Felis/internal/operator/builders.go

package operator

import (
	"fmt"
	"strconv"

	"felis.lolicon.best/internal/apis/felis/v1alpha1"
	"felis.lolicon.best/internal/naming"
	appsv1 "k8s.io/api/apps/v1"
	corev1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/resource"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/util/intstr"
)

// envServiceToken is the environment variable the felis-limbo login plugin reads
// its internal-API bearer credential from. It is injected ONLY into the login
// system server (see buildEnv), sourced from a Secret, never a literal.
const envServiceToken = "FELIS_SERVICE_TOKEN"

// envForwardingSecret is the environment variable a backend reads the Velocity
// modern-forwarding secret from. Unlike the service token it goes to EVERY backend
// (see buildEnv), because Velocity's forwarding mode is proxy-wide.
const envForwardingSecret = "FELIS_FORWARDING_SECRET"

// Workload constants shared by the builders.
const (
	// GamePort is the Minecraft TCP port the proxy and readiness probe target.
	GamePort int32 = 25565

	// DefaultRconPort is the RCON port used when a server does not override
	// spec.rcon.port (see rconPort). It is exported because the platform package's
	// allow-rcon NetworkPolicy opens this port for the control plane — sharing the
	// constant keeps the policy port and the container's default RCON port a single
	// source of truth, so the operator's prober can always reach a default-port
	// server through the fence.
	DefaultRconPort int32 = 25575

	containerName  = "minecraft"
	dataVolumeName = "world"
	dataMountPath  = "/data"

	// felisBinaryPath is where the felis image installs its binary; the
	// forwarding-config initContainer invokes it by absolute path (matches
	// platform.felisBinaryPath — the same image, the same install location).
	felisBinaryPath = "/usr/local/bin/felis"

	// ManagedByValue / ComponentValue are the values of the LabelManagedBy /
	// LabelComponent labels stamped on every per-server pod (see labelsFor). They
	// are exported because the platform package's minecraft-namespace
	// NetworkPolicies select server pods by exactly these labels — keeping the
	// selector and the pod labels a single source of truth, so an isolation policy
	// can never silently stop matching the pods it is meant to fence.
	ManagedByValue = "felis-operator"
	ComponentValue = "server"

	defaultGraceSeconds int64  = 300
	defaultStorageSize  string = "8Gi"
)

// selectorFor returns the immutable selector labels (a StatefulSet selector
// must never change after creation, so it carries only the server identity).
func selectorFor(server *v1alpha1.MinecraftServer) map[string]string {
	return map[string]string{v1alpha1.LabelServer: server.Name}
}

// labelsFor returns the full label set applied to managed objects.
func labelsFor(server *v1alpha1.MinecraftServer) map[string]string {
	return map[string]string{
		v1alpha1.LabelServer:    server.Name,
		v1alpha1.LabelManagedBy: ManagedByValue,
		v1alpha1.LabelComponent: ComponentValue,
	}
}

// podLabelsFor is labelsFor plus the setup-owned system-role label, copied onto
// the pod so the platform's NetworkPolicies can tell the login gate apart from a
// user server (internal/platform loginToInternalAPI). Only the template carries it:
// the StatefulSet selector is immutable and stays selectorFor.
func podLabelsFor(server *v1alpha1.MinecraftServer) map[string]string {
	l := labelsFor(server)
	if role := server.Labels[v1alpha1.LabelSystemRole]; role != "" {
		l[v1alpha1.LabelSystemRole] = role
	}
	return l
}

func headlessServiceName(name string) string { return name + "-hl" }

// rconPort resolves the RCON port, defaulting to the conventional DefaultRconPort.
func rconPort(server *v1alpha1.MinecraftServer) int32 {
	if server.Spec.Rcon.Port > 0 {
		return server.Spec.Rcon.Port
	}
	return DefaultRconPort
}

// graceSeconds resolves the pod termination grace period (spec §7).
func graceSeconds(server *v1alpha1.MinecraftServer) int64 {
	if server.Spec.Lifecycle.TerminationGracePeriodSeconds > 0 {
		return server.Spec.Lifecycle.TerminationGracePeriodSeconds
	}
	return defaultGraceSeconds
}

// rconAddress is the in-cluster RCON endpoint the operator probes for readiness.
func rconAddress(server *v1alpha1.MinecraftServer) string {
	return fmt.Sprintf("%s.%s.svc.cluster.local:%d", server.Name, server.Namespace, rconPort(server))
}

