BREAKING CHANGE: unify UNetStack and CA's CertificationAuthority beha…

…vior (#42)

The UNetStack and CA structures have similar functionality exposed
through a different interface, which causes us to create an interface
and a wrapper for the code in probe-cli.

I noticed about this when I was trying to integrate new netem changes,
and it occurred to me we can just make the interfaces uniform here and
avoid doing some additional work in probe-cli.

Note: this is a breaking change because `(*Ca).CACert` was a field and
now is a method.

Also part of ooni/probe#2531

ca.go

@@ -85,10 +85,7 @@ func caMustNewAuthority(name, organization string, validity time.Duration,
 //
 // SPDX-License-Identifier: Apache-2.0.
 type CA struct {
-	// CACert is the public certificate used by the CA.
-	CACert *x509.Certificate
-
-	// These fields are not exported
+	caCert   *x509.Certificate
 	capriv   any
 	keyID    []byte
 	org      string
@@ -101,6 +98,8 @@ func MustNewCA() *CA {
 	return MustNewCAWithTimeNow(time.Now)
 }
 
+var _ CertificationAuthority = &CA{}
+
 // MustNewCA is like [NewCA] but uses a custom [time.Now] func.
 //
 // This code is derived from github.com/google/martian/v3.
@@ -123,7 +122,7 @@ func MustNewCAWithTimeNow(timeNow func() time.Time) *CA {
 	keyID := h.Sum(nil)
 
 	return &CA{
-		CACert:   ca,
+		caCert:   ca,
 		capriv:   privateKey,
 		priv:     priv,
 		keyID:    keyID,
@@ -132,11 +131,23 @@ func MustNewCAWithTimeNow(timeNow func() time.Time) *CA {
 	}
 }
 
-// CertPool returns an [x509.CertPool] using the given [*CA].
-func (c *CA) CertPool() *x509.CertPool {
-	pool := x509.NewCertPool()
-	pool.AddCert(c.CACert)
-	return pool
+// CACert implements [CertificationAuthority].
+func (ca *CA) CACert() *x509.Certificate {
+	return ca.caCert
+}
+
+// DefaultCertPool implements [CertificationAuthority].
+func (c *CA) DefaultCertPool() *x509.CertPool {
+	p := x509.NewCertPool()
+	p.AddCert(c.caCert)
+	return p
+}
+
+// MustNewServerTLSConfig implements [CertificationAuthority].
+func (ca *CA) MustNewServerTLSConfig(commonName string, extraNames ...string) *tls.Config {
+	return &tls.Config{
+		Certificates: []tls.Certificate{*ca.MustNewCert(commonName, extraNames...)},
+	}
 }
 
 // MustNewCert creates a new certificate for the given common name or PANICS.
@@ -188,26 +199,16 @@ func (c *CA) MustNewCertWithTimeNow(timeNow func() time.Time, commonName string,
 		}
 	}
 
-	raw := Must1(x509.CreateCertificate(rand.Reader, tmpl, c.CACert, c.priv.Public(), c.capriv))
+	raw := Must1(x509.CreateCertificate(rand.Reader, tmpl, c.caCert, c.priv.Public(), c.capriv))
 
 	// Parse certificate bytes so that we have a leaf certificate.
 	x509c := Must1(x509.ParseCertificate(raw))
 
 	tlsc := &tls.Certificate{
-		Certificate: [][]byte{raw, c.CACert.Raw},
+		Certificate: [][]byte{raw, c.caCert.Raw},
 		PrivateKey:  c.priv,
 		Leaf:        x509c,
 	}
 
 	return tlsc
 }
-
-// MustServerTLSConfig generates a server-side [*tls.Config] that uses the given [*CA] and
-// a generated certificate for the given common name and extra names.
-//
-// See [CA.MustNewCert] documentation for more details about what common name and extra names should be.
-func (ca *CA) MustServerTLSConfig(commonName string, extraNames ...string) *tls.Config {
-	return &tls.Config{
-		Certificates: []tls.Certificate{*ca.MustNewCert(commonName, extraNames...)},
-	}
-}

ca_test.go

@@ -112,7 +112,7 @@ func TestCAWeCanGenerateAnExpiredCertificate(t *testing.T) {
 		Handler: http.NewServeMux(),
 		TLSConfig: &tls.Config{
 			Certificates: []tls.Certificate{
-				*serverStack.CA().MustNewCertWithTimeNow(func() time.Time {
+				*serverStack.ca.MustNewCertWithTimeNow(func() time.Time {
 					return time.Date(2017, time.July, 17, 0, 0, 0, 0, time.UTC)
 				},
 					"www.example.com",

example_star_test.go

@@ -77,7 +77,7 @@ func Example_starTopologyHTTPSAndDNS() {
 	}
 	httpsServer := &http.Server{
 		Handler:   mux,
-		TLSConfig: httpsServerStack.CA().MustServerTLSConfig("tyrell.wellick.name"),
+		TLSConfig: httpsServerStack.MustNewServerTLSConfig("tyrell.wellick.name"),
 	}
 	go httpsServer.ServeTLS(httpsListener, "", "") // empty string: use .TLSConfig
 	defer httpsServer.Close()

