0.0-20221205130635-1aeaba878587 // indirect
 	github.com/morikuni/aec v1.0.0 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect

pkg/registry/registry.go

@@ -24,7 +24,9 @@
 package registry
 
 import (
+	"fmt"
 	"log"
+	"math/rand"
 	"net/http"
 	"os"
 )
@@ -34,11 +36,21 @@ type registry struct {
 	blobs            blobs
 	manifests        manifests
 	referrersEnabled bool
+	warnings         map[float64]string
 }
 
 // https://docs.docker.com/registry/spec/api/#api-version-check
 // https://github.com/opencontainers/distribution-spec/blob/master/spec.md#api-version-check
 func (r *registry) v2(resp http.ResponseWriter, req *http.Request) *regError {
+	if r.warnings != nil {
+		rnd := rand.Float64()
+		for prob, msg := range r.warnings {
+			if prob > rnd {
+				resp.Header().Add("Warning", fmt.Sprintf(`299 - "%s"`, msg))
+			}
+		}
+	}
+
 	if isBlob(req) {
 		return r.blobs.handle(resp, req)
 	}
@@ -115,3 +127,12 @@ func WithReferrersSupport(enabled bool) Option {
 		r.referrersEnabled = enabled
 	}
 }
+
+func WithWarning(prob float64, msg string) Option {
+	return func(r *registry) {
+		if r.warnings == nil {
+			r.warnings = map[float64]string{}
+		}
+		r.warnings[prob] = msg
+	}
+}

vendor/modules.txt

@@ -4,8 +4,6 @@ cloud.google.com/go/compute/internal
 # cloud.google.com/go/compute/metadata v0.2.3
 ## explicit; go 1.19
 cloud.google.com/go/compute/metadata
-# github.com/Azure/go-ansiterm v0.0.0-20210617225240-d185dfc1b5a1
-## explicit; go 1.16
 # github.com/Microsoft/go-winio v0.6.0
 ## explicit; go 1.17
 github.com/Microsoft/go-winio
@@ -91,8 +89,8 @@ github.com/klauspost/compress/zstd/internal/xxhash
 # github.com/mitchellh/go-homedir v1.1.0
 ## explicit
 github.com/mitchellh/go-homedir
-# github.com/moby/term v0.0.0-20210610120745-9d4ed1856297
-## explicit; go 1.13
+# github.com/moby/term v0.0.0-20221205130635-1aeaba878587
+## explicit; go 1.18
 # github.com/morikuni/aec v1.0.0
 ## explicit
 # github.com/opencontainers/go-digest v1.0.0