fix(cni): select embedded CNI plugins by arch (arm64 macOS dispatch)

pkg/cni/cni_linux.go

@@ -11,6 +11,7 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
+	"runtime"
 )
 
 //go:embed all:embed
@@ -79,21 +80,26 @@ func (m *Manager) Extract() error {
 	return nil
 }
 
+// findTarball selects the CNI plugins archive matching this binary's arch.
+// The macOS build cross-compiles ephemerd-linux for arm64, but the embed dir
+// can hold BOTH cni-plugins-linux-amd64 and -arm64 (the amd64 one lingers
+// from the CI cache). `//go:embed all:embed` then bundles both, so a naive
+// "first entry" pick returns amd64 and the arm64 Linux VM fails every CNI
+// exec with "exec format error". Select by runtime.GOARCH instead.
 func (m *Manager) findTarball() (string, error) {
 	entries, err := cniFS.ReadDir("embed")
 	if err != nil {
 		return "", fmt.Errorf("reading embedded files: %w", err)
 	}
-
+	names := make([]string, 0, len(entries))
 	for _, e := range entries {
-		name := e.Name()
-		if name == ".gitkeep" {
-			continue
-		}
-		return filepath.Join("embed", name), nil
+		names = append(names, e.Name())
 	}
-
-	return "", fmt.Errorf("no CNI plugins archive found in embedded files (did you run 'make download-cni'?)")
+	name, err := selectCNITarball(names, runtime.GOARCH)
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join("embed", name), nil
 }
 
 func extractTarGz(r io.Reader, dest string) error {

pkg/cni/select.go

@@ -0,0 +1,30 @@
+package cni
+
+import (
+	"fmt"
+	"strings"
+)
+
+// selectCNITarball picks the CNI plugins archive matching goarch from the
+// embed listing. The macOS build cross-compiles ephemerd-linux for arm64 but
+// the embed dir can hold BOTH cni-plugins-linux-amd64 and -arm64 (the amd64
+// one lingers from the CI cache). `//go:embed all:embed` then bundles both,
+// so a naive "first entry" pick returns amd64 and the arm64 Linux VM fails
+// every CNI exec with "exec format error". Select by arch instead.
+func selectCNITarball(names []string, goarch string) (string, error) {
+	want := "cni-plugins-linux-" + goarch + "-"
+	var found []string
+	for _, name := range names {
+		if name == ".gitkeep" {
+			continue
+		}
+		found = append(found, name)
+		if strings.HasPrefix(name, want) {
+			return name, nil
+		}
+	}
+	if len(found) == 0 {
+		return "", fmt.Errorf("no CNI plugins archive found in embedded files (did you run the download targets?)")
+	}
+	return "", fmt.Errorf("no CNI plugins archive for linux/%s in embedded files (have: %s)", goarch, strings.Join(found, ", "))
+}

pkg/cni/select_test.go

@@ -0,0 +1,39 @@
+package cni
+
+import "testing"
+
+func TestSelectCNITarball(t *testing.T) {
+	both := []string{"cni-plugins-linux-amd64-v1.6.2.tgz", "cni-plugins-linux-arm64-v1.6.2.tgz"}
+
+	tests := []struct {
+		name    string
+		names   []string
+		goarch  string
+		want    string
+		wantErr bool
+	}{
+		{"arm64 picks arm64 from both", both, "arm64", "cni-plugins-linux-arm64-v1.6.2.tgz", false},
+		{"amd64 picks amd64 from both", both, "amd64", "cni-plugins-linux-amd64-v1.6.2.tgz", false},
+		{"amd64 alone", both[:1], "amd64", "cni-plugins-linux-amd64-v1.6.2.tgz", false},
+		{"skips gitkeep", []string{".gitkeep", "cni-plugins-linux-arm64-v1.6.2.tgz"}, "arm64", "cni-plugins-linux-arm64-v1.6.2.tgz", false},
+		{"no match errors", both[:1], "arm64", "", true},
+		{"empty errors", []string{".gitkeep"}, "arm64", "", true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := selectCNITarball(tt.names, tt.goarch)
+			if tt.wantErr {
+				if err == nil {
+					t.Fatalf("expected error, got %q", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got != tt.want {
+				t.Errorf("got %q, want %q", got, tt.want)
+			}
+		})
+	}
+}