Use notary library for trusted image fetch and signing

Add a trusted flag to force the cli to resolve a tag into a digest via the notary trust library and pull by digest.
On push the flag the trust flag will indicate the digest and size of a manifest should be signed and push to a notary server.
If a tag is given, the cli will resolve the tag into a digest and pull by digest.
After pulling, if a tag is given the cli makes a request to tag the image.

Use certificate directory for notary requests

Read certificates using same logic used by daemon for registry requests.

Catch JSON syntax errors from Notary client

When an uncaught error occurs in Notary it may show up in Docker as a JSON syntax error, causing a confusing error message to the user.
Provide a generic error when a JSON syntax error occurs.

Catch expiration errors and wrap in additional context.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

docs/registry.go

@@ -2,10 +2,14 @@ package registry
 
 import (
 	"crypto/tls"
+	"crypto/x509"
 	"errors"
+	"fmt"
+	"io/ioutil"
 	"net"
 	"net/http"
 	"os"
+	"path/filepath"
 	"runtime"
 	"strings"
 	"time"
@@ -54,6 +58,54 @@ func hasFile(files []os.FileInfo, name string) bool {
 	return false
 }
 
+// ReadCertsDirectory reads the directory for TLS certificates
+// including roots and certificate pairs and updates the
+// provided TLS configuration.
+func ReadCertsDirectory(tlsConfig *tls.Config, directory string) error {
+	fs, err := ioutil.ReadDir(directory)
+	if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+
+	for _, f := range fs {
+		if strings.HasSuffix(f.Name(), ".crt") {
+			if tlsConfig.RootCAs == nil {
+				// TODO(dmcgowan): Copy system pool
+				tlsConfig.RootCAs = x509.NewCertPool()
+			}
+			logrus.Debugf("crt: %s", filepath.Join(directory, f.Name()))
+			data, err := ioutil.ReadFile(filepath.Join(directory, f.Name()))
+			if err != nil {
+				return err
+			}
+			tlsConfig.RootCAs.AppendCertsFromPEM(data)
+		}
+		if strings.HasSuffix(f.Name(), ".cert") {
+			certName := f.Name()
+			keyName := certName[:len(certName)-5] + ".key"
+			logrus.Debugf("cert: %s", filepath.Join(directory, f.Name()))
+			if !hasFile(fs, keyName) {
+				return fmt.Errorf("Missing key %s for certificate %s", keyName, certName)
+			}
+			cert, err := tls.LoadX509KeyPair(filepath.Join(directory, certName), filepath.Join(directory, keyName))
+			if err != nil {
+				return err
+			}
+			tlsConfig.Certificates = append(tlsConfig.Certificates, cert)
+		}
+		if strings.HasSuffix(f.Name(), ".key") {
+			keyName := f.Name()
+			certName := keyName[:len(keyName)-4] + ".cert"
+			logrus.Debugf("key: %s", filepath.Join(directory, f.Name()))
+			if !hasFile(fs, certName) {
+				return fmt.Errorf("Missing certificate %s for key %s", certName, keyName)
+			}
+		}
+	}
+
+	return nil
+}
+
 // DockerHeaders returns request modifiers that ensure requests have
 // the User-Agent header set to dockerUserAgent and that metaHeaders
 // are added.