// buildHeadlessService backs the StatefulSet's stable network identity.
func buildHeadlessService(server *v1alpha1.MinecraftServer) *corev1.Service {
	svc := &corev1.Service{
		ObjectMeta: metav1.ObjectMeta{
			Name:      headlessServiceName(server.Name),
			Namespace: server.Namespace,
			Labels:    labelsFor(server),
		},
		Spec: corev1.ServiceSpec{
			ClusterIP: corev1.ClusterIPNone,
			Selector:  selectorFor(server),
			Ports:     servicePorts(server),
		},
	}
	return svc
}

// buildClientService is the stable ClusterIP the proxy and operator dial.
func buildClientService(server *v1alpha1.MinecraftServer) *corev1.Service {
	return &corev1.Service{
		ObjectMeta: metav1.ObjectMeta{
			Name:      server.Name,
			Namespace: server.Namespace,
			Labels:    labelsFor(server),
		},
		Spec: corev1.ServiceSpec{
			Selector: selectorFor(server),
			Ports:    servicePorts(server),
		},
	}
}

func servicePorts(server *v1alpha1.MinecraftServer) []corev1.ServicePort {
	ports := []corev1.ServicePort{{
		Name:       "game",
		Port:       GamePort,
		TargetPort: intstr.FromInt32(GamePort),
		Protocol:   corev1.ProtocolTCP,
	}}
	if server.Spec.Rcon.Enabled {
		p := rconPort(server)
		ports = append(ports, corev1.ServicePort{
			Name:       "rcon",
			Port:       p,
			TargetPort: intstr.FromInt32(p),
			Protocol:   corev1.ProtocolTCP,
		})
	}
	return ports
}

// readinessProbe selects the pod readiness probe. By default it is a plain TCP
// check on the game port; when the server declares an HTTP health port
// (StartupSpec.HealthHTTPPort > 0) it becomes an HTTP GET on that port, so an
// RCON-less loader's own "started" signal — not the mere fact that the game
// socket is bound — gates readiness. Timings are identical across both modes.
func readinessProbe(server *v1alpha1.MinecraftServer) *corev1.Probe {
	probe := &corev1.Probe{
		InitialDelaySeconds: 20,
		PeriodSeconds:       10,
		FailureThreshold:    6,
	}
	if hp := server.Spec.Startup.HealthHTTPPort; hp > 0 {
		path := server.Spec.Startup.HealthHTTPPath
		if path == "" {
			path = "/healthz"
		}
		probe.ProbeHandler = corev1.ProbeHandler{
			HTTPGet: &corev1.HTTPGetAction{Path: path, Port: intstr.FromInt32(hp)},
		}
		return probe
	}
	probe.ProbeHandler = corev1.ProbeHandler{
		TCPSocket: &corev1.TCPSocketAction{Port: intstr.FromInt32(GamePort)},
	}
	return probe
}

// buildStatefulSet renders the workload for replicas in {0,1}. Its half of
// graceful shutdown is terminationGracePeriodSeconds, the time the server gets to
// save on SIGTERM; the reconciler flushes the world over RCON before it scales to
// zero (saveBeforeStop).
func buildStatefulSet(server *v1alpha1.MinecraftServer, replicas int32, felisImage string) (*appsv1.StatefulSet, error) {
	storageSize := server.Spec.Storage.Size
	if storageSize == "" {
		storageSize = defaultStorageSize
	}
	storageQty, err := resource.ParseQuantity(storageSize)
	if err != nil {
		return nil, fmt.Errorf("invalid storage size %q: %w", storageSize, err)
	}

	container := corev1.Container{
		Name:      containerName,
		Image:     server.Spec.Image,
		Resources: server.Spec.Resources,
		Env:       buildEnv(server),
		Ports: []corev1.ContainerPort{
			{Name: "game", ContainerPort: GamePort, Protocol: corev1.ProtocolTCP},
		},
		VolumeMounts: []corev1.VolumeMount{
			{Name: dataVolumeName, MountPath: dataMountPath},
		},
		// Readiness defaults to a plain TCP check (spec §5: readinessProbe is only
		// tcpSocket; the RCON gate is enforced by the operator, not the kubelet).
		// An RCON-less loader may instead publish an HTTP health endpoint (see
		// StartupSpec.HealthHTTPPort) that reports true readiness — used below when
		// set.
		ReadinessProbe: readinessProbe(server),
		// The server runs untrusted plugins, so it keeps no capability and can never
		// regain one. The root filesystem stays writable: an arbitrary Paper image
		// may unpack its runtime or write temp files outside /data.
		SecurityContext: hardenedContainerSecurityContext(false),
	}
	if hp := server.Spec.Startup.HealthHTTPPort; hp > 0 {
		container.Ports = append(container.Ports, corev1.ContainerPort{
			Name: "health", ContainerPort: hp, Protocol: corev1.ProtocolTCP,
		})
	}
	if len(server.Spec.Args) > 0 {
		container.Args = append([]string(nil), server.Spec.Args...)
	}
	if server.Spec.Rcon.Enabled {
		container.Ports = append(container.Ports, corev1.ContainerPort{
			Name: "rcon", ContainerPort: rconPort(server), Protocol: corev1.ProtocolTCP,
		})
	}

