Check supported version for CreateNamespaces RPC

We now pre-check if conmon-rs supports the `CreateNamespaces` RPC and
return a wrapped defined error if not.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

go.mod

@@ -4,6 +4,7 @@ go 1.18
 
 require (
 	capnproto.org/go/capnp/v3 v3.0.0-alpha.9
+	github.com/blang/semver/v4 v4.0.0
 	github.com/containers/common v0.51.0
 	github.com/containers/storage v1.45.3
 	github.com/google/uuid v1.3.0
@@ -17,7 +18,6 @@ require (
 )
 
 require (
-	github.com/blang/semver/v4 v4.0.0 // indirect
 	github.com/coreos/go-systemd/v22 v22.5.0 // indirect
 	github.com/cyphar/filepath-securejoin v0.2.3 // indirect
 	github.com/docker/go-units v0.5.0 // indirect

pkg/client/client.go

@@ -17,6 +17,7 @@ import (
 
 	"capnproto.org/go/capnp/v3"
 	"capnproto.org/go/capnp/v3/rpc"
+	"github.com/blang/semver/v4"
 	"github.com/containers/conmon-rs/internal/proto"
 	"github.com/containers/storage/pkg/idtools"
 	"github.com/sirupsen/logrus"
@@ -49,6 +50,7 @@ type ConmonClient struct {
 	attachReaders  *sync.Map // K: UUID string, V: *attachReaderValue
 	tracingEnabled bool
 	tracer         trace.Tracer
+	serverVersion  semver.Version
 }
 
 // ConmonServerConfig is the configuration for the conmon server instance.
@@ -537,6 +539,12 @@ func (c *ConmonClient) Version(
 		return nil, fmt.Errorf("set version: %w", err)
 	}
 
+	semverVersion, err := semver.Parse(version)
+	if err != nil {
+		return nil, fmt.Errorf("parse server version to semver: %w", err)
+	}
+	c.serverVersion = semverVersion
+
 	tag, err := response.Tag()
 	if err != nil {
 		return nil, fmt.Errorf("set tag: %w", err)
@@ -1043,6 +1051,13 @@ func (c *ConmonClient) CreateNamespaces(
 		defer span.End()
 	}
 
+	// Feature not supported pre v0.5.0
+	const minMinor = 5
+	minVersion := semver.Version{Minor: minMinor}
+	if c.serverVersion.LT(minVersion) {
+		return nil, fmt.Errorf("requires at least %v: %w", minVersion, ErrUnsupported)
+	}
+
 	conn, err := c.newRPCConn()
 	if err != nil {
 		return nil, fmt.Errorf("create RPC connection: %w", err)

pkg/client/consts.go

@@ -38,7 +38,7 @@ const (
 type CgroupManager int
 
 const (
-	// Name specifies to use systemd to create and manage
+	// CgroupManagerSystemd specifies to use systemd to create and manage
 	// cgroups.
 	CgroupManagerSystemd CgroupManager = iota
 

pkg/client/errors.go

@@ -2,6 +2,11 @@ package client
 
 import "errors"
 
-// ErrMissingIDMappings gets returned if user namespace unsharing is selected
-// but no IDMappings being provided.
-var ErrMissingIDMappings = errors.New("unsharing user namespace selected but no IDMappings provided")
+var (
+	// ErrMissingIDMappings gets returned if user namespace unsharing is selected
+	// but no IDMappings being provided.
+	ErrMissingIDMappings = errors.New("unsharing user namespace selected but no IDMappings provided")
+
+	// ErrUnsupported gets returned if the server does not the feature.
+	ErrUnsupported = errors.New("feature not supported by this conmon-rs version")
+)