feat(types): validate snapshot name length and shape (#61)

cocoon snapshot save/import previously accepted any string for --name.
A snapshot named with 100 chars or shell-unsafe chars would write
straight into the DB / OCI annotation / cidata propagation chain,
breaking downstream consumers (Linux HOST_NAME_MAX=64, DNS-1123
labels, etc.).

Mirror VMConfig.Validate's `^[a-zA-Z0-9][a-zA-Z0-9._-]{0,62}$` regex
on SnapshotConfig:

- types.SnapshotConfig.Validate() enforces ≤63 chars + safe charset
  (empty Name still allowed — name is optional for snapshots).
- cmd/snapshot/handler.go Save+Import validate the --name flag early
  to fail before the expensive snapshot/import operation.
- snapshot/localfile Create+Import call Validate as defense-in-depth
  so programmatic callers (vk-cocoon, future API) can't bypass.

Empty name remains valid (existing behavior — auto-generated ID is
the fallback identifier).

Author: CMGS

cmd/snapshot/handler.go

@@ -41,6 +41,9 @@ func (h Handler) Save(cmd *cobra.Command, args []string) error {
 	name, _ := cmd.Flags().GetString("name")
 	description, _ := cmd.Flags().GetString("description")
 
+	if err = (&types.SnapshotConfig{Name: name}).Validate(); err != nil {
+		return err
+	}
 	if name != "" {
 		if _, inspectErr := snapBackend.Inspect(ctx, name); inspectErr == nil {
 			return fmt.Errorf("snapshot name %q already exists", name)
@@ -251,6 +254,10 @@ func (h Handler) Import(cmd *cobra.Command, args []string) error {
 	name, _ := cmd.Flags().GetString("name")
 	description, _ := cmd.Flags().GetString("description")
 
+	if err = (&types.SnapshotConfig{Name: name}).Validate(); err != nil {
+		return err
+	}
+
 	var r io.Reader
 	if len(args) > 0 {
 		f, openErr := os.Open(args[0]) //nolint:gosec

snapshot/localfile/import.go

@@ -54,6 +54,10 @@ func (lf *LocalFile) Import(ctx context.Context, r io.Reader, name, description
 	cfg.Name = cmp.Or(name, cfg.Name)
 	cfg.Description = cmp.Or(description, cfg.Description)
 
+	if err = cfg.Validate(); err != nil {
+		return "", err
+	}
+
 	size, sizeErr := utils.DirSize(dataDir)
 	if sizeErr != nil {
 		return "", fmt.Errorf("compute data dir size: %w", sizeErr)

snapshot/localfile/localfile.go

@@ -86,6 +86,9 @@ func (lf *LocalFile) Create(ctx context.Context, cfg *types.SnapshotConfig, stre
 	if id == "" {
 		return "", fmt.Errorf("snapshot ID is required (must be set by caller)")
 	}
+	if err = cfg.Validate(); err != nil {
+		return "", err
+	}
 
 	dataDir := lf.conf.SnapshotDataDir(id)
 	now := time.Now()

types/snapshot.go

@@ -1,6 +1,9 @@
 package types
 
-import "time"
+import (
+	"fmt"
+	"time"
+)
 
 // SnapshotConfig carries the parameters for creating a snapshot.
 // The hypervisor fills ID, Image, ImageBlobIDs, Hypervisor, and resource fields; the CLI adds Name and Description.
@@ -15,6 +18,14 @@ type SnapshotConfig struct {
 	NICs         int                 `json:"nics,omitempty"`
 }
 
+// Validate checks SnapshotConfig caller-controlled fields. Empty Name is allowed (name is optional).
+func (cfg *SnapshotConfig) Validate() error {
+	if cfg.Name != "" && !validName.MatchString(cfg.Name) {
+		return fmt.Errorf("snapshot name %q is invalid: must match %s (max 63 chars)", cfg.Name, validName.String())
+	}
+	return nil
+}
+
 // Snapshot is the public record for a snapshot.
 type Snapshot struct {
 	SnapshotConfig

types/snapshot_test.go

@@ -0,0 +1,32 @@
+package types
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSnapshotConfig_Validate(t *testing.T) {
+	cases := []struct {
+		name    string
+		cfgName string
+		wantErr bool
+	}{
+		{"empty allowed", "", false},
+		{"simple", "my-snap", false},
+		{"with dot underscore", "my.snap_v1", false},
+		{"max 63", strings.Repeat("a", 63), false},
+		{"over 63", strings.Repeat("a", 64), true},
+		{"leading hyphen", "-bad", true},
+		{"space", "bad name", true},
+		{"slash", "bad/name", true},
+		{"control char", "bad\x00name", true},
+	}
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			err := (&SnapshotConfig{Name: tt.cfgName}).Validate()
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Validate(%q): err=%v, wantErr=%v", tt.cfgName, err, tt.wantErr)
+			}
+		})
+	}
+}