integration_test.go

@@ -308,7 +308,7 @@ func TestRoutingWorksHTTPS(t *testing.T) {
 		t.Fatal(err)
 	}
 	httpServer := &http.Server{
-		TLSConfig: serverStack.CA().MustServerTLSConfig("example.local", "10.0.0.1"),
+		TLSConfig: serverStack.MustNewServerTLSConfig("example.local", "10.0.0.1"),
 		Handler:   mux,
 	}
 	go httpServer.ServeTLS(listener, "", "") // empty strings mean: use TLSConfig

model.go

@@ -6,6 +6,7 @@ package netem
 
 import (
 	"context"
+	"crypto/tls"
 	"crypto/x509"
 	"net"
 	"syscall"
@@ -23,6 +24,21 @@ const (
 	FrameFlagDrop
 )
 
+// CertificationAuthority is a TLS certification authority.
+type CertificationAuthority interface {
+	// CACert returns the CA certificate used by the server, which
+	// allows you to add to an existing [*x509.CertPool].
+	CACert() *x509.Certificate
+
+	// DefaultCertPool returns the default cert pool to use.
+	DefaultCertPool() *x509.CertPool
+
+	// MustNewServerTLSConfig constructs a server certificate for
+	// the given common name and extra names, all of which could be
+	// either IPv4/IPv6 addresses or domain names.
+	MustNewServerTLSConfig(commonName string, extraNames ...string) *tls.Config
+}
+
 // Frame contains an IPv4 or IPv6 packet.
 type Frame struct {
 	// Deadline is the time when this frame should be delivered.
@@ -154,14 +170,9 @@ type UDPLikeConn interface {
 
 // UnderlyingNetwork replaces for functions in the [net] package.
 type UnderlyingNetwork interface {
-	// CA returns the CA we're using.
-	CA() *CA
-
-	// CACert returns the CA cert we're using.
-	CACert() *x509.Certificate
-
-	// DefaultCertPool returns the underlying cert pool to be used.
-	DefaultCertPool() *x509.CertPool
+	// CertificationAuthority allows accessing the certification authority
+	// associated with this host or set of hosts.
+	CertificationAuthority
 
 	// DialContext dials a TCP or UDP connection. Unlike [net.DialContext], this
 	// function does not implement dialing when address contains a domain.

ndt0.go

@@ -249,7 +249,7 @@ func RunNDT0Server(
 	}
 
 	// generate a config for the given SNI and for the given IP addr
-	tlsConfig := stack.CA().MustServerTLSConfig(serverIPAddr.String(), serverNames...)
+	tlsConfig := stack.MustNewServerTLSConfig(serverIPAddr.String(), serverNames...)
 
 	// conditionally use TLS
 	ns := &Net{stack}

unetstack.go

@@ -45,9 +45,10 @@ type UNetStack struct {
 }
 
 var (
-	_ HTTPUnderlyingNetwork = &UNetStack{}
-	_ NIC                   = &UNetStack{}
-	_ UnderlyingNetwork     = &UNetStack{}
+	_ CertificationAuthority = &UNetStack{}
+	_ HTTPUnderlyingNetwork  = &UNetStack{}
+	_ NIC                    = &UNetStack{}
+	_ UnderlyingNetwork      = &UNetStack{}
 )
 
 // NewUNetStack constructs a new [UNetStack] instance.
@@ -104,20 +105,19 @@ func NewUNetStack(
 	return stack, nil
 }
 
-// CA implements UnderlyingNetwork.
-func (gs *UNetStack) CA() *CA {
-	return gs.ca
+// CACert implements CertificationAuthority.
+func (gs *UNetStack) CACert() *x509.Certificate {
+	return gs.ca.CACert()
 }
 
-// CACert implements UnderlyingNetwork.
-func (gs *UNetStack) CACert() *x509.Certificate {
-	return gs.ca.CACert
+// DefaultCertPool implements CertificationAuthority.
+func (gs *UNetStack) DefaultCertPool() *x509.CertPool {
+	return gs.ca.DefaultCertPool()
 }
 
-// MustServerTLSConfig is used by [github.com/ooni/probe-cli] code
-// when generating configuration for servers using TLS.
-func (gs *UNetStack) MustServerTLSConfig(commonName string, extraNames ...string) *tls.Config {
-	return gs.ca.MustServerTLSConfig(commonName, extraNames...)
+// MustNewServerTLSConfig implements CertificationAuthority.
+func (gs *UNetStack) MustNewServerTLSConfig(commonName string, extraNames ...string) *tls.Config {
+	return gs.ca.MustNewServerTLSConfig(commonName, extraNames...)
 }
 
 // Logger implements HTTPUnderlyingNetwork.
@@ -160,11 +160,6 @@ func (gs *UNetStack) Close() error {
 	return gs.ns.Close()
 }
 
-// DefaultCertPool implements UnderlyingNetwork.
-func (gs *UNetStack) DefaultCertPool() *x509.CertPool {
-	return gs.ca.CertPool()
-}
-
 // DialContext implements UnderlyingNetwork.
 func (gs *UNetStack) DialContext(
 	ctx context.Context, network string, address string) (net.Conn, error) {