	// Every server first hands its world volume to the game uid (prepareDataInitContainer),
	// since the pod runs as that uid and a world an older root-run release wrote would
	// otherwise be read-only to it. An arbitrary user Paper image then gets the forwarding
	// config written for it (it does not consume FELIS_FORWARDING_SECRET itself); system
	// servers (login/lobby) are Felis-built and handle forwarding in their own
	// entrypoints. Without a felis image name there is nothing to run either step with.
	var initContainers []corev1.Container
	if felisImage != "" {
		initContainers = append(initContainers, prepareDataInitContainer(felisImage))
		if server.Labels[v1alpha1.LabelSystemRole] == "" {
			initContainers = append(initContainers, forwardingInitContainer(felisImage))
		}
	}

	grace := graceSeconds(server)
	pvc := corev1.PersistentVolumeClaim{
		ObjectMeta: metav1.ObjectMeta{Name: dataVolumeName},
		Spec: corev1.PersistentVolumeClaimSpec{
			AccessModes: []corev1.PersistentVolumeAccessMode{corev1.ReadWriteOnce},
			Resources: corev1.VolumeResourceRequirements{
				Requests: corev1.ResourceList{corev1.ResourceStorage: storageQty},
			},
		},
	}
	if sc := server.Spec.Storage.StorageClassName; sc != "" {
		pvc.Spec.StorageClassName = &sc
	}

	sts := &appsv1.StatefulSet{
		ObjectMeta: metav1.ObjectMeta{
			Name:      server.Name,
			Namespace: server.Namespace,
			Labels:    labelsFor(server),
		},
		Spec: appsv1.StatefulSetSpec{
			Replicas:    &replicas,
			ServiceName: headlessServiceName(server.Name),
			Selector:    &metav1.LabelSelector{MatchLabels: selectorFor(server)},
			Template: corev1.PodTemplateSpec{
				ObjectMeta: metav1.ObjectMeta{Labels: podLabelsFor(server)},
				Spec: corev1.PodSpec{
					TerminationGracePeriodSeconds: &grace,
					InitContainers:                initContainers,
					Containers:                    []corev1.Container{container},
					// A Minecraft server runs untrusted user worlds and plugins and
					// has no business calling the K8s API, so its pod must NOT carry the
					// default ServiceAccount token: a compromised plugin could otherwise
					// authenticate as the namespace default SA (spec §21: user servers
					// default to no SA-token mount). The pod keeps the default SA but
					// with automounting explicitly disabled.
					AutomountServiceAccountToken: boolPtr(false),
					SecurityContext:              gamePodSecurityContext(),
				},
			},
			VolumeClaimTemplates: []corev1.PersistentVolumeClaim{pvc},
		},
	}
	return sts, nil
}

