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feat(ssh): persist ed25519 host key in the bucket filesystem
Signed-off-by: Xe Iaso <me@xeiaso.net>
author
Xe Iaso
date
(May 28, 2026, 11:12 PM -0400)
commit
a626c13c
a626c13c4d5ab748d140a4f4fa54ec357c3422ef
parent
d1fec8cf
d1fec8cfb0993f6bd541ae0eabac9a805e3963ba
+127
+76
cmd/objgitd/ssh.go
+76
cmd/objgitd/ssh.go
···
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package main
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import (
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"crypto/ed25519"
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"crypto/rand"
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"encoding/pem"
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"errors"
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"fmt"
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"io"
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"log/slog"
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"os"
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"path/filepath"
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"github.com/go-git/go-billy/v6"
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gossh "golang.org/x/crypto/ssh"
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)
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const hostKeyPath = ".objgit/ssh_host_ed25519_key"
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// loadOrCreateHostKey loads the server's ed25519 host key from fs, generating
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// and persisting one on first use so the key survives restarts.
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func loadOrCreateHostKey(fs billy.Filesystem) (gossh.Signer, error) {
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f, err := fs.Open(hostKeyPath)
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if err == nil {
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defer f.Close()
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pemBytes, err := io.ReadAll(f)
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if err != nil {
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return nil, fmt.Errorf("reading ssh host key: %w", err)
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}
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signer, err := gossh.ParsePrivateKey(pemBytes)
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if err != nil {
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return nil, fmt.Errorf("parsing ssh host key: %w", err)
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}
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return signer, nil
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}
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if !errors.Is(err, os.ErrNotExist) {
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return nil, fmt.Errorf("opening ssh host key: %w", err)
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}
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// Generate a new ed25519 key.
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_, priv, err := ed25519.GenerateKey(rand.Reader)
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if err != nil {
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return nil, fmt.Errorf("generating ssh host key: %w", err)
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}
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block, err := gossh.MarshalPrivateKey(priv, "")
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if err != nil {
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return nil, fmt.Errorf("marshaling ssh host key: %w", err)
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}
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pemBytes := pem.EncodeToMemory(block)
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// Persist the key. MkdirAll first in case the parent dir doesn't exist.
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if err := fs.MkdirAll(filepath.Dir(hostKeyPath), 0o700); err != nil && !errors.Is(err, os.ErrExist) {
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return nil, fmt.Errorf("creating ssh host key directory: %w", err)
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}
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wf, err := fs.Create(hostKeyPath)
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if err != nil {
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return nil, fmt.Errorf("creating ssh host key file: %w", err)
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}
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if _, err := wf.Write(pemBytes); err != nil {
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wf.Close()
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return nil, fmt.Errorf("writing ssh host key: %w", err)
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}
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if err := wf.Close(); err != nil {
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return nil, fmt.Errorf("closing ssh host key file: %w", err)
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}
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signer, err := gossh.ParsePrivateKey(pemBytes)
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if err != nil {
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return nil, fmt.Errorf("parsing generated ssh host key: %w", err)
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}
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slog.Info("created ssh host key", "path", hostKeyPath)
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return signer, nil
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}
+51
cmd/objgitd/ssh_test.go
+51
cmd/objgitd/ssh_test.go
···
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package main
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import (
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"bytes"
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"io"
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"testing"
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"github.com/go-git/go-billy/v6/memfs"
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)
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func TestLoadOrCreateHostKey(t *testing.T) {
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fs := memfs.New()
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s1, err := loadOrCreateHostKey(fs)
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if err != nil {
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t.Fatalf("first call: %v", err)
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}
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// The key must have been persisted.
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f, err := fs.Open(hostKeyPath)
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if err != nil {
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t.Fatalf("host key not persisted at %s: %v", hostKeyPath, err)
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}
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first, err := io.ReadAll(f)
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f.Close()
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if err != nil {
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t.Fatal(err)
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}
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// A second call must reuse the same key, not regenerate.
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s2, err := loadOrCreateHostKey(fs)
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if err != nil {
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t.Fatalf("second call: %v", err)
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}
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if !bytes.Equal(s1.PublicKey().Marshal(), s2.PublicKey().Marshal()) {
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t.Error("second call returned a different key; expected the persisted one to be reused")
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}
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f2, err := fs.Open(hostKeyPath)
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if err != nil {
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t.Fatal(err)
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}
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second, err := io.ReadAll(f2)
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f2.Close()
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if err != nil {
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t.Fatal(err)
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}
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if !bytes.Equal(first, second) {
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t.Error("host key file changed on the second call; it must not be rewritten")
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}
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}