## Proxy implementation

In its initial implementations, the ztunnel was actually implemented in 3 different ways: a bespoke Rust implementation, a bespoke Go implementation, and in Envoy.

In the end, [after evaluation](https://docs.google.com/document/d/1c2123cKuYsBDpIon9FFdctWTUIMFweSjgwG7r8l3818/edit), the decision was to move forward with a Rust implementation.

* The Gateway Class controller is a simple controller that just writes a default `GatewayClass` object describing our implementation.

// election record to be accurate because these timestamps may not have been
// produced by a local clock. The implementation does not depend on their
// accuracy and only uses their change to indicate that another client has
// renewed the leader lease. Thus the implementation is tolerant to arbitrary
// clock skew, but is not tolerant to arbitrary clock skew rate.
//
// However the level of tolerance to skew rate can be configured by setting

environment-specific details. This means that the test code can (and should, where possible) be written in an
environment-agnostic manner, so that they can be run against any Istio implementation.

For example, the following code creates and then interacts with a Galley and Pilot component:

```go
func TestMyLogic(t *testing.T) {
    framework.
        NewTest(t).

func createFallbackStringMatch(s string) *networking.StringMatch {
	// If the string is empty or a wildcard, return nil
	if s == "" || s == "*" || s == "/*" || s == ".*" {
		return nil
	}

	// Note that this implementation only converts prefix and exact matches, not regexps.

	// Replace e.g. "foo.*" with prefix match
	if strings.HasSuffix(s, ".*") {
		return &networking.StringMatch{

	RootCertFilePath string
}

// Client interface defines the clients need to implement to talk to CA for CSR.
// The Agent will create a key pair and a CSR, and use an implementation of this
// interface to get back a signed certificate. There is no guarantee that the SAN
// in the request will be returned - server may replace it.
type Client interface {

type ClientBuilder = func(kubeConfig []byte, clusterId cluster.ID, configOverrides ...func(*rest.Config)) (kube.Client, error)

// Controller is the controller implementation for Secret resources
type Controller struct {
	namespace            string
	configClusterID      cluster.ID
	configCluster        *Cluster
	configClusterSyncers []ComponentConstraint

	ClientBuilder ClientBuilder

messages:
  - name: "InternalError"
    code: IST0001
    level: Error
    description: "There was an internal error in the toolchain. This is almost always a bug in the implementation."
    template: "Internal error: %v"
    args:
      - name: detail
        type: string

  - name: "Deprecated"
    code: IST0002
    level: Warning

// See the License for the specific language governing permissions and
// limitations under the License.

// Provides utility methods to generate X.509 certificates with different
// options. This implementation is Largely inspired from
// https://golang.org/src/crypto/tls/generate_cert.go.

package util

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"

	// queryable and should be preserved when modifying objects.
	Annotations map[string]string `json:"annotations,omitempty"`

	// ResourceVersion is an opaque identifier for tracking updates to the config registry.
	// The implementation may use a change index or a commit log for the revision.
	// The config client should not make any assumptions about revisions and rely only on
	// exact equality to implement optimistic concurrency of read-write operations.
	//