// buildEnv assembles the container environment: heap sizing, user-supplied
// vars, and the RCON_* pair (password sourced from the referenced Secret, never
// inlined into the CRD).
func buildEnv(server *v1alpha1.MinecraftServer) []corev1.EnvVar {
	var env []corev1.EnvVar
	if mem := server.Spec.JavaMemory; mem != "" {
		env = append(env, corev1.EnvVar{Name: "JAVA_MEMORY", Value: mem})
	}
	if len(server.Spec.JavaFlags) > 0 {
		env = append(env, corev1.EnvVar{Name: "JAVA_FLAGS", Value: joinFlags(server.Spec.JavaFlags)})
	}
	for _, e := range server.Spec.Env {
		env = append(env, corev1.EnvVar{Name: e.Name, Value: e.Value})
	}
	if server.Spec.Rcon.Enabled && server.Spec.Rcon.SecretRef.Name != "" {
		env = append(env,
			corev1.EnvVar{Name: "RCON_PORT", Value: strconv.Itoa(int(rconPort(server)))},
			corev1.EnvVar{Name: "RCON_PASSWORD", ValueFrom: &corev1.EnvVarSource{
				SecretKeyRef: &corev1.SecretKeySelector{
					LocalObjectReference: corev1.LocalObjectReference{Name: server.Spec.Rcon.SecretRef.Name},
					Key:                  server.Spec.Rcon.SecretRef.Key,
				},
			}},
		)
	}
	// The login system server is the ONE workload that authenticates to the
	// felis-api internal face (its felis-limbo plugin mints bind codes and polls
	// link status), so it — and only it — receives a token: felis-limbo-token,
	// which the api serves on those routes alone. Injected
	// from a Secret in this namespace, never inlined into the CRD (the same
	// discipline as RCON_PASSWORD above; the CRD's EnvVar type has no valueFrom
	// precisely so a user server cannot mount an arbitrary secret). Require both
	// the reserved name and the setup-owned system-role label: the label prevents
	// a legacy user server named "login" from receiving the token after upgrade.
	// The Secret must exist in this (minecraft) namespace; the installer applies it
	// there and `felis setup` replicates it from the control namespace.
	if server.Name == naming.SystemLoginServer &&
		server.Labels[v1alpha1.LabelSystemRole] == naming.SystemLoginServer {
		env = append(env, corev1.EnvVar{
			Name: envServiceToken,
			ValueFrom: &corev1.EnvVarSource{
				SecretKeyRef: &corev1.SecretKeySelector{
					LocalObjectReference: corev1.LocalObjectReference{Name: naming.LimboTokenSecretName},
					Key:                  naming.ServiceTokenSecretKey,
				},
			},
		})
	}
	// The Velocity modern-forwarding secret goes to EVERY backend, system and user
	// alike — not because user servers are trusted, but because Velocity's forwarding
	// mode is one proxy-wide setting: with it on, a backend that cannot verify the
	// signed handshake rejects every login the proxy sends it. Withholding the secret
	// from user servers would not harden them, it would simply make them unjoinable.
	// It is the backend's proof that a login really came from the proxy (and so that
	// the player's UUID is Mojang-verified, not offline-derived) — the pod-level fence
	// against bypassing the proxy is the NetworkPolicy, not this value's secrecy.
	//
	// The Felis-built images (deploy/limbo, deploy/lobby) read this in their
	// entrypoints. An arbitrary user Paper image does NOT — so the operator also runs
	// a forwarding-config initContainer (see forwardingInitContainer) that writes the
	// Velocity block into the shared world volume before the server starts, making a
	// stock Paper image joinable without modifying it.
	env = append(env, forwardingSecretEnvVar())
	return env
}

// forwardingSecretEnvVar sources FELIS_FORWARDING_SECRET from the Secret the setup
// provisioner replicas into this namespace. Optional so a cluster whose proxy is
// not in modern mode — no Secret provisioned — still schedules its pods instead of
// wedging them all in CreateContainerConfigError; the init and lobby/limbo
// entrypoints treat an empty value as "not in modern mode" and leave config alone.
func forwardingSecretEnvVar() corev1.EnvVar {
	return corev1.EnvVar{
		Name: envForwardingSecret,
		ValueFrom: &corev1.EnvVarSource{
			SecretKeyRef: &corev1.SecretKeySelector{
				LocalObjectReference: corev1.LocalObjectReference{Name: naming.ForwardingSecretName},
				Key:                  naming.ForwardingSecretKey,
				Optional:             boolPtr(true),
			},
		},
	}
}

// forwardingInitContainer writes Velocity modern-forwarding config into the shared
// world volume before the server container starts, so an arbitrary Paper image Felis
// did NOT build becomes joinable behind the proxy without being modified. It runs the
// felis image's `init-forwarding` subcommand, which merges the proxies.velocity block
// into config/paper-global.yml and forces online-mode=false in server.properties.
//
// It runs as the game uid like the server container (the pod securityContext), after
// prepareDataInitContainer has handed the volume to that uid, so it needs no privilege
// at all: no capability, a read-only root filesystem, and the files it writes are
// owned by the very uid that rewrites them on boot.
//
// Only user servers get it: the Felis-built system images (login limbo, lobby) already
// consume the secret in their own entrypoints, and the login limbo is not Paper at all.
func forwardingInitContainer(felisImage string) corev1.Container {
	return corev1.Container{
		Name:    "init-forwarding",
		Image:   felisImage,
		Command: []string{felisBinaryPath, "init-forwarding"},
		Env:     []corev1.EnvVar{forwardingSecretEnvVar()},
		VolumeMounts: []corev1.VolumeMount{
			{Name: dataVolumeName, MountPath: dataMountPath},
		},
		Resources:       initContainerResources(),
		SecurityContext: hardenedContainerSecurityContext(true),
	}
}

// prepareDataInitContainer runs `felis init-volume`, which chowns every world-volume
// entry not already owned by naming.GameUID:GameGID. It is the one container in the
// pod that runs as root, and it holds only what a chown walk needs: CHOWN to change
// an owner and DAC_OVERRIDE to descend into a directory some other uid left at 0700.
// Both are inside the PodSecurity baseline profile; everything else is dropped, the
// root filesystem is read-only, and it exits before the server container starts.
//
// fsGroup (gamePodSecurityContext) alone would not do: kubelet skips it for hostPath
// volumes, which is what a k3s local-path PV is underneath, and it only fixes the
// group besides.
func prepareDataInitContainer(felisImage string) corev1.Container {
	return corev1.Container{
		Name:    "prepare-data",
		Image:   felisImage,
		Command: []string{felisBinaryPath, "init-volume", "--data", dataMountPath},
		VolumeMounts: []corev1.VolumeMount{
			{Name: dataVolumeName, MountPath: dataMountPath},
		},
		Resources: initContainerResources(),
		SecurityContext: &corev1.SecurityContext{
			RunAsUser:                int64Ptr(0),
			RunAsGroup:               int64Ptr(0),
			RunAsNonRoot:             boolPtr(false),
			Privileged:               boolPtr(false),
			AllowPrivilegeEscalation: boolPtr(false),
			ReadOnlyRootFilesystem:   boolPtr(true),
			Capabilities: &corev1.Capabilities{
				Drop: []corev1.Capability{"ALL"},
				Add:  []corev1.Capability{"CHOWN", "DAC_OVERRIDE"},
			},
		},
	}
}

// gamePodSecurityContext pins every container in a server pod to the game uid,
// whatever USER its image declares, and to the runtime's default seccomp filter.
// fsGroup makes a volume type that supports ownership management group-writable
// for that uid; OnRootMismatch keeps kubelet from re-walking a large world on every
// start once the volume root already carries the group.
func gamePodSecurityContext() *corev1.PodSecurityContext {
	onRootMismatch := corev1.FSGroupChangeOnRootMismatch
	return &corev1.PodSecurityContext{
		RunAsNonRoot:        boolPtr(true),
		RunAsUser:           int64Ptr(naming.GameUID),
		RunAsGroup:          int64Ptr(naming.GameGID),
		FSGroup:             int64Ptr(naming.GameGID),
		FSGroupChangePolicy: &onRootMismatch,
		SeccompProfile:      &corev1.SeccompProfile{Type: corev1.SeccompProfileTypeRuntimeDefault},
	}
}

// hardenedContainerSecurityContext drops every capability and forbids gaining one
// back through a setuid binary. readOnlyRoot is set for the felis-image containers,
// which write nothing outside the world volume.
func hardenedContainerSecurityContext(readOnlyRoot bool) *corev1.SecurityContext {
	sc := &corev1.SecurityContext{
		Privileged:               boolPtr(false),
		AllowPrivilegeEscalation: boolPtr(false),
		Capabilities:             &corev1.Capabilities{Drop: []corev1.Capability{"ALL"}},
	}
	if readOnlyRoot {
		sc.ReadOnlyRootFilesystem = boolPtr(true)
	}
	return sc
}

// initContainerResources bounds the two felis-image initContainers. Both are short
// file walks; the memory ceiling stops a pathological volume from taking the node's
// memory with it, and no CPU limit keeps a large world's chown from being throttled
// into the pod's start-up time.
func initContainerResources() corev1.ResourceRequirements {
	return corev1.ResourceRequirements{
		Requests: corev1.ResourceList{
			corev1.ResourceCPU:    resource.MustParse("10m"),
			corev1.ResourceMemory: resource.MustParse("32Mi"),
		},
		Limits: corev1.ResourceList{
			corev1.ResourceMemory: resource.MustParse("128Mi"),
		},
	}
}

func boolPtr(b bool) *bool { return &b }

func int64Ptr(i int64) *int64 { return &i }

func joinFlags(flags []string) string {
	out := ""
	for i, f := range flags {
		if i > 0 {
			out += " "
		}
		out += f
	}
	return out
}